(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: To present the results from IROC Total Body Irradiation (TBI) phantom measurements and propose credentialing acceptance criteria.
Methods: Pediatric phantoms of the 10-year-old model were purchased from CIRS. An in-house machinist drilled holes in 13 different points to hold TLD and manufactured arms. Phantoms were shipped to institutions participating in NCI-sponsored clinical trials that allowed TBI treatments. Sites delivered 3 Gy to the umbilicus using the delivery method that they normally followed. Protocols require dose throughout the body to be within 10% of the prescription dose. TLDs were located at three locations in each lung; at the mid-line for the brain, neck, mediastinum, umbilicus, and pelvis; and at the left and right abdomen locations.
Results: Twenty institutions delivered 43 irradiations. Most institutions irradiated once with an open field and once with lung blocks or shields. Some institutions tested each of their multiple delivery methods. 14 irradiations were in the decubitus position, 4 sitting, 2 standing, 13 supine and 10 supine/prone. There were 33 AP/PA directions, 6 lateral, 2 sweeping arcs, and 2 helical. Unblocked lung doses averaged 3.1 ± 0.3 Gy and blocked averaged 1.8 ± 0.8 Gy. The average measured dose delivered to the umbilicus was 99% of the prescription dose. Lung does calculated according to the institutions ratio of blocked to open treatments. Scaled to a 12 Gy prescription, 7 of 23 combinations limited the average lung dose to =8 Gy and 11 limited it to =9 Gy. The proposed criteria of 5% agreement at the prescription point and non-lung does to be within 15% of the prescription dose would cause 4 of the irradiation combinations to fail.
Conclusion: A wide variety of TBI treatment practices exists in the community. Lung doses vary from site to site as well as within the lung.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by IROC-Houston NCI grant #CA180803.
Keywords
Taxonomy
TH- External Beam- Photons: Quality Assurance - Linear accelerator
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