A dosimetric evaluation of a single urethral constraint for high-dose-rate prostate brachytherapy

The American Brachytherapy Society (ABS) consensus guidelines for high-dose-rate (HDR) prostate brachytherapy suggest 11 different dose constraints for the urethra. The purpose of this study is to evaluate whether a single urethral constraint of D0.1 cm³ < 110% could meet all the proposed ABS urethral constraints and to evaluate the heterogeneity and similarities of other portions of the dose-volume histogram (DVH) when only optimizing to a single constraint.

This is a retrospective study of 18 consecutively treated HDR prostate brachytherapy patients treated between May 2018 to November 2018. Nine patients underwent HDR brachytherapy combined with external beam radiation therapy, and nine underwent HDR brachytherapy as monotherapy. Additional DVH values were extracted for the whole, proximal, middle, and distal urethra and compared for differences.

None of the ABS suggested constraints were violated when optimizing the urethra D0.1 cm³ dose to be less than 110% of the prescription. An evaluation of the DVHs for the whole, proximal, middle, and distal urethra showed a large variation in the shape of the remainder of the DVH for all parts of the urethra. The largest standard deviations in dose to the whole and middle urethra were at the V14 dose level, and that to the proximal and distal urethra were at the V10 dose level.

A single urethral dose constraint of D0.1 cm³ < 110% can meet all the proposed ABS constraints. There is high variability in other parts of the urethra DVH when only using a single constraint. Additional data is needed to determine ideal constraints for the entirety of the urethra DVH.