(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Investigate the radiation dose of patient pacemaker in intracranial SRS treatment (2) Evaluate the pacemaker dose at different couch angles in the single target and single-iso multi-mets SRS plans.
Methods: typical 3-arcs VMAT plans for single-iso plans were developed to cover a single target at 99% of PTV volume with radiation dose of 20Gy. In Plan_S_0, one of the arcs (Arc_0) was in the same plane of isocenter and pacemaker. In Plan_S_10 and Plan_S_20, the couch was further clicked 10 and 20 degrees more, respectively, using same arc gantry angles, to investigate the beam geometry impact. Three 4-arcs VMAT plans for single-iso multi-mets were developed to cover all 5 targets at 99% of PTV volumes by 20Gy. In Plan_M_0, Arc_0 was in the same plane of isocenter and pacemaker. Plan_M_0, Plan_M_10, and Plan_M_20 have same couch and gantry angles as Plan_S_0, Plan_S_10 and Plan_S_20. All plans were recalculated on Arc_0 only with fixed MUs to evaluate its own contribution.
Results: single-target plans, pacemaker dose shows strong relationship with couch angle at Arc_0, as the majority is existing dose from isocenter plane. The Max/Mean dose are 24.4cGy/13.2cGy, 1.7cGy/0.7cGy and 0.4cGy/0.3cGy on pacemaker in Plan_S_0, Plan_S_10 and Plan_S_20, respectively. In single-iso multi-mets plans, pacemaker dose is less dependent on couch angle in a certain range with various target locations. The Max/Mean dose on pacemaker are 14.5cGy/4.4cGy, 22.8cGy/13.9cGy and 23.6cGy/8.8cGy in Plan_M_0, Plan_M_10 and Plan_M_20. Max/Mean dose does not change in all re-calculated Arc_0 only plans.
Conclusion: general, pacemaker dose from the exiting beams in SRS is below the threshold in TG-203. However, it is worth attention on the pacemaker dose-rate effect (TG-203 recommends <0.2Gy/min) due to FFF mode. Pacemaker should be included in CT scan if clinically feasible, and couch and arc angles should be selected carefully in VMAT planning.
Keywords
Not Applicable / None Entered.
Taxonomy
TH- External Beam- Photons: intracranial stereotactic/SBRT
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