PO-314 PRESCRIPTION DOSE EVALUATION FOR APBI WITH NON-INVASIVE BREAST BRACHYTHERAPY USING EQUIVALENT UNIFORM DOSE

World Congress of Brachytherapy 2012 current study was performed to determine the relationship of breast conservation with radiotherapy in TN breast cancer. Materials and Methods: Total 109 triple negative breast cancer women underwent breast conservation (WLE, lumpectomy, quadrentectomy) followed by radiation 60GY in 30 fraction (200cGy/day 5 days a week). Chemotherapy was given either in neoadjuvant or adjuvant setting in all patients Results: Median follow- up after treatment was 36months.Median age of the patients was 43 years (26-73). 90% patients were early stage and 10 % were locally advanced while 62% were node negative and 38% were node positive. Locoregional recurrence was seen in only 3.7% patients (total 3, chest wall 1) while Distant metastasis was seen in 22.9% patients. At 4.38 years Kaplan Meier estimated disease free survival was 54% and overall survival was 81%. Conclusions: Patients with TN breast cancer are not at significantly increased risk for isolated LRR at 5-years so remain appropriate candidates for breast conservation. There is increased risk of distant failure even in early stage disease associated with poor disease free survival .Targeted therapies are required in clinical trials to find new and better ways to treat it. PO-313 EVALUATION OF IN VIVO DOSIMETRY IN BREAST CANCER BRACHYTHERAPY USING MOSFET DETECTORS D. Nahajowski1, E. Byrski1, R. Kudzia1, D. Dybek1, A. Dziecichowicz1, T. Dabrowski1, A. Kukielka1 1 Centre of Oncology - Institute MSC Kraków, Cancer Centre, Krakow, Poland Purpose/Objective: To evaluate MOSFET detector-based in vivo skin dose in breast cancer brachytherapy performed using the Breast Template SetTM (Nucletron) needle applicator technique. Materials and Methods: In vivo measurements, using TN-502 RDM (Best Medical System) MOSFET detectors were made for 81 female patients undergoing breast cancer brachytherapy by the Breast Template Set (NUCLETRON) needle applicator technique. Prior to patient exposure using the NUCLETRON MicroSelectron HDR system, the MOSFET detectors were positioned between the templates and breast skin at two locations, shown in Fig. 1: at the tip-end template, and at the connector-end template, in both cases along the inner (transfer tube) sides of the templates. Calibration of the MOSFET detectors was performed in a breast fantom made of bolus gel, specially prepared to imitate the clinical conditions. Values of absorbed dose measured by these detectors were compared with values calculated at the detector positions by the PLATO TPS (NUCLETRON).

Results: The mean absolute difference between 81 pairs of measured and planned dose values were -2.1% ± 5.9% (1 SD), for the tip end location and 1.2% ± 6.0% (1 SD) for the connector end location. The observed differences between the MOSFET-measured and TPS-planned dose values may be due to uncertainties in measuring the needle lengths, instability of MOSFET detectors, inaccuracies of detector calibration and inaccuracies in the TPS calculations of the planned dose at detector locations.

S 125 Conclusions: The described method of MOSFET-based in vivo dosimetry applied in breast brachytherapy, by providing an adequately accurate evaluation of dose delivered to the breast skin, is able to effectively assess the dose delivered to the target area. PO-314 PRESCRIPTION DOSE EVALUATION FOR APBI WITH NON-INVASIVE BREAST BRACHYTHERAPY USING EQUIVALENT UNIFORM DOSE K.L. Leonard1, D.E. Wazer2, M.J. Rivard1, S. Sioshansi3, J.R. Hiatt4, C.S. Melhus1, J.T. Hepel4 1 Tufts Medical Center Tufts University School of Medicine, Radiation Oncology, Boston MA, USA 2 Tufts Medical Center Tufts University School of Medicine and Rhode Island Hospital Warren Alpert School of Medicine of Brown University, Radiation Oncology, Boston MA and Providence RI, USA 3 UMass Memorial Medical Center, Radiation Oncology, Worcester MA, USA 4 Rhode Island Hospital Warren Alpert School of Medicine of Brown University, Radiation Oncology, Providence RI, USA Purpose/Objective: A Phase I/II APBI trial using a non-invasive breast brachytherapy device (NIBB) was initiated. Calculations of equivalent uniform dose (EUD) were performed to identify the appropriate NIBB dose. Materials and Methods: APBI plans were developed for 24 patients: 5 with 3D-conformal APBI (3D-CRT), 5 with multi-lumen intracavitary balloons (M-IBB), 4 with single-lumen intracavitary balloons using multiple dwell positions (SM-IBB), 5 with single-lumen intracavitary balloons using a single dwell position (SS-IBB), and 5 simulated in the prone position with compression paddles for both the craniocaudal (CC) and mediolateral (ML) orientations simulating NIBB treatment (Figure).

