Room: ePoster Forums
Purpose: To verify the feasibility of using HDR source for spatially fractionated grid radiation therapy for bulky skin lesions.
Methods: Ir-192 HDR source was used to generate a spatially fractionated skin lesion radiation therapy plan. The 1, 2, 3, 5 and 10 mm step sizes were used to check if a spatially fractionated grid dose distribution can be made at the skin. The plans were optimized using the distance-based dose optimization method to prescribe an absolute dose of 10 Gy at prescription depth of 1 cm from source (5 mm from the skin). A 2D-matrix of calculation points at the size of 6x6 cm^2 was created to get the 2D dose distribution at the skin. EBT3 films were used to verify the dose value Vs TG43. In this preliminary study, in order to improve the measurement reproducibility and reduce the film cost, a commercially available Freiburg flap applicator and a 3x3 cm^2 field size formed by 4 channels were used. The maximum dose, minimum dose, mean dose and the peak/valley dose ratios were obtained.
Results: At the 1, 2, 3, 5 and 10 mm step sizes, the skin maximum dose was 20.34, 21.99, 22.42, 23.36 and 24.88 Gy, the peak and valley dose ratios are 1.27, 1.49, 1.52 1.71 and 1.97. The maximum peak/valley dose ratio was shown at the largest step size.
Conclusion: The traditional grid collimator with 6 MV beam can achieve the peak/valley ratio of 5.4 at the 1.5 depth, the spatially fractionated grid therapy with HDR source only can achieve 36% of the peak/valley ratio of 6 MV beam. However, because HDR source has a favorable penetration feature, it can spare more distant normal tissues than the 6MV beam, so the HDR source grid therapy can be formulated for treating shallow or skin bulky lesions.