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Optimal source distribution for focal boosts using high dose rate (HDR) brachytherapy alone in prostate cancer
Pittaya Dankulchai1, Roberto Alonzi2, Gerry J Lowe2
1Mount Vernon Cancer Centre, Northwood, United Kingdom; Division of Radiation Oncology, Department of Radiology, Faculty of Medicine Siriraj Hospital, Mahidol University, Bangkok, Thailand.
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 10mm 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 5mm spacing rather than 10mm 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.
