ESTRO 2020 Abstract Book

S586 ESTRO 2020

Conclusion In this study, older patients had a higher rate of acute urinary symptoms, in comparison with younger ones, but there was no records of grade 3 genitourinary acute toxicity (RTOG). It was found a significant higher rate of acute haematological toxicity and a trend to more frequent diarrhoea and rectal incontinence. Regarding late toxicity patterns there were no significant discrepancy noted between age-groups. PO-1110 Bladder dose constraints for conformal radiotherapy in rectal cancer: adaptation to prescribed dose N. Fourati 1 , L. Farhat 1 , Z. Fessi 1 , M. Frikha 1 , W. Siala 1 , W. Mnejja 1 , J. Daoud 1 1 Faculté de médecine Université de Sfax, Oncology Radiotherapy Department- Habib Bourguiba Hospital, Sfax, Tunisia Purpose or Objective Tolerance doses in the bladder are less than prescribed doses during conformational radiation therapy (CRT) for rectal cancer. So, the dose constraints proposed by expert are not adapted to CRT in this location. We have, in a previous study, proposed bladder dose constraints that could be applied in this indication. The purpose of our current study was to verify the applicability of these constraints in clinical routine. Material and Methods Retrospective dosimetric study of 59 patients with rectal cancer treated with preoperative CRT in our department. The prescribed dose at planning target volume (PTV) was 45 Gy (1.8 Gy / fraction, 5 fractions per week). All patients were treated with 4 orthogonal fields (anterior, posterior and 2 lateral). During dosimetric planning, the bladder was contoured as a solid organ. We retrospectively noted the doses received by this organ: mean dose (Dmean) and the volume which receives more than 40 Gy (V40). We then checked if these doses respect