Development and demonstration of end-to-end testing for intra-fraction motion-managed workflows

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Intra-fraction motion management techniques (beam gating, intra-fraction drift correction) are used on MR-linacs to reduce motion's dosimetric impact.
• Residual motion can cause deviations from planned doses, and conventional end-to-end (E2E) testing does not account for this known motion.
• This limits the evaluation of motion-managed workflows' accuracy.

Purpose of the Study:

• To develop and demonstrate novel methods for incorporating known motion into reference dose distributions for E2E testing.
• To enable accurate E2E testing of intra-fraction motion-managed workflows.

Main Methods:

• Developed two motion-included reference dose distributions: A Priori Motion-Included (APriMI) and Posteriori Motion-Included (PostMI).
• APriMI uses known periodic motion to estimate and incorporate motion's influence on dose; PostMI uses external triggers to correlate beam time with motion for non-periodic or drift motion.
• Evaluated static, unmanaged, and motion-managed (gated, IDC) scenarios on a Unity MR-linac using film dosimeters, comparing measured doses to static, APriMI, and PostMI references.

Main Results:

• High agreement was found between measured and reference doses in the static benchmark scenario.
• Excellent agreement was observed between measured and calculated doses in motion-included scenarios using APriMI or PostMI (geometric shift <0.3 mm, gamma index >95.5%).
• Using static dose distributions as reference resulted in significant deviations (geometric shifts up to 9.0 mm, gamma pass rates as low as 17.8%).

Conclusions:

• APriMI and PostMI dose distributions enable effective E2E testing for intra-fraction motion-managed workflows.
• Motion-included reference dose distributions show strong agreement with measurements, unlike static references.
• Accurate assessment of E2E accuracy requires reference dose files that incorporate actual motion during treatment delivery.