Dosimetric predictors of biochemical control of prostate cancer in patients randomised to external beam radiotherapy with a boost of high dose rate brachytherapy

Abstract

BackgroundTo correlate dose and volume dosimetric parameters (D90 and V100) with biochemical control in advanced prostate cancer treated with high-dose rate brachytherapy (HDR-BT). MethodsOne hundred and eight patients received external beam radiotherapy (EBRT) to 35.75Gy in 13 fractions followed by HDR-BT of 2×8.5Gy. Kaplan–Meier freedom-from-biochemical relapse (FFbR; nadir+2μg/L) fits were grouped by the first (Q1), second (Q2) and third (Q3) D90 and V100 quartiles. Groups were compared with the log-rank test. Univariate and multivariate Hazard Ratios (HR) for D90 and V100 and other co-variates (PSA, androgen deprivation therapy (ADT) were obtained using Cox’s proportional hazard model. ResultsFFbR was significantly higher in patients whose D90 and V100 were at or above the second and third quartile (log rank p⩽0·04). In multivariate analysis D90, V100 were significant covariates for risk of relapse. ConclusionsDichotomising the data using 6 levels of response (above and below Q1, Q2 and Q3) showed a progressive and continuous improvement in biochemical control of disease across the entire dose (and volume) range. The data show that a minimum D90 of 108% of the prescribed dose should be the target to achieve.