ulice union of light-ion centres in europe...tional code of practice published by the international...

D.JRA 2.4 – Joint dosimetry protocol structure . . . Dissemination level PU

Project co-funded by the European Commission within the FP7 (2007 – 2013)

Grant agreement no.: 228436

ULICEUnion of Light-Ion Centres in Europe

Project type: Combination of CP & CSAIntegrating Activities / e-Infrastructures / Preparatory phase

Start date of project: 1st September 2009 Duration: 48 months

D.JRA 2.4 – Joint dosimetry protocol structure enabling inter-comparison betweencentres, including modern dosimetric and microdosimetric approaches (e. g.

selection of stopping powers)

Delivery date: M 24 2011/08/31

WP n{ and title: WP 2 – Concepts and terms for dose volume parameters and for out-come assessment in hadron-therapy integrating applied biology, medi-cal physics and clinical medicine in ULICE

WP leader: Ramona Mayer, Jacques Balosso

Reporting period: 2nd

Name Partner

2011/08/31Author(s): Stanislav Vatnitsky MEDAContributor(s): Alexander Ableitinger,

Thomas Schreiner,Dietmar Georg

MEDA,MEDA,MUW

Pillar coordinator: Richard Pötter MUWApproved by TPB and CPO signature

Dissemination LevelPU Public XPP Restricted to other programme participants (including the Commission Services)RE Restricted to a group specified by the consortium (including the Commission Services)CO Confidential, only for members of the consortium (including the Commission Services)

ULICE-GA n{228436 of 34


TABLE OF CONTENTS

LIST OF ABBREVIATIONS AND DEFINITIONS 5

PUBLISHABLE SUMMARY 7

CONTENTS AND SPECIFIC DOCUMENT STRUCTURE 8

1 Introduction 8

2 Procedures of dose per MU calibration with scanning ion beams 92.1 Paul Scherrer Institute . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92.2 Gesellschaft für Schwerionenforschung – Heidelberg Ion-Beam Therapy Centre . . . 92.3 M. D. Anderson Cancer Centre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102.4 Summary of dosimetry calibration procedures . . . . . . . . . . . . . . . . . . . . . 11

3 Dosimetry auditing procedure based on end-to-end test 113.1 Selection of the phantom and detectors . . . . . . . . . . . . . . . . . . . . . . . . . 123.2 Practical steps of the end-to-end testing procedure . . . . . . . . . . . . . . . . . . . 143.3 Results of the pilot study . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.3.1 Assembling the phantom . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.3.2 Scanning of the phantom at the planning CT . . . . . . . . . . . . . . . . . . 153.3.3 Treatment planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.3.4 Dose delivery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163.3.5 Evaluation of the dosimetry results . . . . . . . . . . . . . . . . . . . . . . . 173.3.6 Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

A Questionnaire 20

B Summary of the responses to the questionnaire 23

C Some details on the responses to the questionnaire 26C.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26C.2 Particle accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26C.3 TPS, dose calibration and dose recording . . . . . . . . . . . . . . . . . . . . . . . . 27C.4 Phantom material, CT data conversion and PTV margins . . . . . . . . . . . . . . . 27C.5 Position verification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27C.6 Final motivation for a dosimetric audit . . . . . . . . . . . . . . . . . . . . . . . . . 28

D Reporting spreadsheets for end-to-end test auditing procedure 28D.1 CT scanning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28D.2 Treatment planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29D.3 Irradiation of the detectors in treatment beamline . . . . . . . . . . . . . . . . . . . 30D.4 Verification measurements with ionisation chamber . . . . . . . . . . . . . . . . . . 31

CONCLUSIONS 32

REFERENCES 33



LIST OF ABBREVIATIONS AND DEFINITIONS

60Co Cobalt-60 is a radioactive isotope of cobalt.

CT Computed Tomography is a medical imaging technique using a large series of two-dimensional X-ray images.

FWHM Full Width at Half Maximum is an expression of the extent of a function, given by thedifference between the two extreme values of the independent variable at which thedependent variable is equal to half of its maximum value.

GSI Gesellschaft für Schwerionenforschung – Centre for Heavy Ion Research located atDarmstadt, Germany.

Gy Gray is the name of the special unit of absorbed dose of ionising radiation, i. e. theabsorption of one joule of ionising radiation by one kilogram of matter.

HIT Heidelberger Ionenstrahl-Therapiezentrum – Heidelberg Ion-Beam Therapy Centre lo-cated at the Heidelberg University Hospital, Germany.

IAEA International Atomic Energy Agency is an international organisation that seeks to pro-mote the peaceful use of nuclear energy, and to inhibit its use for any military purpose,including nuclear weapons. The IAEA was established as an autonomous organisationin 1957.

ICRU International Commission on Radiation Units and Measurements is a standardisationbody set up in 1925 by the International Congress of Radiology.

IMRT Intensity-Modulated Radiation Therapy is an advanced type of high-precision radiationtherapy technique.

LET Linear Energy Transfer is a measure of the energy transferred to material as an ionisingparticle travels through it.

MU Monitor Unit is a measure of machine output of the accelerator in radiation therapy.

NPL National Physical Laboratory is the national measurement standards laboratory for theUnited Kingdom, based at Bushy Park in Teddington, London, England. It is the largestapplied physics organisation in the United Kingdom.

PMMA Polymethyl Methacrylate is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass.

PSI Paul Scherrer Institute – the largest research centre for natural and engineering scienceswithin Switzerland located at Villigen.

RE Relative Effectiveness.

RPC Radiological Physics Center in Houston has been funded by the National Cancer In-stitute continuously since 1968 to provide quality auditing of dosimetry practices atinstitutions participating in cooperative clinical trials.

TL Thermoluminescence is a form of luminescence that is exhibited by certain crystallinematerials, such as some minerals, when previously absorbed energy from electromag-netic or other ionising radiation is re-emitted as light upon heating of the material.



TPS Treatment Planning System used in radiation therapy for planning the doses in the tu-mour and the surrounding healthy tissue (critical organs).

WED Water Equivalent Density.



PUBLISHABLE SUMMARYThe technological development of radiation therapy with protons and carbon ions enabled the im-plementation of scanning beam delivery techniques and the next generation of ion beam facilities inEurope aim to employ only scanning beams. However, the procedure of reference dosimetry andconsequently the calibration of dose monitors in scanning beams is usually defined by the output ofthe treatment planning system (TPS). Therefore the calibration may include several additional stepscompared to the dose monitor calibration of clinical beams produced with the passive beam deliverytechnology. The features of scanning beam delivery complicate dosimetric intercomparison betweenfacilities and require specific procedure. The most efficient solution for the dosimetry intercomparisonof scanning beam delivery systems is to use so-called end-to-end test auditing procedure.

