A Low-Cost Method to Assess the Performance of Surface Guidance Imaging Systems at Non-Zero Couch Angles.

Elizabeth L Covington,Richard A Popple

doi:10.7759/cureus.14278

Abstract

A procedure is presented to assess performance at non-zero couch angles and perform routine quality assurance (QA) on surface-guided radiotherapy (SGRT) imaging systems used for stereotactic radiosurgery (SRS). A low-cost anthropomorphic phantom was used to assess the system under patient-like conditions. The phantom is embedded with a tungsten ball bearing (BB) to facilitate the use of surface imaging (SI) with concurrent megavoltage (MV) imaging to cross-compare and validate SI-reported offsets. Data analysis is done via in-house software that utilized the SGRT system’s log files for automated analysis. This procedure enables users to assess and inter-compare MV-reported offsets with their SGRT system. The analysis provides SGRT system residual error so that users are aware of inherent offsets present in addition to increases in translational offsets due to couch walkout. The procedure was validated with two commercial SGRT systems. The procedure can be used with any surface imaging system and linear accelerator system.

Highlights

Frameless stereotactic radiosurgery uses an open face thermoplastic mask in place of a traditional metal frame to increase patient comfort and improve the efficiency of treatments [1,2,3]
We present a detailed procedure that can be used during commissioning and routine quality assurance (QA) of surface imaging systems used for intrafraction patient monitoring during Frameless stereotactic radiosurgery (fSRS) to assess performance at non-zero couch angles
The largest variation between the reference position and non-zero couch angle was found to be in the longitudinal direction after an analysis of a large patient cohort [7, 13], MV imaging was chosen to benchmark Surface-guided radiotherapy (SGRT) system performance

Summary

Introduction

Frameless stereotactic radiosurgery (fSRS) uses an open face thermoplastic mask in place of a traditional metal frame to increase patient comfort and improve the efficiency of treatments [1,2,3]. We present a detailed procedure that can be used during commissioning and routine quality assurance (QA) of surface imaging systems used for intrafraction patient monitoring during fSRS to assess performance at non-zero couch angles This process uses a simple, low-cost phantom that is readily available. If the MV images reported a couch walkout of 0.2 mm lateral (x) and 0.3 mm longitudinal (y), but the SGRT system reported (0.6 mm, 0.8 mm) the corresponding SGRT residual error would be (0.4 mm, 0.5 mm) with a magnitude of 0.64 mm This test was repeated with the BB located at various depths within the phantom to determine if SI performance degrades with increasing the distance between isocenter (BB) and tracking surface.

Discussion

Conclusions

Disclosures