Abstract
Abstract only
242
Background: To evaluate 12 sector analysis in the assessment and comparison of pre- and post- implant dosimetric parameters during the development of an I-125 prostate brachytherapy (PPB) service.
Methods: 50 consecutive men being treated with PPB had dose volume analysis in 12 sectors of their pre implant ultrasound (PI
US
) and post implant CT (PI
CT
) data using a Variseed 8.0 treatment planning system. PI
US
dosimetry was performed 2 weeks prior to implantation and PI
CT
dosimetry 4 weeks post implant. Individual sectors were created by dividing the cranio-caudal prostate length into 3 equal lengths creating prostate base (PB), midgland (PM) and apex (PA). Each of these volumes was then divided into four axial sectors (right and left anterior, right and left posterior). The planning target volume (PTV), dose to 90% of prostate (D
90
), prostate volume enclosed by 100% (V
100
), 150% (V
150
) and 200% (V
200
) dose were recorded in each sector on PI
US
and PI
CT
. Adjacent sectors on PI
US
were assessed for dose-volume homogeneity as were adjacent sectors on PI
CT
. Differences in individual sectors on PI
US
and PI
CT
were evaluated.
Results: Adjacent sector analysis demonstrated dose homogeneity in all sectors of PI
US
and the majority of sectors on PI
CT
. Statistically significant differences between PI
US
and PI
CT
were noted in target volume, particularly in PB with PI
CT
>PI
US
. When individual sectors on PI
US
and PI
CT
were compared, statistically significant differences were noted in the majority of dosimetric parameters. The anterior PB and PM were significantly lower on PI
CT
(p value < 0.001) and significantly higher at the posterior PM and PA (p value < 0.05). These changes were consistent across all analysed parameters. In particular, significant absolute differences in D90 in equivalent sectors on PI
US
and PI
CT
were seen.
Conclusions: 12 sector analysis allows rapid assessment of PI
US
and PI
CT
dose and volume homogeneity. It offers a scientific method of identifying areas of relative over and under dosing on PI
CT
when compared with PI
US
providing both clinicians and physicists with a learning tool to refine dosimetric analysis and highlight sectors where implant quality could be improved.