S47Abstracts / Brachytherapy 9 (2010) S23eS102

Results: The results show increased PE absorption with decreased averageenergy of the source. While photons interact mainly through Comptonscattering in tissue, they interact almost exclusively through the PE effectin AuNPs. The number of PE events per AuNP per 2Gy using 103Pdexceeds the number of PE events for the 6MV source by 3 orders ofmagnitude.

131Cs, 125I and 103Pd all give rise to a 10-fold increase in PE eventscompared to the 300kV ortho-voltage source. To put these numbers inperspective, our current research suggests that a concentration of 2.5Eþ5AuNPs (30nm) per tumor cell can be clinically achieved. Combining thisassumption with the results presented here, the number of PE eventsarising from a clinically achievable concentration of AuNPs is ~9.70Eþ03 PE events per tumor cell using 103Pd seeds compared to 7 PEevents per tumor cell using a 6MVp photon spectrum. Though the rate ofPE absorption can be a surrogate to dose enhancement, these resultsshould be analyzed prudently. At higher photon energies, the PE effectoccurs mainly through the K-shell (binding energy ~ 81keV), while atlower energies the PE effect occurs through the L-shells (binding energies~ 13keV). There is therefore an 83% reduction in energy imparted tophoto/auger-electrons from lower energy sources. However, this reductionis overcompensated by the dramatic increase in the number of PE events.Furthermore, lower energy electrons deposit their energy in a moreconformal fashion at the cellular scale and may produce a pronouncedbiological effect, such as DNA double strand breaks.Conclusions: This study demonstrates that the most efficient conversion ofphotons into photo/auger electrons by AuNPs occurs in lower energy rangesassociated with brachytherapy seeds. These results reveal that AuNPs area practical and effective candidate for dose enhancement in conjunctionwith brachytherapy. Future research will aim at examining the nano-scaledose enhancement due to AuNP radiosensitization.

OR51 Presentation Time: 1:50 PM

Design of a Minature Electronic Brachytherapy X-Ray Source and

Its TG-43 Dosimetric Parametrization Using Monte Carlo

Simulation Technique

Habib Safigholi, M.S.1, Reza Faghihi, Ph.D.2, Ali Meigooni, Ph.D.2,3

1Science and Research Branch, Islamic Azad University, Tehran, Iran;2Nuclear Engineering and Radiation Center, Shiraz University, Shiraz,

Iran; 3Radiation Medicine, North Shore University Hospital, Manhasset,

NY.

Purpose: In this project a method has been developed for the design ofa miniature electronic brachytherapy (EBT) x-ray source and itsdosimetric parameterization according to the TG43U1 protocol using theMonte Carlo code. This source was designed for the energy range of 25to 80keV.

Materials and Methods: Two geometries of target layer; hemispherical andconical hemisphere shapes were under consideration for two materials of theAu and W anodes. These configurations were analyzed by MCNP4C MonteCarlo code with several different optimizations techniques. Firstoptimization was to on the target thickness layers versus energy in therange of 25 to 80keV. Second optimization was on the electron source forbombardment of the target layer. Third optimization was to obtain theapex of the cone of target in electron bombardment to have morepenetration of radiation dose in the tissue and to gain a dose anisotropyfactor close to unity. Finally, for all optimized cases studies, radial andaxial dose function and dose anisotropy factor according to TG-43U1protocol were calculated.Results: The results show the optimized thickness versus energy variationcan be fitted by 2-polynomial equations Y (mm) 5 0.00021639X2(keV) e0.023221X (keV) e 0.23874 with R250.99981(R-Square Value) and Y(mm) 5 0.000089532X2(keV) e 0.033533X (keV) e 0.48912 withR250.99984 for W and Au target, respectively, which shows a goodagreement with experimental data. The conical shape geometry of targethas a much better 2D anisotropy parameter than the hemispherical one,because electron beam collide with the target layer at the same angle forthe whole target area. The conical anode is similarly less sensitive tochanges in the electron beam. The best dose anisotropy factor will beobtained using a source of electron in the shape of a disk with 0.09 cmradius and optimized angle is calculated to be 60 degree which fits wellwith published data from Xoft Co. Calculated radial dose functions atgp(5) were 0.137, 0.191, 0.247, 0.331 for 40, 50, 60 and 80keV inhemisphere target shape, respectively, and this values for conicalhemisphere target are achieved 0.165, 0.239, 0.305, 0.416, respectively.Calculated values for 2D anisotropy functions have ranged from F (1cm,0o) 51.438 to F (6 cm, 0o) 51.465 in 30 and 80keV, respectively, forhemispherical target shape and this values for conical hemisphere targetare achieved 1.091 and 1.241, respectively.Conclusions: A method of designing a typical EBT x-ray source anddetermining its dosimetric characteristics following the TG-43U1protocol using Monte Carlo MCNP4C code have been presented here.Also parameters that effect the dose distribution such as shape, materialand angle of target, thickness target, target buffer layer, dose reduction inbuffer layer and electron source shape for the bombardment of the targetlayer and x-ray spectra were evaluated.

