The Thoracic Absorption Dose and Secondary Tumor Risk Caused by Different Imaging Methods in Image-Guided Particle Radiotherapy.

Background: Image-guided radiation therapy uses imaging methods such as CBCT to effectively improve treatment precision. Kilovoltage-imaging technology provides high soft tissue contrast at low doses, whereas megavoltage-imaging technology better displays deep and bony structures at high doses. Proton therapy is more sensitive to tissue density and positional accuracy, so it requires more stringent image guidance and higher precision than traditional X-ray therapy.

Objective: This study evaluates radiation doses from CBCT systems (TrueBeam, Halcyon, ProBeam, TOMO) in both adult and pediatric phantoms, measuring dose variations and predicting secondary tumor risks using a radiobiological model.

Methods: Absorbed doses in organs of adult and pediatric phantoms were measured with OSLDs across imaging systems. The risk of secondary tumors was estimated using the BEIR VII model.

Results: Halcyon 2.0 and TOMO's MV-level imaging systems showed significantly higher doses than KV-level systems. Pediatric patients received 2-3 times higher doses than adults. In KV-level imaging, Halcyon 2.0 resulted in the highest lung tissue dose in both age groups (17.464 mGy for pediatric, 9.109 mGy for adult), whereas ProBeam had the lowest (6.844 and 4.073 mGy, respectively). The lifetime attributable risk for lung cancer correlated with the dose, with higher risks in children.

Conclusions: Higher radiation doses lead to greater secondary tumor risk, with the risk being more pronounced in pediatric patients. Continuous thoracic CBCT can deliver up to 1 Gy in thoracic organs, posing a significant risk of secondary tumors, especially in younger patients. Careful consideration of this risk is essential in treatment planning.