S61Abstracts / Brachytherapy 12 (2013) S11eS77

source dwell position and dwell time to achieve better conformal dosecoverage in target volume. The results obtained with Acuros werecorroborated with Monte Carlo calculations.

Figure 1. Comparison of dose distributions for a case with a Mammosite

breast patient plan calculated with homogeneous (left) and heterogeneous

(right) environment. The corresponding DVH comparison for PTV (ma-

gent), skin (green), lung (light green) and ribs (orange) are shown (Acuros

shown with triangles, TG-43 shown with squares).

PO16

Dose Volume Histogram Analysis for Plans Using 7 Channels versus

6 Peripheral Channels for the High-Dose-Rate Brachytherapy

Miami Multi-Channel Applicator

Ileana Iftimia, PhD, Eileen T. Cirino, MS, Herbert W. Mower, ScD, Andrea

B. McKee, MD. Radiation Oncology, Lahey Clinic, Burlington, MA.

Purpose: The goal of this work was to compare the treatment plans for thehigh-dose-rate (HDR) brachytherapy Miami multi-channel applicator whenusing all 7 channels (6 peripheral and one central) versus using only the 6peripheral channels. For our initial plans the central channel was not used,so the planning and treatments were performed by using the 6 peripheralchannels only. The new plans were performed retrospectively by using the6 peripheral channels and the central channel, mimicking that a straighttandem is placed in the center of the cylinder, advanced up to the cervix.Materials and Methods: Recently we implemented the Miami HDRbrachytherapy approach in our clinic. The patients treated using theMiami approach had 25-28 fractions EBRT prior to the HDRbrachytherapy boost. A step by step treatment planning approach wasdeveloped to ensure appropriate coverage for the tumor (D90 O100%prescribed dose of 700 cGy/fraction for 3 fractions) and the uninvolvedvaginal surface (dose for the entire treatment lengthO600 cGy/fraction),while keeping the organs at risk below the tolerance doses. Thecumulative EBRT plus HDR critical structure doses were recorded interms of EQD2 Gy3 and kept below the tolerance values published by theABS (i.e., 90, 75, 75, and 120 EQD2 Gy3, for bladder, rectum, sigmoid,and upper vaginal wall mean dose, respectively). For our first cases weused only the 6 peripheral channels. Even though all DVH criteria weremet we decided to investigate the use of a central tandem when treatingvaginal tumors. We found out a way to use a straight tandem in thecentral channel, advancing it up to but not through the cervix.Retrospective treatment plans were generated for 5 patients and comparedwith the original plans. The following DVH parameters were analyzed:tumor D90, D100, V100, V150, V200, bladder/rectum/sigmoid D0.1cc,D1cc, D2cc, and upper vaginal wall D0.1cc, D1cc, D2cc, and mean dose.Since the D5cc for the walls of critical structures (bladder, rectum, andsigmoid) may be related to late toxicity we decided to retrospectivelycontour these structure walls and record this parameter, which will alsobe monitored for all future patients. This parameter was obtainedretrospectively for the original plans and also for the new plans using 7channels. For consistency, the following structures were contoured for allpatients: BW3mm (3-mm thick bladder wall), BW5mm (5-mm thickbladder wall), RW3mm (3-mm thick rectal wall), RW5mm (5-mm thickrectal wall), and SW1mm (1-mm thick sigmoid wall).Results: The use of the central channel did not have a subtantial impact ontumor coverage or critical structure sparing. The parameters monitoring thetumor coverage and hotspots (D90, D100, V100, V150, and V200) andbladder, rectum, and sigmoid D0.1cc, D1cc, and D2cc were not clinicallysignificant different from the values obtained for the original plans. Also,

bladder, rectum, and sigmoid wall D5cc were comparable for the 7-channel and 6-channel plans. For the patients studied here D5cc was: lessthan 4 Gy/fraction for BW5mm and RW5mm, less than 3 Gy/fraction forBW3mm and RW3mm, and less than 2 Gy/fraction for SW1mm. The useof the central channel allowed for a more homogeneous dose distributionon the surface of the applicator, reducing the small volume hotspots(D0.1cc) on the uninvolved vaginal wall. It also increased the planflexibility and somewhat tumor coverage for the tumors located superiorto the vagina.Conclusions: For all future patients we will acquire the CT images with thecentral tandem in place. Plan flexibility and dose homogeneity will increasewhen using 7 channels.

PO17

Analysis of Medical Events in High-Dose-Rate Brachytherapy

Wanbao Gao, PhD. Southern Advanced Medical Physics, Inc., Long

Beach, MS.

Purpose: The present study reviewsmedical events (MEs) in high-dose-ratebrachytherapy in order to understand the nature of these events and toinvestigate how to prevent the occurrences of errors in HDRbrachytherapy procedures.Materials and Methods: MEs in HDR brachytherapy reported to theNuclear Regulatory Commission (NRC) or agreement states from January1999 to December 2011 are reviewed and divided into five categoriesbased on the nature of the events.Results: From 1999 to 2011, a total of 137 medical event reports involving181 patients were recorded in the NRC database.

The events consist of: (i) wrong treatment site; (ii) treatment planning error;(iii) treatment delivery error; (iv) failure in source retraction mechanism,and (iv) others. The most frequent cause of MEs in HDR brachytherapy isthe use of incorrect catheter/transfer tube length (approximately 42%),resulting in missing treatment targets by distances ranging from 4 mm to30 cm.Conclusions: Unlike permanent brachytherapy in which treatmentdeliveries can be verified with post-implant dosimetry, errors in HDRbrachytherapy can go undetected for multiple fractions or patients.Mistakes can still happen even when a well-established procedure iscorrectly followed, such as the incorrect measurement of catheter lengthdue to obstruction. A test run using film should be performed for eachtype of treatment technique to confirm the geometric accuracy. In-vivodosimetry can be utilized in the first fraction to detect gross target miss orplanning error in the early stage of a treatment course.

PO18

Dosimetry Quality Assurance for COMS Eye Plaques

Ron Sloboda, PhD1,2. 1Medical Physics, Cross Cancer Institute,

Edmonton, AB, Canada; 2Oncology, University of Alberta, Edmonton, AB,

Canada.

Purpose: To develop and implement a quality assurance (QA) process toverify Plaque Simulator dose calculations for patients treated with