Abstract
The present work investigates the benefits and challenges of applying surface guided radiation therapy (SGRT) to breast cancer treatments on the Halcyon™ (Varian, USA). Inter-fraction setup accuracy and treatment time were assessed by comparing CBCT shifts registered following SGRT-based vs. standard tattoo-based patient setup in two randomly selected groups of ten breast patients. Next, using a torso phantom and a volunteer, intra-fraction motion tracking accuracy and surface coverage were assessed for 3 adjusted central ceiling camera positions. SGRT was shown to significantly reduce setup errors (mostly within ± 2 mm) compared to tattoos (up to 2.1 cm) in all translational directions (p-value < 0.001). Treatment throughput and efficiency were also significantly improved with SGRT (p = 0.038). Meanwhile, intra-bore surface coverage with an adjusted central SGRT camera proved insufficient, suffering from patient self-occlusions (invisible body parts occluded by patients’ own morphology such as breasts, bellies, arms, etc.) and bore-induced camera obstructions. Tracking accuracy remained satisfactory (sub-0.5 mm) but 6 degrees-of-freedom motion monitoring, critical in stereotactic radiosurgery, stereotactic body radiation therapy and deep inspiration breath hold techniques and clinical applications, was not possible. Standard ceiling-mounted SGRT systems reduce inter-fraction breast setup errors and treatment duration while intra-fraction motion tracking is insufficient for O-ring linear accelerators.
Highlights
Recent years have witnessed the development of surface guided radiation therapy (SGRT) as a means for fast and accurate patient setup, live and continuous monitoring of intrafraction patient motion and increased treatment efficiency and throughput (Li et al, 2011; Herron et al, 2018; Kost et al, 2019).SGRT has been used with various delivery techniques and for all anatomical sites including standard intracranial, torso and pelvic applications
SGRT was found to positively improve postural alignment of the patient eliminating gross rotational errors which may be frequent when solely using tattoos for patient setup and which cannot be corrected with the 3 DOF HalcyonTM treatment couch
Tracking the patient treatment time showed that SGRT offers significant (p = 0.038) time sparing compared to tattoos with treatment times of 10.9 ± 1.4 vs. 11.3 ± 2.1 min respectively
Summary
SGRT has been used with various delivery techniques (for example protons, photons: conformal/conventional, intensity modulated radiotherapy, and volumetric modulated arc therapy) and for all anatomical sites including standard intracranial, torso and pelvic applications. Showing clinical outcomes (local/regional tumor control, actuarial survival rates, radiation-induced toxicities) equivalent to image-guided radiotherapy (Li et al, 2013; Pham et al, 2014; Batin et al, 2016; Zagar et al, 2017; Heinzerling et al, 2020). A recent publication reported the use of SGRT for initial patient setup on Halcyon for non-SRS intracranial treatments showing faster setup and treatment time along with a 50% reduction of repeat imaging (Flores-Martinez et al, 2020). Benefits of SGRT for other clinical sites such as breast, one of the most widely treated cancer on HalcyonTM accelerators, have not been previously reported.
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