[Dose comparison between three planing prostate: 3D conformational radiotherapy, coplanar arctherapy and non-coplanar arctherapy].

Purpose: Comparative study between a classical conformational prostate radiotherapy (3DRTC) and two arctherapy techniques, a coplanar (AT-C) and the other non-coplanar (AT-NC).

Patients And Methods: The comparison has been made retrospectively on 30 patients with localized prostate cancer (T2-T3a, PSA< 20 ng/ml, Gleason<7). The objective criteria for comparison were the NTCP, EUD, and dose volume (on DVH), for the volumes of bladder wall, rectal wall, femoral heads, small bowel, prostate (P) and seminal vesicles (VS). The treatment was 46Gy on PTV1 (VS+P+margins), and then an overdose of 30Gy on PTV1 (P+margins).

Results: For prostate volumes exceeding 75 cm(3), arctherapy leads to a decrease in uniformity in the target volume and an increase in the dose received by the femoral heads, this method does not seem appropriate. For prostate volumes less than 75 cm(3), in addition to the coverage almost tumor, and radiation toxicity equivalent to the bladder and the small intestine, there is a significant increase in the dose to the femoral heads, while the remaining is still within limits, such as clinically tolerable. The contribution of arctherapy is mainly observed at the level of rectal doses. The dose received by 30% of the rectum is reduced by -12% for AT-C and -11.7% for AT-NC, and EUD rectum -5.2% and -4.8%.

Conclusion: In this virtual study, the arctherapy seems to generate a true dose reduction in the rectum wall. These results encourage us to continue the investigation for a possible integration in a dynamic clinical routine.