The purpose of the developed end-to-end test auditing procedure is not just to validate beam linemonitor calibration but to confirm that the entire logistic chain of radiation treatment starting fromCT imagining, treatment planning, monitor calibration, and beam delivery is operable and leads tothe desired results with sufficient accuracy. Such test has been designed based on the use of a plasticphantom that hosts a set of alanine detectors and in addition radiochromic films distributed over thepredefined target volume. Alanine detectors are provided by the National Physical Laboratory (NPL)as well as the assistance in detectors’ readout and conversion of the signal to absorbed dose for ionbeams. Following the procedure the user should image the phantom on the CT scanner, transfer the CTdata to the TPS, perform planning to deliver the prescribed dose to the requested target volume, andthen to execute the plan in a way similar to the patient’s treatment. The doses registered by detectorsare compared to the planned values. The procedure was tested through a pilot study in proton andcarbon beams and the results were analysed to finalise the practical steps.

The developed end-to-end test auditing procedure may be used for new ion beam facilities to detectand eliminate any possible systematic errors occurring in the dosimetry process. If such institutionsare planning to participate in clinical trials, external auditing dosimetry studies are considered manda-tory and the proposed test may serve as a credentialing procedure.



CONTENTS AND SPECIFIC DOCUMENT STRUCTURE

1 Introduction

A formalism for absorbed dose-to-water determinations with ionisation chambers having 60Co cali-bration coefficients was implemented into dosimetry practice of radiation therapy with high-energyphoton and electron beams within the last decade. This formalism has been applied also for protonsand heavier ions. An ionisation chamber dosimetry based on instruments calibrated in a 60Co beamwas established as the main reference dosimetry technique for clinical ion beams worldwide. It isexpected that the implementation of the procedures and basic physics data described in the Interna-tional Code of Practice published by the International Atomic Energy Agency (IAEA) TRS-398 [1]and International Commission on Radiological Units and Measurements (ICRU) Report 78 [2] willallow harmonisation of dosimetry guidelines at ion beam facilities and to ensure exact delivery of pre-scribed dose with clinical beams. However, the lack of international and national dosimetry standardsfor protons and heavier ion beams complicated this harmonisation and demanded an alternative ap-proach compared to the practice of clinical high-energy photon and electron beams that are supportedby primary dose standards.

When primary standard is not available, dosimetry intercomparison is the effective methodology toconfirm the integrity of the dosimetry techniques used at different ion beam facilities [2]. Such com-parison studies are extremely useful, especially for new facilities, to detect and eliminate any possiblesystematic errors occurring in the dosimetry process. Comparison studies of dosimetry practice arealso important for interchange of clinical experience and treatment protocols between facilities, andallow providing standardisation of dosimetry in radiation-biology experiments. If institutions are plan-ning to participate in the clinical trials, such comparison dosimetry studies are considered mandatoryand may serve as a credentialing procedure.

Several dosimetry intercomparisons were organised in the past to verify the validity of beam calibra-tion of ion beams [3–5]. A comparison of dosimetry techniques of 13 proton facilities based on ICRUReport 59 recommendations is an example of such activity [5]. Three beam energies were used in thisstudy where the reference beam calibration technique of the participants based on the use of an ioni-sation chamber dosimetry was compared for a passive beam delivery system. Each participant placedan institutional ionisation chamber at a reference depth in a water phantom and the same amounts ofmonitor units were delivered during each session. Then the participants were requested to report thedelivered dose based on their measured data.

The technological development of radiation therapy with protons and carbon ions enabled the im-plementation of scanning beam delivery techniques [2] so that the next generation of the ion beamfacilities in Europe will employ only scanning beams. Due to the diversity of scanning beam deliv-ery techniques, the control of dose delivery and procedure of calibration of primary dose monitorsfor beam lines with modulated scanning dose delivery is usually correspondent to the specific outputinformation of the treatment planning system (TPS) used at the facility. Therefore the calibration pro-cess may include several additional steps compared to the dose monitor calibration of clinical beamsproduced with the passive beam delivery technology. The features of scanning beam delivery com-plicate dosimetric intercomparison between facilities and require specific approach. Such approachshould not be restricted to the dosimetry calibration, but include the auditing of the whole dosimetrychain of the treatment process. The goal of the current work was to develop the dosimetry auditingprocedure for the facilities with scanning beam delivery systems and to test the procedure through thepilot study in proton and carbon beams.



2 Procedures of dose per MU calibration with scanning ion beams

The process of calibrating the response of a beamline monitor in terms of dose per monitor unit (MU)is based on the measurement of absorbed dose-to-water under reference conditions for all treatmentsystem modalities that will be used clinically [2]. The reference conditions are usually chosen toprovide a point at a depth of clinical interest where the signal of the used detector (usually an ion-isation chamber having calibration factor traceable to the standards laboratory) can be converted toabsorbed dose-to-water using known correction factors. Due to a lack of standards of absorbed dosefor ion beams, ionisation chambers with 60Co-based calibration factors traceable to national standardsdosimetry laboratories are currently employed at ion beam facilities for dose per MU calibration [2].

The procedures for calibrating the beamline monitors for passive scattering beam delivery and uniformscanned ion beams is similar to that used with high-energy X-ray or electron beams. The proceduresfor calibrating the beamline monitors in modulated scanning beams are, however, substantially differ-ent than for scattered or uniform scanned beams. This is because the dose is delivered to the patientin many small pieces that are explicitly defined by the TPS. These pieces needed for execution of thetreatment plan include the energies, spot locations, monitor units per spot location, etc. The monitorcalibration procedure therefore includes several intermediate steps. Typical procedures of primarydose monitor calibration used at the facilities with modulated scanning are described below.

