A method that can measure the delivered patient dose in Total Marrow Lymphoid Irradiation IMRT treatment based on kilovolt fan-beam CT-linac

Abstract

Abstract Background: A novel CT-linac (kilovolt fan-beam CT-linac) has been introduced into total marrow and lymphoid irradiation (TMLI) treatment. Its integrated kilovolt fan-beam CT scanner enables accurate evaluation of the dose distribution difference between plan and delivery, which is crucial for the TMLI treatment improvement for the future. Purpose: This study evaluated the technical feasibility of kilovolt fan-beam CT-linacfor TMLI treatment and investigated the true dose distribution of the delivery. Methods: 11 sets of data from 5 male and 6 female patients who had underwent the TMLI treatment with uRT-linac 506c were selected for this study. The planning target volumes consist of all skeletal bones exclusion of the mandible and lymphatic sanctuary sites. A planned dose of 10Gy was prescribed to all skeletal bones exclusion of the mandible in two fractions and 12Gy in two fractions was prescribed to lymphatic sanctuary sites. Each TMLI plan contained two sub-plans, one dynamic IMRT for the upper body and the other VMAT for the lower extremity. Two attempts were made to obtain homogeneous dose in the overlapping region, i.e., applying two plans with different isocenters for the treatment of two fractions, and using a dose gradient matching scheme. The CT scans, including planning CT and fan-beam CT (obtained during image-guided radiation therapy) were stitched to a whole body CT scan for dose distribution evaluation. Results: Firstly, the kilovolt fan-beam CT-linac can provide the adequate target dose coverage (90% for planning and delivery) and critical organ sparing that satisfied the clinical requirements. Secondly, the beam-on time of kilovolt fan-beam CT-linac is apparently shorter than helical tomotherapy for the TMLI treatment. Thirdly, there exists the dose distribution difference of PTVs between plan and delivery (p<0.05, Wilcoxon signed-rank test), but the PTV coverage of delivery is clinically acceptable (larger than 90%). There is no significant difference (p>0.05) between the dose distribution of the plan and delivery for most organs at risk, except for right len. Fourthly, for the treatment delivery, applying two plans with different isocenters for one patient in two fractions performed better than employing only one plan for one patient in two fractions on PTV coverage for PTVbone, maximum dose for small bowel, heart, and liver. Conclusion: This radiation therapy treatment planning has proved to be effective. This research first exhibited that the dose difference between planning and delivery was evaluated, which is important for treatment evaluation and plan improvement for the future studies.