171 Background: Concurrent radiotherapy to the pelvis plus a prostate boost with long term androgen deprivation is a standard of care for LAPC. IMRT has the ability to deliver highly conformal dose to the target while lowering the irradiation of critical organs around the prostate. However, delivery time is signicantly prolonged with static gantry IMRT. VMAT is able to reduce treatment time but results concerning organ sparing are controversial when compared to static gantry IMRT. Methods: 10 patients with locally advanced prostate cancer were included in this dosimetric study. The planning target volumes (PTV) 1 was defined as the pelvic lymph nodes, the prostate and the seminal vesicles plus set up margins. The PTV 2 consisted of the prostate with set up margins. The aimed dose to PTV1 was 54 Gy in 37 fractions and to PTV2, 74 Gy in 37 fractions, in a single plan using the integrated boost method, by means of a 7 coplanar static split fields IMRT, a one arc (RA1) and a two arc (RA2) Rapidarc planification. Results: All three techniques allow a very good coverage of both PTVs with an acceptable homogeneity. Static IMRT enables a better homogeneity for PTV 2 than Rapidarc techniques. Sliding-window IMRT and VMAT permitted to maintain doses to OAR within acceptable levels with a low risk of side-effects for each organ. Nevertheless, VMAT plans result in clinically and statistically significant reduction in doses to bladder (IMRT Vs RA2: Mean dose: 50.1 ± 4.6 Vs 47.1 ± 3.9 Gy, p = 0.037), rectum (Mean dose: 44 ± 4.5 Vs 41.6 ± 5.5 Gy, p = 0.006) and small bowel (V30: 76,47 ± 14,91% Vs. 47,49 ± 16,91%, p = 0.002). Conclusions: VMAT allows for better OAR sparing as compared to sliding-window IMRT while maintining PTV coverage into acceptable levels for WPI of LAPC.
Simultaneous integrated boost plan comparison of volumetric-modulated arc therapy and sliding window intensity-modulated radiotherapy for whole pelvis irradiation of locally advanced prostate cancer
