1091 poster QUALITY ASSURANCE OF BRACHYTHERAPY TREATMENT PLANNING SYSTEM FOR I-125 EYE PLAQUE DOSIMETRY

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D ISEASE SPECIFIC ISSUES

a need to use an uniform protocol in order to be able to compare the parameters used in different studies. The general use of the ESTRO/EAU/EORTC recommendations could solve this problem. 1091 poster QUALITY ASSURANCE OF BRACHYTHERAPY TREATMENT PLANNING SYSTEM FOR I-125 EYE PLAQUE DOSIMETRY S. Deshpande1 , R. Kumar2 , P. Patwe1 , R. Mhatre1 , V. Anand1 1

P.D. H INDUJA N ATIONAL H OSPITAL, Department of Radiation Oncology, Mumbai, India B HABHA AUTOMIC R ESEARCH C ENTRE, RPAD, Mumbai, India

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Conclusions: A conventional brachytherapy TPS and a new brachytherapy dose distribution comparison technique were used to evaluate the superposition principle for elongated and curved 192 Ir and 103 Pd brachytherapy sources. The optimal line-segment lengths for wire and toroidal sources were determined by comparing dose distributions based on MC methods and the TPS. 1090 poster INTERPRETATION OF DOSIMETRIC PARAMETERS FOR PERMANENT PROSTATE BRACHYTHERAPY: IMPORTANCE OF THE ESTRO/EAU/EORTC RECOMMENDATIONS E. Verhenne1 , K. Stellamans1 , A. Lambrecht1 1 A.Z. G ROENINGE C AMPUS L OOFSTRAAT, Department of Radiotherapy, Kortrijk, Belgium Purpose: In our center, we use real-time intra-operative dosimetry with ultrasound verification of seed positioning for permanent prostate brachytherapy. In this study we compared the variation in dosimetric outcome for the different dosimetric parameters between our approach and the recommendations of ESTRO/EAU/EORTC regarding implant and post-implant dosimetry. Materials: During implantation procedure we take 5mm steps ultrasound images and we outline the prostate as the visible contour without any expansion. The prescribed dose is 145Gy to the 100%-isodoseline which encompass the prostate on most places by one to a few millimeters in the different directions except for the posterior border where the 100%-isodoseline follows this border. For post-implant evaluation, CT-images are taken 4 to 6 weeks after implantation and the prostate as such is outlined on the different slices.For this study, a second clinical target volume (CTV) according the ESTRO/EAU/EORTC recommendations was outlined: prostate with an expansion of 3mm in each direction except for the anterior rectal wall and the bladder neck. For post-implant dosimetry we used two different CTV-delineations. The CTV-P is the post-implant contour of the prostatic gland defined by the capsule, where the CTV-PM is the CTV-P with a three-dimensional expansion of 3mm. We have included 70 patients in this study, being treated from january 2009 until august 2010, for which we have calculated the dosimetric parameters D90, V100 and V150 with the Variseedanning system for the different CTV-delineations. Results: First we evaluated the intra-operative implant dosimetry. If we add the margin to the prostate we have an increase in volume for the CTV with a mean of 28.0% (SD= ±3.3%). The mean D90 for the prostate is 179.0Gy (SD= ±3.2Gy). For the CTV the D90 drops to a mean of 157.3Gy (SD = ±7.4Gy). The V100 of the prostate has a mean of 98.7% (SD= ±0.6%) which becomes for the CTV a mean of 94.0% (SD= ±2.3%). 45 of 70 patients (64.3%) didn’t meet the required V100 95%. The V150 for the prostate has a mean of 64.6% (SD = ±4.6%) and for the CTV the mean is 55.4% (SD = ±4.0%).For the post-implant dosimetry we found the following results. By adding the margin to the prostate we see an increased volume for the CTVPM with a mean of 51.0% (SD = ±8.1%). The mean D90 for the CTV-P is 182.5Gy (SD ±15.5Gy) and for the CTV-PM mean D90 is 141.1Gy (SD = ±12.4Gy). The requirement of D90 above 145Gy was not fulfilled for only 1 patient regarding the CTV-P definition but for the CTV-PM there are 45 patients (64.3%) who didn’t fulfill the requirement. For the CTV-P mean V100 is 97.6% (SD= ±1.9%), the mean of the CTV-PM is 87.9% (SD= ±5.1%). The mean V150 of the CTV-P is 73.1% (SD= ±9.1%), the mean V150 of the CTV-PM is 55.9% (SD= ±8.2%). Conclusions: This study shows that the value of the dosimetric parameters in one patient can vary a lot if different specifications of CTV are used. There’s

