Commissioning of the First Surface Guided Radiation Therapy System Using 5-camera in a Proton Half-gantry Room With Three Imaging Isocenters

Abstract

was used to predict dysphagia probability, based on the dose to superior PCM and supraglottis. Results: The average percent change for PTV volume and overlap with superior, middle and inferior PCMs in a pool of 20 patients was-19%,-37%,-59% and-45.2%. The new rotational PTV causes more reduction in the superior PCM overlap in base of tongue lesions compared to tonsillar lesions (57.8% versus 25.8%, p Z 0.01 as well as middle PCM overlap (73% versus 49%). The smallest isotropic expansion that covers the target when the spine rotates AE5 was 5 mm. 35% of patients required an expansion more than 3 mm to account for off-axis rotation. In 10 patients randomly selected for VMAT planning, the average change to the volume overlap of PTV70 with superior PCM using the standard and new PTV was 45% (8-100%), with an average mean dose reduction of 2.7 Gy. Based on the NTCP model, 50% of cases had a 30% or more probability of swallowing complications. Using the new technique, the NTCP decreased to less than 30% in 80% of these patients. Considering other Organs at Risk (OARs) constraints, there was not a difference between the new plan versus the standard plan. Conclusion: Designing a new PTV based on spinal rotation result in less volume overlap between PTV and PCM and can ultimately lead to less mean superior PCM dose and risk of dysphagia. A standard 3mm isotropic expansion is insufficient to cover the target volume due to spine rotation, and a 5mm margin is needed.