2.1 Paul Scherrer Institute

The treatment planning system developed at the Paul Scherrer Institute (PSI) uses an empirical modelto calculate the dose distribution of the small diameter proton beam that is scanned [6]. The modeltakes into account both multiple Coulomb scattering and losses due to nuclear interactions. Based onthis model and the parametrisation data stored in look-up tables, the TPS predicts absolute doses inthe patient per proton traversing the beam monitor. To get a calibration factor in terms of absorbeddose per proton that is correspondent to the information output from the TPS, a calibration in termsof protons per MU is performed with a Faraday cup for single pencil beams at multiple energies.In principle, a Faraday cup measurement could serve as the primary calibration method for the dosemonitors of scanning beam delivery systems, however, it is preferable to back up the fluence-baseddosimetry with another reference dosimetry method [7]. At PSI then, a further calibration in terms ofdose per MU is performed with ionisation chamber dosimetry to verify the Faraday cup measurements.In this step, an ionisation chamber with a calibration factor in terms of absorbed dose-to-water atthe reference quality Q0 (60Co) is placed in a water phantom at the isocentre and at a depth thatcorresponds to a residual range of 5g/cm2. An one litre irradiation volume (10cm×10cm×10cm)is then defined with its centre at the isocentre and it is irradiated uniformly to provide a homogeneousdose of 2 Gy. Based on the ionisation chamber measurements, corrections to the Faraday cup resultsmay be determined and a combined result used as a final calibration. As the TPS model is able topredict the number of protons per Gray required for any field, the monitor calibration derived in thecalibration procedure is valid as a global factor.

2.2 Gesellschaft für Schwerionenforschung – Heidelberg Ion-Beam Therapy Centre

The treatment planning system used at the Gesellschaft für Schwerionenforschung (GSI) generates anabsolute number of particles to deliver a prescribed dose. Similar to the procedure used at PSI, themonitor for a dynamic beam delivery system using modulated scanning in combination with energy



modulation of carbon ions is also calibrated in units of particles per MU [8]. The difference betweenthe GSI and PSI approaches is that, with the use of a biological model, the GSI treatment planning sys-tem also optimises the energy weighting (including biological optimisation) to yield the desired depthdose distribution along each ray-line in every treatment field to provide scanner control parameters.Using this procedure, the resulting spread-out-Bragg-peaks change their widths and slopes within thetreatment field. The final optimised scan control parameters include: a) the lateral position of the scanpoints for each energy and b) the absolute number of carbon ions to be applied at all individual scanpoints at all energies. The first parameter is monitored by multi-wire proportional chambers, whilethe second parameter is controlled by a beam flux monitor. Consequently, the beam flux monitor iscalibrated for each energy in terms of particle numbers.

The GSI calibration procedure [9] is performed with an ionisation chamber placed in the plateauregion, i. e. in the entrance region, of the dose distribution. There are two reasons for the selectionof this depth. First, the spread-out-Bragg-peaks produced by the GSI machine have different shapesat different positions in the field as well as for every patient. Second, because the calibration isenergy dependent, a calibration must be performed and validated throughout the range of availableenergies. The determination of the particle number per MU is based on a measurement of absorbeddose-to-water so that no direct fluence measurement (such as performed at PSI using a Faraday cup)is required. For this measurement, the ionisation chamber, having a calibration factor in terms ofabsorbed dose-to-water (reference beam quality is a 60Co beam), is placed in a plastic phantom at adepth of 7 mm and irradiated in a carbon ion beam with a selected single energy and a field size of5cm× 5cm. The measurement is performed at six representative energies ranging from 100MeV/uto 350MeV/u. The calibration factor at carbon beam energy E, K(E), may be defined as a number ofparticles N per monitor unit, MU , and is given by

K(E) =N

MU=

Dmeas

SE(z) MU×∆x ∆y (1)

where Dmeas is the absorbed dose determined in a phantom at reference conditions for scanning beamsand SE is the mass stopping power of ions with initial energy E at the depth of measurement z. ∆xand ∆y are the distances between the scan points in the x- and y-directions. For a pencil beam with5 mm FWHM these spacings can be selected as 2 mm. An example of the energy dependence of thecalibration factor is illustrated in Figure 1. The calibration factors for arbitrary treatment energiescan be interpolated from the graph. Typically the functional dependence of this interpolation curve isuniversal since it is solely determined by the energy loss in the detector gas of the monitor chambers.The only parameter that requires fitting is the overall scaling factor.

2.3 M. D. Anderson Cancer Centre

The method of calibrating dose per MU for discrete spot scanning with proton beams used at the M. D.Anderson Cancer Centre [10] is quite similar to the procedures described above, but uses a slightlydifferent technique. For the first step, the primary beam monitor is calibrated using a Farmer chamberwith an absorbed dose-to-water calibration factor (reference beam quality is a 60Co beam). Then theresponse of the dose monitor for each proton energy is determined using a cross-calibrated large areaparallel-plate ionisation chamber. The chamber is placed at the entrance region of the depth dosedistribution at a depth of 2 cm to ensure that this location is within a low-dose gradient region for allproton energies to be used. The large area parallel-plate ionisation chamber provides an integral dosemeasurement and, using the mass stopping power at 2 cm depth, the integral dose can be converted



a carbon ion beam with a homogeneous monoenergetic fieldwith a size of 535 cm2. The measurement is performed atsix representative energiesE ranging from 100 to 350MeV/u, which correspond to depths of penetration in waterof 2.5 cm to 21.8 cm.

The phantom consists of a water equivalent plastic mate-rial ~RW-3 by PTW, Freiburg, Germany! and the chamber issituated with the center at a depth of 3.9 mm in the phantom.The total distance from the surface of the phantom to thecenter of the sensitive volume of the chamber including thethickness of the monitor systems amounts to 5.55 mm. Theabsorbed dose is determined by multiplying the reading ofthe dosimeterM , corrected for incomplete saturation anddensity effects, the calibration factor for the chamber interms of absorbed dose to water in a Cobalt-60 field,Nw ,and a radiation beam quality factorkQ :

Dmeas~Peff!5MkQNw . ~1!

Here,Peff denotes the effective point of measurement in thecarbon ion beam andkQ accounts for the differences in beamquality relative to the calibration beam quality. This methodis described in detail in Ref. 11 and is essentially the same asproposed by the IAEA in the TRS-398.1 The determinationof the effective point of measurement is described in Ref. 12.

The calibration factor at energyE, K(E), is defined as anumber of particlesN per monitor unit MU, and is thengiven by

K~E!5N

MU5

Dmeas

SE~x!MUDxDy, ~2!

whereDmeasis the absorbed dose measured in the phantom,SE(x) is the mass stopping power of carbon ions with theinitial energyE at the depth of measurementx. Dx andDyare the spacing between the scan points in thex andy direc-tions. The spacing chosen for the calibration of the monitoris always set toDx5Dy52 mm, using a circular Gaussianshaped beam spot of 5 mm full width at half maximum. TheMU is the same at each scan point.

