Image-Guided Volumetric Modulated Arc Therapy for Total Body Irradiation: A Single Institution Experience

Abstract

<h3>Purpose/Objective(s)</h3> The use of multi-isocentric volumetric mediated arc therapy (VMAT) for total body irradiation (TBI) improves dose uniformity and organ-at-risk avoidance and offers better patient comfort, but is limited by time-intensive planning and positioning errors at treatment delivery. We present a system that utilizes automated contouring and planning scripts run in widely-available software combined with image-guided delivery for an efficient simulation-to-treatment workflow. We hypothesize that this system will improve target dose coverage and normal tissue avoidance compared to conventional TBI. <h3>Materials/Methods</h3> Patients were simulated supine in both head-first and feet-first positions. Automated planning software scripts were used to co-register the two simulation scans into a single whole-body CT, to contour organs at risk and planning target volume (PTV), to divide the PTV into sub-targets with junction region overlap, and to place isocenters. Treatment was planned with VMAT for the entire body except for legs and feet, which were planned with conventional AP/PA fields. Image guidance was used for treatment delivery. Plans were evaluated for quality, planning time, delivery time, and setup accuracy. The dosimetric parameters of VMAT-TBI plans versus conventional AP/PA TBI plans were compared. <h3>Results</h3> Twelve patients were simulated and treated with VMAT-TBI: three pediatric patients and nine adult patients (age range: 9-59). Compared with conventional whole-body AP/PA technique, VMAT-TBI improved dose coverage to the whole body: PTV V₁₀₀ was improved from 71.4% ± 11.1% to 88.1% ± 2.6% (<i>P</i> < 0.001). Mean lung dose was reduced from 11.1 Gy ± 0.9 Gy to 9.3 Gy ± 1.0 Gy (<i>P</i> < 0.001). With a beam monitor unit (MU) rate of 200 MU/minute, mean lung dose rate was 15.5 centiGray (cGY)/minute. Robust planning and image-guided delivery reduced setup uncertainty. VMAT-TBI planning time was one working day. Total time on the treatment table was approximately one hour per fraction. All patients were able to complete the treatment course as prescribed. <h3>Conclusion</h3> A robust treatment planning technique and an image-guided delivery workflow were developed for VMAT-TBI. Planning efficiency was improved using automation with scripts, making planning time comparable to traditional TBI. Compared with classic AP/PA whole body fields, VMAT-TBI improved whole body prescription dose coverage and lung sparing. Time on treatment table was comparable to treatment time for traditional TBI, and patient comfort was improved due to ability to deliver treatment in the supine position. VMAT planning should be considered for all myeloablative transplant protocol patients being treated with TBI.