PTV_eval was contoured for 3D-CRT and IBB techniques per the NSABP B-39 protocol. For NIBB, PTV_eval was contoured on both the CC and ML scans and comprised the tumor bed with a 1 cm margin limited by the chestwall and 5 mm from the skin surface. Prescription doses of 34 Gy and 38.5 Gy were delivered in 10 fractions for IBB and 3D-CRT, respectively. Prescription doses ranging from 34-38.5 Gy were considered for NIBB, with plans generated using first-generation round applicators in the CC and ML orientations. Dose for each axis contributed equally to total dose. This method does not model tissue deformation and composite dosimetry between axes, which may influence EUD calculations. All plans were generated in Pinnacle treatment planning systems. DVH data from all 3D-CRT, M-IBB, and NIBB plans were used to calculate the biologically effective EUD and corresponding EUD to the PTV_eval using the following equation: EUD = EUBED/[n(1 + EUD/α/β)]. EUD was calculated for SS-IBB and SM-IBB using the equation EUD = 10{[v(40BEDtrue/α/β) – 10]/(20/α/β)}. An α/β = 10 Gy or 4.6 Gy (as per the START trial) was assumed for breast tumor. For 3D-CRT, generalized EUD (gEUD) was also calculated in Pinnacle with local control (a = -7.2) as the endpoint. EUDs for varying NIBB prescription doses were compared to EUDs for the other APBI techniques.

S126



Results: Mean PTV_eval volume was largest for 3D-CRT (454 cm3) and was similar for NIBB and M-IBB (86.8 and 87.2 cm3, respectively). Mean gEUD was similar to calculated EUD for 3D-CRT plans (38.8 and 38.4 Gy, respectively). For M-IBB, calculated EUD ranged from 33.1 – 40.3 Gy, reflecting differences in treatment plan geometry. Changing α/β from 4.6 to 10 increased EUD by 2% on average. The Table displays the mean EUD for each treatment modality. EUDα/β = 10 (std dev) 3D-CRT (38.5 Gy) 38.4 (0.9) M–IBB (34 Gy)

35.7 (3.0)

SM-IBB (34 Gy)

38.0 (0.3)

SS–IB (34 Gy)

38.8 (0.9)

NIBB (34 Gy)

34.1 (0.4)

NIBB (35 Gy)

35.1 (0.4)

NIBB (36 Gy)

35.9 (0.2)

NIBB (37 Gy)

37.0 (0.4)

NIBB (38.5 Gy)

38.5 (0.4)

Conclusions: For APBI, 36-38 Gy prescribed to the 100% isodose line delivered with NIBB using first-generation round applicators is the uniform dose equivalent of 34 Gy in 10 fractions delivered with IBB techniques and of 38.5 Gy in 10 fractions delivered with 3D-CRT. Alternatively, 34 Gy with NIBB can be prescribed to the 95% isodose line. PO-315 CAN WE IMPROVE THE DOSE DISTRIBUTION FOR SINGLE OR MULTILUMEN INTERSTITIAL BREAST BALLOON USED FOR APBI? G. Bieleda1, G. Zwierzchowski1, A. Chichel2, M. Kanikowski2, M. Dymnicka1, J. Skowronek1 1 Great Poland Cancer Centre, Medical Physics, Poznan, Poland 2 Great Poland Cancer Centre, Brachytherapy, Poznan, Poland Purpose/Objective: The aim of the study was to verify dose distribution parameters for Contura and artificially created singlelumen balloon applicator application for the same patient using two optimisation algorithms: Inverse Planning Simulated Annealing (IPSA) and dose point optimisation with distance option. Materials and Methods: Group of 24 patient with Contura multi-lumen balloon applied were investigated. Each had ten-fraction treatment with prescribed dose of 3.4 Gy per fraction. For every patient 4 treatment plans were prepared. First for five-lumen balloon optimized with IPSA algorithm, with optimization parameters adjusted for each case. Second for the same applicator optimized with dose point optimisation with distant option. Two other plans were prepared for single-lumen applicator, created by removing four peripheral lumens, optimized with both algorithms. Results: The highest D95 parameter was obtained for plans of Contura patients optimized with IPSA algorithm, mean value 99,32 percent of prescribed dose, and it was significantly higher than Contura plans optimized with dose point algorithm (mean= 83,50%, p<0,0001), IPSA single-lumen balloon plan (mean=83,50%, p=0,0037) and optimized to dose point single-lumen balloon (mean=85,51%, p<0,0001). There was no statistically significant differences concerning maximum doses distributed to skin surface for neither application nor optimization method. On the other hand the mean maximum dose deposited to ribs were lower for Contura plan IPSA optimized (92,52%) than singlelumen IPSA optimized plans (105,96%) with p=0,0067. Volumes receiving 200% of prescribed dose in PTV were higher for Contura dose point optimized plans (mean=8,78%)than for other plans (IPSA Contura plan – mean=7,37%, p<0,0001, single-lumen IPSA – mean=7,20%, p<0,0001, single-lumen dose point – mean=7,19%, p<0,0001). Conclusions: Basing on performed survey, better dose distribution parameters are obtained for patients with multi-lumen balloon applied and optimized using IPSA algorithm with individualized optimization parameters.

