Recent proceedings in Brachytherapy Physics

Frank-André Siebert

UKSH, Campus Kiel, GermanyClinic of RadiotherapyDept. Medical Physics

Physical characteristics ofbrachytherapy

(Courtesy Luc Beaulieu, published in Advances in Medical Physics 2016).

Physical characteristics ofbrachytherapy

Brachytherapy is very conformal!!

but, geometry is essential !!

Dose distributions for cervixcarcinoma patients

Georg et al. IJROBP 2008

Brachytherapy outcome: Cervix

Clinic of Radiotherapy

Gill B et al. IJROBP 2014;90:1083Sturdza et al. Improved local control and survival in LACC through Image guided adaptive brachytherapy, (2016)

Image guided adaptive Brachytherapy4D

2D

15%

10%

Brachytherapy outcome: Prostate

Grimm et al (2012) BJUI, meta analysis of 52.087 patients

Low risk prostate cancer High risk prostate cancer

Brachytherapy outcome: Breast

www.thelancet.com Vol. 387, 2016

However, decrease of brachytherapy applications

Brachytherapy clinically successful

• Complex logistics ?• Education ?• Reimbursement ?• Not „sexy“ enough ?• Other techniques catched up ?

Dose calculation

TG-43 formalism

• Standardized• Completly described• Consensus data available for most LDR and HDR sources• Good results• Fast computation

http://www.uv.es/braphyqs/

Dose calculation algorithms

Standard: TG-43 Formalism

Dose calculation possible in all volume data

(CT, MRI, US, …)

TG-43 considers not:

• Tissue inhomogeneities

• Curved sources (wires)

• Lack of scattering from surfaces

• Inter-source absorption

• Shielding-effects in applicators

Modern dose calculation algorithms

• Monte-Carlo

• Boltzmann transport equation

• Collapsed cone

• …

Similar to External beam radiotherapy

Lu et al. 2013

Real-time imaging for brachytherapy

Treatment planning systemUS probe and tracked stepper

Ultrasound system Tracked stepper

Real-time imaging for brachytherapy

• Enhanced patient follow-up data with LDR prostate real-time planning

Matzin et al. Radiat Oncol 2013

n=1176, mean FU 47 monthsI-125 prostate implants

Delineation in T2 data

Ref.: light blue

De Brabandere et al. Radiother Oncol 2012

Impact of interobserver variability on D90

CT T1+T2 CT+T2

Pat ient 1

Patient 2

CT T1+T2 CT+T2

Contouringlarge interobserver variability for D90for all techniques

Seeds� CT: small interobserver spread for D90

� slightly larger for technique (b), using T1 for seeds

Fusion� T1 + T2 : interobserver variability

relatively small, but patient dependent

� CT + T2 : large interobserver variability

Patient 3 BRAPHYQS WP: De Brabandere et al. Radiother Oncol 2012

More information on usage of image fusion in brachytherapy needed.

New BRAPHYQS WP20 (chair JamemaSwamidas)

Risk management, treatment verification

As we know, errors occur!!

Uncertainties vs. errors

Brachytherapy treatment:• Everything is prepared and planned well• But how can we be sure that the dose is delivered correctly??

Possible errors in Brachytherapy

• Afterloader malfunction

• Swapped channels

• Wrong patient

• Incorrect single dose

• Incorrect indexer length

• Wrong air kerma strength

• Wrong step size

• Incorrect applicator position

• Movement of applicator

• …

Risk management

Increasing interest in risk managment in radiotherapy

• AAPM: TG100 report

• Europe: ACCIRAD report

Risk management

• European guidelines for Risk Management exist

– Room for individual implementation of risk management– Not dedicated to brachytherapy– Applicable to brachytherapy

• National guidelines are complementing European report

• German guidelines contain external beam radiotherapy, brachytherapy,

nuclear medicine

Risk management

Actual Target

Problem Severity Likelihood Detectability Risk Severity Likelihood Detectability Risk

Connectingapplicators

Swapping ofchannels

7 4 2 56 7 2 1 14

Procedure to reduce risk:four eyes-principle, identification (coding) of catheters

0 ≤ S, L, D ≤ 10

Treatment verification in BT

The missing puzzle piece in brachytherapy…

Is not a new approach …

• TLDs• MOSFET• Diodes• Alanine• …

Challenges:• High-gradient dose - > precise detector placement• Large range of dose and dose rate

23% of the clinics in Europe use in-vivo dosimetry in BT

Guedea et al. 2010

Treatment verification in BT

Typical practise for prostate, gynae treatments:

5-fold rectum diode array

Sagittal view K. Tanderup et al. 2013

K. Tanderup, et al. 2013

EBRT Onboard imaging„Real-time“

Treatment verification in BT

New approaches needed

• Applicator misplacements ≥ 5 mm were detected

• Many channel connection errorswere detected (17 out of 20)

New techniques: unidirectional sources

• Pd-103 brachytherapy source with shielding• Unidirectional sources• Flexible LDR BT device (CivaSheet)• Head&neck, colorectal cancer, soft tissue sorcoma, skin, …

New techniques: 3D printing

…

WP7 Phantom studies for physics part (completed)

WP8 Evaluation of clinical part (completed)

WP9 New recommendations (completed)

WP10 DVH calculation evaluation (completed)

WP11 Physics data on radiation protection (completed)

WP12 QA for prostate implant dosimetry in LDR and HDR

WP13 Uncertainties in Brachytherapy (completed)

WP14 In-Vivo dosimetry

WP15 Interobserver variability study (completed)

WP16 Integral doses in BT (completed)

WP17 DICOM standard in Brachytherapy

WP18 Dosimetry of LDR sources at clinical level (new)

WP19 Commissioning of BT treatment planning systems (new)

WP20 Image Fusion in BT (new)

GEC ESTRO BRAPHYQS Work Packages

BRAPHYQS/UroGEC meeting Benidorm 2016

Kiel-Phantom

BRAPHYQS work package results: (Multi centric mailed phantominvestigations)• Reconstruction independant on clinic and software• CT slice thickness should be ≤ 3mm

Impact on seed reconstructiontested:Seed type ����Slice thickness ����

Field of view ����

Axial or spiral ����Tube current ����Treatment planning system ����

CT scanner ����

Impact on seed reconstructiontested:Seed type ����Slice thickness ����

Field of view ����

Axial or spiral ����Tube current ����Treatment planning system ����

CT scanner ����

FA Siebert et al. Radiother Oncol 2007

Patient case

WP7 Phantom studies

Chair: M De Brabandere, FA Siebert

WP11 Physics data on radiation protection

Chaired: F Ballester, P Papagiannis, D Baltas

• No radioprotection data on design ofbrachytherapy vaults with maze exist

• Study of several Ir-192/Co-60 bunkers

• Geant4 used for computation againstNCRP report no. 151

• NCRP overestimates needed wall thickness

WP 13 Uncertainties in Brachytherapy

Brachytherapy: (only) treatment form in radiotherapy with systematic description ofuncertainties, GEC ESTRO BRAPHYQS project, publ. 2013.

Chair: C. Kirisits

WP16 Integral doses in BT

Chair: A Henry

“This study shows both LDR and HDR brachytherapy monotherapy result in low estimatedrisks of radiation-induced rectal and bladder cancer. … Compared to external beam techniques, second rectal and bladder cancer risks were lowest for brachytherapy.“

Murray et al. Radiother Oncol (2016)

WP18 Dosimetry of LDR sources at clinical level

Chair: J Perez-Calatayud

Aim: how to assay low energy photon sources at hospital level?-> GEC ESTRO recommendation

• Different regulations in Europe

• What equipment ?

• How many sources to be checked (Sk) ?

• Batches ?

• Level of uncertainty ?

• Measurement vs. source certificate

WP19 Commissioning and QA of BT treatment planning systems

Chair: M De Brabandere, A Rijnders

1. Geometry/Imaging: correct image import, image processing,

contouring scaling/dimensions/orientation/zooming/…

2. Source and afterloader specification: source type, nuclide, decay

factor, dose rate constant, TG43-parameters

3. Dose calculation accuracy and representation: TG43, point/line

source, anisotropy, shielding, single source/multiple sources, possible

correction for dose contribution during source movement, isodoses, DVH,

point and line doses

4. Applicator specifications (library): types, dimensions, material?,

specific parameters (no commissioning of the applicator)

5. Output/Data transfer: printouts/reports, export to the afterloader

Dose point dose test

Hand calculation

TPS

GyhUcGyhUD 28.12205794.0635.0 11 =⋅⋅= −−

WP19 Commissioning and QA of BT treatment planning systems

• DVH of great importance

Reporting, dose contraints

• DVHs should be checked

• DVH calculations differ between TPSs

WP19 Commissioning and QA of BT treatment planning systems

BT Data Flow

Brachytherapy TPSTG-43, MBDCAs

Afterloading deviceApplication of seeds, eye plaques, wires, …

Imaging: CT, MRI, … TRUS and stepper

Oncology Information System, PACS

WP19 Commissioning and QA of BT treatment planning systems

Close cooperation betweenGEC ESTRO and AAPM

Thank you for your attention !