S39Abstracts / Brachytherapy 12 (2013) S11eS77

The decrease in procedures was observed for LDR (23.5 in 2007; 17.6 in2011) and the HDR (11.0 in 2007; 8.2 in 2011). The decrease inprocedures was observed for interstitial technique (34.5 in 2007; 25.8 in2011) but minimal changes were observed for intracavitary technique(46.3 in 2007; 45.3 in 2011).Conclusions: The average number of brachytherapy procedures performedby radiation oncology residents in ACGME programs decreased by 12%from 2007 to 2011. Most of the decrease has occurred with LDR andinterstitial methods.

POSTER DISCUSSION: PHYSICS

Friday, April 19, 2013

8:00 AM-9:30 AM

PD10

WITHDRAWN

PD11

Optimized Geometry for a Directional, High-Dose-Rate

Brachytherapy Source Using 103Pd, Based on Monte Carlo

Simulation

Athena Y. Heredia, MS1, Douglass L. Henderson, PhD2, Bruce R.

Thomadsen, PhD1,2. 1Medical Physics; 2Engineering Physics, University

of Wisconsin-Madison, Madison, WI.

Purpose: The purpose of this work was to optimize the geometry ofa palladium-103 (103Pd) directional high-dose-rate (d-HDR) source foruse in brachytherapy applications using Monte Carlo N-Particle (MCNP5)transport code, and contrasting dosimetric parameters with previousdesign, according to TG-43U1 formalism. A cylindrically shaped versionof the d-HDR seed was presented at AAPM, Charlotte, N.C. (2010) along

Figure 1. (A). Optimized d-HDR azimuthal dose distribution. (b).

Contrast between previous cylindrical shaped version and optimized D-

shaped version of d HDR seeds. (C). Left relative dose distribution as

a function of angle for cylindrical seed desgin: right relative dose distribu-

tion for D-shaped showing more uniform dose profile.

with dosimetric information. This work presents a more optimizedgeometry of the directional seed to improve dose distribution.Materials and Methods: The source material consisted of 0.01009 cm3 ofactive 103Pd urrounded by a 0.001 cm thick titanium encapsulation. A layerof 0.003 cm of Osmium (density 5 22.57 g/cm3, TVL50.0018 cm) wasemployed as the shielding material. The geometry of this seed wasdesigned to be D-shaped, as opposed to the previously modeled d-HDRcylindrical source. Monte Carlo simulations were performed using the F6energy-deposition tallies as well as the F4 flux-density tallies. For the F6tally, 1mm3 volumes were placed along the perpendicular bisector of thesource at radii ranging from 0.25 to 100 cm and fifty polar and azimuthalangles, in 7.2� increments ranging from 0� to 352.8�. For the F4 tally,a cylindrical mesh was superimposed over the simulation geometry inorder to calculate the output of the source. The code was benchmarkedthrough comparison with published data for the Theragenics model 200source (Monroe and Williamson, Monte Carlo-aided dosimetry.Results: Dosimetric parameters were found using the recommended TG-43U1 formalism. For the optimized version of the d-HDR, the dose rateL5 0.6645 � 0.003 cGy h-1 U-1 compared to the cylindrical version wherethe dose rate was slightly higher at L 5 0.6856 � 0.003 cGy h-1 U-1. Thegeometry function, was calculated at GL(r51 cm, q590�) 5 0.927, this isthe same as the previous value. The anisotropy function, F(r,q), wascalculated at F(r51 cm, q50�) 5 1.328. The relative azimuthal dosedistributions at r51 cm are shown in Figure1 below.Conclusions: An optimized version of the d-HDR seed has been presentedusing the TG-43U1 dosimetric parameters obtained fromMCNP5. The newD-shaped d-HDR seed shows a flatter dose profile, allowing the dose to bemore uniformly distributed in a tissue volume. This is an improvement overthe cylindrical version which had a rounder dose profile, attributed to itscurved shielding. Preliminary data show an improvement in the new D-shaped geometry. Further data are being collected to fully characterize thesource.

PD12

MRI-Alone-Based Brachytherapy Treatment Planning: Accuracy

and Inter-Planner Variation of Applicator Delineation for

a Titanium Tandem and Ring Applicator

Jing Cai, PhD, Yun Yang, PhD, Beverly Steffey, MS, Junzo Chino, MD,

Oana Craciunescu, PhD. Radiation Oncology, Duke Unviersity Medical

Center, Durham, NC.

Purpose: Clinical implementation of MRI-alone-based brachytherapytreamtment planning is chanllenging because significant susceptibilityimage artifacts of MR images hampers accurate delineation of theapplicator. The objective of this study was to investigate the accuracy andinter-planner variation in delineating a titanium and ring (T&R)applicator for MRI-alone-based planning.Materials and Methods: Three patient who had HDR breachytherapy witha CT/MR compatible T&R applicator (Varian Medical Systems, Inc.) forcervical cancer were retrospecitvely included in the study. All patientswere treated using a MR-CT-hybrid planning (PHBRD) method in whichCT and MR images were fused for applicator delineation and contouring.Multiple T2-w frFSE MR scans were acuqired in different planes(transverse, sagittal, coronal, oblique-axial, oblique-coronal, oblique-sagittal views) for contouring of high-risk clinical target volume(HRCTV) and organs-at-risk (OARs). T1-w 3D-fGRE MR scan werefused with CT for applicator delineation. MRI-alone-based planning(PMRI) were retrospecitvely carried out on a total of 13 fractions, from the3 patients, by placing solid applicators directly on the T1-w 3D-fGREMR images. Four physicists with various years of experience inbrachytherapy independently perfromed the MRI-alone-based planning totest the inter-planner variation. Positions of T&R applicator, defined by 3points at tip of the tandem (TT), center of the ring (RC), and tip of thering (RT), were measured for each plan. Differences in the applicatorpositions were calculated as the square root of the 3D distance of thesereference points. Comparision in application postion was perfomed