OR52 Presentation Time: 2:00 PM

Dosimetric Evaluation of an Intrauterine Balloon Technique for

HDR Treatment of Medically Inoperable Endometrial Cancer

Susan Richardson, Ph.D., Perry Grigsby, M.D. Radiation Oncology,

Washington University School of Medicine, St. Louis, MO.

Purpose: The standard of care for endometrial cancer typically is surgeryfollowed by vaginal apex brachytherapy. In the case of medicallyinoperable patients, the uterine serosa is treated through a variety of high-dose-rate brachytherapy applicators including tandems, Heyman capsules,and multi-channel applicators. We report on the dosimetric evaluation ofa new technique consisting of an intrauterine balloon applicator.Materials and Methods: Our clinical protocol is to treat patients with HDRbrachytherapy once a week for 6 weeks. Four patients were treated with anintrauterine balloon technique. Due to the investigational nature of thedevice, the patients were treated with more than one applicator type overthe course of treatment. Patients received at least 2 fractions (out of 6total) with the balloon. Other applicators included a tandem, and tandemand ovoids with Heyman capsules. The dose distributions were analyzedfor patients treated with all of the following: tandem, tandem and ovoidswith Heyman capsules, and balloon. The treatments were evaluated interms of target coverage and dose to organs at risk. The bladder andrectum 2 cc doses were reported, as well as the mean, maximum, andminimum dose to the uterus.Results: All patients tolerated the brachytherapy treatment well and nopatients experienced any acute toxicity. Figure 1 shows the dosedistributions from various high-dose-rate applicators in the same patient.The left distribution is from a tandem, ovoids, and five Heyman capsules.

S48 Abstracts / Brachytherapy 9 (2010) S23eS102

The middle distribution is the intrauterine balloon, and the distribution onthe right is tandem alone.

Overall, the mean dose to the uterus is highest with a tandem alone; howeverthis represents a very heterogeneous dose distribution with high midlinedoses and lower peripheral doses compared to either the balloon or thetandem, ovoid, and Heyman capsule applications. The tandem alsoresulted in the highest 2cc and mean rectal doses. The balloon providedthe highest peripheral or minimum dose to the uterus. In addition, a betterdepth dose is achieved because the balloon pushes away the tissuedirectly adjacent to the source. The balloon provided the lowest meandose to the bladder, while the tandem, ovoid, and Heyman capsuleapplication had the lowest 2cc bladder dose.Conclusions: The intrauterine balloon technique is a safe and well toleratedmethod for the treatment of medically inoperable endometrial carcinomaand yields a dose distribution similar to other well established treatmentdevices. It has the benefit of being easily implementable and iscomfortable to the patient since no packing is required. Additionally,visualization of the balloon and the subsequent dwell positions are readilyfound on CT making the treatment planning easier than for morecomplicated multi-channel devices. This shortens the overall patienttreatment time and can potentially increase through-put. However, longterm clinical followup and further dosimetric investigation in comparisonto other applicators is needed to determine whether this device should befavored over other commercially available products.

OR53 Presentation Time: 2:10 PM

Risk Assessment in Intracavitary Brachytherapy Based on Failure

Mode and Effective Analysis

Jamema V. Swamidas, M.Sc., Dip. R.P.1, Smriti Sharma1, Umesh M.

Mahantshetty, D.M.R.T., M.D., D.N.B.2, Nehal Khanna2, Vijaya Somesan1,

Deepak D. Deshpande, Ph.D.1, Shyam K. Shrivastava, M.D., D.N.B.2

1Medical Physics, Tata Memorial Hospital, Mumbai, India; 2Radiation

Oncology, Tata Memorial Hospital, Mumbai, India.