World Congress of Brachytherapy 2012 PO-316 LUMEN LENGTH VARIATIONS ON THE CONTURATM APPLICATOR FOR BREAST BRACHYTHERAPY C. Lee1, H. Kuo1, L. Hong1, K. Mehta1, W. Bodner1, M. Rosenstein1, S. Kalnick1, A. Wu2, D. Mah3 1 Montefiore Medical Center, Department of Radiation Oncology, Flushing, USA 2 Thomas Jefferson University, Department of Radiologic Sciences, Philadelphia, USA 3 ProCure Proton Therapy Center, Medical Physics and Dosimetry, Somerset, USA Purpose/Objective: ConturaTM multi-lumen balloon applicators (SenoRx, CA) have been recently used for the breast brachytherapy in our department. The applicator has three components with one central lumen and four peripheral lumens, the distal and proximal components are hard parts while the middle component is a flexible soft tube. We noticed on our pre-treatment measurements that the peripheral lumen length varied by up to 4 mm on daily basis, while the central lumen length was stable. In this study, we investigate the cause of the lumen length variation and its potential impact to the delivered dose distribution. Materials and Methods: We observed that the bending and rotation of middle soft flexible tube caused variations in lumen length. We fixed the proximal end of the applicator and positioned the distal end such that different bending angles were generated in the soft tube. We also rotated the soft tube around the central lumen with fixed bending angles. We used a source position simulator (Nucletronâ, MD) to measure the length of lumens for each bending angle and rotation angle.The dosimetric effect of the lumen length variations in different applicator positions were calculated by comparing the original plan with new lumen lengths. Results: The peripheral lumen length varied as a function of bending angle of the soft tube. Specifically, bending angles of 20°, 40°, 60° led to length variations up to 1mm, 2.5mm and 3mm respectively. Lumen length also varied as the applicator rotated around the central lumen without changing the bending angle. It could vary as much as 4mm as the applicator rotated 90° with 60° bending angle. The dose volume for PTV V90% could change up to 4% between corrected and uncorrected distributions due to lumen length variations. Conclusions: Four peripheral lumens within the soft tube of ConturaTMwould decrease or increase in length due to different tension directions on each lumen as applicator bend or rotate around the central lumen. Users should keep the applicator straight as much as possible and check the rotation of the applicator on daily basis. Users are advised to do daily measurements of the lumen length and correct the channel length accordingly for accurate dose delivery. PO-317 DOSIMETRIC IMPACTS OF TISSUE INHOMOGENEITIES IN ACCELERATED PARTIAL BREAST TREATMENTS USING HDR BRACHYTHERAPY V. Narra1, J. Yue1, T. Chen1, L. Kim1, A. Khan1 1 Cancer Institute of New Jersey, Department of Radiation Oncology, New Brunswick NJ, USA Purpose/Objective: Accurate dose determination is critical in accelerated partial breast irradiation (APBI) using high dose rate (HDR) brachytherapy, especially with respect to the target volume coverage, skin and chest wall doses. Currently, most of treatment planning systems are based on the AAPM TG-43 formalism which assumes a water equivalent homogeneous environment for patient anatomy in dose calculation. However, the factual presence of inhomogeneities such as air pockets, contrast materials, and bony structures may introduce potentially significant dose deviations. The aim of the current study is to examine the dosimetric impacts of tissue inhomogeneities in APBI HDR treatments using a newly introduced model based dose calculation algorithm platform Acuros™ (Varian). Materials and Methods: Acuros™ is an advanced brachytherapy software platform that utilizes a Grid-Based Boltzmann Solver (GBBS) and provides dose calculation accuracy similar to the Monte Carlo approaches. Twenty two APBI patients were treated at our institution using single-entry balloon HDR brachytherapy devices. The treatment planning for the treatment deliveries was performed based on