Prophylactic Α-Blockers for Radiotherapy-Induced LUTS in Men with Prostate Cancer: A Phase III Randomized Trial Analysis

PURPOSE/OBJECTIVE(S)

Radiation therapy (RT) to the pelvis is one of the curative approaches for patients with localized prostate cancer. Most patients treated with prostate RT experience some degree of radiation-induced lower urinary tract symptoms (RI-LUTS). The present phase III randomized trial assessed the efficacy of prophylactic versus therapeutic α-blockers at improving RI-LUTS in prostate cancer patients receiving external beam radiotherapy (EBRT).

MATERIALS/METHODS

A total of 148 prostate cancer patients were randomized 1:1 to receive either prophylactic Silodosin at day one of EBRT or at the time of RI-LUTS. LUTS were quantified using the International Prostate Symptom Score (IPSS) at regular intervals during the study. The primary endpoint was the change in the IPSS from baseline to the last day of radiotherapy (RT). Secondary endpoints included changes in IPSS from baseline to 4 weeks and 12 weeks after the start of RT.

RESULTS

Patient demographics, baseline IPSS and prescribed radiation doses were balanced between arms. On the last day of RT, the mean IPSS was 14.8 (SD 7.6) in the experimental arm and 15.7 (SD 8.5) in the control arm (95% CI -4.5 to 1.8, p = .40). There were no significant differences in IPSS between the study arms in the intention-to-treat (ITT) analysis at baseline, last day of RT, 4 weeks and 12 weeks post-RT. The as-treated analysis however, identified statistically significant difference at 4 weeks post-RT (95% CI -6.4 to -0.4, p = .03) in favor of prophylactic α-blockers. In an exploratory analysis, patients with prostate volumes less than or equal to 50 cc benefited at 4 weeks post-RT from prophylactic α-blocker (95% CI -8.4 to -0.3, p = .04).

CONCLUSION

Prophylactic α-blocker was not effective at significantly reducing RI-LUTS in prostate cancer patients treated with EBRT. Treating patients with α-blocker at the onset of RI-LUTS will avoid unnecessary drug exposure and toxicity. There may be a benefit for prophylactic α-blocker in patients with smaller prostate. This however, needs to be further studied in a larger study.

Phase III Study of Hypofractionated, Dose Escalation Radiotherapy vs. Conventional Pelvic Radiation Therapy followed by High Dose Rate Brachytherapy Boost for High Risk Adenocarcinoma of the Prostate (PCS VI): Acute Toxicity Results

PURPOSE/OBJECTIVE(S)

The low α\β ratio of 1.2-2 for prostate cancer (PCa) suggests high radiation-fraction sensitivity and predicts a therapeutic advantage of lager fraction size. We have recently shown (PCS5) that high risk prostate cancer patients can safely and effectively be treated with moderate hypofractionated radiation therapy (HF-RT). To date there has been no phase-III randomized clinical-trial comparing moderately HF-RT with EBRT and HDR boost (HDRB). We are reporting the acute safety of EBRT+HDRB compared to moderate HF-RT in this phase III Canadian trial.

MATERIALS/METHODS

From January 2015-June 2022, 308 high-risk localized PCa patients were randomized to receive either HF-RT or EBRT+HDRB. All patients received neo-adjuvant, concurrent, and long-term adjuvant androgen deprivation therapy (ADT). EBRT+HDRB consisted of 46 Gy in 2 Gy per fraction to the pelvis and a 15 Gy in one fraction HDR boost within 3 weeks of EBRT. HF-RT include concomitant dose escalation of 68 Gy in 2.72 Gy per fraction to the prostate, and 45 Gy in 1.8 Gy per fraction to the pelvic lymph-nodes.

RESULTS

Of the 308 patients, 148 received HF-RT and 144 EBRT+ HDRB. The remainder either withdrew from the study or were treated with standard (2 Gy per fraction) fractionation for technical reasons. In both intention to treat and as treated analysis, using log-Rank, there were more grade 1 or worse (G1+) acute GI and GU events and more G2+ acute GI events in the HF-RT than EBRT+HDRB. As treated analysis the acute G1+ and G2+ GI events were 92 vs 77 (60.1% vs. 53.5%; p < 0.017) and 21 vs 10 (13.7% vs. 6.9%; p = 0.052), respectively for HF-RT and EBRT + HDRB. Similarly, the G1+ acute GU events were 123 vs. 101 (80.4% vs.70.1%; p < 0.001) respectively for HF-RT and EBRT+HDRB. There were only four G3 GI and one G3 GU acute toxicities in both arms. No grade 4 toxicities were reported.

CONCLUSION

This is the first study of EBRT+HDRB compared to moderate HF dose escalated RT in high-risk prostate cancer patients treated with long-term ADT and pelvic RT. Our results demonstrate that both treatment approaches are well-tolerated and that EBRT+HDRB carries less G2+ GI and G1+ GU acute toxicities.