SU-E-J-31: Direct Point Dose Verification Using IGRT for Actual Beam Delivery.

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Radiation therapy planning relies on initial CT scans, but patient anatomical changes (tumor shrinkage, weight loss) and daily positioning errors can lead to inaccurate delivered doses.
• Accurate assessment of the actual delivered radiation dose is crucial for evaluating the clinical and dosimetric consequences in head-and-neck cancer patients undergoing radiation therapy.

Purpose of the Study:

• To experimentally evaluate the usefulness of Image-Guided Radiation Therapy (IGRT) procedures for accurate irradiations.
• To determine the actual delivered dose for a head-and-neck site using direct point dose measurements with metal-oxide-semiconductor field-effect transistor (MOSFET) detectors.

Main Methods:

• An anthropomorphic phantom simulating a head-and-neck site was used for treatment planning and beam delivery experiments.
• MOSFET detectors were placed inside the phantom, which was immobilized and scanned using simulation-CT.
• Positioning was verified using mega-voltage cone-beam CT (MVCBCT) before irradiation, and measured doses were compared with calculated doses.

Main Results:

• IGRT, specifically MVCBCT, enabled precise patient positioning within 1 mm in all directions.
• Measured doses from MOSFET detectors closely matched calculated doses, with agreement within ±3%, even in high dose gradient regions.

Conclusions:

• The study experimentally validated the actual delivered dose for a head-and-neck site using MOSFET detectors.
• The findings confirm that IGRT procedures are effective in ensuring accurate radiation delivery.