ESTRO 37 Abstract book

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ESTRO 37

decay-and-treat method utilizing the original catheter dwell-times for the initial fraction), and calculated the dose to OAR (CD).The RD and CD were compared to detect variation. Statistics: Spearman’s correlation coefficient(r). Results a) Outcomes and QoL: After median follow-up of 32 months (1-74), 3-year disease-free survival (DFS), local relapse-free survival (LRFS) and pelvic relapse-free survival (PRFS) 92.5%,95.7% and 93.8%, respectively. PRFS was worse in grade 3 tumors compared to grade 1-2 (77% vs 100%, p=0.017). No patients had G3-4 toxicity. Vaginal chronic toxicity (Grade 1-2) was seen in 24% of patients. Patients reported excellent QoL in the C30 questionnaire which showed functional scores above 70% and symptoms scores below 35%. The global health status and QoL scale was 70%. In the EN24 questionnaire the worse scores were sexual enjoyment and vaginal problems (MS 70% and 35%, respectively). b) Planning: We observed mean bladder doses of 5.11Gy vs 4.7Gy and 5.08Gy vs 4.44Gy, mean rectal doses of 4.67Gy vs 4.36Gy and 4.8Gy vs 4.14Gy, for RD and CD in second and third aplication respectively. Absolute variations between the RD and CD for 2cc-bladder and 2cc-rectum were 10% (95% CI:1.8) and 11.9% (95% CI:2.3), for the second application, and 12.8% (95% CI:2.3) and 14.1% (95% CI:2.2) for the third application. There were a strong correlation between the RD and CD for the second and third applications in 2cc-rectum (r=0.821,p<0.001 and r=0.841,p<0.001, respectively) and 2cc-bladder (r=0.678,p<0.001 and r=0.731,p<0.001, respectively). Conclusion In this series 3D adyuvant VB in EC-I achieved good local control rates with excellent results in QoL. Our data show no advantage of replanning prior to each VB fraction. EP-2224 Dosimetry of the peritoneal cavity as a surrogate for bowel outlining during cervical brachytherapy M. Zahra 1 , R. Fullerton 1 , P. Drewell 1 , W. Keough 1 1 Edinburgh Cancer Centre, Western General Hospital, Edinburgh, United Kingdom Purpose or Objective The GEC-ESTRO recommendations regarding the dose constraints for the bowel during cervical brachytherapy assume that the bowel loops are not moving in the interval between obtaining the planning scans and treatment delivery. Studies have shown that the position of the bowel loops especially the sigmoid and small bowel can vary over the period of several hours needed to produce a treatment plan and deliver the treatment. Whilst this may be mitigated to an extent when using fractionated treatments, this can become more relevant in PDR as the single plan generated is assumed to reflect the dose to the bowel over an even longer time frame. We have investigated the D2cc dose to the peritoneal cavity in the vicinity of the uterus and correlated it with the dose calculated to the individual bowel loops of the sigmoid and small bowel. Material and Methods 10 patients had radical treatment for cervical cancer, they received a dose of 45Gy in 25 fractions of external beam radiotherapy to all the pelvis, followed by HDR CT- guided brachytherapy aiming to deliver a total combined dose of 85Gy (alpha/beta ratio of 10Gy) to the d90 HRCTV. The brachytherapy was delivered in 3 fractions. For the purpose of the study each brachytherapy fraction CT scan the peritoneal cavity was outlined as a separate OAR starting from the level of the uterine fundus and extending caudally up to the broad ligament. The D2cc was calculated for the OARs for the individual fractions and also the total combined from the EBRT and all 3 fractions (using an alpha/beta ratio of 3 Gy), and correlations where assessed using a paired t-test and a

Pearson’s correlation co-efficient with 2-tailed significance testing at a level of 0.05. Results A total of 30 CT scans were contoured and the doses calculated. The median volumes, d2cc per fraction and total combined dose were calculated and are shown in table 1. Small bowel Sigmoid Peritoneum Volume in cc (range) 113 (0 - 377) 91 (21 - 467) 726 (367 - 1136) d2cc per fraction in Gy (range) 3.4 (0 - 6.4) 4.75 (0 - 6.4) 6.5 (0.8 - 10.7) d2cc combined total dose in Gy (range) 56.2 (43.2 - 72.8) 64.5 (54.9 - 69.6) 79.9 (57.8 - 113) The d2cc of the peritoneal sac correlated positively with the d2cc of the sigmoid correlation co-efficient of 0.27(p<0.01) and d2ccsmall bowel 0.52(p<0.01). Conclusion The peritoneum next the uterus represents a potential space that receives a significant radiation dose during cervical brachytherapy and that can be filled by bowel loops which may be exposed to a higher radiation dose than that calculated from outlining the individual bowel loops. This study shows that high doses can be delivered to the peritoneum and if it is to be used to reflect the potential dose delivered to the bowel than new dose constraints would need to be identified. Even though the numbers in this study are small a correlation was identified between the d2cc to the peritoneum and to the sigmoid and small bowel indicating the potential use as an OAR in cervical brachytherapy. EP-2225 Boost modalities in cervical cancer: intracavitary BT vs. intracavitary + interstitial BT vs. SBRT A. De Caluwé 1 , K. Diakité 2 , S. Poeta 3 , C. Vanderkhove 3 , D. Van Gestel 1 1 Institut Jules Bordet ULB, Radiation Oncology, Brussels, Belgium 2 Centre Hospitalier Universitaire Mohamed VI, Radiation Oncology, Marrakech, Morocco 3 Institut Jules Bordet ULB, Department of Medical Physics, Brussels, Belgium Purpose or Objective Standard of care treatment for locally advanced cervical cancer consists of concurrent chemoradiotherapy followed by brachytherapy (BT) boost. In recent years, stereotactic body radiotherapy (SBRT) has emerged as a new boost modality administered in an estimated 15% of patients in the USA in 2011. However, SBRT boost was shown to be associated with an increased mortality risk (hazard ratio 1.86, after controlling for significant factors affecting survival). The purpose of the present study is to dosimetrically compare three different boost modalities: intracavitary (IC) BT alone, IC coupled with interstitial (IS) BT and SBRT. The ultimate goal is to find dosimetric explanations for the observed survival differences. Material and Methods Twenty-four consecutive patients treated with IC+IS BT boost were identified. Two additional treatment plans were created for each patient: 1 IC BT and 1 SBRT. MRI- based contouring was performed according to GEC-ESTRO guidelines. No PTV or PRV margin was applied for any structure, hence all structures were identic for each boost modality. Two different normalisations were performed: 1) Normalisation to the target : prescription of 7.1 Gy to the D90% of the high-risk CTV (HR-CTV), thereby enabling