Purpose: In support of a novel compensator-based IMRT system for low- and middle-income countries, here we demonstrate commissioning in Eclipse. This allows for high-quality treatment plans created locally and integration into the Radiation Planning Assistant, a web-based automatic planning system being developed specifically for resource-limited clinics.
Methods: The treatment device consists of a cobalt-60 unit and nine field compensator arrays. Each compensator has a 3D-printed plastic mold filled with reusable 2mm tungsten beads and is mounted around the patient. We commissioned it in Eclipse (v15.6). Validation tests described in MPPG 5.a were performed using Monte Carlo (MC) data calculated by GATE. Dose distributions and penumbra were evaluated for basic dose validation using a gamma index for the compensator-based IMRT dose validation. Compensator-based IMRT plans with the cobalt-60 unit were generated for five head-and-neck cancer cases, and PTV coverage and OAR sparing were compared to linac-based plans reviewed by physicians.
Results: The PDDs and profiles of the Eclipse deviated from the MC simulation by 0.65±0.41% (Range: 0.1-2.1) and 1.02±0.99% (Range: 0.1-3.6) and are within 2% tolerance. The 80%-20% penumbra deviation is 0.5±0.3mm and is within 3mm tolerance. The gamma passing rate with criteria of 2%/2mm was 92.6%. Cobalt-60 compensator IMRT plans were found to deliver comparable quality treatment plans with standard linac-based VMAT plans based on DVHs. PTV D95% and D5% were within 1% for both plans evaluated. Each PTV received a conformal dose based on homogeneity index (0.04 vs. 0.05 for linac-based VMAT plan and compensator-based IMRT plan). Doses for critical structures were slightly higher in the cobalt-60 compensator plans but within clinical tolerances.
Conclusion: The compensator-based cobalt-60 device can generate highly conformal IMRT plans on par with clinical linac-based technologies at a reduced cost. We are developing a test device with clinical partners in low- and middle-income countries.
Funding Support, Disclosures, and Conflict of Interest: Funded by National Cancer Institute