ESTRO 2024 - Abstract Book

S2312

Clinical - Urology

ESTRO 2024

Radiation Oncology, Ramat Gan, Israel. 14 Tel Aviv University, Sackler School of Medicine, Tel Aviv, Israel. 15 Centre Georges-François-Leclerc, Methodology and biostatistics, Dijon, France

Purpose/Objective:

Stereotactic body radiotherapy (SBRT) is an emerging treatment option for localized prostate cancer (PCa) patients that, despite the overall low toxicity profile, lead to erectile dysfunction (ED) as a common side effect. The dose to the penile base structures have been correlated with ED with mixed results. In this study we aimed to assess the correlation between the dose to the penile bulb (PB), internal pudendal arteries (IPA), and crura with the development of ED after ultra hypofractionation as part of a phase II randomized trial of once-a-week (QW) versus every-other-day (EOD) urethra-sparing prostate SBRT (NCT01764646).

Material/Methods:

Among the 170 patients with localized PCa from 9 centers randomized to receive 36.25Gy in 5 fractions (6.5Gy/fraction to the urethra) delivered either EOD or QW, 90 patients aged between 51 and 81 years old (median 69) presenting with CTCAE v4.0 grade 0-1 ED (ED-) at baseline were selected for the present analysis. Twenty patients (22%) received 6 months of androgen deprivation therapy. The PB, the crura, and the IPA Dmean and D2% were recorded and correlated with development grade 2-3 ED (ED+). The impact on quality of life (QoL) assessed by the EORTC PR-25 questionnaire was also analyzed.

Results:

After a median follow-up of 6.5 years, 43% (n=39) of the patients developed ED+, while 57% (n=51) remained ED-. The corresponding ED+ free-survival at 5 years and 6-years were 61.9% and 56.2% respectively. The dose delivered to the crura was significantly higher in ED+ patients than in ED- patients (7.7 Gy vs 3.6 Gy (p=.014) for the Dmean and 18.5 Gy vs 7.2 Gy (p=.015) for the D2% respectively). No statistically significant difference was observed for the dose delivered to the PB and the IPA between ED+ and ED- patients. The median ED+ free-survival was worse in patients receiving a crura Dmean ≥ 4.7 Gy vs < 4.7 Gy (51.5% vs 71.7%, p=0.005), and a crura D2% >12 Gy vs ≤ 12 Gy (54.9% vs 68.9%, p =.015), respectively. No ED+ free-survival differences were observed for doses delivered to PB (Dmean >6.6 Gy vs ≤ 6.6 Gy; D2% >21.4 Gy vs ≤ 21.4 Gy), and IPA (Dmean >13.9 Gy vs ≤ 13.9 Gy; D2% >23.4 Gy vs ≤ 23.4 Gy). Decline in EORTC PR-25 sexual functioning was significantly more pronounced in patients with higher Dmean and D2% doses to the crura.

Conclusion:

Although ED rates following urethra-sparing SBRT are promising, treatment optimization to the crura may further help to preserve erectile function in patients with localized PCa. By keeping a Dmean and D2% to crura below 4.7 Gy and 12 Gy respectively, the risk to develop ED+ following prostate SBRT may be significantly reduced.

Keywords: sexual function, penile structures, dose