ESTRO 36 Abstract Book

S513 ESTRO 36 2017 _______________________________________________________________________________________________

There is little existing data guiding urethral dose constraint but study in peri-urethral cancer has demonstrated a higher risk of urethral toxicity in patients with a urethral EQD2 of >85Gy. Our median EQD2 was below this level but with a wide range, indicating the degree of adaptation using image guidance. Given the poor correlation of applicator angle and length with dose to OARs choice of applicator should remain dictated by the patients’ anatomy. PO-0934 Brachytherapy as part of the conservative treatment for primary and recurrent vulvar carcinoma C. Chargari 1,2 , P. Castelnau-Marchand 1 , A. Escande 1 , I. Dumas 1 , R. Mazeron 1 , P. Maroun 1 , E. Bentivegna 3 , S. Gouy 3 , A. Cavalcanti 3 , P. Morice 3 , C. Haie-Meder 1 1 Gustave Roussy Cancer Campus, Brachytherapy unit- Radiation oncology, Villejuif, France 2 French Military Health Services Academy, French Military Health Services Academy, Paris, France 3 Gustave Roussy Cancer Campus, Department of Surgery, Villejuif, France Purpose or Objective There are only scarce data on the place of brachytherapy (BT) for treatment of vulvar carcinoma. Our institutional experience of interstitial BT for vulvar carcinoma patients is reported. Material and Methods Clinical records of patients receiving low-dose rate (LDR) or pulsed-dose rate (PDR) BT as part of the primary treatment for primary/recurrent vulvar squamous cell carcinoma or as part of adjuvant treatment between 2000 and 2015 were included. Patients, tumors and treatments characteristics as well as clinical outcome were examined. Results A total of 26 patients treated with BT were identified. BT was delivered as part of primary intent treatment for locally advanced/recurrent cancer in 11 patients, and as part of adjuvant treatment in 15 patients. Median age at time of BT was 63 years (range: 41 – 88 years). PDR and LDR were used in 15 patients and 11 patients, respectively. BT was performed as a boost to the tumour bed following EBRT (n=13) or as only irradiation modality (n=13). Total median dose at the level of primary tumor was 60 GyEQD2 (range: 55 – 60 GyEQD2). With mean follow-up of 41 months (range: 5 months – 11.3 years), 11 patients experienced tumour relapse. Ten patients experienced local relapse as first event, associated with synchronous extra-vulvar events in 8/10 patients. Three- year estimated disease-free survival and overall survival rates were 57% (95%CI: 45–69%) and 81% (95%CI: 72-90%). All toxicities were grade 2 or less. Conclusion Interstitial BT used as part of the primary or adjuvant treatment of vulvar carcinoma is feasible with a satisfactory toxicity profile. Prognosis remains however, dismal, with a high frequency of local and distant failures in patients with locally advanced tumors. PO-0935 Modeling to compensate for intra-fractional bladder dose variations in gynecological brachytherapy Z. Siavashpour 1 , R. Jaberi 2 , M.R. Aghamiri 1 , C. Kirisits 3 1 Shahid Beheshti University, Medical Radiation Engineering, Tehran, Iran Islamic Republic of 2 Tehran University of Medical Sciences, Radiotherapy, Tehran, Iran Islamic Republic of 3 Comprehensive Cancer Center- Medical University of Vienna, Department of Radiotherapy and Oncology, Vienna, Austria Purpose or Objective Proposing a model to compensate for intra-fractional bladder dose variations during gynecological (GYN) brachytherapy. 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