Local confidence limits for IMRT and VMAT techniques: a study based on TG119 test suite.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• The American Association of Physicists in Medicine (AAPM) Task Group (TG) 119 report provides benchmarks for intensity modulated radiation therapy (IMRT) commissioning and delivery.
• Establishing local confidence limits (CLs) is crucial for validating radiotherapy techniques like IMRT and volumetric modulated arc therapy (VMAT).

Purpose of the Study:

• To generate local confidence limits (CLs) for IMRT and VMAT at Waikato Regional Cancer Centre.
• To compare these local CLs against AAPM TG 119 benchmarks.
• To assess the accuracy and quality of VMAT implementation in the clinic.

Main Methods:

• Utilized the AAPM TG 119 test suite, including primary and clinical tests.
• Downloaded pre-defined structure sets from the AAPM website and used a locally designed phantom.
• Generated IMRT and VMAT plans using Eclipse Treatment Planning System, adhering to TG 119 dose prescriptions and planning objectives.
• Performed point dose measurements and analyzed planar dose distribution using gamma criteria (3%/3 mm).

Main Results:

• For IMRT, local CLs were: 2.49% (high dose point dose), 2.95% (low dose point dose), 2.12% (individual field gamma), and 5.9% (composite gamma).
• For VMAT, local CLs were: 2.56% (high dose point dose), 2.6% (low dose point dose), 1.46% (individual field gamma), and 0.8% (composite gamma).
• All generated CLs for both IMRT and VMAT were within the recommended TG 119 benchmarks.

Conclusions:

• The local clinic has successfully commissioned IMRT and VMAT techniques with adequate accuracy, validated against AAPM TG 119 standards.
• The generated CLs support clinical confidence in the routine use of IMRT and VMAT.
• These findings provide a foundation for expanding the use of these advanced radiotherapy techniques to different clinical sites.