Radiotherapy of Prostate Cancer Using Rapid Arc: Dosimetric Study of Military Teaching Hospital Mohamed V, Morocco

Abstract

Background: RapidArc®, the Varian solution of Volumetric-modulated arc therapy (VMAT) is currently used in the curative treatment of localized prostate cancer. The aim of this study was to evaluate the dosimetric parameters (effectiveness and efficiency) of the arc dynamic therapy at the Teaching Hospital Mohamed V. Materials and methods: Thirty two patients were treated with curative intent, between June 2013 and December 2014, for localized prostate cancer with RapidArc. Computed tomography (CT) based treatment planning was performed in the supine position with immobilization devices. The patients were instructed to have a comfortably full bladder and an empty rectum at CT acquisition and before each treatment. Delineation of target volume and organs at risk (OARs) was based on the consensus recommendations of the RTOG. The dose prescription was performed with simultaneous integrated boost (SIB) method. Data was collected from dose-volume histograms (DVH) either for planning target volumes (PTV2) or OARs. We calculated the homogeneity index (HI) and the conformity index (CI). We also reported acute and late toxicity related to radiation therapy. Results: The mean age was 66.63 ±7.24 years old. Of the 32 patients, 24(75%) defined as high-risk. All PTV received dose ranging from 95% to 107% of the prescribed dose. The homogeneity and conformity index was very close to 1 of all treatment plans. The dose limits were respected in all OARs as recommended in QUANTEC reviews 2010. Respectively, the analysis of the HDV in the rectum and the bladder found a V70 at 7.15 ± 5.63% and 16.88 ± 8.62% and a V60 at 16.32 ± 7.97% and 27.68 ± 10 32%. The V50 in the femoral heads was 0.39 ± 0.57% on the right and 0.71 ± 1.35% on the left. The V50, V40 and V30 in the bowel bag were 38.76 ± 39.73 cc, 155.38 ± 85,60 cc and 320.09 ± 180.41 cc, respectively. The mean MU was 555.94 ± 86.34 and delivery treatment time (min) was 1.99 ± 0.47. After three months of radiation therapy, no grade 3 or 4 toxicity was reported. The median control PSA was very low at 0,052 [0.012, 0.417] ng/ml. Conclusion: This present study demonstrated that RapidArc showed optimal PTV coverage and the best OARs sparing with less number of MUs and short treatment time. Acute GI and GU toxicities were very low. Further studies are needed to evaluate late toxicities and tumor control.