Tsvang Lev, Pfeffer Raphael, Symon Zvi
Chaim Sheba Medical Center, Ramat Gan.
Med Phys. 2012 Jun;39(6Part19):3843. doi: 10.1118/1.4735688.
Pelvic irradiation is controversial in prostate cancer and has been associated with significant late toxicity, but may be beneficial in patients with high risk disease. To evaluate dose reduction to organs at risk (OAR), we compared volumetric intensity modulated arc therapy with hypofractionated concomitant integrated prostate boost (VMAT) to sequential 3-D conformal 4 field pelvis plan and prostate IMRT boost (Sequential IMRT).
The planning CT's of 20 consecutive high risk prostate cancer patients were utilized for this study. Dose planning using triple A algorithm (Varian Eclipse). CTV included prostate and proximal seminal vesicles. These were expanded by 6 mm for the PTV1 . Pelvic LN were delineated and expanded by 3 mm for the PTV2. Volume based equivalent dose at 2Gy/fx (EQD2) doses were calculated using alpha/beta ratios of 1.5 Gy for the prostate and 3 Gy for normal tissues. VMAT prescription was 73.6 Gy (EQD2-80 Gy) to PTV1 and 54.4 Gy to PTV2 (EQD2-50 Gy) in 32 fractions of 2.3 Gy and 1.7 Gy, respectively. Sequential prescription was 46 Gy to the pelvis and 34 Gy for IMRT boost to a total of 80 Gy in 40 fractions of 2 Gy each.
A significant reduction in mean dose was observed for rectum, bladder, bowel, femur head, and penile bulb for VMAT vs. Sequential IMRT (p<0.001) (table 1). Rectal V75 and V70 was 6.2% and 11.2% for VMAT and 13.6% and 19% for Sequential IMRT (p<0.001). Bowel V50 was 0.35 cm vs. 24.1 cm (p<0.001), respectively. The 98% isodose conformity index for the PTV was 1.44 for VMAT vs. 1.69 for Sequential IMRT (p<0.001).
VMAT with concomitant boost significantly reduced dose to OAR compared to Sequential IMRT, potentially leading to less late toxicity, while providing excellent target coverage and conformity. Furthermore, reduction of treatment planning time and both individual fraction and overall treatment delivery time inherent in this approach, offer significant advantages for both providers and patients.
盆腔放疗在前列腺癌治疗中存在争议，且与显著的晚期毒性相关，但对于高危疾病患者可能有益。为评估对危及器官（OAR）的剂量降低情况，我们将容积调强弧形放疗联合超分割同步整合前列腺增敏（VMAT）与序贯三维适形四野盆腔计划及前列腺调强放疗增敏（序贯调强放疗）进行了比较。
本研究使用了连续20例高危前列腺癌患者的计划CT。采用AAA算法（瓦里安Eclipse）进行剂量规划。临床靶区（CTV）包括前列腺和近端精囊。对于计划靶区1（PTV1），将其外放6mm。勾画盆腔淋巴结并对于计划靶区2（PTV2）外放3mm。使用前列腺的α/β比值为1.5Gy、正常组织的α/β比值为3Gy来计算基于体积的2Gy/分次（EQD2）等效剂量。VMAT的处方剂量为PTV1 73.6Gy（EQD2 - 80Gy），PTV2 54.4Gy（EQD2 - 50Gy），分别在32次分割中给予2.3Gy和1.7Gy。序贯放疗的处方剂量为盆腔46Gy，调强放疗增敏34Gy，共80Gy，分40次分割，每次2Gy。
与序贯调强放疗相比，VMAT在直肠、膀胱、肠道、股骨头和阴茎球部的平均剂量显著降低（p<0.001）（表1）。VMAT的直肠V75和V70分别为6.2%和11.2%，序贯调强放疗为13.6%和19%（p<0.001）。肠道V50分别为0.35cm和24.1cm（p<0.001）。PTV的98%等剂量适形指数VMAT为1.44，序贯调强放疗为1.69（p<0.001）。
与序贯调强放疗相比，同步增敏的VMAT显著降低了对OAR的剂量，可能导致更少的晚期毒性，同时提供了良好的靶区覆盖和适形性。此外，这种方法减少了治疗计划时间以及单次分割和总体治疗交付时间，对医护人员和患者都具有显著优势。
