Room: Exhibit Hall
Purpose: The treatment of skin with high-dose-rate (HDR) brachytherapy is commonly planned using the American Association of Physicists in Medicine TG-43 formalism. However, model based calculation algorithms (TG-186) have been implemented to account for heterogeneities in, or around the field of treatment that are not considered otherwise. We are interested in comparing the calculated dose distributions between the TG-43 and TG-186, specifically with regards to skin treatments where lead shielding is often used.
Methods: A 6-channel Freiburg Flap skin applicator was scanned atop 6 cm of solid water and imported into the Oncentra Brachy treatment planning system. A plan was generated so that a 3 mm depth received 500 cGy using TG-43. The plan was delivered with film at three different depths (surface, 3 mm, and 5 mm), with and without 3 mm lead surrounding the applicator. A second plan will be generated with density corrections using TG-186 also known as Oncentraâ€™s Advanced Collapsed-cone Engine (ACE). We will deliver this version of the calculated dose distribution with same experimental setup stated previously to compare relative dose.
Results: The relative surface dose within the target area was consistently increased with periphery lead shielding. The average increase in surface dose was 6.7 Â± 1.2%. There was <1.0% difference at a depth of 3 mm. At the 5 mm depth, the lead setup decreased the dose in the target area by 4.54%. When the plan is calculated using ACE, we expect these differences in dose to be minimal or nonexistent.
Conclusion: Currently, Oncentraâ€™s TG-43 dose calculation algorithm assumes uniform density. The overall outcome of our work will allow us to treat HDR patients more accurately and with higher confidence.