Purpose: Normal liver tissue changes after proton beam therapy (PBT) were investigated in patients at 1 and 2 years after the therapy.
Materials and methods: Changes in normal liver tissue volume were examined. The dose distribution of the normal liver tissue was also simulated on the follow-up CTs.
Results: The normal liver tissue volume was 1149 ± 215 cm3 before treatment, 1089 ± 188 cm3 at 1 year, and 1080 ± 236 cm3 at 2 years after treatment. The normal liver tissue volume was increased in 10 and decreased in 20 patients at 2 years and was smaller than that before the treatment in total (P = 0.03). The simulated volume that received more than 30 Gray equivalent [V30 (cm3)] at 1 year was 258 ± 187 cm3 and that at 2 years (244 ± 171 cm3) was smaller than that before treatment (297 ± 140 cm3) (P = 0.03).
Conclusions: The changes in the shape and volume of normal liver tissue are not constant, which cause a large dose distribution discrepancy in the normal liver for 2 years. Therefore, careful consideration of the dose distribution of normal liver tissue is required when planning re-irradiation.
Keywords: HCC; Image registration; Liver; Proton beam therapy.