Predicting toxicity caused by high-dose-ratebrachytherapy boost for prostate cancer

Abstract: Introduction Treating localized prostate cancer with combination radiotherapy consisting ofexternal beam radiotherapy (EBRT) and high-dose-rate brachytherapy (HDR-BT) has beenproven to result in better disease outcome than EBRT only. There is, however, a decreasingtrend in utilization of combination therapy, partially due to concerns for elevated toxicityrisks. Aim To determine which parameters correlate to acute and late (≤ 6 months) urinary toxicity(AUT and LUT) and acute and late rectal toxicity (ART and LRT), and thereafter createpredictive models for rectal toxicity. Methods Data on toxicity rates and 32 patient, tumor and treatment parameters were collectedfrom 359 patients treated between 2008 and 2018 with EBRT (42 Gy in 14 fractions) andHDR-BT (14.5 Gy in 1 fraction) for localized prostate cancer at Örebro University Hospital.Bivariate analyses were conducted on all parameters and the outcome variables AUT, LUT,ART and LRT grade ≥ 1, graded according to the RTOG-criteria. Parameters correlating toART and LRT in this and previous studies were included in multivariate logistic regressionanalyses for creation of predictive models. Results Most toxicities, 86%, were of grade 0 or 1, only 9% of patients had grade 2 – 3toxicity. Only 2 – 4 parameters correlated to the respective toxicities in bivariate analyses.Logistic regressions generated no significant predictors of ART or LRT. Therefore, nopredictive models were obtained. Conclusion None of the included parameters have enough discriminative abilities regardingrectal toxicity. Predictive models can most probably be obtained by including otherparameters and more patients.