The Spinning Manny Indexed Overlay System for VMAT total body irradiation

While modern intensity-modulated techniques for total body irradiation (TBI) offer superior organ sparing and improved dose coverage compared to conventional TBI, their complexity has limited widespread adoption. Specifically, when treating individuals with Volumetric Modulated Arc Therapy (VMAT-TBI), a transition between the head-first-supine (HFS) and feet-first-supine (FFS) orientations is typically required. This study introduces and evaluates the Spinning Manny Indexed Overlay System, an in-house developed rotational platform designed to streamline VMAT-TBI treatments.

The Spinning Manny platform is a carbon fiber overlay that indexes securely to the treatment table, allowing for accurate and reproducible patient rotation. Weight-bearing assessments, isocenter reproducibility evaluation, and dosimetric characterization through CT imaging and attenuation measurements were made. End-to-end testing was performed using anthropomorphic and solid water phantoms, with dosimetric verification using film and thermoluminescent dosimeters (TLDs). The system was clinically implemented for VMAT-TBI at Stanford University. Workflow efficiency and dose delivery accuracy were assessed through in vivo dosimetry and treatment plan comparisons.

Commissioning tests confirmed the mechanical stability and dosimetric integrity of the Spinning Manny platform. Weight-bearing tests demonstrated support up to 159 kg, and isocenter reproducibility after rotation was within 1 mm. Attenuation at 6 MV was measured to be 4.3% and 1.3% at beam angles 30° and 90°, respectively, relative to the couch surface. For 10 MV, the attenuation was 3.4% and 1.0% at the same angles. Gamma passing rates in the end-to-end tests were 96.9% (3%/2 mm) for the lung regions and 92.6% (5%/3 mm) for the VMAT/AP/PA matchline. Clinical implementation across 136 patients (age range: 1-64 years old, height range: 83.6-197.3 cm) demonstrated efficient workflow integration, with 83% requiring HFS-to-FFS transitions. In vivo dosimetry confirmed accurate dose delivery at the matchline (96.1% ± 5.5% relative to prescription dose).

The Spinning Manny Indexed Overlay System effectively addresses a key logistical barrier in VMAT-TBI by enabling accurate and reproducible HFS-to-FFS transitions. Its mechanical stability, low attenuation, and high isocenter reproducibility support its clinical reliability, with successful implementation across patients of varying sizes and ages. By sharing this design, we aim to support the expansion and access of VMAT-TBI worldwide.