From dose to decision: IAEA TECDOC-870–based risk modeling of CBCT and practical protocol recommendations

This study evaluates organ-specific radiation doses and cancer risks from Cone Beam Computed Tomography (CBCT) in head/neck and chest radiotherapy. Using an anthropomorphic phantom and Optically Stimulated Luminescence Dosimeters (OSLDs) on a Varian Halcyon™ 2.0 system, two protocols were assessed: head (100 kV, 126 mAs) and thorax fast (125 kV, 270 mAs). Measured mean organ doses were 11.98 mGy (brain), 15.84 mGy (thyroid), 10.16 mGy (heart), and 8.32 mGy (lungs). The EQD2 was highest for the thyroid (17.2 Gy, α/β=3), followed by lungs (9.8 Gy, α/β=10). Sex-specific excess relative risk (ERR) analysis revealed substantial variation, with females exhibiting higher risks. The thyroid (head protocol) showed maximal ERR (79.99% females, 55.79% males), followed by brain (38.99% vs. 22.78%) and thyroid in thoracic scans (40.81% vs. 28.46%). Lung ERR reached 35.90% (females) vs. 12.53% (males), while esophagus and heart risks showed pronounced sex differences. Key findings: (1) significant dose heterogeneity, with thyroid receiving highest exposure, (2) elevated biological risks for late-responding tissues, and (3) consistently greater cancer risks in females. These results highlight the need for protocol optimization through dose reduction and gender-specific considerations in CBCT imaging, balancing quality with safety.