Volumetric modulated arc therapy dosimetry and treatment time compared with conventional intensity-modulated radiotherapy for unresectable cholangiocarcinoma

Background: Cholangiocarcinoma is a locally extending tumor with a high incidence in Thailand. Most patients are diagnosed when the tumor is unresectable, which requires concurrent chemotherapy and/or radiation. Volumetric modulated arc therapy (VMAT) and conventional intensity-modulated radiotherapy (cIMRT) are advanced techniques that improve survival and reduce radiation-induced complications. Objectives: To compare conformity, homogeneity, and treatment time between VMAT and cIMRT in unresectable cholangiocarcinoma. Methods: Between September 2004 and December 2010, CT images of 11 unresectable cholangiocarcinoma patients were retrieved and replanned by VMAT and cIMRT. Comparison was made in conformation number, homogeneity index, and monitor units using a Wilcoxon signed-rank test. Dose constraints for critical organs such as the liver, kidneys, and spinal cord were restricted by Quantitative Analyses of Normal Tissue Effects in the Clinic criteria. Results: Mean conformation number was 0.91 in both the VMAT and cIMRT plans (p = 0.477). Mean homogeneity index was 2% different, 1.11 in VMAT plans and 1.09 in cIMRT plans (p = 0.008). Mean monitor units was 529 in VMAT plans and 1,279 in cIMRT plans (p = 0.003). Conclusion: This study is the first VMAT study in unresectable cholangiocarcinoma. Conformity was not different, but treatment time was shorter by VMAT as reported in other cancer studies. Homogeneity was 2% statistically higher by VMAT; however, clinical differences should be evaluated.