First clinical application and dosimetric verification of total body irradiation with volumetric modulated arc therapy / 中华放射肿瘤学杂志

ABSTRACT

Objective:To investigate the implementation procedures and dosimetric verification of the first patient treated with total body irradiation (TBI) based on volumetric modulated arc therapy (VMAT).Methods:Two sets of CT images were acquired under the head-in first and foot-in first to contour the planning target volume (PTV) of the cranial and caudal segments to accomplish the treatment of the whole body length, on which two interrelated plans of 5 subsequent isocenters with a total of 15 VMAT fields were performed to cover all PTVs. The plans were prescribed to ensure 90% PTV dose coverage with a total dose of 12 Gy in 6 fractions. Firstly, a dose optimization was performed on the caudal CT images, then the cranial CT images were optimized based on the dose distribution of the caudal CT images. The evaluation of the final treatment plan was carried out based on a plan sum of both two sets of images. The parameters of PTV and organs at risk (OARs) were measured by dose volume histograms from the accumulated plan. The quality assurance comprised the verification of the VMAT plans for each individual isocenter via Delta4 phantom. The dose distribution in the overlapped region between two adjacent central fields was verified with EBT3 film. The absolute dose at the overlapped region between two images was measured via Pinpoint chamber. In vivo dosimetry on the patient′s skin was monitored by MOSFET dosimeters. The results of planning parameters and treatment duration were analyzed. Results:The mean doses of two segments of PTVs were 12.45 Gy and 12.37 Gy. The mean dose for the lung was 10.8 Gy. The machine unit (MU) and mean treatment delivery time were 2 883 MU and 24.3 min, and the mean total time per fraction was 121 min. The mean 3%/3 mmγ-analysis pass rate for each isocenter VMAT plan was (99.74±0.42)%, and the mean 5%/5 mmγ-analysis pass rate for the overlapped region was (90.11±2.72)%. The average deviation of absolute dose in the overlap region of the caudal and cranial images was (3.6±0.4)%. In vivo measurement of 8 points on the patient showed that the dose of each region was ranged from 1.57 Gy to 2.04 Gy. Conclusion:According to the results of dosimetric verification, TBI based on multi-isocenter VMAT can be applied in clinical practice, which remains to be improved in terms of dose distribution, measurement results and clinical efficiency.