Optical surface guidance for submillimeter monitoring of patient position during frameless stereotactic radiotherapy

Abstract

Purpose To evaluate the accuracy of monitoring intrafraction motion during stereotactic radiotherapy with the optical surface monitoring system. Prior studies showing a false increase in the magnitude of translational offsets at non‐coplanar couch positions prompted the vendor to implement software changes. This study evaluated two software improvements intended to address false offsets. Methods The vendor implemented two software improvements: a volumetric (ACO) rather than planar calibration and, approximately 6 months later, an improved calibration workflow (CIB) designed to better compensate for thermal drift. Offsets relative to the reference position, obtained at table angle 0 following image‐guided setup, were recorded before beam‐on at each table position and at the end of treatment the table returned to 0° for patients receiving SRT. Results Prior to ACO, between ACO and CIB, and after CIB, 223, 155, and 436 fractions were observed respectively. The median magnitude of translational offsets at the end of treatment was similar for all three intervals: 0.29, 0.33, and 0.27 mm. Prior to ACO, the offset magnitude for non‐zero table positions had a median of 0.79 mm and was found to increase with increasing distance from isocenter to the anterior patient surface. After ACO, the median magnitude was 0.74 mm, but the dependence on surface‐to‐isocenter distance was eliminated. After CIB, the median magnitude for non‐zero table positions was reduced to 0.57 mm. Conclusion Ongoing improvements in software and calibration procedures have decreased reporting of false offsets at non‐zero table angles. However, the median magnitude for non‐zero table angles is larger than that observed at the end of treatment, indicating that accuracy remains better when the table is not rotated.

Surface guided imaging during stereotactic radiosurgery with automated delivery

“…Similar to a previous study, RTDs at non‐zero couch angles were larger than RTDs observed at the end of treatment, indicating SI system performance is still sub‐optimal at non‐zero couch angles. Additionally, the largest component of the translation magnitude continues to be from offsets reported in the longitudinal direction as shown in Table 2 Minimal offsets in the vertical direction are also consistent with previously reported aggregate data 16 . Larger RTDs were noted on the 270° side of the treatment couch suggesting differences that may be attributed to camera pod geometry or an individual camera's performance.…”

“…This choice sets the exposure times of the cameras and are aimed to improve the variations that can affect the performance of RTDs due to skin tone. Darker skin tones will absorb more Minimal offsets in the vertical direction are also consistent with previously reported aggregate data 16. Larger RTDs were noted on the 270°side of the treatment couch suggesting differences that may be attributed to camera pod geometry or an individual camera's performance.…”

“…We have previously reported on system performance before and after the utilization of ACO. 16 HyperArc TM requires the use of the Encompass mask; therefore, all patients in this study were immobilized with the Encompass sys- The user selected skin tone setting is not documented in the SI log file; therefore, demographics in ARIA were used to identify the race of each patient as a surrogate for skin tone. Patients were classified in the following groups per ARIA: White, Black, or not-specified (NS).…”

Recent advances in Surface Guided Radiation Therapy

“…For treatments with non-coplanar couch angles, accurate knowledge about the coincidence between radiation and couch rotation isocenter becomes important, as it is not possible to correct for couch walkout during treatment delivery. Regular Winston-Lutz checks provide accurate information about the radiation isocenter for different gantry, collimator and couch angles and can also indirectly provide information about the accuracy of the system [ 19 , 54 , 55 ].…”

The potential of an optical surface tracking system in non‐coplanar single isocenter treatments of multiple brain metastases

“…Optical Surface Tracking (OST) seems to be a sophisticated and suitable option, as it intends to reduce set-up errors and provides real-time non-invasive monitoring to detect patient movement during treatment, without the use of ionizing radiation. [24][25][26] The aim in this work is to demonstrate how a commercial OST system can be implemented to monitor patient positioning during treatment for a non-coplanar single isocenter VMAT technique for multiple BM and to show the feasibility of this system by defining treatment tolerances without compromising the treatment margins.…”