Optimal source distribution for focal boosts using high dose rate (HDR) brachytherapy alone in prostate cancer

Abstract

Purpose

To investigate the optimal distribution of sources using high dose rate brachytherapy to deliver a focal boost to a dominant lesion within the whole prostate gland based on multi-parametric magnetic resonance imaging (mpMRI).

Methods

Sixteen patients with prostate cancer underwent mpMRI each of which demonstrated a dominant lesion. There were single lesions in 6 patients, two lesions in 4 and 3 lesions in 6 patients. Two dosimetric models and parameters were compared in each case. The first model used 10 mm intervals between needles, and the second model used additional needles at 5 mm intervals between each needle in the boost area.

Results

Three of thirty-two plans did not achieve the plan objectives. These three plans were in the first model. A higher median urethral volume was seen in the ‘unsuccessful’ group (2.7 cc, and 1.9 cc, respectively, p-value = 0.12). Conformity indices of the second model were also better than the first model (COIN index; 0.716 and 0.643, respectively).

Conclusions

Focal monotherapy based on mpMRI achieves optimal dosimetry by individualizing the needle positions using 5 mm spacing rather than 10 mm spacing within the boost volume. A larger urethral volume may have an adverse effect on this distribution. Formal clinical evaluation of this approach is currently underway.