A prerequisite for the application of Eq.~2! is that thescanned field delivers a homogeneous dose. This is checkedindependently by irradiating a radiochromic film and using alaser scanner for readout. If the field used for the calibrationmeasurements were not homogeneous, Eq.~2! is no longervalid.

The resulting calibration factors at the six energies arethen interpolated, so that a calibration for each treatmentenergy will be available. The functional dependence of thisinterpolation curve is fixed, since this is solely determined bythe energy loss in the detector gas of the monitor chambers.The only parameter that requires fitting is an overall scalingfactor.

The following differences can be summarized with re-spect to the reference conditions recommended in TRS-398:

~1! A solid state phantom rather than a water phantom isused.

~2! The reference depth is chosen to be in the plateau of amonoenergetic Bragg peak instead of the center of aSOBP.

~3! The calibration is dependent on the initial particle en-ergy.

~4! A field size of 535 cm2 rather than 10310 cm2 is used.

All other conditions such as chamber type and referencepoint of the chamber are the same in both methods.

III. RESULTS

Values of the monitor calibration factor, measured at thesix different energies, are shown in Fig. 1. Repeating themeasurement at each energy ten times, it was found that thereproducibility of the results is within 0.5%. In daily routine,each measurement is performed at least twice. Also shown inFig. 1 as a full line is the fit of the energy dependence to thedata. The calibration factorK(E) measured at six energies isthen interpolated by a parametrized function of the relativeenergy dependenceF(E) and a scaling factorkfit :

K~E!5kfit

F~E!

5kfit

3.11023102311.1865E2117.2493E22 . ~3!

The parameters of the functionF(E) are kept fixed, as theshape of the curve may not change with time. Only the factorkfit is fitted daily and may be used as measure for the con-stancy of the particle monitors. A plot of this factor as afunction of time over a period of 26 days is shown in Fig. 2.The observed daily changes are smaller than 1% and most ofthem are below 0.5%.

The homogeneity of the scanned fields is checked forvarious field sizes and energies~see Ref. 13 for details!. Thedose homogeneity is generally required to be better than 5%in both directions of the treatment field. The homogeneity of

FIG. 1. Monitor calibration factorK(E) as measured according to Eq.~2! forsix different energies of the carbon ion beam. The fit to the data uses theformula in Eq.~3!.

1011 Jakel et al. : A calibration procedure for beam monitors 1011

Medical Physics, Vol. 31, No. 5, May 2004

Figure 1: Monitor calibration factor, K(E), as measured according to Equation (1) for six different energies ofthe carbon ion beam [9].

into a number of particles:

K(E) =N

MU=

DAPw(z)SE(z) MU

(2)

where DAPw(z) is an integral dose determined from the measurements with large area parallel-plateionisation chamber. Following this technique the user should check that the size of the used chamberwas large enough to capture the entire spot at the calibration depth. If the size of the chamber wasnot large enough, then the measured value of DAPw(z) will be underestimated due to not covering thefull tail of the lateral dose distribution. Correction factors for this lack of tail contribution may beobtained from film measurements exposed in a plastic phantom at the calibration depth or be derivedfrom Monte Carlo simulations.

2.4 Summary of dosimetry calibration procedures

It can be summarised from the examples described above that the control of the absolute dose deliveredwith scanning beams needs quite a different approach to beam monitoring and dosimetry than thatusing passive scattering methods. The whole procedure is becoming very much facility-dependentand the dosimetry intercomparison protocol used in the past for passive beam delivery facilities withverification of dose determined in one reference point of the phantom is not valid anymore. It ispossible to validate each step of calibration procedure separately, but this will require complicatedinstrumentation and substantial effort should be invested into the evaluation of the results.

3 Dosimetry auditing procedure based on end-to-end test

The most efficient solution for dosimetry auditing at scanning beam facilities is to use a protocolbased on so-called end-to-end test. The purpose of this auditing is not just to validate beam linemonitor calibration but to confirm that the entire logistic chain of radiation treatment starting from



CT imagining, treatment planning, monitor calibration, and beam delivery is operable and leads to thedesired results with sufficient accuracy. End-to-end test may be performed with a plastic phantom thathosts a set of detectors distributed over the predefined volume. The user should scan the phantom,transfer the data to the TPS, perform planning to deliver the prescribed dose to the requested targetvolume, and then to execute the plan in a way similar to the patient’s treatment. The auditing procedureof the TPS based on end-to-end test with CIRS phantom was established at the International AtomicEnergy Agency (IAEA) and allowed to verify planned dose delivery for typical treatment techniquesin high-energy photon beams [11]. The Radiological Physics Center (RPC) in Houston used theauditing procedure when credentialing the institutions involved into IMRT [12]. Currently RPC isdeveloping auditing procedure for proton facilities based on thermoluminescence (TL) detectors aswell [13]. However, the TL detectors used by RPC for dosimetry measurements may not providesuitable accuracy for scanned carbon beams as the LET dependence for TL detectors requires seriouseffort in understanding and evaluation of correction factors.

Alanine detectors were successfully used at National Physical Laboratory (NPL) for measurementsin proton beams and were proposed as detectors for postal dosimetry intercomparisons [14]. Theresponse of these detectors also depends on LET and requires determination of the correction factors.However, it is possible to calculate the response in the given particle field with a reasonable accuracyand hence it is possible to use these detectors for absolute dosimetry [14, 15].

3.1 Selection of the phantom and detectors

An alanine detector was selected as the detector for end-to-end test in scanned ion beams. The fol-lowing advantages of alanine detectors can be emphasised:

• Alanine is nearly water equivalent in terms of stopping powers and density (pellet densitiesactually close to PMMA).

• Alanine is an integrating dosimeter with very stable post-irradiation signal and no destructivereadout making, thus is suitable as an archiving dosimeter.

• There is no dose rate dependence until extremely high dose rates making it very suitable forscanning ion beams.

• The disadvantage of alanine dosimetry is that there is also an LET dependence, but it can beaccounted [14, 15].

• The sensitivity may be an issue: 5 Gy is needed for a 1 % reproducibility and 15 Gy is neededfor 0.3 % reproducibility.