Purpose: Dosimetric verification tobrachytherapy treatment planning system (BTPS) (BrachyVision) for I-125 eye plaque dosimetry using Gafchromic film. Materials: Bhabha Atomic Research Centre (BARC) developed Iodine (I125) Occu-Prosta source was configured in brachytherapy treatment planning system (BTPS) (Brachyvision; Varian Medical System, USA). Published dosimetric parameters as per AAPM TG43U1 of the source: dose rate constant, anisotropy functions, radial dose function and geometry function were used for configuration of the BTPS. Gafchromic film (EBT film, ISP Inc USA) was used to compare the dose calculated by treatment planning from single I-125 source at different depths. CT images of virtual water phantom sheets were imported into the planning system for dose calculation. Similar set-up was repeated during experimental measurements. Depth dose curve due to a single source was calculated by BTPS and measured using the Gafchromic films. Dose at depth of 5 mm and 10 mm were calculated by BTPS for single source and films at these spatial positions were irradiated for the corresponding calculated dose time. Eye plaque of 14 mm diameter with twelve I-125 seeds source geometry was entered in treatment planning system. Gafchromic film was placed at 5mm and 10mm from center of curvature of plaque for BTPS calculated time. Irradiated EBT Gafchromic films were scanned with flatbed scanner (Epson Expression 10000XL; EPSON, UK). The scanned images were analyzed using the ImageJ software (NIH, USA).Gafchromic film was calibrated with 6 MV x-ray photon beam from a medical linear accelerator and proper energy correction factor was applied in estimating the dose from the I-125. Results: Measured depth dose curveshows good agreement with BTPS calculated depth dose curve. Measured and calculated dose values by single source at 5 mm and 10 mm were within acceptable limit. Calculated and measured doses at 5 mm and 10 mm for 14 mm eye plaque were in good agreement. Conclusions: BrachyVision treatment planning system calculated dose shows good agreement with measured values..

Disease specific issues 1092 poster GASTRIC CANCER TREATMENT: THE EXPERIENCE OF O. Santa Cruz1 , A. L. Vasconcelos1 , F. Pina1 , J. Cerveira2 , G. Marcelino2 , I. Monteiro Grillo1 1 U NIVERSITY H OSPITAL S ANTA M ARIA, 1st Clinical Oncology Department, Lisboa, Portugal 2 U NIVERSITY H OSPITAL S ANTA M ARIA, School Medicine, Lisboa, Portugal Purpose: The aim of this analysis is to compare our results with the standard treatment reference, and to analyse the correlation between the degree of resection and survival Materials: 61 patients (pts) with gastric cancer undergone surgery between February 2003 and Febreuary 2010 followed by adjuvant QT/RT according to the INT 0116 trial, and were included in this retrospective study. 56.2% of pts underwent a total gastrectomy. Localization was proximal in 18.7%, middle in 37.5% and distal in 43.7%. D1 dissection was performed in 75% pts, with 50% tumor size less than 50mm; 31 (50%) pts had grade 3 tumors. Splenectomy was performed in 10.8% of pts. Localization, type of resection, linfadenectomy D1 or D2 and percentage of removed nodes vs positive nodes (nodal ratio) were analysed. Recurrence was classified according to locoregional (surgical bed and regional nodes), peritoneal and metastatic disease. Results: The median follow-up was 30 months (95% CI=18-40mths). The overall survival was 52.4% (32pts). Ten pts (16.4%) were lost for follow-up and 19 pts died, (four with no evidence of disease). Median age was 62 years and 62.3% of pts were males. The mean overall and specific survival was 16 mths (95% IC=8-31 mths) and 15mths (95% IC=7-31 mths) respectively. Eleven pts (18%) had recurrence disease: 6 pts with peritoneal recurrence, 6 pts with metastatic disease and 1 pt with locorregional recurrence. Between pts who are alive 54.8% (p=0.04) had a nodal ratio