Benefits and challenges of standard ceiling-mounted surface guided radiotherapy systems for breast treatments on Halcyon

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.