Varian ethos online adaptive radiotherapy for prostate cancer: Early results of contouring accuracy, treatment plan quality, and treatment time.

The Varian Ethos system allows for online adaptive treatments through the utilization of artificial intelligence (AI) and deformable image registration which automates large parts of the anatomical contouring and plan optimization process. In this study, treatments of intact prostate and prostate bed, with and without nodes, were simulated for 182 online adaptive fractions, and then a further 184 clinical fractions were delivered on the Ethos system. Frequency and magnitude of contour edits were recorded, as well as a range of plan quality metrics. From the fractions analyzed, 11% of AI generated contours, known as influencer contours, required no change, and 81% required minor edits in any given fraction. The frequency of target and noninfluencer organs at risk (OAR) contour editing varied substantially between different targets and noninfluencer OARs, although across all targets 72% of cases required no edits. The adaptive plan was the preference in 95% of fractions. The adaptive plan met more goals than the scheduled plan in 78% of fractions, while in 15% of fractions the number of goals met was the same. The online adaptive recontouring and replanning process was carried out in 19 min on average. Significant improvements in dosimetry are possible with the Ethos online adaptive system in prostate radiotherapy.

Investigating the impact of tumour motion on TomoTherapy stereotactic ablative body radiotherapy (SABR) deliveries on 3-dimensional and 4-dimensional computed tomography.

TomoTherapy can provide highly accurate SABR deliveries, but currently it does not have any effective motion management techniques. Shallow breathing has been identified as one possible motion management solution on TomoTherapy, which has been made possible with the BreatheWell audiovisual biofeedback (AVB) device. Since both the shallow breathing technique and the clinical use of the BreatheWell device are novel, their implementation requires comprehensive verification and validation work. As the first stage of the validation, this paper investigates the impact of target motion on a TomoTherapy SABR delivery is assessed on both 3D CT and 4D CT using a 4D respiratory phantom. A dosimetric study on a 4D respiratory phantom was conducted, with the phantom's insert designed to move at four different amplitudes in the superior-inferior direction. SABR plans on 3D and 4D CT scans were created and measured. Critical plan statistics and measurement results were compared. It is found that for TomoTherapy SABR deliveries, by reducing the targets respiratory motion, target coverage, organ-at-risk (OAR) sparing, and delivery accuracy were improved.