Image-guided intensity-modulated radiotherapy with reduced margins in patients with prostate cancer: Results of the...

Intensity-modulated (IMRT) and image-guided (IGRT) radiotherapies reduce radiation-induced toxicities in localized prostate cancer. This randomized phase II trial (NCT03254420) evaluated late pelvic toxicity (LPT) and quality of life after IMRT/IGRT with standard or reduced margins in patients with low- to intermediate-risk prostate cancer.

Between August 2016 and May 2022, 74 patients were randomized (1:2) to IMRT/IGRT with standard (Control, n = 30) or reduced (Experimental, n = 44) margins. Control IGRT used cone-beam computed tomography (CBCT), while experimental IGRT combined CBCT with real-time tracking (Calypso® 4D Localization System) and smaller margins. Prostate margins were 3 mm in the Experimental arm versus 1 cm (0.5 cm posteriorly) in the Control arm. The primary endpoint was grade ≥ 2 LPT (CTCAE v4.03). Toxicities were assessed by physician-scored CTCAE and patient-reported quality-of-life outcomes.

Grade ≥ 2 LPT occurred in 5 patients in each arm. Over the study period, 88.6 % (95 % CI: 75.4-96.2) of patients in the Experimental arm and 80.8 % (95 % CI: 60.6-93.4) in the Control arm did not experience a grade ≥ 2 LPT. Under conventional fractionation, the Experimental arm had significantly lower rectal (V_70Gy, D_50%) and bladder (D_50%, V_70Gy, V_76Gy) doses (p < 0.01), but higher rectal (D_1%, V_76Gy) and bladder (V_80Gy) doses (p < 0.01). At two years post-radiotherapy, urinary symptom scores were significantly lower in the Experimental arm (mean 12.3 vs. 21.2, p = 0.028).

IMRT/IGRT with reduced margins is feasible and may improve some dosimetric outcomes. Both arms had low LPT rates, but reduced margins may improve patient-reported urinary symptoms.