Related Experiment Video
Updated: Jan 16, 2026
Dynamic Lung Tumor Tracking for Stereotactic Ablative Body Radiation Therapy
Published on: June 7, 2015
Quality assurance of single isocentre multiple target stereotactic radiosurgery: Findings from long-term off-axis
Joel Poder1,2,3,4, Robert Chambers1, Harry Porter1
1St George Hospital Cancer Care Centre, Kogarah, NSW, Australia.
Background:
Single-isocenter multiple-target stereotactic radiosurgery (SIMT SRS) has emerged as an efficient treatment for multiple brain metastases. However, this technique demands exceptional geometric accuracy, particularly off-axis, to ensure optimal dose delivery while sparing healthy tissue. Traditional quality assurance (QA) methods require adaptation for SIMT SRS, highlighting the need for robust testing protocols.
Purpose:
This study aimed to evaluate the long-term off-axis targeting accuracy of three Varian TrueBeam linear accelerators using a dedicated off-axis Winston-Lutz test (OAWLT) and to investigate correlations with routine varian machine performance check (MPC) results.
Materials & Methods:
Weekly OAWLT measurements were performed over a 6-month period on three TrueBeam linacs using the Sun Nuclear StereoPHAN phantom and MultiMet-WL cube. The test delivered 6 MV flattening filter-free beams to multiple off-axis targets via eight beam orientations, simulating clinical SIMT SRS workflows. Concurrently, daily MPC assessments evaluated geometric parameters including isocenter size, kV isocenter offset, beam center, and couch radiation-induced offset.
Results:
Median OAWLT errors were 0.38, 0.44, and 0.59 mm for the three linacs included in this study, with maximum errors of 1.12, 1.08, and 1.54 mm. Notably, off-axis errors increased with target off-axis distance, with the worst performance observed at 7 cm off-axis.
Conclusion:
Routine OAWLT is an effective and sensitive QA tool for monitoring off-axis targeting accuracy in SIMT SRS. Despite the convenience of daily MPC, it cannot substitute for a dedicated OAWLT. The study supports implementing weekly OAWLT in clinical practice to ensure high-quality, consistent treatment delivery for SIMT SRS treatments.
