Dual-Activity on LDR Brachytherapy Prostate Plans?
Abstract
Purpose
To compare and evaluate the benefit of having dual activity on LDR prostate implants as opposed to one single activity to either decrease dose in organs at risks (OARs) urethra and rectum or increase dose to inaccessible areas as in pubic arc obstruction.
Methods
An in-house brachy dose calculation engine using AAPM TG43 formalism was designed (Python) to assign two different activities to the LDR brachy plans. The process is as following: the plan is calculated in the TPS (Variseed) using all seeds with the higher activity and all seeds with the lower activity. The 3D dose distributions of both plans are compared with the calculation done by the in-house software. Then, a third calculation is done having the centralized and peripheral needles with lower and higher activity, respectively. The activities used in this study are 0.385U, 0.418U and 0.453U for treatments with 144Gy prescription dose.
Results
When central needles have activity 0.385U and peripheral 0.418U, the dose on rectum and urethra decreases 5% when compared to one single activity plan (0.418U). There is also reduction on the 200% isodose line. When using 0.453U and 0.385U in peripheral and central needles respectively, there is 5% dose increase on the anteriorly aspect of prostate with no impact on the OARs when compare with plans with one single activity (0.418U). There is not detriment on target coverage in both cases.
Conclusion
Dual-activity is an option to improve the optimization of the dose 3D dose distribution on LDR brachytherapy treatments. It provides dose reduction up to 5% to rectum and urethra without compromising the target coverage (prostate). It is also an alternative to increase the dose on the anterior aspect of prostate, if pubic arc obstruction is a concern, and still keep the OARs within dose tolerances.