Evaluation of a surface imaging system's isocenter calibration methods

Surface Guided Radiotherapy (SGRT) is a relatively new technique for positioning patients and for monitoring patient movement during treatment. SGRT is completely non‐invasive since it uses visible light for determining the position of the patient surface. A reduction in daily imaging for patient setup is possible if the accuracy of SGRT is comparable to imaging. It allows for monitoring of intrafraction motion and the radiation beam can be held beyond a certain threshold resulting in a more accurate irradiation. The purpose of this study was to investigate setup uncertainty and the intrafraction motion in non‐gated whole breast cancer radiotherapy treatment using an integrated implementation of AlignRT (OSMS) system as SGRT. In initial setup, SGRT was compared to three‐point setup using tattoos on the patient and orthogonal kV imaging. For the investigation of intrafraction motion, OSMS monitored the patient with six degrees of freedom during treatment. Using three‐point setup resulted in a setup root‐mean‐square error from the isocenter of 5.4 mm. This was improved to 4.2 mm using OSMS. For the translational directions, OSMS showed improvements in the lateral direction (P = 0.0009, Wilcoxon rank‐sum), but for the longitudinal direction and rotation it was not possible to show improvements (P = 0.96 and P = 0.46, respectively). The vertical direction proved more accurate for three‐point setup than OSMS (P = 0.000004). Intrafraction motion was very limited with a translational median of 1.1 mm from the isocenter. While OSMS showed marked improvements over laser and tattoo setup, the system did not prove accurate enough to replace the daily orthogonal kV images aligned to bony anatomy.

Section: Me Th Odsmentioning

confidence: 99%

Section: Me Th Odsmentioning

confidence: 99%

Evaluation of setup and intrafraction motion for surface guided whole‐breast cancer radiotherapy

Hattel

Andersen

Wahlstedt

et al. 2019

“…Even for currently available surface imaging techniques such as OSMS and C‐RAD, there is reduced accuracy for couch rotations. These inaccuracies are caused by the misalignment of the calibration plate during the calibration process . By mounting a 3D camera in the same frame‐of‐reference as the patient provides a novel and feasible way to monitor patient position during the treatment.…”

Section: Discussionmentioning

confidence: 99%

“…These inaccuracies are caused by the misalignment of the calibration plate during the calibration process. 10 By mounting a 3D camera in the same PosiƟon the paƟent to the desired posiƟon and acquire the current posiƟon as the reference For future work, it is not only critical to know if the patient position deviates from the plan, but also to send the correcting shift back to the treatment console. Through collaboration with vendors, it is feasible that the program will send out the delta to correct the patient position to the treatment console in real time via the motion management interface (Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Optical surface monitor systems, such as OSMS, AlignRT, C‐RAD, and humediQ, are some of the solutions for non‐coplanar treatments . However, there are a few known issues with those surface imaging systems: (a) the systems are calibrated to accurately monitor the patient around the isocenter and may not be accurate for non‐isocentric treatments, (b) some systems require manual couch angle input, which complicates dynamic couch treatments, (c) increased uncertainty occurs when one or more cameras are blocked by the gantry (blind spots), and (d) the inaccuracy of the optical system increases for couch rotations, due to misalignment effects during the calibration process . This proposed couch‐mounted system allows the tracking data to be unaffected by the movement of the couch, blind spots and allows easy calibration due to the fact that a three‐dimensional (3D) camera is in the same frame‐of‐reference as the patient.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Patient motion tracking for non‐isocentric and non‐coplanar treatments via fixed frame‐of‐reference 3D camera

Gasparyan¹,

Ko²,

Skinner³

et al. 2020

Purpose As C‐arm linac radiation therapy evolves toward faster, more efficient delivery, and more conformal dosimetry, treatments with increasingly complex couch motions are emerging. Monitoring the patient motion independently of the couch motion during non‐coplanar, non‐isocentric, or dynamic couch treatments is a key bottleneck to their clinical implementation. The goal of this study is to develop a prototype real‐time monitoring system for unconventional beam trajectories to ensure a safe and accurate treatment delivery. Methods An in‐house algorithm was developed for tracking using a couch‐mounted three‐dimensional (3D) depth camera. The accuracy of patient motion detection on the couch was tested on a 3D printed phantom created from the body surface contour exported from the treatment planning system. The technique was evaluated against a commercial optical surface monitoring system with known phantom displacements of 3, 5, and 7 mm in lateral, longitudinal, and vertical directions by placing a head phantom on a dynamic platform on the treatment couch. The stability of the monitoring system was evaluated during dynamic couch trajectories, at speeds between 10.6 and 65 cm/min. Results The proposed monitoring system agreed with the ceiling mounted optical surface monitoring system in longitudinal, lateral, and vertical directions within 0.5 mm. The uncertainty caused by couch vibration increased with couch speed but remained sub‐millimeter for speeds up to 32 cm/min. For couch speeds of 10.6, 32.2, and 65 cm/min, the uncertainty ranges were 0.27– 0.73 mm, 0.15–0.87 mm, and 0.28–1.29 mm, respectively. Conclusion By mounting a 3D camera in the same frame‐of‐reference as the patient and eliminating dead spots, this proof of concept demonstrates real‐time patient monitoring during couch motion. For treatments with non‐coplanar beams, multiple isocenters, or dynamic couch motion, this provides additional safety without additional radiation dose and avoids some of the complexity and limitations of room mounted systems.

Efficient quality assurance method with automated data acquisition of a single phantom setup to determine radiation and imaging isocenter congruence

Kang

Patel

Roeske

2019

We developed a quality assurance (QA) method to determine the isocenter congruence of Optical Surface Monitoring System (OSMS, Varian, CA, USA), kilovoltage (kV), and megavoltage (MV) imaging, and the radiation isocenter using a single setup of the OSMS phantom for frameless Stereotactic Radiosurgery (SRS) treatment. After aligning the phantom to the OSMS isocenter, a cone‐beam computed tomography (CBCT) of the phantom was acquired and registered to a computed tomography (CT) scan of the phantom to determine the CBCT isocenter. Without moving the phantom, MV and kV images were simultaneously acquired at four gantry angles to localize MV and kV isocenters. Then, Winston‐Lutz (W‐L) test images of the central BB in the phantom were acquired to analyze the radiation isocenter. The gantry and couch were automatically controlled using the TrueBeam Developer Mode during MV, kV, and W‐L image acquisition. All the images were acquired weekly for 17 weeks to track the congruence of all the imaging modalities' isocenter in six‐dimensional (6D) translations and rotations, and the radiation isocenter in three‐dimensional (3D) translations. The shifts of isocenters of all imaging modalities and the radiation isocenter from the OSMS isocenter were within 0.2 mm and 0.2° on average over 17 weeks. The maximum discrepancy between OSMS and other imaging modalities or radiation isocenters was 0.8 mm and 0.3°. However, systematic shifts of radiation isocenter anteriorly and laterally relative to the OSMS isocenter were observed. The measured discrepancies were consistent from week‐to‐week except for two weeks when the isocenter discrepancies of 0.8 mm were noted due to drifts of the OSMS isocenter. Once recalibration was performed on OSMS, the discrepancy was reduced to 0.3 mm and 0.2°.By performing the proposed QA on a weekly basis, the isocenter congruencies of multiple imaging systems and radiation isocenter were validated for a linear accelerator.