Room: Exhibit Hall
Purpose: A novel method of radiation delivery, Spatially Optimized Radiation Therapy (SORT), has been proposed using the traditional grid block technique to improve radiation induced anti-tumor immune response. In contrast to conventional RT, which aims to achieve uniform dose over the PTV, SORT dose distributions are highly heterogenous within the target. The goal of this work is to commission source-to-axis-distance (SAD) grid-based technique in the clinic and perform end-to-end testing of treatment delivery.
Methods: Commissioning data collected for a .decimalÂ® grid included measurements for depth dose curves, profiles, and field-size output factors. Several different detectors were utilized in the process for comparison purposes. Incorporation into the TPS required generating the grid template for Pinnacle 3D planning. User-defined tray and block factors were chosen per field size to closely match the MU and PDD values from the TPS calculation to output factor measurements. Beam data was also imported into RadCalc software to provide a Physics second check. End-to-end testing was performed using a variety of equipment: film, ion chamber in solid water, and ion chamber in an irregular surface phantom.
Results: With the grid, output is reduced by approximately 10% at dmax. It creates an overall â€œsofterâ€? beam quality with a dose reduction of ~5% as compared to an open beam. Block transmission between the holes is ~21%. The end-to-end testing yielded dose measurements within 2% of the treatment planning system for both SSD and SAD set ups, showing that both the traditional SSD set-ups and isocentric treatments can be accurately modeled.
Conclusion: There has been renewed interest in the use of block grid therapy due to the enhanced therapeutic ratio. After successful commissioning with SAD set-up, the future use of the grid will lead towards the exploration of the synergistic effect between immunotherapy drugs and SORT for systemic anti-tumor response.