Implementation and evaluation of an end-to-end IGRT test

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Imaging

Background:

• Accurate patient positioning is critical for effective radiation therapy.
• Image-guided radiation therapy (IGRT) utilizes imaging to improve setup accuracy.
• Verifying the accuracy of IGRT setup relative to the radiation isocenter is essential.

Purpose of the Study:

• To develop and evaluate an end-to-end test for determining and verifying image-guided radiation therapy setup accuracy.
• To assess the accuracy of patient positioning relative to the radiation isocenter using a novel phantom-based method.
• To quantify short-term and clinical reproducibility of IGRT setup accuracy.

Main Methods:

• A cube phantom with a central tungsten sphere was used, offset from isocenter by fixed or random amounts.
• Cone-beam CT and megavoltage (MV) imaging were acquired after aligning the phantom's sphere.
• Winston-Lutz analysis was performed on acquired images to determine isocenter agreement.

Main Results:

• Short-term reproducibility showed a mean 3D vector displacement of 0.9 ± 0.15 mm.
• Clinical reproducibility yielded mean displacements of 1.1 ± 0.4 mm (5.0 mm offset) and 0.9 ± 0.3 mm (random offset).
• Displacements were observed in all directions and were independent of couch shift magnitude.

Conclusions:

• The developed end-to-end test is quick and easy to implement in a clinical setting.
• The test effectively highlighted setup inaccuracies in an image-guided radiation therapy environment.
• This method provides valuable verification of IGRT setup accuracy, contributing to treatment precision.