ESTRO 36 Abstract Book

S979 ESTRO 36 _______________________________________________________________________________________________

Purpose or Objective To retrospectively evaluate the incidence, magnitude, and dosimetric impact of any air pockets between the vaginal cylinders and the vaginal mucosa using CT-scan images. Material and Methods 120 postoperative vaginal cuff brachytherapy cases were analyzed for receiving the prescribed dose to 5 mm depth from the cylinder wall. CT-Based treatment planning was performed in each fraction. The incidence, vaginal mucosa displacement and air volume were assessed in each treatment. A Monte Carlo study has also been done to evaluate the dosimetric effect of air pockets around the vaginal cylinder. Results In 50 patients, a total of 90 air pockets were observed in 150 procedures. Four patients had pocket free insertion during the whole treatment sessions. The volume of air pockets ranged between 0.01 cm3 and 4.5 cm3 with average value of 2.5cm3, and the maximum displacement of vaginal mucosa from cylinder surface was between 0.2 and 2 cm with average value of 0.8cm. Thirty patients had no air pockets on their first fraction but in subsequent fractions. Twenty patients had incorrect applicator insertion as they have an air gap between applicator tip and cylinder dome ranged between 0.3 cm and 1.1 cm with average value of 0.8 cm. The Monte Carlo dosimetry also shows that the average dose reduction to the vaginal surface and 5mm-depth, at the air pocket, is respectively about 9.2% and 7.3% per 1 mm of the air thickness. Conclusion Air pockets between vaginal cylinder and the vaginal mucosa are observed in the majority of treatment fractions, and the probability of occurrence varies from patient to patient and procedure to procedure. The dose reduction effect of air pockets needs to be considered especially around the vaginal cuff using imaged based treatment planning in each fraction and the effect on the clinical outcome should be put under more investigation. EP-1782 Effect of the amount of bladder filling on normal tissue doses in 3D-HDR vaginal vault brachytherapy I. Er 1 , S. Kınay 1 , R. Kandemir 1 , F. Obuz 2 , A.N. Demiral 1 1 Dokuz Eylul Univ. Health Sciences Institute, Radiation Oncology, IZMIR, Turkey 2 Dokuz Eylul Univ. Health Sciences Institute, Radiology, IZMIR, Turkey Purpose or Objective In this retrospective study, it was aimed to compare the dose volume parameters of organs at risk for the bladder filling of 50 cc versus 150 cc in high dose rate (HDR) three- dimensional (3-D) vaginal cuff (VC) brachytherapy (BRT). Material and Methods The dosimetric data of the 8 hysterectomized patients with gynecological malignancy who received postoperative pelvic external radiotherapy (RT) + 3-D HDR VC-BRT between March 2015 and August 2015 were analyzed. Computerized tomography (CT) sectional images obtained for VC BRT treatment planning were used for the study. The proximal 1/3 portion of vagina, drawn as a layer of 0.5 cm thickness from the vaginal mucosa (cylinder surface), had been delineated as clinical target volume (CTV). A total dose of 18 Gy (3x6Gy) had been prescribed to the CTV. For the study, bladder, rectum, sigmoid, bowel and CTV were recontoured in a 3-D manner by the same radiation oncology resident. Then the contours were controlled and corrected first by a staff radiation oncologist and then a staff radiologist. Afterwards, treatment planning was performed by the medical physicist using BRT treatment planning system. Mean CTV dose-volume parameters (D90%, D100%,

D50%/D90%, V100%, V150%) for all patients were similar in the treatment plans for two different bladder fillings. Bladder V50%, D50% and D2cc, rectum D2cc, sigmoid D2cc, bowel D50% and D2cc were recorded from the dose- volume histograms obtained in the treatment planning system. Paired comparisons were made for the parameters above for the bladder filling of 50 cc versus 150 cc. Different bladder fillings were compared using Wilcoxon Signed-Rank Test in the SPSS 15.0 statistics program. Results It was observed that as the amount of bladder filling increases, bowel is displaced cranially from the applicator. Bladder D50% decreases (p=0.012) while bladder D2cc increases (p=0.025) in case of 150 cc bladder filling instead of 50 cc. Rectum D2cc shows a statistical trend for increase (p=0.05), however bowel D50% decreases (p=0.012) in 150 cc bladder filling compared to 50cc. Conclusion The statistically significant decrease in bladder and especially bowel D50% parameters supports filling bladder with 150 cc instead of 50 cc in 3D VC-BRT. EP-1783 Acute toxicity with Xoft Axxent Electronic Brachytherapy (XB) in endometrial or cervical cancer A. Mendez Villamon 1 , A. Miranda Burgos 1 , M. Gascón Ferrer 1 , M. Puertas Valiño 1 , S. Lozares Cordero 2 , A. Gandia Martinez 2 , J. Font Gomez 2 , M. Tejedor Gutierrez 1 1 H.U. Miguel Servet, RADIATION ONCOLOGY, Zaragoza, Spain 2 H.U. Miguel Servet, MEDICAL PHYSICIST, Zaragoza, Spain Purpose or Objective To analyze acute toxicity outcomes after treatment with Xoft Axxent Electronic Brachytherapy (XB) in postsurgical endometrial or cervical cancer patients treated at our medical centre. Material and Methods Prospective study in which we selected 29 patients that received treatment with Xoft Axxent Electronic Brachytherapy (XB) administered twice a week after endometrial or cervical cancer surgery, with 3D planification. The patients were selected from September 2015 to September 2016. They were divided in two groups: Group 1 (15/29) considered high risk and group 2 (14/29) considered intermediate risk. Group 1 received external beam radiotherapy (46Gy) followed by XB (15Gy in 5Gy fractions) and group 2 received exclusive XB (25Gy in 5Gy fractions). We analyzed the median dose in bladder, rectum and sigmoid D2cc, V50, V35 with XB comparing the doses with Ir-192. The vaginal mucosa, gastrointestinal (GI) and genitourinary (GU) toxicities were analyzed with the Common Terminology Criteria for Adverse Events (CTCAE 4.0) scale. Results The median dose in bladder with XB vs. Ir-192 was: 2cc 66,4% vs. 71.6%, V50 7,2 vs. 11.9 Gy, V35 14.8 vs. 26,6. In rectum XB vs. Ir-192 was: D 2cc 68,4% vs. 73.5% , V50 9.9 vs. 16.7 Gy, V35 19.9 vs. 36. In sigmoid XB vs. Ir-192 was: D 51.4%vs. 59.8%, V50 12.9 vs. 21.3 Gy, V35 28.8 vs. 41.5. The median follow-up was six and a half months (range 3- 12 months). In group 1, acute vaginal mucositis (G1) was observed in 40% of the patients, GI toxicity (G1) occurred in 13% and GU toxicity (G1, G2, G3) was not present. In group 2, we observed acute vaginal mucositis (G1 and G2) in 57% of the patients, GI toxicity (G1) occurred in 7% and GU toxicity (G1) was present in 29%. There was no grade 3 or greater toxicity in any of the groups. At 3 months follow-up, all of the patients were asymptomatic. Conclusion The dose received by the organs at risk with the Xoft Axxent Electronic Brachytherapy is less compared to Ir-