Purpose: This study evaluated the technical feasibility of uRT-linac 506c for TMLI treatment and investigated the true dose distribution of the delivery.
Methods: Retrospective analysis of 11 patients who had underwent the TMLI treatment with uRT-linac 506c were selected for this study. 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 uRT-linac 506c can provide the adequate target dose coverage and critical organ sparing that satisfied the clinical requirements. Secondly, the beam-on time of uRT-linac 506c 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),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 paper demonstrated the efficiency and feasibility of the TMLI treatment with uRT-linac 506c, which is a novel CT-linac.