Purpose: Non-isocentric dynamic trajectory radiotherapy (DTRT) is enabled through additional dynamic table translations in synchrony with dynamic gantry, table and collimator rotation during beam on. The purpose of this work is to explore use cases of non-isocentric DTRT.
Methods: To create non-isocentric DTRT plans, paths describing the gantry, collimator and table rotation and table translations are determined, along which the intensity modulation optimization is performed. In a first use case, the distance between the gantry and patient of an isocentric DTRT plan for a brain case is increased to reduce the risk of collisions. Dosimetric treatment plan quality of the resulting non-isocentric DTRT plan is compared to the isocentric DTRT plan. In a second use case, a non-isocentric DTRT plan for a craniospinal irradiation (CSI) case is created, consisting of a table translation along the spinal cord followed by a gantry rotation around the brain and a table translation back along the spinal cord. Plan quality and delivery time of the non-isocentric DTRT plan is compared to an IMRT plan. The non-isocentric DTRT plans are delivered on a TrueBeam linear accelerator in developer mode and dose distributions are measured using radiochromic films and compared to the calculated dose distributions using gamma analysis (3% (global)/ 2 mm, 10% threshold).
Results: The non-isocentric DTRT plan for the brain case shows similar dosimetric plan quality as the isocentric DTRT plan. The non-isocentric DTRT plan for the CSI case shows similar dosimetric plan quality as the IMRT plan, but 45% reduced delivery time. Both non-isocentric DTRT plans are successfully delivered without collisions and the gamma passing rates are higher than 95% for both plans.
Conclusion: Two possible use cases of non-isocentric DTRT, enabled through dynamic table translations in DTRT, were demonstrated and the dosimetric accuracy was validated.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by grant 200021_185366 of the Swiss National Science Foundation and by Varian Medical Systems.