(Tuesday, 7/31/2018) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 4
Purpose: Total body irradiation (TBI) has conventionally utilized extended SSD, large open fields, compensators, and point-based hand calculations to deliver uniform dose (±10%) to adult and pediatric patients. The purpose of this work is to present a workflow for computerized treatment planning of lateral TBI akin to standard external beam radiation therapy (EBRT) and increasing dose uniformity to ±5%
Methods: A prototype couch top that mimics the CT indexing system for immobilization devices was developed in-house and fixed to a mobile gurney. Treatment planning accuracy was preliminarily assessed by comparing measured dose profiles acquired in a solid water cubic phantom at 320 cm SSD to calculated values in a digital phantom. Measurements were performed at 15 MV using an ion chamber at a depth of 10 cm. All measurements were normalized to the central axis measurement and compared to calculated values.
Results: The treatment couch design allows for patient setups with folded legs as we are bounded by the maximum SSD possible for a commercial treatment planning algorithm. Immobilization air bags can be designed to be equipped with indexer locking mechanisms that offer simulation to treat reproducibility with patient arms in the desired position. Calculated and measured beam profiles at extended SSD are within ±5%. The maximum field size projection at treatment couch midline is 165 cm with a collimator setting of 45 degrees.
Conclusion: Commercial treatment planning systems can be utilized to calculate TBI dose with an accuracy of ±5%. Additional improvements to the calculation algorithm at extended SSD may reduce the variation to within 1-2%. Using the prototype couch with standard immobilization equipment, we estimate setup reproducibility that is within ±2mm. Future work includes establishing a laser localizing system for accurate patient setup and utilization of 3D printing of physical compensators.
Keywords
Taxonomy
TH- External beam- photons: Development (new technology and techniques)
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