A preliminary study of the protection of bone marrow in craniospinal irradiation

Abstract

Objective To analyze the relationship between the dose volume of bone marrow and acute hematologic toxicity in craniospinal irradiation (CSI), and preliminarily explore the dosimetric differences in bone marrow between helical tomotherapy (HT) and volumetric modulated arc therapy (VMAT). Methods Clinical data and HT plans of twenty patients treated with CSI in the First Affiliated Hospital of Kunming Medical University were collected, and the HT plans were transferred back to the MIM system. The skull, mandible, clavicle, sternum, scapula, ribs, vertebrae and pelvis were successively delineated on the CT images and then the V2, V5, V10, V15, V20, V25, V30, V35, Dmax, Dmean of each aforementioned bone and total bone were read on DVH images. The correlation between those indexes and the incidence of ≥grade Ⅱ hematologic toxicity was subsequently analyzed. The images of 6 patients were selected and transferred to Monaco TPS and VMAT plans were completed. The dosimetric differences of those indexes were statistically compared between HT and VMAT. Statistical analyses were performed by using Spearman correlation analysis and Wilcoxon symbol rank-sum test. Results The incidence of ≥grade Ⅱ leukopenia was positively correlated with the V25 of pelvis and the V5 of total bones (P=0.038); the risk of ≥ grade Ⅱ thrombocytopenia was positive associated with the V20 of pelvis (P=0.041); the incidence of ≥ grade Ⅱ neutropenia was positively correlated with the V10 of vertebrae (P=0.036). There was no dosimetric difference of dose volume of vertebral and pelvis between HT and VMAT plans (P>0.05). Conclusions There is a positive correlation between ≥ grade Ⅱ leukopenia and the V25 of pelvis and the V5 of total bones. The V20 of pelvis shows a positive correlation with ≥ grade Ⅱ thrombocytopenia. A positive correlation is found between ≥ grade Ⅱ neutropenia and the V10 of vertebrae. The indices of vertebral and pelvis between HT and VMAT plans show no significant differences. Key words: Helical tomotherapy; Volumetric modulated arc therapy; Craniospinal irradiation; Bone marrow-sparing