Author: Emily Hansen, Alois M. Ndlovu, Niara Rowe, Roland Teboh 👨🔬
Affiliation: Hackensack University Medical Center 🌍
Purpose: The accuracy of SCINTIX biology-guided radiotherapy (BgRT) on the RefleXion X1 is dependent on the correct alignment of the isocenter between all subsystems, including setup lasers, kV imaging, MV treatment, and PET detectors.
Methods: On each SCINTIX BgRT treatment day, two quality assurance tests must be completed, both using the UMA phantom supplied by RefleXion. The UMA phantom has markings for laser alignment, central radiopaque markers for kVCT alignment, a slot to insert a positron-emitting point source for
PET alignment, and two slots to insert films orthogonally through the phantom center in axial and coronal planes. Firstly, the manufacturers’ required PET System Performance Check (SPC) must be completed, using only the UMA phantom and inserted point source. Then, the Multimodality Alignment (MMA) must be performed, again using the UMA phantom and point source with Gafchromic films inserted. The PET SPC will verify the alignment between the laser setup plane, kVCT imaging plane and PET detectors. The Multimodality Alignment verifies the alignment between the laser setup plane, kVCT imaging plane, PET detectors, and the treatment plane.
Results: Over a 6-month period, the MMA test was run twenty times, and the PET SPC was run forty times. The PET SPC provided an average calculated isocenter difference of 0.4066 mm, and the MMA Films resulted in an average offset of 0.5387 mm, with 0.4706 mm in XY and 0.2244 mm in XZ.
Conclusion: For the initial 6 months post-commissioning, the alignment between the laser setup plane, kVCT imaging plane and PET detectors was well within the 4 mm tolerance, according to the PET SPC. Based on the MMA film analysis, the alignment between the laser setup plane, kVCT imaging plane, PET detectors, and the treatment plane was also well within the recommended 2 mm tolerance.