Sector analysis of prostate implants.

The analysis of treatment plans generated following prostate implants (post plans) is an essential part of the patient's treatment regimen. The results are used to determine the adequacy of the individual implant and, just as importantly, to provide an evaluation of the institution's brachytherapy technique. Compiled post plan results can be used to compare data from different institutions and help determine guidelines that should be established as dosimetric goals. Sector analysis, or spatial dose mapping, is a novel method of analyzing brachytherapy results that has been developed for this purpose. The display of isodose curves provides spatial information pertaining to the dosimetric evaluation of post plans but is an unwieldy tool; ill suited to the creation of general conclusions for comparative efforts. Dose-volume histogram (DVH) analysis is an excellent tool for examining dosimetric results, but the spatial information is lost. Sector analysis bridges the gap between isodose curves and DVH analysis in post plan analysis. To perform sector analysis we divide the gland into three regions in the cranial-caudal direction (base, midgland, and apex) and four regions on each transverse slice (anterior, posterior, left and right). This gives twelve sectors, each identified by its location in the cranial-caudal direction and position on the transverse slice, e.g., posterior midgland. DVH analysis is performed for each region separately and compiled for display. We present an example of the use of this technique wherein we have analyzed a sequential series of 118 implants performed by a single practitioner (BRP) at two institutions over a calendar year. The implants were performed using two different techniques at the two institutions. Sector analysis was used to compare the results of the implants at the two institutions.