Purpose: Cervical cancer is the most common cancer among women inIndia and our hospital experiences a burden of large number ofintracavitary brachytherapy procedures. Although the procedure is wellestablished to prevent errors, the recent transition from 2D to 3D-CT/MRimage based dosimetry, introduction of new applicators, inverse planning,multiple planners and growing numbers suggests for more systematicapproach for quality assurance/management. The purpose of this studywas to evaluate the safety in Intracavitay brachytherapy procedure forcervix cancer using Failure mode and effective analysis (FMEA).Materials and Methods: The concept described in TG 100 was used in thestudy. It consists of the following steps a) creation of a process tree, based onthe overview of the entire process b) assigning risk probability numbers(RPN) based on likelihood of occurrence (O), severity of the effects offailure (S) and detectability (D) each on a scale of 1-10. c). To identifythe high RPN numbers and the potential causes of failures and feasibleand effective ways to improve these processes.Results: The process tree in the present study starts from the procedureleading to high-dose-rate intracavitary brachytherapy for cervix cancer.Both conventional dosimetry based on orthogonal radiographs and CT/

MR image-based planning were considered as we routinely practice all ofthem based on departmental protocol. The main branches of the tree wereas follows: applicator placement, measurement of air kerma/activity ofHDR source, machine performance quality assurance, imaging, volumedelineation, reconstruction, dose calculation/optimization, planevaluation, plan transfer and treatment delivery. The process treeconsisted of 89 nodes, with RPN numbers ranging from 1-320. RPNnumbers of more than 100 were considered for process improvements.We identified 37 such processes with RPN numbers more than 100, andeach was associated with a cause of failure and an effective means toimprove the process. Out of 37 high RPN, the top 20 processes wereconsidered for immediate improvements and implemented in the routinepractice. The other processes were also found to be implementable andwould be carried out in the immediate future. Some of the high scoringRPNs are as follows: accuracy of experimental setup for air kermameasurements, entering a new source in TPS, decay/time zone, machineperformance QA, integrity of applicators and transfer tubes, dwellposition accuracy, MR imaging protocol, reconstruction, doseprescription, optimization, connection of appropriate catheters forinterstitialþintracavitary application, and volume delineation of HR CTVin MR image based dosimetry. The philosophy of common causes offailure was found to be lack of attention and work pressure. We havemodified the existing standard procedures for example, checks of theapplicators/transfer tubes, rechecking the plan by a second physicist,recheck by a technologist. We marked the process map and found that thefailure processes were uniformly distributed throughout the process tree.Conclusions: The FMEA method was found to be a useful tool ina systematic approach for quality management for a specific process. Theexperience gained in the implementation of the FMEA for intracavitarybrachytherapy procedure would pave way for larger and much complexprocesses in radiation oncology department in our hospital. FMEA isa ideal tool for quality management especially in a high volume center.

OR54 Presentation Time: 2:20 PM

Drug Eluting Brachytherapy Spacers: A Potential for Biologically-

Enhanced Brachytherapy

Robert A. Cormack, Ph.D.1, Dattatri Nagesha, Ph.D.2, Evin Gultepe2,

Paul Nguyen, M.D.1, Anthony V. D’Amico, M.D.1, Srinivas Sridhar,

Ph.D.2, Mike Makrigiorgos, Ph.D.1 1Radiation Oncology, Dana-Farber

Cancer Institute/Brigham and Women’s Hospital, Boston, MA; 2Electronic

Materials Research Institute, Northeastern University, Boston, MA.

Purpose: Ultrasound-guided prostate brachytherapy routinely implantsspacers between the 125I radiation sources, that provide no therapeuticbenefit although they are essential to the technical completion of theimplant. The spacers offer a vehicle for in-situ delivery of radio-sensitizer, or other agents, which could increase the biologic effectivedose of the radiation. This work studies the achievable drug coverage asa function of the chemical and physical properties of the drugs and devices.Materials and Methods: Fluorescent doxorubicin in a polymer suspensionand gold substrate were used to evaluate the ability to create a radio-opaquedrug eluter. Elution kinetics from polymer coating of gold substrate wasmeasured via fluorescence spectrometry. An analytic solution to thediffusion elimination equation was used to perform computer modeling ofdrug distributions produced by configurations of eluters placed withinultrasound guided prostate implants. Measures of tumor coverage andnormal tissue involvement are evaluated for multiple combinations ofeluter sizes and diffusion elimination moduli 4b.

Results: Timed-release of doxorubicin from a polymer coating on a goldsubstrate, as shown in the top half of the figure, is technically possible.The many spacers used in prostate brachytherapy are sufficient tosensitize a portion of the prostate with values of 4b close to the calculatedones. The use of drug-eluting brachytherapy spacers would enable a morelocalized enhancement in biologic effective dose than what can bedelivered by a local brachytherapy boost. The bottom half of the figureshows a prostate implant at treated at our institution and and how it couldbe locally enhanced with the addition of a small number of drug elutingspacers.