Bladder dose constraints for conformal radiotherapy in rectal cancer: adaptation to prescribed dose
PO-1110
Abstract
Bladder dose constraints for conformal radiotherapy in rectal cancer: adaptation to prescribed dose
Authors: Fourati|, Nejla(1)*[nejla_fourati@yahoo.fr];Farhat|, Leila(1);Fessi|, Zied(1);Frikha|, Mariem(1);Siala|, Wicem(1);Mnejja|, Wafa(1);Daoud|, Jamel(1);
(1)Faculté de médecine Université de Sfax, Oncology Radiotherapy Department- Habib Bourguiba Hospital, Sfax, Tunisia;
Show Affiliations
Hide Affiliations
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 the proposed constraints: Dmean ≤37 Gy and V40 ≤50%. For patients with overload, we realized an optimized treatment plan to try to respect the constraints.
Results
For the planning plan, mean Dmean and V40 were 35 Gy [28-44] and 42% [9-96] respectively. Dose constraints were respected in 39 cases (66.1%) and in 38 cases (64.4%) for Dmean and V40 respectively. A total of 23 optimized plans were realized. After optimization, mean Dmean and V40 were 34 Gy [28-44] and 39% [9-91] respectively. Dose constraints were respected in 52 cases (88%) for Dmean and in 49 cases (83%) for V40.
Conclusion
Our study results show that the proposed dose constraints (Dmean ≤37 Gy and V40 ≤50%) are suitable for routine use : they can be respected in more than 80% of cases. For the remaining 20% of cases, the bladder volume should be checked and an intensity modulated radiotherapy discussed each time the overrun is important.