Feasibility of canine minibeam radiotherapy (MBRT) with a dual-robot kilovoltage x-ray system.

To evaluate the feasibility of delivering minibeam radiotherapy (MBRT) to a canine glioblastoma patient using a novel low-cost dual-robot kilovoltage (kV) x-ray system. 
 
Approach: A workflow to perform MBRT using a tungsten collimator with 300 μm slits was developed for the 225 kVp x-ray source system. A Monte Carlo (MC) model of MBRT was built in TOPAS and validated with EBT4 measurements in-air and in a solid water phantom. A non-coplanar MBRT treatment plan with 2 mm Al- and 0.5 mm Cu-filtered beams was created for the canine patient and compared to a clinical 6 MV VMAT plan. A full set and individual minibeam fields were delivered to a canine head phantom with an intracranial film to verify plan feasibility.

Main results: Measured and MC-simulated peak-to-valley dose ratios in-air and in the water phantom agreed within ≤ 2σ. Open-beam and collimated peak dose measurements at depths acquired with films in the water phantom agreed with simulations with mean relative differences of 1% and 2%, respectively. MBRT treatment plan spatial fractionation was preserved in healthy tissue for tissue-sparing benefits. Mean MBRT doses to organs at risk were within 15% of VMAT, except for skin (+52% for Al- and +48% for Cu-filtered beams), bone (+28% for Al and +22% for Cu) and the right ear (-39% for Al and -42% for Cu). Dose difference map average in the canine head phantom was 2.3 ± 1.2% for one and 3.5 ± 2.2% for two minibeam fields. 

Significance: These results demonstrate the feasibility of MBRT delivery using the novel x-ray system to a canine due to spatial fractionation and adequate depth dose delivered to the tumor.