Program Information
Novel Technique to Implement GRID Therapy in a Commercial Treatment Planning System
H Park*, M Mohiuddin , D Yaldo , B Tom , N Worlikar , Advocate Health Care, Park Ridge, IL
Presentations
SU-C-BRB-3 (Sunday, July 12, 2015) 1:00 PM - 1:55 PM Room: Ballroom B
Purpose: Due to the difficulty of creating an accurate multi-aperture block in treatment planning systems (TPS), spatially fractionated radiation therapy (GRID Therapy) is limited to clinical setups using simple monitor unit calculations. In this work, we present a novel approach to accurately model a grid block in a TPS and evaluate its dosimetric accuracy.
Methods: An acrylic GRID block was fashioned such that the hole size and spacing were the same dimensions of the brass GRID block (dotDecimal) at isocenter. Holes were non-divergent and drilled 1 cm deep. CT scans (RT Lightspeed, GE Healthcare) of the block were acquired using axial slices with a thickness of 0.625 mm. These were imported into Eclipse (version 11, Varian Medical Systems) and holes were auto-contoured into structures. The GRID block was created in Eclipse by forming apertures around the hole structures using a simple three step process. Treatment plans were created in a water-equivalent phantom using 6 and 10 MV beams, delivered with a linear accelerator (Clinac iX, Varian Medical Systems) and measured using a water tank, film and a diode array.
Results: Comparisons of percent depth dose curves and profiles at depths of maximum dose, 5cm, and 10cm for field sizes ranging from 5 cm² to 25 cm² using water and film were within 3% of their respective positions in Eclipse. GRID plans utilizing various jaw sizes and MLC blocking measured with film and a diode array showed pass rates with an average of 97% using Gamma analysis at 3%/ 3 mm and no lower than 93%.
Conclusion: We have developed a simple yet accurate method of incorporating a GRID block into a commercially available TPS and demonstrated that the TPS accurately reflects the dose delivered. This will allow for real-time planning using patient scans and encourage new methods for GRID therapy.
Funding Support, Disclosures, and Conflict of Interest: Support provided by dotDecimal, Sanford, FL
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