Alanine pellets for end-to end test have been supplied by the NPL. The NPL will not only providethe detectors for pilot studies and perform the evaluation of the results through the established postalservice procedures [16], but also will participate in the research activity. A dose value of 10 Gy(physical dose) will be delivered to alanine detectors through the pilot studies at different facilities.The NPL alanine detectors consist of 90.9 % by weight L-α-alanine and 9.1 % high melting pointparaffin wax. The average density is 1.23g/cm3. The pellets with a diameter of 5.05 mm and witha thickness of 2.27 mm that are normally used in a dose range of about 5 kGy to 70 kGy will beemployed in the dosimetry auditing. Dosimeters are conditioned at 55 % relative humidity for tenweeks prior to use in order to reduce post-irradiation fading. The exposed dosimeters will be shippedto the NPL, where they will be read out following the standard procedure as described in detail in [16].This procedure has a precision of better than 0.05 Gy.



Axial view (in the contrary direction of the beam)

The outer ring (A,D) has a radius of 3 cm from the middle of the pellets and the central axis. The

inner pellets (B/C) are arranged at distances of zero and 1 cm to the both axis of symmetry.

20 cm

20 cm

A1

D2 A2

D3

A3

D4

A4 D5

A5

D1 B5/C5

C1 C2

C3 C4

B1

B2

B3

B4

8 cm

8 cm

12 cm

12 cm

12 cm

12 cm

GafChromic

Sagittal view

D C B A

1 2 3 4 5 6 7

A2

A1

A3

A5

A4

B1/B3/B5

B4

B2 C1/C2

C3/C4

C5

D5

D4

D1

D3

D2

21 cm

3 cm 3 cm 3 cm 3 cm 3 cm 3 cm 3 cm

12 cm

ca. 1 mm

GafChromic

8 cm

Figure 2: Schematic view of the phantom: left – beam eye view; right – sagittal view. The target volume isoutlined in red.

Other type of detectors – radiochromic films – will be employed to provide additional two dimensionaldose distribution. Gafchromic® EBT films were selected for pilot as the response of this film wasrecently studied in details by the Heidelberg group [17].

The phantom material was made from black polystyrene. The schematic of the phantom is given inFigure 2. The size of the phantom was selected to be 20cm×20cm×21cm to represent the head area.The assembled phantom is shown in Figure 3 – left; the parts of disassembled phantom are shown inFigure 3 – right. The study of water equivalent density (WED) of the phantom material was performedat PSI in a 167 MeV monoenergetic proton beam. A WED value of 1.04g/cm3 was obtained from thecomparison of measured depth dose curves in water.

The structure of the plates and the placement of the detectors are shown in Figure 4. The left part ofthis figure shows the placement of the detectors in one of the plates as well as the depression to placethe EBT film. The right part of the Figure 4 shows all four plates with alanine detectors. This patternof detector placement allows to cover the target volume and minimise the shadowing of the detectors.

Figure 3: The view of the assembled phantom – left; the parts of the disassembled phantom – right.



Figure 4: The placement of the detectors in one of the plates as well as the depression to place the EBT film –left; four plates with alanine detectors – right.

3.2 Practical steps of the end-to-end testing procedure

The purpose of end-to-end test is to confirm that the entire logistic chain of radiation treatment startingfrom CT scanning, treatment planning, monitor calibration, and beam delivery is operable and leadsto the desired results with sufficient accuracy. A questionnaire (see Appendix) was developed andthen sent to the European ion beam facilities to collect the data related to the treatment systems(accelerators, beam delivery systems), dose per MU calibration approaches, and treatment planningsystems used in clinical practice. The second part of the questionnaire had the purpose to identify thepreferences and possible suggestions in the implementation of the auditing procedure. The receivedresponses were analysed and used in the further design of the auditing procedure.

The description of the developed end-to-end procedure is provided below. The steps of the procedureare documented through the set of Excel data-sheets that are filled by the participating institution.The data-sheets are given in Appendix. End-to-end test will be performed using the plastic phantomdescribed above. Each measurement is using 20 alanine pellets and two EBT films as shown in Fig-ure 4. The phantom with the detectors is placed on the CT table and the scanning is performed as perpatient head scanning protocol used at the facility. The data are transferred to the treatment planningsystem. The user will create inside a the phantom a target volume as a rectangular object with a side of8cm×8cm and a height of 12 cm. The target volume is placed with its centre located at the centre ofthe phantom and the axis of the target volume is parallel to the beam direction. The user will create aplan to deliver to the target volume a predefined dose of 10 Gy and will transfer the plan for executionto the treatment beam line. Lateral and distal margins are selected following the institution’s protocol.The phantom will be set up for irradiation following the standard position verification procedure usedfor patient’s set-up and the planned delivery of the requested dose to the target volume will be exe-cuted. After irradiation the phantom will be disassembled and the alanine pellets will be transferred tothe shipping containers that have marked depressions to document the location of each detector duringthe test. The phantom is then assembled having the central plate with the cavity for placement of anionisation chamber. The phantom will be again set up for irradiation following the standard positionverification procedure used for patient’s set-up and the chamber will be inserted into the cavity. Theplanned delivery of the requested dose to the target volume will be executed and the measured chargewill be converted into absorbed dose per IAEA TRS-398 recommendations.



The exposed detectors will be sent to NPL for the processing and the report will be generated. Thecorrection factors will be defined following the results presented in [14, 15]. It is foreseen that theresults of the testing will be reported only to the participated institution and will not be published orreported without common agreement.

3.3 Results of the pilot study

The pilot study was performed at the Heidelberg Ion-Beam Therapy Centre (HIT) during the last weekof June 2011. The measurements were done in both proton and carbon scanning beams. The auditingprocedure was divided into several parts and each part is covered by correspondent worksheet that isfilled by the auditing team.

3.3.1 Assembling the phantom

The alanine detectors were provided by NPL and were placed into the phantom as well as the EBTfilms prior the study. 20 alanine pellets and two EBT films are used per measurement in proton beamand the same amount of the detectors were used in carbon beam. The assembled phantom and someparts are shown in Figures 3 and 4.

3.3.2 Scanning of the phantom at the planning CT

The assembled phantom is placed at the flat top insert of the CT table and aligned using lasers. Thephantom scanning set-up is shown in Figure 5.

Figure 5: The phantom scanning set-up on the CT table.



3.3.3 Treatment planning

The CT data are transferred to the treatment planning system. The plan to deliver homogeneousphysical dose to the target volume is prepared and then transferred to the treatment beamline. Theplanned dose distributions are shown in Figure 6.

Figure 6: Planned dose distributions for the target volume.

