ESTRO 36 Abstract Book

S518 ESTRO 36 _______________________________________________________________________________________________

Material and Methods Thirty advanced cervical cancer patients treated with HDR ( 192 I source) intracavitary brachytherapy were selected. Rotterdam applicators (tandem-ovoids) were used for them. Patients pelvic CT scans were done twice; pre- and post-treatment (about 30 min after dose delivery), with applicator in situ. Flexiplan ® (version 2.6, Isodose control, the Netherlands) as a 3D treatment planning software was used. Applicator reconstruction and organs delineation were done by the same physicist /physician on both image sets. Totally identical plans (dwell times/positions) were applied to both image sets and DVH parameters were recorded; planning aims: 80-90 Gy (EQD2) for D 90 of CTV HR and less than 85, 75, and 75 Gy for D 2cm³ of bladder, rectum, and sigmoid, respectively. RT-Structure files (in DICOM format) of the patients for whom intra-fractional dose (D 2cm³ ) variations were higher than 5% were exported from planning system. Applicator- organs distances along the active length of three applicators were extracted by some in-house MATLAB written codes. Source dwell times were extracted from treatment planning report files (in xps format). A model was design to propose new source dwell times to compensate for the bladder wall to applicators walls distances intra-fractional variations, considering the TG43 algorithm and inverse square law. Some dwell times acceptance criteria were considered during modeling such as: D 90 of CTV HR and CTV IR have not changed to be less than 85 Gy 70 Gy, respectively. New dwell times were applied to the plans to test their influences on DVH parameters. Also, the model was further optimized to reduce the executing time by searching for the most impressive part of the applicators lengths on bladder dose. Results For one third of the considered patients bladder dose changes were higher than 5%. Mean ± SD of D 2cm³ intra- fractional relative changes ((D 2cm³(before) - D 2cm³(after) )/ D 2cm³(before) × 100) of these ten cases were 19.3 ± 18.0 %. After correcting the plans these variations became 10.5 ± 14.5. More bladder dose correction would lead to a significant decrease in dose to CTV HR and was unjustifiable. Model runtime was about 3 minutes (Intel corei7 laptop, RAM = 8 GB, CPU = 2 GHz). Conclusion A model was developed to correct the bladder dose to be as similar as possible to the pre-treatment plan one. It is a semi-online model that can be used in the routine clinical workflow to reduce the GYN image-guided adaptive brachytherapy uncertainties. The model can be generalized to other organs at risk. PO-0936 Dose effects of draining rectal gas in image- guided brachytherapy for gynecological cancer H. Takase 1 , N. Ii 2 , Y. Yamao 1 , T. Kawamura 2 , M. Naito 1 , Y. Watanabe 2,3 , Y. Toyomasu 2 , A. Takada 2 , H. Tanaka 2 , T. Yamada 1 , H. Maki 1 , H. Sakuma 4 , Y. Nomoto 5 1 Mie University Hospital, Department of Radiology, Tsu, Japan 2 Mie University Hospital, Department of Radiation Oncology, Tsu, Japan 3 Matsusaka central hospital, Department of Radiation Oncology, Matsusaka, Japan 4 Mie University Graduate School of Medicine, Department of Radiology, Tsu, Japan 5 Mie University Graduate School of Medicine, Department of Radiation Oncology, Tsu, Japan Purpose or Objective To verify the usefulness of draining rectal gas in image- guided high-dose-rate brachytherapy for gynecological cancer, we quantified the dose delivered to the rectum and urinary bladder with and without draining rectal gas. Material and Methods From October 2013 to July 2014, 116 brachytherapy fractions from 34 patients were performed in our

department for gynecological cancer. After the applicators were inserted, cone beam computed tomography (CT) images were obtained. Rectal gas was observed in 11 brachytherapy fractions from 8 patients. After draining rectal gas with a Nelaton catheter, cone beam CT images were obtained again. Brachytherapy was prescribed to point A using standard two-dimensional dosimetry and planning. To quantify the dose delivered to the rectum and urinary bladder, three-dimensional dose distributions were calculated using the images from before and after draining rectal gas. The dose to the rectum and urinary bladder was evaluated based on dose- volume histograms. The influence of the volume of discharging rectal gas (pre-draining rectal volume – post- draining rectal volume) on the rectal dose was investigated. The minimum doses to the maximum exposed 0.1, 1 and 2 cc (D 0.1cc , D 1cc and D 2cc ) volumes were evaluated using the dose from point A. Statistical analyses were conducted using the paired t-test and a linear regression model. Results The mean rectal dose after draining rectal gas was significantly lower than that before draining. The rectal doses (D 0.1cc , D 1cc and D 2cc ) relative to point A at post- draining vs. pre-draining were as follows: 106.9% vs. 121.2%, 88.3% vs. 98.6% and 81.5% vs. 90.9%, respectively (p<0.05). The mean urinary bladder dose was not significantly different after draining rectal gas from before. The urinary bladder doses (D 0.1cc , D 1cc and D 2cc ) relative to point A at post-draining vs. pre-draining were as follows: 136.0% vs. 133.2%, 112.3% vs. 111.8% and 103.3% vs. 102.4%, respectively. The volume of discharging rectal gas slightly correlated with the rectal dose at D 0.1cc (R2=0.45); however, no significant correlation was found for D 1cc or D 2cc (R2=0.10 and -0.01, respectively). Conclusion Our data suggested that draining rectal gas is useful for reducing the rectal dose in high-dose-rate brachytherapy for gynecological cancer. PO-0937 HDR image-guided interstitial brachytherapy for postoperative local recurrent uterine cancer K. Yoshida 1 , H. Yamazaki 2 , T. Takenaka 2 , T. Kotsuma 3 , K. Masui 2 , T. Komori 1 , T. Shimbo 1 , N. Yoshikawa 1 , H. Yoshioka 1 , Y. Uesugi 4 , T. Hamada 1 , M. Nakata 1 , H. Matsutani 1 , M.M. Ueda 3 , Y. Tsujimoto 3 , E. Tanaka 3 , Y. Narumi 1 1 Osaka Medical College, Radiology, Takatsuki, Japan 2 Kyoto Prefectural University of Medicine, Radiology, Kyoto, Japan 3 National Hospital Organization Osaka National Hospital, Radiation Oncology, Osaka, Japan 4 Kansai University of Welfare Sciences, Rehabilitation Sciences, Kashiwara, Japan Purpose or Objective In order to evaluate the usefulness of high-dose-rate (HDR) image-guided interstitial brachytherapy (ISBT) for postoperative local recurrent uterine cancer, we analyzed We investigated 48 patients treated with HDR-ISBT at National Hospital Organization Osaka National Hospital and Osaka Medical College between May 2003 and January 2014. All patients received radical surgery and 10 patients also received post-operative radiotherapy as previous treatments. Histologic finding was squamous cell carcinoma (SCC), endometrioid adenocarcinoma (AD), mucinous adenocarcinoma (MAD) and the others (serous/adenosquamous/endocrine/undifferentiated) for 20, 17, 5 and 6 patients. The median maximum tumor diameter was 25 mm (range; 5-79 mm). In 38 patients who had non-irradiation history, 23 patients also received external beam radiotherapy (EBRT). The median ISBT our clinical experience. Material and Methods