Impact of Anatomical Phantoms On Organ Dose Estimates for Patients Undergoing Fluoroscopically-Guided Interventions (FGIs)
S Streitmatter1*, J Shin2, C Lee3, (1) University of Utah Hospitals, Salt Lake City, UT, (2) National Cancer Institute, Bethesda, MD, (3) National Cancer Institute, Bethesda, MD
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PO-GePV-I-95 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To quantify the impact that anatomical phantoms have on organ dose estimates for patients undergoing fluoroscopically-guided interventions (FGIs), specifically the difference between simple stylized/geometric computational phantoms and voxel/hybrid models.
Methods: The National Cancer Institute dosimetry system for Radiography and Fluoroscopy (NCIRF) program was used to calculate organ doses for a variety of common projection angles (RAO 25 CAU 25, RAO 25 CRA 25, LAO 25 CAU 25, LAO 25 CRA 25, PA) used in cardiac catheterizations. For comparison, A PC Program for X-ray Monte Carlo (PCXMC) was used to calculate organ doses with stylized phantoms, matching the NCIRF beam projections, spectra, and DAP as best as possible. In NCIRF, common kVp and HVL pairs are user-selectable and the one that matched the best with the average angio technique for thorax-equivalent attenuation was 70 kVp, 6.83 mm Al HVL. In PCXMC, kVp and mm of Al and Cu can be prescribed. It was determined by measurement that 70 kVp with 21.5 mm Al filtration was the closest equivalent. Organ doses were calculated for the standard adult male and female phantoms in NCIRF and in the standard adult hermaphroditic phantom in PCXMC.
Results: Beam qualities between the two programs were < 1% different in effective energy and shape of Bremsstrahlung spectra matched well. Key organ doses were compared and, overall, there was good agreement for sensitive organs and effective dose (10%), but active marrow and the adrenals were overestimated by PCXMC, thyroid underestimated.
Conclusion: It is expected for there to be differences in organ doses when switching from an idealized geometric anatomical phantom to a more realistic voxelized/hybrid model. The varying beam angles used in FGIs can further accentuate the differences in anatomical phantom structure and composition, thus further supporting the need to move to more realistic anatomical representations for dosimetry.
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