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.

Evaluation of surface-guided radiation therapy for breast cancer using the Halcyon system

“…Nguyen et al reported that SGRT signi cantly reduced setup errors compared with tattoos in all translational directions in patients with breast cancer [14]. They also showed that additional information acquired by the SGRT system can improve the positioning accuracy of breast cancer patients compared with the laser-based setup [14]. However, our study showed that only the average residual translational error in the vertical direction decreased signi cantly, but increased in the longitudinal direction.…”

“…Because it is probably a comparison for the cranial region that are not affected by respiration in their study, which could be predominantly affected by chest wall motion caused by respiratory in our study. Nguyen et al reported that SGRT signi cantly reduced setup errors compared with tattoos in all translational directions in patients with breast cancer [14]. They also showed that additional information acquired by the SGRT system can improve the positioning accuracy of breast cancer patients compared with the laser-based setup [14].…”

“…In particular, because breast tissue is highly deformable, reproducing the patient setup is often challenging in patients with breast cancer. Several studies have shown SGRT to be a useful method for improving the accuracy and e ciency of the patient setup compared to conventional tattoo/laser-based method with the potential to reduce the frequency of routine image guided radiation therapy [8, 9,14].…”

“…However, it is di cult to correct for rotational errors because the couch in the Halcyon device only allows for translational movement. [14,15] If a rotational error occurs during the initial setup, the additional imaging dose and the overall setup time increase because the patient must be manually repositioned. Therefore, the initial patient setup in the virtual isocenter is critical since it affects the accuracy and e ciency of the overall treatment.…”

Reproducibility of Deep-Inspiration Breath Hold treatments on Halcyon™ performed using the first clinical version of AlignRT InBore™: Results of CYBORE study

“…Fortunately, recent O-ring type linear accelerators such as the Halcyon™ (Varian Medical Systems, Palo Alto, USA) offer fast imaging times (within 17 s) compatible with a single BH and a wide-enough FOV (a longitudinal scan range of 24.5 cm) to allow for the validation of target and OAR positioning in DIBH. While standard SGRT systems cannot track intra-fractional surface motion inside the bore even with adjusted central camera positioning [22] , we used and evaluated here the new AlignRT InBore™ solution dedicated for closed-bore linacs [23] .…”