3.3.4 Dose delivery

The assembled phantom is placed on the patient positioner and aligned using in-room equipment. Thephantom set-up during irradiation in the treatment room is shown in Figure 7. After finishing theirradiation the phantom is disassembled, detectors are removed; the central plate is replaced with the



Figure 7: The assembled phantom set-up during irradiation in the treatment room.

plate having a cavity for placement of the ionisation chamber (PTW 30010). The irradiation procedureis repeated, the measured values of the chamber responses are recorded and the dose per MU iscalculated using the recommendations of the IAEA TRS-398 [1]. The results of dose determinationare given in Table 1.

It can be seen from Table 1 that the agreement of measured data with the dose monitor calibration iswithin the uncertainty of ionisation chamber measurements. The planned dose values were correctedfollowing the results of the dose per MU measurements.

dose/MU measured uncertainty dose/MU(TRS-398) 1σ calibration output

protons 0.971 2.0 % 0.988carbon ions 0.977 3.0 % 0.988

Table 1: Results of dose per MU measurements in proton and carbon beams.

3.3.5 Evaluation of the dosimetry results

The alanine pellets irradiated during both sessions are packed into labelled containers and shippedto the NPL for the readout through established postal service procedure [16]. The water equivalentdepth at front surface of each pellet is reported based on the data of the treatment plan. These dataare needed to determine the relative effectiveness (RE) of each detector due to the irradiation in theion beam. The relative effectiveness, RE, as a function of energy, E, and depth, z, is defined as the



relation between the applied dose and the isoeffective dose of 60Co [14, 15]:

RE(E,z) =D60CoDion

(3)

where D60Co is the dose deposited with 60Co, which causes the same detector response as the dosedeposited by the ion beam Dion. The RE values for both irradiations were calculated at the AarusUniversity based on the method described in [14, 15]. The resulted doses to the alanine pellets wereobtained from the data reported by the NPL using the correspondent values of RE factors. The com-bined results are given in Table 2 where the mean values of differences between measured doses of 20detectors are given for proton and correspondingly for carbon ion cases.

mean difference σ uncertainty(20 detectors)

protons 2.0 % 1.0 % 2.7 %carbon ions 1.0 % 1.1 % 2.7 %

Table 2: Comparison of planned and measured doses in proton and carbon beams.

It can be seen from Table 2 that the planned doses are in a good agreement with the delivered doses.The maximal deviation of the measured and planned values did not exceed 3 % in both beams. Thestated uncertainty of the measurements includes the uncertainty of the results from the NPL, the

Figure 8 Measured proton dose distributions - left, measured carbon beam dose distributions – right

There are no established criteria for agreement between measurements and calculations for scanned ion beams.

The most reasonable analysis of these criteria was performed by Jaekel et al. [17]. If several test target volumes

of different geometrical shapes defined in a homogeneous medium are employed for verification of dose delivery

of ion beams with modulated scanning, then following the recommendations given in [17], the mean deviation

between measured and calculated doses should be less than 3% while the maximum deviation should be less than

5%. The data given in Table 2 are in compliance with the proposed criteria.

It can be concluded that the results of the pilot study show that the described procedure of auditing of

scanning beam facility may be used for verification of scanning beam delivery with sufficient

accuracy.

The participation of the following persons in the performed pilot study is gratefully acknowledged:

Hugo Palmans, Peter Sharpe, National Physical Laboratory;

Oliver Jaekel, Swentje Ecker, Naved Chaudhri, Heidelberg Ion-Beam Therapy Center;

Niels Bassler, Rochus Herrmann, Aarus University:

Additional reference:

[17] O. Jaekel, G. H. Hartmann, C. P. Karger, P. Heeg, and J. Rassow (2000)” Quality assurance for a treatment

planning system in scanned ion beam therapy” Med. Phys. 27, 7:1588-1600

Measurement:Plate A Plate C

central profiles for both films along the x-axis (lateral)

Measurement:Plate A Plate C

central profiles for both films along the x-axis (lateral)

Figure 8: Measured proton dose distributions – left, measured carbon beam dose distributions – right.



uncertainty of the calculated RE factors and the uncertainties associated with the phantom irradiation.The relative dose distributions obtained with the Gafchromic films that are given in Figure 8 alsosupports the results of the alanine dosimetry. The cross-sectional profiles shown at the bottom part ofFigure 8 demonstrate homogeneity of dose distribution over the target area within 3 % for both protonand carbon ion beams, with slightly more “bumpy” profiles for carbon ion beam.

There are no established criteria for agreement between measurements and calculations for scannedion beams. The most reasonable analysis of these criteria was performed by Jäkel et al. [18]. Ifseveral test target volumes of different geometrical shapes defined in a homogeneous medium areemployed for verification of dose delivery of ion beams with modulated scanning, then following therecommendations given in [18], the mean deviation between measured and calculated doses shouldbe less than 3 % while the maximum deviation should be less than 5 %. The data given in Table 2 arein compliance with the proposed criteria.

It can be concluded that the results of the pilot study show that the described procedure of auditing ofscanning beam facility may be used for verification of scanning beam delivery with sufficient accuracy.

3.3.6 Acknowledgement

The participation of the following persons in the performed pilot study is gratefully acknowledged:

• Hugo Palmans, Peter Sharpe, National Physical Laboratory;

• Oliver Jäkel, Swentje Ecker, Naved Chaudhri, Heidelberg Ion-Beam Therapy Center;

• Niels Bassler, Rochus Herrmann, Aarus University.



A Questionnaire

This questionnaire was sent to the European ion beam facilities to collect the data related to the treat-ment systems (accelerators, beam delivery systems), dose per monitor unit calibration approaches,and treatment planning systems used at the facilities. These data are summarised under Part I of thequestionnaire. The purpose of the second part of the questionnaire was to identify the preferencesand possible suggestions in the implementation of the auditing procedure. These data are summarisedunder Part II of the questionnaire.

Q u e s t i o n n a i r eInstitution:Address:Medical director:Chief medical physicist:

Person completing this questionnaire (please provide your contact information)Name:Phone: FAX: email:Date completed:

I. General description of the treatment systemI.1 Particle accelerator:

• Is your accelerator a cyclotron 2 or synchrotron 2 ?

• Is it a proton 2 or a dual particle facility (protons and carbon ions) 2 ?

I.2 Beam energy per nucleon (range):• Protons• Carbon ions

I.3 Beam delivery system:• Passive, briefly describe:

• Scanning beams, briefly describe:

I.4 What treatment planning system is used at the facility for planning radiation ther-apy (manufacturer, software release)?

