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

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.

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.

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.

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.