SU‐E‐T‐339: Dosimetric Verification of New Accuboost Applicators

Purpose: To confirm dose, dose coverage, and dose homogeneity for two new types of Accuboost™ applicators. Methods: Measurements were performed with the newly designed Skin Dose Optimized (SDO) and Dose Rate Optimized (DRO) Accuboost™ applicators used with an Elekta High Dose Rate (HDR) after‐loader. 5 cm, 6 cm, and 7 cm diameter applicators were tested for both the SDO and DRO designs. Landauer nanoDot dosimeters (OSLD) were placed along the central axis of the applicators at a depth of 2 cm. Dwell times determined for a dose of 200 cGy and a separation of 40 mm were calculated for the standard parallel‐opposed setup. A single posterior applicator was then used to deliver 100 cGy. Dose measured using a parallel plate Markus chamber and the earlier applicator design (7 cm round) was used to normalize the measurements. The Markus chamber was then used to further verify doses from the new applicator designs. Relative film dosimetry was also performed to assess the dose distribution. Gafchromic film was sandwiched between solid water plates at a depth of 2 cm. Results: nanoDot‐measured dose differences ranged from −4.9% to 2.4% for both SDO and DRO applicators across all sizes. Ion chamber measurement differences ranged from −2.76% to 1.1% and from — 2.21% to 0.17% for DRO and SDO applicators, respectively. Gafchromic films were normalized such that the 100% value was consistent with nominal dimension of the applicator. Maximum doses ranged from 130% — 150% and showed reasonable dose distributions in both axial and coronal irradiated films. Conclusion: All applicators showed good dose distribution as well as absolute dose values. Treatments with these applicators should deliver the prescription doses and coverage as intended.