Abstract
Abstract only
262
Background: To use sector based pre- and postimplant dosimetric analysis to evaluate the effect of changes in implant technique in a developing I-125 permanent prostate brachytherapy program (PPB). Methods: 109 men treated with PPB were divided into two groups by implant technique. The first 50 patients (group 1) had needle-by-needle seed deposition under axial ultrasound (USS) guidance and subsequent 59 patients (group 2) having needle placement row-by-row then seed deposition under sagittal USS guidance. Twelve sector dose volume analysis of pre-implant ultrasound (US
pre
) and postimplant CT (CT
post
) study was performed in all cases. Individual sectors were created by dividing the cranio-caudal prostate into three equal lengths creating prostate base, midgland and apex. Each of these volumes was then divided into four axial sectors (right and left anterior, right and left posterior). The difference in the minimum dose delivered to 90% of prostate volume (D
90
) and the prostate volume receiving 100%, 150%, and 200% of the prescribed dose (V
100
, V
150
, and V
200
) was compared between both groups. Results: In both groups, the volume of prostate in sectors one through six (entire base and anterior midgland) were significantly larger on CT
post
when compared to equivalent sectors in US
pre
(p < 0.001), conversely the volumes in sectors 11 and 12 (posterior apex) were significantly smaller (p =0.001). When comparing dosimetric parameters of all equivalent sectors in CT
post
of both groups, it was found that D
90
of sector seven and eight (posterior midgland) in Group 1 received increased dose leading to elevated dose to the rectum but was significantly reduced in Group 2 (p < 0.01), which resulted in achieving the dose as planned in US
pre
. Prostate implant dosimetry was significantly improved in group 2 with a trend to increased equivalent dose between CT
post
and US
pre
to each sectors and significant decrease in V
150
and V
200
in majority of the sectors. Conclusions: The row-by-row technique under sagittal USS guidance significantly improved our post implant dosimetric parameters when compared to single needle source placement under axial USS guidance as assessed by 12 sector analysis.