Author: Haiqa Arain, Ping Xia, Zhexuan Zhang 👨🔬
Affiliation: Cleveland Clinic 🌍
Purpose: To quantify water contents and thickness of wet towel (as a flexible bolus) on curved surface dose for partial breast irradiation.
Methods: Two VMAT partial breast plans (3000 cGy in 5 fractions) were generated on a RANDO phantom with and without bolus. For the bolus plan, the PTV_b extended to the skin surface, with a 5 mm bolus created in the treatment planning system (TPS) with a size of 14x18 cm2. For the no-bolus plan, the PTV_nb was created by retracting the PTV_b 5 mm from the skin surface. Surface doses were measured using MOSFET, with reduced dose of 200 cGy to preserve the lifespan of the MOSFET leads. The bolus plan was delivered using following configurations: a 5 mm Superflab bolus (as a benchmark), dry towel, and wet towels with varying water content and thickness (defined as number of towel layers).
Results: The average measured surface dose for the no-bolus plan was 179 ± 12 cGy, consistent with the TPS-calculated dose. The average measured surface doses for the bolus plans were 199 ± 6 cGy for Superflab and 153 ± 2 cGy for dry towel. For two-layer towel bolus, average surface doses were 180 ± 6 cGy with 25 cc water per layer and 186 ± 10 cGy with 45 cc water per layer, respectively. For three-layer towel, the average surface dose was188 ± 8 cGy with 25 cc water per layer and 196 ± 8 cGy with 45 cc water per layer.
Conclusion: Three layers of wet towel with a water content of 45 cc per layer (0.18 cc per cm2) provided equivalent surface dose to a 5 mm bolus and there is no need to increase water content beyond 45 cc per layer.