ESTRO 38 Abstract book

S1178 ESTRO 38

below this value, IN implant did not significantly improve CTV coverage. But for cervix uteri for which r is higher than 2, IN implant was a great help to increase CTV doses (D90 of CTVHR increases by an average of 16Gy, and D90 of CTVIR by an average of 9,2Gy – p=0.00195), without significant variation of doses received by OARs (p>0,2). Conclusion Interstitial needles implants can improve target volumes coverage when the high risk volume presents a r ratio higher than 2, with no change on organ at risk near- maximum doses. EP-2130 Dose integration of intensity-modulated arc therapy and interstitial brachytherapy of cervix cancer G. Fröhlich 1 , J. Vízkeleti 1 , N. Anhhong Nguyen 1 , T. Major 1 , C. Polgár 1 1 National Institute of Oncology, Centre of Radiotherapy, Budapest, Hungary Purpose or Objective Comparative analysis of EQD2 total doses resulted with intensity-modulated arc therapy (IMAT) complemented with image-guided adaptive interstitial brachytherapy (ISBT) versus conventional treatment techniques in cervix cancer using a personalised biological dose integration method. Material and Methods 21 locally advanced cervical cancer patients, treated with IMAT with 2 full arcs plus manual optimised ISBT, were selected. Additional plans were created: conformal teletherapy (TT) plans and inverse optimised interstitial (is.), optimised intracavitary (ic.), non-optimised ic. brachytherapy (BT) plans. Since neither the rigid nor the deformable image registration result appropriate fit of interested volumes in the proximity of the applicator, manual registration method is needed. As the critical organs receive the maximal total dose in the region where the dose maximum is in BT, the most exposed 2 cc volume (D2) of bladder, rectum and sigmoid in BT were identified manually on TT CT images individually for every patient. Biological total doses (EQD2) of these volumes were calculated and compared between each combination of TT and BT plans using 2-way ANOVA and Fisher-LSD post hoc test. This dose integration method was compared with the GEC-ESTRO recommended method, uniform dose conception (UDC) in IMAT and conformal TT plans with Wilcoxon-matched pairs test. Results The D90 of High-Risk CTV, D2 of bladder and sigmoid were different in BT techniques only: p=0.0149, <0.001, <0.001, respectively. The most advantageous values were obtained in the manual optimised ISBT plans, inverse optimised is. plans did not differ dosimetrically from these, while optimized ic. plans resulted in worse dose- volume parameters, and the worst of all were ic. plans without optimization. The D2 of rectum was significantly lower with IMAT than with conformal TT plans (p=0.037) and showed the same trend in BT plans than the other parameters (p<0.001) (Table). The UDC dose summation method overestimates D2 of the bladder with 12% and 8.5%, the rectum with 55% and 26.5% and the sigmoid with 17.2% and 12% in the case of IMAT and conformal TT plans, respectively (p<0.001 for all).

external radiation 50 Gy in 25 fractions over 5 weeks with weekly cisplatin. Rectum and rectal mucosa were delineated along with other organs at risk. The dose received by 0.1, 1, 2, 5 cc of rectum, RM, and sigmoid were assessed for dosimetric analysis. The 2Gy equivalent dose was evaluated for all the organs at risk. With assessment and grading of toxicities on the follow up, the predictive factors associated with rectal toxicities with brachytherapy were assessed using univariate analysis. The Coverage Index (CI), dose homogeneity index (DHI), overdose index (OI), dose non-uniformity ratio (DNR), external volume index (EI), conformity index (COIN) and dose volume parameters recommended by GEC-ESTRO were evaluated. The patients were followed up and toxicities were graded as per the RTOG scales and local control rates and disease-free survival were evaluated. Results The median follow- up of the patients was 30 months and grade II and grade III toxicities were seen in 5 (14.2%) and 1 (2.8%) patient respectively. The mean CTV volume was 154 cc. The median number of needles was 18 (Range 15 - 20). Median CI, DHI, V150, V200, DNR, OI, EI and COIN was 0.81 (range: 0.74 – 0.87), 0.7 (range: 0.59 - 0.79), 81cc, 29 cc, 0.42 (range: 0.25 - 0.47), 0.07 (range: 0.05 - 0.14), 0.12 (range: 0.06 - 0.16) and 0.81 (range: 0.69 - 0.89). On Univariate Analysis, D0.1-cc Rectal Mucosa dose >70 Gy (p = 0.02), D1-cc Rectal Mucosa dose >67 Gy (p<0.001), D2-cc Rectal Mucosa dose and D5-cc Rectal Mucosa dose >60 Gy (p = 0.001) correlated with Grade ≥II toxicity.The 2Gy equivalent dose for D2 cc rectum and rectal mucosa associated with 10 and 20% risk of rectal toxicity were found to be 56 and 67Gy and 54Gy and 64Gy respectively. Conclusion CT based planning using MUPIT for gynecological brachytherapy implants has good outcomes as assessed in our study. Plan evaluation and documentation using various indices and parameters recommended by GEC- ESTRO assist in objective evaluation and reproducibility and correlate with clinical outcomes in the disease. Limiting 2-cc RM and rectal doses within the proposed thresholds can minimize Grade ≥II toxicity for gynecologic high-dose-rate interstitial brachytherapy. EP-2129 A decision tool for interstitial needles implants in uterovaginal pulsed dose rate brachytherapy M. Sandt 1 , F. Gassa 1 , P. Pommier 1 1 Centre Léon Bérard, Radiothérapie, Lyon, France Purpose or Objective Implants of interstitial needles (IN) in uterovaginal brachytherapy treatments has proved its efficiency in case of parametrial invasion [1],[2] . The aim of the present study is to analyze patient anatomy and to determine cases where interstitial needles implants could help to cover the high-risk volume. Material and Methods Fifteen patient plans with interstitial needles were considered. On MRI or CT images post implantation, following dimensions where reported: the smallest distance between uterin probe and the nearest organ at risk in the anterior direction (frequently the bladder), and secondly the biggest lateral dimension between uterin probe and the edge of high-risk CTV. The ratio of these two values is called r. PDR dose plans were calculated and optimized on Oncentra® TPS using the same dosimetric method by a single operator, with and without needles activation. CTV coverage (D90 of CTVHR and CTVIR) and organ at risk near-maximum doses (D2cc for bladder, rectum and sigmoid) were reported and compared. Results Doses comparison of CTV coverage showed that r=2 is a threshold. Wilcoxon test for paired samples reveals that