ESTRO 36 Abstract Book

S166 ESTRO 36 _______________________________________________________________________________________________

V30, and V40) were obtained. Receiver operating characteristic (ROC) curve identified DVH thresholds that predicted for grade≥ II HT toxicity with highest specificity. All data was dichotomized across these cut-offs. Univariate and multivariate analysis was performed with SPSS, version 20. Results Of the 94 patients randomized to IMRT arm, 74 received concurrent cisplatin (median cycles=4). Grades I-V HT was seen in 55.5%, 32.5%, 5%, 0% and 0% patients, respectively demonstrating low incidence of HT during bowel sparing IMRT. Leukopenia, neutropenia, anemia, and thrombocytopenia ≥ grade II was observed in 24.3%, 5.3%, 17.6%, and 0%, respectively. None of the HT resulted in treatment break. On comparing BM delineation techniques the FH sub volumes were 25%-47% of WB sub-volumes. The mean V 5 , V10, V20, V30, and V40 for WP FH and WB were 99%, 93%, 77%, 60%, and 36%; and 99%, 94%, 80%, 60%, and 36%, respectively suggesting unintended desirable BM sparing. On univariate analysis WPL FH V30 > 55% (p=0.04) predicted for overall grade ≥ II HT, WP V10 >95% (p= 0.04) for grade ≥ II leucopenia and ilium V20 > 90% (p=0.04) for hemoglobin toxicity. On multivariate analysis, only WP FH V10 >95% (p value 0.04, OR 3.3 (1-11.5) was statistically significant for grade ≥ II leucopenia. Conclusion The IMRT arm of NCT01279135 (PARCER study) that employed strict bowel constraints also had unintentional dosimetrically desirable BM sparing. This was associated with low absolute rates of HT. Within the setting of bowel sparing IMRT WP FH V10 should be restricted to ≤95% for simultaneous bowel and BM sparing. However as none of the other dosimetric variables predicted for HT, WB marrow contours could serve as a resource sparing strategy while planning pelvic IMRT. OC-0319 Cervix cancer: dose-volume effects in pathologic lymph nodes W. Bacorro 1 , R. Mazeron 2 , I. Dumas 3 , A. Escande 2 , A. Huertas 2 , R. Sun 2 , P. Castelnau-Marchand 2 , C. Haie- Meder 2 , C. Chargari 2 1 Benavides Cancer Institute- UST Hospital, Radiation Oncology, Manila, Philippines 2 Gustave Roussy, Radiation Oncology, Villejuif, France 3 Gustave Roussy, Medical Physics, Villejuif, France Purpose or Objective Whereas clear dose-volume relationships have been demonstrated for the tumor and organs at risk in locally advanced cervix cancer, the optimal threshold to reach for pathologic lymph nodes remains uncertain. The objective was to identify planning aim for pathologic nodes. Material and Methods Patients treated with curative intent for a cervical cancer with nodal involvement were identified. Their treatment combined external beam radiotherapy (EBRT) and image- guided brachytherapy (IGABT). Nodal boosts were performed sequentially or using the simultaneous integrated boost (SIB) technique depending on the EBRT technique used. The contributions of EBRT, IGABT (D 98 ) and nodal boosts were converted in 2-Gy equivalent (α/β=10 Gy) and summed. Each node was considered individually, and followed from diagnosis to relapse. Resected nodes during para-aortic node surgical staging were not considered. Statistical analyses comprised log- rank tests (univariate analyses), Cox proportional model (factors with p ≤0.1 in univariate) and probit analyses. Results One hundred and fifteen patients were included, with a total number of nodes of 288 (2.5 per patient). PET-CT was performed in 90.6% of the patients; para-aortic dissection in 53.8%. Histologic subtypes comprised squamous cell carcinomas (SCC) in 88.9%, adenocarcinomas in 8.5% and adenosquamous in 2.6%. The

mean pathologic node volume at diagnosis was 3.4±5.8 cm 3 . The mean EBRT and nodal boost doses were 44.3±0.9 Gy and 10.0±2.9 Gy respectively. The mean IGABT contribution to pelvic nodes was 4.2±2.6 Gy. Finally the mean total dose to lymphadenopathies was 55.3±5.6 Gy. Concomitant chemotherapy was administrated in 96.5% of the patients. After a median follow-up of 33.5 months, 20 patients (17.4%) experienced relapses in nodes initially considered pathologic at diagnosis (local relapse). Among them recurrences were observed in a total of 44 nodes (15.3%). The mean time from treatment completion to relapse was 9.0±11.8 months. There was no significant relationship between the dose delivered to pathologic nodes and local control probability (p=0.38). Univariate analyses tested various factors: subtypes (SCC versus others, p=0.35), concomitant chemotherapy (p=0.39), use of SIB (p=0.07), volume at diagnosis (threshold: 3 cm 3 , p<0.0001) and dose (≥ 57.5 Gy, p=0.039). The last three factors were entered in a multivariate analysis. Volume (HR=8.2, 4.0-16.6, p<0.0001) and dose (HR=2, 1.05-3.9, P=0.034) remained independent, whereas SIB was not (p=0.99). Subsequent Probit analysis combining dose and volume showed significant relationships with the probability of local control (Figure).

Conclusion The initial volume was the main prognostic factor of control in pathologic lymph nodes. A dose superior to 57.5 Gy was also associated with a better local control probability. Further studies are required to refine these findings.

Poster Viewing : Session 7: Upper and lower GI

PV-0320 Stereotactic body radiotherapy for liver metastases based on functional treatment planning M.M. Fode 1 , J. Petersen 2 , E. Worm 2 , M. Sørensen 3 , K. Bak-Fredslund 3 , S. Keiding 3 , M. Høyer 4 1 Aarhus University Hospital, Department of Oncology, Aarhus C, Denmark 2 Aarhus University Hospital, Department of Medical Physics, Aarhus C, Denmark