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Commissioning of a Novel Dedicated Treatment Unit for Total Body Irradiation

J Burmeister

J Burmeister1,2*, A Nalichowski2 , M Snyder1,2 , R Halford2 , G Baran2 , B Loughery2 , J Rakowski1,2 , T Bossenberger2 , (1) Wayne State University School of Medicine, Detroit, MI, (2) Karmanos Cancer Center, Detroit, MI


SU-F-205-3 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 205

Purpose: We present results from the commissioning of the first GammaBeam 500 Total Body Irradiator (Best Theratronics, Ottawa, CA) in clinical operation.

Methods: The GammaBeam 500 is a Co-60 teletherapy unit with extended field size and imaging capabilities for Total Body Irradiation (TBI). We performed radiation safety and output measurements, mechanical and imaging tests, and developed clinical and QA procedures. Beam data was collected for TAR-based dose calculations, calibration was performed using a modified TG-51 technique, and external dosimetric validation was obtained through the Imaging and Radiation Oncology Core (IROC). End-to-end testing included ion chamber, film, diodes, and OSLDs in a modified Rando phantom. An in-house system was developed to fabricate 3D-printed forms for creating patient-specific Cerrobend lung blocks.

Results: All radiation safety tests satisfied relevant NRC requirements and mechanical tests were within acceptable limits to provide TBI dose distributions meeting all recommendations of AAPM Report #17. With a 14,000Ci source, the dose rate at patient midplane using the maximum source to couch distance is approximately 19 and 33 cGy/min using the attenuating and non-attenuating flattening filters, respectively. The maximum useful field size (defined by the 90% isodose line) at this location is 220cm x 78cm with field flatness within 5% over the central 178cm x 73cm. Custom block placement is easily facilitated using the flat panel imaging system with exposure times of 0.01min. Measured output agreed with IROC validation within 0.5%. End-to-end ion chamber and diode measurements agreed with calculated doses within 3%, and all measured OSLD and film doses were within ±10% in accordance with tolerances recommended by AAPM Report #17.

Conclusion: A novel dedicated TBI unit has been commissioned and clinically implemented. Its mechanical, dosimetric, and imaging capabilities are suitable to provide state-of-the-art TBI for patients as large as 220cm in height and 78cm in width.

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