Purpose: To compare doses calculated with TG-43 and AcurosBV (Varian, USA) algorithms in heterogeneous media pertaining to HDR skin treatments.
Methods: HDR skin plans were generated on CT scans of a 7x7 cm2 Freiburg Flap (Elekta, Sweden) placed atop of two heterogeneous phantoms. The first phantom (P1) was built with cork (10mm) and solid water (SW) (53mm); the second phantom (P2) consisted of stacked thermoplastic mask (3mm), SW (3mm), bone (20mm), and SW (50mm) to simulate skin treatment of the scalp. Superflab layers of 1 cm or 2 cm were placed over both phantoms to add additional scatter material. Plans were generated in BrachyVision 15.5 with TG-43 requiring 100% target coverage and a skin max dose smaller than 150% of the prescription, then recalculated with AcurosBV. Treatments were delivered with GammaMedPlus (Varian, USA) for dose measurements using Gafchromic EBT3 placed within P2 under the SW and bone layers.
Results: After dose re-calculation with AcurosBV, the target coverage decreases to 95.7% for P1 and 99.0% for P2. Adding 1cm and 2cm Superflab increases the coverage to 99.4% and 99.7% (P1) and 97.4% and 99.8% (P2) for AcurosBV. Point doses along the target central axis are 2.5% higher with TG-43 and agree with AcurosBV within 1.0% after adding the Superflab. The dose calculation times were 3 - 5 minutes for AcurosBV, vs. < 1s for TG-43. Measured dose in P2 with additional 1cm Superflab agrees with TG-43 and AcurosBV calculations with a passing rate greater than 90% for 2%/2mm gamma criterion.
Conclusion: Dose calculations with TG-43 and AcurosBV for skin HDR with Freiburg flap applicators show 3% difference in treatment regions. Adding 1 cm Superflab on top of the applicator will provide more realistic doses, when treating scalp lesions with HDR brachytherapy. Additional measurements will be required to confirm the results.