Purpose/objective(s): Surface-guided radiation therapy (SGRT) can track the patient surface noninvasively to complement radiographic image-guided radiation therapy with a standard 3-camera system and a single radiation/image isocenter. Here we report the commissioning of a novel SGRT system that monitors three imaging isocenters locations in a proton half -gantry room with a unique 5-camera configuration. Materials/methods: The proton half -gantry room has three image isocenters, designated ISO-0, ISO-1, and ISO-2, to cover various anatomical sites via a robotic ceiling-mounted cone-beam CT. Although ISO-0 and ISO-1 are used to image the cranium, head and neck, and thoracic regions, ISO-2 is often used to image body and extremity sites and contiguous craniospinal target volumes. The five-camera system was calibrated to the radiographic isocenter by using a stereotactic radiosurgery cube phantom for each image isocenter. Results: The performance of this 5-camera system was evaluated for 6 degrees of freedom in three categories: (1) absolute setup accuracy relative to the radiographic kV image isocenter based on the DICOM reference; (2) relative shift accuracy based on a reference surface capture; and (3) isocenter tracking accuracy from one isocenter to another based on a reference surface capture. The evaluation revealed maximum deviations of 0.8, 0.2, and 0.6 mm in translation and 0.2 • , 0.1 • , and 0.1 • in rotation for the first, second, and third categories, respectively. Comparing the dosimetry and latency with static and gated irradiation revealed a 0.1% dose difference and positional differences of 0.8 mm in X and 0.9 mm in Y with less than 50 ms temporal accuracy. Conclusion:The unique 5-camera system configuration provides SGRT at the treatment isocenter (ISO-0) and also imaging isocenter locations (ISO-0, ISO-1, and ISO-2) to ensure correct patient positioning before and after radiographic imaging, especially during transitions from the offset imaging isocenters to the treatment isocenter.

We introduce a custom-made silicone-filled vaginal spacer for use during treatment of female patients receiving pelvic proton radiation therapy. Commercially available vaginal dilators can be purchased as hollow objects; when filled with a media, they can act as a beam stopper and/or tissue spacer while pushing uninvolved vaginal wall away from a high-dose region. Dosimetric advantages of these specifically constructed silicone-filled vaginal spacers were investigated when compared to the unaltered commercially available product or no vaginal spacer in pediatric proton therapy.

convolution-superposition algorithm (Pinnacle v9.8) for the conventional Linac. Dosimetric parameters of interest from the target, OARs, and airtissue interface volumes for each patients' clinical treatment plans were extracted and compared. For 10 representative patients, in vivo skin doses during a single fraction of MRL and conventional Linac treatment were obtained using an Optically Stimulated Luminescent Dosimeter (OSLD) placed in a defined location on the patient's skin near the Planning Target Volume (PTV). Student's t-test and Wilcoxon signed-rank test were used to compare parameters between Monaco and Pinnacle. Spearman's correlation was used to assess the relationship between in vivo OSLD measurements and TPS skin dose. Threshold for statistical significance was P < 0.05. Results: Most patients were treated for high grade glioma (76% Grade III or IV, 24% Grade II), and median PTV was 257.4 cm 3 (range, 37.1-570.3 cm 3 ). MRL and conventional Linac had similar V100, V95, D98, and D95 for PTV, and D3cc for optic chiasm, optic nerves, and each cochlea (P = NS). However, clinically delivered Monaco plans had significantly greater doses within air cavities (mean Dmean higher by 1.3 Gy, P < 0.0001) and skin (mean Dmean higher by 1.9 Gy, P < 0.0001; mean D2cc higher by 8.1 Gy, P < 0.0001; mean V20 Gy higher by 7.2 cm 3 , P < 0.0001), compared to clinically delivered Pinnacle plans. In vivo OSLD skin readings were 14.5% greater for treatments delivered on the MRL (P = 0.0027), and were more accurately predicted by Monaco (r = 0.95, P < 0.0001) vs. Pinnacle (r = 0.80, P = 0.0096). Conclusion:In this prospective study of clinically treated glioma patients on both MRL and conventional Linac, the dosimetric impact of the magnetic field was minimal for the target and standard OARs. However, higher doses to skin and air cavities were observed. In vivo correlation of dose to skin was more accurately predicted with Monaco. Future MRL planning processes are being designed to account for skin dosimetry and treatment delivery.

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.

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