Methodology of thermal drift measurements for surface guided radiation therapy systems and clinical impact assessment illustrated on the C-Rad Catalyst+ HD system

Surface-guided radiotherapy improves rotational accuracy in gynecological cancer patients

Background

The aim of this study was to determine if rotational uncertainties in gynecological cancer patients can be reduced using surface imaging (SI) compared to aligning three markers on the patient's skin with in-room lasers (marker-laser).

Materials and methods

Fifty gynecological cancer patients treated with external-beam radiotherapy were retrospectively analyzed; 25 patients were positioned with marker-laser and 25 patients were positioned with SI. The values of rotational (pitch and roll) deviations of the patient positions between the treatment-planning computed tomography (CT) and online cone-beam computed tomography (CBCT) were collected for both subcohorts and all treatment fractions after performing automatic registration between the two image sets. Statistical analysis of the difference between the two set-up methods was performed using the Mann-Whitney U-test.

Results

The median pitch deviation were 1.5° [interquartile range (IQR): 0.6°-2.6°] and 1.1° (IQR: 0.5°-1.9°) for the marker-laser and SI methods, respectively (p < 0.01). The median roll deviation was 0.5° (IQR: 0.2°-0.9°), and 0.7° (IQR: 0.3°-1.2°) for the marker-laser and SI methods, respectively (p < 0.01). Given the shape of the target, pitch deviations had a greater impact on the uncertainty at the periphery of the target and were considered more relevant.

Conclusion

By introducing SI as a set-up method in gynecological cancer patients, higher positioning accuracy could be achieved compared with the marker-laser set-up method. This was demonstrated based on residual deviations rather than deviations corrected for by image-guided radiotherapy (IGRT).

ExacTrac Dynamic workflow evaluation: Combined surface optical/thermal imaging and X-ray positioning

In modern radiotherapy (RT), especially for stereotactic radiotherapy or stereotactic radiosurgery treatments, image guidance is essential. Recently, the ExacTrac Dynamic (EXTD) system, a new combined surface-guided RT and image-guided RT (IGRT) system for patient positioning, monitoring, and tumor targeting, was introduced in clinical practice. The purpose of this study was to provide more information about the geometric accuracy of EXTD and its workflow in a clinical environment. The surface optical/thermal- and the stereoscopic X-ray imaging positioning systems of EXTD was evaluated and compared to cone-beam computed tomography (CBCT). Additionally, the congruence with the radiation isocenter was tested. A Winston Lutz test was executed several times over 1 year, and repeated end-to-end positioning tests were performed. The magnitude of the displacements between all systems, CBCT, stereoscopic X-ray, optical-surface imaging, and MV portal imaging was within the submillimeter range, suggesting that the image guidance provided by EXTD is accurate at any couch angle. Additionally, results from the evaluation of 14 patients with intracranial tumors treated with open-face masks are reported, and limited differences with a maximum of 0.02 mm between optical/thermal- and stereoscopic X-ray imaging were found. As the optical/thermal positioning system showed a comparable accuracy to other IGRT systems, and due to its constant monitoring capability, it can be an efficient tool for detecting intra-fractional motion and for real-time tracking of the surface position during RT.

ESTRO-ACROP guideline on surface guided radiation therapy

Surface guidance systems enable patient positioning and motion monitoring without using ionising radiation. Surface Guided Radiation Therapy (SGRT) has therefore been widely adopted in radiation therapy in recent years, but guidelines on workflows and specific quality assurance (QA) are lacking. This ESTRO-ACROP guideline aims to give recommendations concerning SGRT roles and responsibilities and highlights common challenges and potential errors. Comprehensive guidelines for procurement, acceptance, commissioning, and QA of SGRT systems installed on computed tomography (CT) simulators, C-arm linacs, closed-bore linacs, and particle therapy treatment systems are presented that will help move to a consensus among SGRT users and facilitate a safe and efficient implementation and clinical application of SGRT.