Dosimetric impact of intrafraction changes in MR-guided high-dose-rate (HDR) brachytherapy for prostate cancer.

Brachytherapy

Radiation Medicine Program, Princess Margaret Cancer Centre, University Health Network, Toronto, Canada; Department of Radiation Oncology, University of Toronto, Toronto, Canada. Electronic address:

Published: July 2018

Purpose: To assess changes in implant and treatment volumes through the course of a prostate high-dose-rate brachytherapy procedure and their impact on plan quality metrics.

Methods And Materials: Sixteen MRI-guided high-dose-rate procedures included a post-treatment MR (ptMR) immediately after treatment delivery (135 min between MR scans). Target and organs at risk (OARs) were contoured, and catheters were reconstructed. The delivered treatment plan was applied to the ptMR image set. Volumes and dosimetric parameters in the ptMR were evaluated and compared with the delivered plan using a paired two-tailed t-test with p < 0.05 considered statistically significant.

Results: An average increase of 8.9% in prostate volume was observed for whole-gland treatments, resulting in reduction in coverage for both prostate and planning target volume, reflected in decreased V (mean 3.3% and 4.6%, respectively, p < 0.05), and D (mean 7.1% and 7.6%, respectively, of prescription dose, p < 0.05). There was no significant change in doses to OARs. For partial-gland treatments, there was an increase in planning target volume (9.1%), resulting in reduced coverage and D (mean 3.6% and 12.4%, respectively, p < 0.05). A decrease in D for bladder (3%, p < 0.05) was observed, with no significant changes in dose to other OARs.

Conclusions: Volumetric changes were observed during the time between planning MR and ptMR. Nonetheless, treatment plans for both whole- and partial-gland therapies remained clinically acceptable. These results apply to clinical settings in which patients remain in the same position and under anesthesia during the entire treatment process.

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http://dx.doi.org/10.1016/j.brachy.2017.06.001DOI Listing

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