J Huang, K Schaefer*, M Lawless, L DiMaso-Myers, T Tyson, K Bradley, University of Wisconsin, Madison, Wisconsin

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  K Schaefer

WE-C1030-IePD-F4-4 (Wednesday, 7/13/2022) 10:30 AM - 11:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 4

Purpose: Our institution’s low dose (≤4Gy) linac-based total body irradiation (TBI) program utilizes lateral beams and patient arms positioned to shield the lungs. However, to modernize our program and allow for higher doses and lung blocking, a new program with AP/PA beams and the patient lying in a lateral decubitus position was commissioned. This abstract describes the design of new equipment, commissioning measurements, and workflow changes of our new program.

Methods: A new TBI apparatus with an aluminum frame, beam spoiler (3/8” acrylic), patient foam supports, and an adjustable lung block holder was designed and fabricated. Additionally, a ceiling laser was installed to increase ease of patient setup and reproducibility (375cm SAD). Commissioning measurements, including TMR, output, uniformity, and transmission for adult and pediatric sized lung blocks, were performed using solid water and ionization chambers. An end-to-end measurement was performed with TLDs. Imaging for block placement verification was performed using a portable X-ray unit.

Results: The total cost of the TBI frame and foam support materials was approximately $7500. The 40cm x 40cm field (collimator 45°) was uniform within 5.0% within 80cm of the central axis at 10cm depth. For our TBI geometry, the TMR at 10cm was measured to be 85.2%, which agrees well with our 100cm SAD TMR of 87.2% (30x30 field). Using TG-51 formalism at extended distance (375cm SAD), the output at dmax was measured to be 0.0792cGy/MU. Cerrobend transmission was found to be dependent on block size. End-to-end measurements with TLDs were within 4% of expected for depths ≤10cm.

Conclusion: By designing and fabricating a custom TBI frame tailored to our program’s workflow requirements and utilizing hospital resources (i.e., a portable X-ray unit from radiology), we were able to improve and redesign our low dose TBI program to accommodate improved patient positioning and lung blocking.

Keywords

Commissioning, TBI

Taxonomy

TH- External Beam- Photons: Development (new technology and techniques)

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