Purpose: The RefleXionTM X1 is a novel ring gantry-based radiotherapy machine that utilizes rapid rotation and a new pneumatic spring-based binary multi-leaf collimator that transitions at 100Hz. These features may provide better dosimetric conformality, which is especially pertinent in very high-dose regimens such as single-dose radiotherapy (SDRT). SDRT itself is attractive– particularly for multiple target (oligometastatic) scenarios– as a means of reducing interfraction error, treatment time, cost, and patient inconvenience. As such, this investigation was carried out to assess the SDRT performance of the RefleXion X1 in multiple target scenarios using ArcCHECK (AC) analysis.
Methods: Three multi-target lung cancer cases, each with 2-lesions ≤ 5 cm were planned with a free-breathing single-dose (28 Gy) regimen protocol (TROG 13.01 SAFRON-II). The treatment plans were carried out using a research version of the RefleXion treatment planning system which utilizes a Collapsed Cone Convolution Superposition algorithm, using a single-isocenter technique. Afterward, the SDRT plans were delivered in stereotactic treatment mode to an AC dosimetry device. Sun Nuclear patient-software was used to compare the AC measured dose with planned dose using the 2%/2mm gamma criteria with 10% low-dose threshold, as demonstrated by the absolute gamma passing rate (GP) > 90%.
Results: All three patient plans met dosimetric coverage and organ-at-risk avoidance goals. With the treatment machine set at 850MU/Min, the average delivery duration was 46.19 mins (range: 37.47-59.98 mins). The delivery duration was associated with the lesion volume size with a correlation coefficient of 0.97 (P=0.11). Likewise, the 2-lesion plan deliveries met the GP for delivery accuracy with an average of 98.13% (range: 95.5-100%).
Conclusion: RefleXion plans for SDRT in the multiple target setting met dosimetric and physics quality criteria. These results demonstrate treatment planning robustness and treatment delivery feasibility for relevant clinical scenarios such as SDRT or oligometastatic disease using the RefleXion X1.
Funding Support, Disclosures, and Conflict of Interest: Research supported by RefleXion Medical.