Minibeams on a Budget: Canine Spatially Fractionated Radiotherapy with the KOALA Dual-Robot System
Abstract
Purpose
To evaluate the feasibility of delivering minibeam spatially fractionated radiation therapy (SFRT) using a novel, low-cost, dual-robot system, the Kilovoltage Optimized AcceLerator for Adaptive therapy (KOALA).
Methods
A workflow to performing SFRT was developed for KOALA’s 225kVp X-ray source, including the design of angle specific cutouts, as well as the fabrication of a 3D-printed holder to support a 1cm thick diverging tungsten collimator composed of twelve 300μm slits separated by 415μm. An SFRT treatment plan was developed for a glioma canine patient and compared against a clinical 6MV VMAT plan. Experimental dose distributions were assessed using radiochromic EBT4 films placed on top of the collimator holder and at 1cm intervals in a solid water phantom. Additionally, a 2D dose map at depth was obtained by placing film in a canine head phantom. The physical setups were then reproduced in TOPAS MC and experimental results were compared to simulations.
Results
The SFRT treatment plan achieved adequate PTV coverage for a prescription dose of D50=27.7Gy, while preserving spatial fractionation in healthy tissue for tissue-sparing benefits. Mean OAR doses were within 20% of VMAT, except for in bone and the left ear. Open-beam and collimated PDD measurements acquired with films in the solid water phantom had excellent agreement with MC simulations (within 1σ). Measured and MC-simulated peak-to-valley dose ratios (PVDRs) for films positioned in contact with the collimator holder were consistent with values of approximately 25, exceeding the accepted SFRT PVDR threshold of ~5 required to reduced normal-tissue damage.
Conclusion
These results demonstrate the feasibility of SFRT delivery using the KOALA system in a small canine model. This was achieved by high spatial fractionation of the kilovoltage X-ray beam and adequate dose delivered to the tumor at depth, as validated by experiments and MC simulations.