• Is this TPS used for planning of proton therapy only 2 ?

• Is this TPS used also for planning of carbon ion therapy 2 ?

• Can this TPS be also used for planning combined treatments (if patients receiveproton, or carbon beam and also photon treatment) 2 ?



I.5 What is the output of TPS to characterise calibration of proton (carbon ion) dosemonitors?• Number of particles per Gy 2 ?

• Number of MUs 2 ?

• Other 2 ?

I.6 What calibration procedure is followed for the proton beam dose per MU calibra-tions?

I.7 What calibration procedure is followed for the carbon beam dose per MU calibra-tions?

I.8 What instruments are used for the absolute dose calibrations?

I.9 How is the dose recorded in the chart?• Physical dose 2 ?• Co-Gy equivalent dose 2 ?• Other 2 ?

II. Preferences and possible suggestions on the implementation of the auditingprocedure based on the end-to-end test

If you are agreeing with the proposed procedure please answer the following questions.

II.1 Please identify any preference of the material for test phantom• PMMA 2 ?• Polystyrene 2 ?• Other 2 ?

II.2 How CT data conversion to proton (and/or carbon ions) stopping powers is per-formed in the TPS?

II.3 Are CT data conversion tables provided by the vendor or should the tables becreated by the user of the TPS? If provided by the vendor, can the user of TPSmodify CT data conversion tables?



II.4 Please describe how PTV lateral margins are selected? What margins were usedin the plan?

II.5 Please describe how the treatment margin in the direction of the beam are defined?What distal margins were used in the plan?

II.6 How will the position of the phantom and placement of isocentre be verified?• Using orthogonal X-ray images compared to DRRs 2 ?

• Using X-ray BEV images compared to DRRs 2 ?

• Both 2 ?

II.7 Do you use automated software to establish the agreement between the verifica-tion images and DRRs and calculate shifts of the patient positioning system?

If yes, please identify vendor?

II.8 Do you have any estimates of the doses received by patients during position veri-fication procedure?

II.9 Any additional comments, suggestions



B Summary of the responses to the questionnaire

Particle Accelerator

Type of Acc Particles and Energy Beam Delivery System

PSI cyclotron p: 250 MeV discrete spot scanning (38 range shifter plates,magnetic scanning, table movement)

CNAO synchrotron p: 60 – 250 MeVC:100 – 400 MeV/u

quasi-discrete, 3D active scanning (like GSI,HIT), fixed beamlines: horizontal and vertical

INFN cyclotron p: 62 MeV eye proton therapy facility (double scattering,range shifter, modulator, nozzle for shapedpatient collimator, bolus)

HIT synchrotron p: 48.12 – 221 MeVC: 88.8 – 430.1 MeV/u

intensity modulated raster scanning system(with feedback for position control)

PTZ synchrotron p: 40 – 220 MeVC: 73 – 430 MeV/u

Siemens system like HIT (similar to GSI pro-totype)

WPE cyclotron p: 230 MeV single scattering of small fields, double scat-tering of larger fields, uniform scanning (sim-ulated scattering) in 1 gantry and 1 horizontalbeamline, pencil beam scanning for 3 gantriesand horizontal beamlines, IBA equipment

ITEP synchrotron p: 80 – 220 MeV single scattering of small fields, double-scattering of larger fields (modulation withRF), summarising BP for modulation, energychange with degrader



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Position Verification

Position Verification Automated software usedfor shift

Dose used for verification

PSI orthogonal X-ray images vs.DRR

in-house developed extremely low

CNAO orthogonal X-ray images vs.DRR

Medcom, Verisuite-Particle,Darmstadt

very low;stereoscopic imaging:in the order of mGy

INFN orthogonal X-ray images vs.DRR; BEV vs. DRR

— Not reported

HIT orthogonal X-ray images vs.DRR

Siemens RTT-PT system < 1 µSv/image

PTZ orthogonal X-ray images vs.DRR; later CBCT

Siemens PT(3 transl. + 3 rot.)

not reported

WPE orthogonal X-ray images vs.DRR or laser, depending onaccuracy requirement

Medcom Verisuite usedwith CT/MRI pre-positioning image guidance

not reported

ITEP orthogonal X-ray images vs.DRR; BEV vs. DRR

— not reported

C Some details on the responses to the questionnaire

C.1 General

Seven institutes filled out the questionnaire (PSI – Villigen, CNAO – Pavia, INFN – Catania, HIT– Heidelberg, PTZ – Marburg, WPE – Essen, ITEP – Moscow), whereas two of them (PTZ, WPE)are not yet clinical. Furthermore three institutes (NRoCK – Kiel, Curie Institute – Orsay, Skan-dionkliniken – Uppsala) did not fill the questionnaire, but provided useful comments and expressedwillingness to participate in the auditing in future. The data include the response of the INFN, whichis a facility dedicated exclusively to eye proton therapy. In the following short overview the differentused systems, their similarities and their differences, are emphasised.

C.2 Particle accelerator

Four of the seven facilities are using a synchrotron, whereas the other three institutes, which are onlydoing proton treatments, are working with a cyclotron. Carbon ions are available in three centres(CNAO, HIT, PTZ). Concerning the energy range of the used proton and carbon ion beams, there arealmost no differences between the centres. The highest energy for protons used in the clinics reachestypically from 220 MeV to 250 MeV, with the exception of INFN (62 MeV). For carbons the typicalused energy spectra are between 73 MeV/u and 430 MeV/u where the lowest and the highest availableenergy is varying a little bit from centre to centre. Most of the participating facilities are using an



intensity modulated raster scanning system or some similar types of scanning technologies for theirbeam delivery system. Only at ITEP, INFN (eye treatments) and WPE (in addition to scanning) ascattered beam is used for the treatments.

C.3 TPS, dose calibration and dose recording

For the calculation of proton plans different treatment planning systems are in use. Some of themare made in-house like PSIplan or ITEP-ProCom. Two commercial solutions, Raysearch and CMSXiO, are going to be used in the future at WPE. The currently only available commissioned TPS forcarbon ions is Siemens Syngo PT which is used in different versions by all of the participating carbonfacilities. Due to the different output of the treatment planning systems (MU calibrated, particlesper Gray or particles per spot) also the calibration procedures worked out at the institutes is verymuch different. Whereas most of the facilities are using ion chambers (as recommended in IAEATRS 398) for MU/Gy determination, the general approach for a scanning beam is another calibrationin absolute particle numbers which is performed very differently. The dosimetry equipment is nearlythe same except of ITEP, where an activation dosimetry instead of measurements with ion chambersis performed. The typical combination is a PTW UNIDOS electrometer with an air filled ion chamberlike Farmer type or Markus type. Concerning the recording of the delivered dose it seems that nocommon code of practice is in use. Either the physical dose or the 60Co-equivalent dose is primarilyrecorded in the chart. As an additional record sometimes the biologically weighted dose DRBE(GyRBE)is taken into account.

