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Measurements of Leakage Radiation and Barrier Shielding Calculations for the RefleXion Biology-Guided Radiotherapy (BgRT) System

A Purwar*, J Rogers, R Bassalow, D Zaks, D Nett, P Lilagan, RefleXion Medical, Hayward,CA


(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 302

Purpose: The RefleXion Biology guided radiotherapy (BgRT) System utilizes PET emissions for real-time tumor tracking and treatment delivery. This report reviews the radiation measurements for the leakage and scatter along with workload calculations that can be used for the design of site shielding so that exposures to public and users stay within acceptable levels.

Methods: Radiation measurements were done in different locations around the system, and the patient plane using survey meters (Fluke 451P). The leakage measurements were done with MLC and jaws closed, the gantry rotating at 30 rpm and the beam delivery at 850 MU/min (1 MU = 1 cGy at SSD = 85 cm and depth 15 mm). The scatter measurement was done with MLC fully open and jaws open to the maximum field size of 40 cm x 3 cm and with a patient equivalent scattering material at the isocenter. The clinical workload was estimated using two different techniques: NCRP 151 method based on IMRT modulation factor and an alternative method based on beam-on duty cycle.

Results: The mean leakage dose fraction was 1.3x10��, while the mean scatter dose fraction was 2.2 x 10��. This is almost two orders of magnitude below the IEC 60601-2-1 requirement of 10�³. Head leakage dose fraction was measured at 7.38 x 10��, above the electron gun with static gantry and jaws and MLC closed. Beam stop transmission fraction was measured at 8.13x10�� for maximum clinical field size of 40 cm x 2 cm. Sample workload was estimated to be 1.58x10� MU/wk.

Conclusion: Leakage and scatter radiation measurements were performed to assist with design of facility shielding for the RefleXion BgRT system. Sample workload calculations are also given.

Funding Support, Disclosures, and Conflict of Interest: This research was supported by RefleXion Medical


Not Applicable / None Entered.


TH- External beam- photons: protection and shielding

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