Focal prostate brachytherapy with 103Pd seeds

Abstract

PurposeExamine modifications to seed placement and target margins necessary to accomplish focal brachytherapy with 103Pd. MethodsOur proposed focal brachytherapy program will be primarily favorable intermediate-risk patients with a unilateral index lesion confirmed by transperineal template-guided mapping biopsies (TTMB). The dimensions and location of the TTMB core with the index lesion were placed within the 3-D ultrasound planning volume. Implants were planned for the prostate and the focal targets with generous margins. Planning goals were to cover the target with the 125Gy prescription dose and keep D90 (minimum dose covering 90% of the target) between 125% and 150% of the prescription while minimizing urethral and rectal hot spots. Radiobiological parameters — biologically effective dose (BED) and tumor control probability — were integrated over fractional sub-volumes and focal plans compared to whole gland brachytherapy. ResultsA typical 30.1cm3 prostate was expanded to create a 50.6cm3 planning target volume (PTV) and needed 22 needles containing 86 103Pd seeds of strength 3.20U to deliver the prescribed dose. The hemi-prostate required 39 seeds in 12 needles, and the focal core expanded to a target volume of 11.6cm3 required 29 seeds in 8 needles. All cancerous PTVs and sub volumes had a tumoricidal BED while organs at risk (OAR) met the dose constraints minimizing morbidity. ConclusionsFor this single case study, both hemi-prostate and focal brachytherapy using 103Pd seeds met the same target dosimetric goals and OAR constraints as whole prostate plans but with the expected reduction in number of seeds and needles.