C.4 Phantom material, CT data conversion and PTV margins

The preferred phantom material of the institutes was PMMA. The reason for that could be that PMMAis often used for routine checks and therefore the handling and behaviour of the material is quitefamiliar. The conversion of CT data into HU and finally into stopping powers is typically done bylook-up tables. Most of the participating proton and carbon facilities have created their own tables bya stochastic calibration procedure for each scanning protocol and particle type. Only at INFN the TPS(Eyeplan) assumes for simplicity a spherical, homogeneous volume with given density of 1.5g/cm3.Regarding the use of margins a large variation between the clinical protocols of the institutes can beseen. The range for lateral margins goes from 2 mm over 3 mm to 5 mm and up to 10 mm. At thedistal end of the treated volume typically 1 mm to 3 mm are used.

C.5 Position verification

All participating institutes are verifying the patient’s correct position by comparing the orthogonalX-ray images with DRRs from the TPS. INFN and ITEP has the further possibility to check the set-upwith images in beams eye view. Whereas PSI is using an in-house made, automated software forshifting the patient, two other solutions are currently in use: “Medcom Verisuite” at the CNAO andlater at the WPE, and “Siemens RTT-PT” at the HIT and later at the PTZ. Concerning the dose usedfor position verification all institutes who answered the question agreed that the dose received by thepatient is very low. However, no measured data were reported.



C.6 Final motivation for a dosimetric audit

After the comparison of various answers given by the institutes it can be seen that the use of differentdelivery systems also includes different calibration procedures. Especially for scanning systems ageneral code of practice is missing. It is accepted by all recipients that the lack of primary standardsfor such systems require an additional dosimetric check of the whole delivery chain to avoid any kindof systematic errors. This could be achieved by a multi-centre end-to-end test auditing including CTscanning, planning and the irradiation of a specific test phantom to determine the output of a givenprescribed dose.

D Reporting spreadsheets for end-to-end test auditing procedure

In order to register the results of the audit and standardise the reporting procedure a set of the Excelspread-sheets was prepared to document each step of the end-to-end test: CT scanning, treatmentplanning, irradiation, and dosimetry verification with ionisation chamber. Examples of the spread-sheets are given below.

D.1 CT scanning

①

Institute:

Address:

Medical Director:

Chief med. Physicist:

Assisting Physicist:

Isocenter: Center of the phantom

(Middle of plate 4)

PTV: 8cm x 8cm x 12cm symmetric around Isocenter

Prescription: 10 Gy, physical dose

Phantom: with Alanine and film

Scan:

Head

kV

mA

mAs

mm

proton: MeV

carbons: MeV/u

5cm x 5cm x 2cm in 4th plate

CT - Scanning

HUmean in ROICenter:

Stoppingpowers for HUmean :

ROICenter:

CT-Scanner:

Scanprotocol:

Scanparameter:

Slicewidth:

# Slices:

Dose from Scan:



D.2 Treatment planning

②a

Institute:

Address:

Medical Director:




(Middle of plate 4)



TPS:

Protons:

Plan Parameter

absolute [Gy] relative [%] Definition (ICRU 83)

Dmax : max. Dose

D2%: dose from 2% of volume

Dmin : min. Dose



Dmean: mean dose

TPS calculated

HI: (D2%-D98%)/D50%

CI: V100%/PTV

Beam Parameter

spotsize:

# spots:

layer 1:

layer 2:

layer 3:

layer 4:layer 5:

layer 6:

layer 7:

layer 8:

layer 9:

layer 10:

layer 11:

layer 12:

layer 13:

layer 14:

layer 15:

layer 16:

layer 17:

layer 18:

layer 19:

layer 20:

PTV

Planning



D.3 Irradiation of the detectors in treatment beamline

③a

Institute:

Address:

Medical Director:




(Middle of plate 4)



Dose from Verification: µSv

Protons:

Alanine & films:

p: hPa

T: °C

Dose:TPS Measurement TPS/Measured

A1

A2

A3

A4A5

B1

B2

B3

B4B5

C1

C2

C3C4

C5

D1

D2

D3

D4D5

Irradiation

Residual range, cm



D.4 Verification measurements with ionisation chamber

③a

Institute:

Address:

Medical Director:




(Middle of plate 4)



Dose from Verification: µSv

Protons:Ion Chamber:Electrometer

SN Electrometer:

SN ion chamber:

ND,W:

p: hPa Rres:

T: °C kQ,Q0:

kt,p: KS:

M1:

M2:

mean:

Dose:

Irradiation



CONCLUSIONSThe technological development of radiation therapy with protons and carbon ions enabled the im-plementation of scanning beam delivery techniques and the next generation of ion beam facilities inEurope aim to employ only scanning beams. The most efficient solution for the dosimetry intercom-parison of scanning beam delivery systems is to use an end-to-end test auditing procedure.

A questionnaire was developed and then sent to the European ion facilities to collect the data re-lated to the treatment systems (accelerators, beam delivery systems), dose per monitor unit calibrationapproaches, and treatment planning systems used in clinical practice. The second part of the question-naire had the purpose to identify the preferences and possible suggestions in the implementation ofthe auditing procedure. The received responses were analysed and used in the design of the auditingprocedure.

The dosimetry auditing procedure has been developed based on the use of a plastic phantom that hostsa set of alanine detectors distributed over a predefined volume and as well as EBT films. Alaninedetectors are provided by the National Physical Laboratory and the dose delivered to the selectedtarget volume during the irradiation is 10 Gy.

The purpose of the end-to-end test auditing procedure is not just to validate beamline monitor cali-bration but to confirm that the entire logistic chain of radiation treatment starting from CT imagining,treatment planning, monitor calibration, and beam delivery is operable and leads to the desired resultswith sufficient accuracy. Following the procedure the user should image the phantom on the CT scan-ner, transfer the CT data to the treatment planning system, perform planning to deliver the prescribeddose to the requested target volume, and then to execute the plan in a way similar to the patient’streatment. The procedure was validated through a pilot study.



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