Program Information
Increased Dose Near the Skin Due to 4D Electromagnetic Localization System Array
J Ready*, J Perks , UC Davis Medical Center, Sacramento, CA
Presentations
WE-RAM3-GePD-IT-4 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Imaging ePoster Theater
Purpose: To measure and assess the effect of the Calypso (Varian Medical Systems, Palo Alto, CA) electromagnetic array on surface dose to the patient when used during treatment.
Methods: MOSFET detectors (with an inherent buildup of approximately 0.8 mm) were used to measure the surface dose to a solid water phantom with and without the Calypso array positioned within the beam (SSD 95 cm, 10 x 10 cm2 field size, 100 MU) for 6, 10, and 15 MV photon energies. IMRT QA measurements for three prostate SBRT, one lung SBRT, and one pelvis VMAT treatment plans were performed with the MOSFET detectors placed on the surface of an ArcCheck QA phantom, with and without the Calypso panel.
Results: For normal incident beams, the near-skin dose was measured to increased by a factor of 2.0, 2.3, and 2.3 for 6 MV, 10 MV, and 15 MV photon beams, respectively, with the Calypso array in the beam. While the Calypso panel showed no effect on the overall pass rate of IMRT QA measurements, there was an average increase by a factor of 1.5 in surface dose (range 1.4–1.6) with the Calypso panel in place.
Conclusion: AAPM’s TG-176 suggests that the Calypso array be included in the treatment planning system to account for effects on patient dose. However, there are no reports of this being performed. Our study confirms that there is a measurable increase in the surface dose due to the presence of the Calypso device, and particularly for targets near the patient’s surface, should be accounted for in clinical practice.
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