Dominant intraprostatic lesion boosting in sexual-sparing radiotherapy of prostate cancer: A planning feasibility study

Abstract Aim Radical radiotherapy of prostate cancer requires a relatively high dose to achieve an optimal tumor control probability and a reduced dose to the critical structures related to the sexual function (S_OARs) in order to avoid erectile dysfunction. The aim of this study was to perform a planning feasibility analysis of a 3-level dose prescription with Simultaneous Integrated Boost (SIB) on the dominant intraprostatic lesion (DIL) and with S_OARs sparing. Material and methods Twelve patients with clinically localized intermediate risk prostate cancer were included. The prostate, seminal vescicles, and DIL Clinical Target Volumes were delineated on rigid fused MRI-CT simulation images using mp-MRI as a separate guide. A 5 mm margin was added to define the PTVs. Penile bulb (PB), corpora cavernosa (CC), internal pudendal arteries (IPAs) and neurovascular bundles were contoured as S_OARs. The following doses were prescribed in 25 fractions: 56.25 Gy to PTVsv, 67.50 Gy to PTVp, and 75 Gy to PTVdil. Standard plans (SD-VMAT) were created to fulfil targets coverage and Quantec constraints for conventional OARs (SD_OARs: rectum, bladder, and femoral heads). For each patient, a new “sexual-sparing” plan (SS-VMAT) was created adding new objectives for S_OARs with priority to minimize mean doses to IPAs, CC, and PB. Dose-volume histogram end points were compared between the 2 plans using Wilcoxon test. Results D 98% were >95% of prescribed doses for all targets and techniques. No significant differences were found in sparing SD_OARs for considered metrics. Regarding S_OARs, SS_VMAT plans provided a significant reduction of the dose. Mean dose reduction for IPAs, CC, PB, and neurovascular bundles was 32.4% (11.2 Gy, p  = 0.002), 22.5% (4.1 Gy, p  = 0.006), 10.0% (4.6 Gy, p  = 0.010), and 2.6% (1.8 Gy, p  = 0.020), respectively. Conclusions We showed that a significant dose sparing for S_OARs using VMAT-SIB strategy is feasible allowing “sexual-sparing” and highly conformal plans with dose escalation to the DIL.