Defining the potential for sexual structures-sparing for prostate cancer external beam radiotherapy: A dosimetric study

Purpose

The purpose of the study was to evaluate the dosimetric impact of sexual-sparing radiotherapy for prostate cancer, with magnetic resonance-only treatment planning.

Material and methods

Fifteen consecutive patients receiving prostate cancer radiotherapy were selected. A synthetic CT was generated with a deep learning method from each T2-weighted MRI performed at the time of treatment planning. For each patient, two plans were performed: standard treatment planning and sexual-structures sparing treatment planning. The treatment plan was designed to deliver a dose of 78 Gy to the prostate and 50 Gy to the seminal vesicles in 2 Gy daily fractions, using volumetric arc therapy. Dose–volume histograms were computed to compare treatment plans.

Results

All plans fulfilled dosimetric objectives and were equivalent regarding planning target volume coverage. The doses delivered to both rectum, bladder, and femoral heads were similar between plans (P = 0.20). Sexual-sparing plans enabled to decrease all dosimetric parameters on sexual organs-at-risk. The mean penile bulb dose in sexual-sparing plans was significantly reduced (21.1 Gy ± 20.7 versus 13.4 Gy ± 14.0, P < 0.01), however with large variability observed between individuals. The mean dose delivered to the corpora cavernosa was also significantly reduced within sexual-sparing plans (13.1 Gy ± 16.7 versus 8.6 Gy ± 10.4, P < 0.01). A significant reduction was also observed in the highest doses delivered to internal pudendal arteries (D10%: 48.4 Gy ± 8.3 versus 33.1 Gy ± 4.6, P < 0.05; D5%: 52.0 Gy ± 8.7 versus 36.8 Gy ± 5.5, P < 0.05).

Conclusion

Sparing of sexual structures appears feasible, without compromising neither planning target volume coverage nor doses delivered to non-sexual organs at risk. The clinical significance of this dose-reduction requires prospective evaluation.