Predicting toxicity caused by high-dose-rate brachytherapy single boost for prostate cancer

Abstract

Purpose: Treating localized prostate cancer (PC) with combination radiotherapy consisting of external beam radiotherapy (EBRT) and high-dose-rate brachytherapy (HDR-BT) has been proven to result in better disease outcome than EBRT only. We aimed to evaluate the incidence of toxicities due to combination therapy and identify parameters correlated to acute or late urinary, rectal, and erectile toxicities.

Material and methods: Data on symptoms and tumor/treatment parameters were collected from 359 patients treated between 2008 and 2018 with EBRT (42 Gy in 14 fractions) and HDR-BT (14.5 Gy in one fraction) for localized PC, at the Örebro University Hospital. Urinary, rectal, and erectile symptoms were presented descriptively, and bivariate analyses for correlation between grade ≥ 2 toxicity and potential predictors were performed. To evaluate prognostic models, multivariable analyses were applied.

Results: Urinary toxicity grade ≥ 2 was observed in 154 patients (47% of patients without pre-existing symptoms grade ≥ 2), of which 15 were grade 3. Rectal toxicity grade 2 was observed in 22 (6%) patients. Any grade erectile dysfunction was evident in all patients without pre-existing dysfunction (n = 103), whereas only 7 recovered completely. In bivariate analyses age was correlated with higher risk of acute urinary toxicity, and irradiated volume was associated with both urinary and rectal toxicities. However, we found no multivariable model of clinical and statistical significance to predict the risk of urinary or rectal toxicities.

Conclusions: In our study cohort, the severity of toxicities was in general mild or moderate and temporary, whereas the incidence of severe toxicity was considerably low. Although we found no predictive models for toxicities, our findings are reassuring that this treatment approach as curative therapy for localized PC is well-tolerated.

Keywords: HDR; boost; brachytherapy; hypo-fractionation; predictive model; prostate cancer; toxicity.

Fig. 1

Baseline and follow-up status for lower urinary tract symptoms (LUTS), rectal symptoms and erectile dysfunction. Proportion of the patients with data, n = 357 (baseline), 356 (3 weeks), 328 (6 months), 306 (1 year), 262 (2 years), 245 (3 years), 145 (4 years), 133 (5 years), 75 (6 years), 51 (7 years)

Fig. 2

Cumulative events (complement of the Kaplan-Mei- er estimator). Every time a new toxicity grade ≥ 2 arises it is counted as an event. Recovery is not taken into account. Patients with baseline ED grade 2 are excluded from the ED curve

Fig. 3

Cumulative recovery (complement of the Ka- plan-Meier estimator). Every time a toxicity grade ≥ 2 is improved to a lower toxicity grade it is counted as an event. Time is counted from the point where the toxicity first occurred