Dosimetric Effect of Target Position Accuracy on Single-Isocenter Multiple Liver Metastases SBRT

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Accurate radiation delivery is crucial for stereotactic body radiotherapy (SBRT).
• Intrafraction motion, including baseline shifts and rotational errors, can compromise treatment accuracy.
• Four-dimensional computed tomography (4D-CT) guided SBRT is used for multiple liver metastases (MLMs).

Purpose of the Study:

• To assess the dosimetric impact of combined intrafraction baseline shifts and rotational errors.
• To evaluate these effects on 4D-CT guided SBRT for MLMs.
• To determine the relationship between error magnitude and target coverage degradation.

Main Methods:

• Retrospective analysis of 10 patients with MLMs.
• Simulation of baseline shifts (0.5-2.0 mm) and rotational errors (0.5°-1.5°).
• Analysis of dose to 95% of planning target volume (D95) and volume receiving 95% of prescribed dose (V95).

Main Results:

• Minimal errors (0.5° rotation, <0.5 mm shift) maintained target coverage (>95%).
• 1.0° rotation with shifts significantly reduced coverage (36.3% <95%).
• Increased shifts to 1.0 mm and 2.0 mm further degraded coverage, with only 11.4% of targets meeting criteria at 2.0 mm shifts.

Conclusions:

• Combined baseline shifts and rotational errors significantly impair target dose coverage in MLM SBRT.
• Reduced target volume, increased baseline drift, and rotational errors worsen coverage.
• These findings highlight the need for precise patient positioning and motion management in liver SBRT.