SU-E-T-129: Rescaling of IMRT Verification Deviations from Detector Arrays into the Patient

Area of Science:

• Medical Physics
• Radiation Oncology
• Image-Guided Therapy

Background:

• Intensity-Modulated Radiation Therapy (IMRT) requires precise verification of radiation dose delivery.
• Gamma-Index analysis is a common method for evaluating IMRT plan quality using detector arrays.
• Failures in Gamma-Index analysis necessitate a method to assess their clinical significance in terms of patient dose.

Purpose of the Study:

• To present and evaluate a novel method for "rescaling" Gamma-Index failures detected by detector arrays into patient-specific dose deviations.
• To enable re-evaluation of IMRT verifications by translating array-based failures into clinically relevant dose errors within the patient.

Main Methods:

• A model was developed where plane signals from ionisation chamber arrays during IMRT verification are deconvoluted into photon fluence and detector response kernels.
• Gamma-Index deviations were "back-projected" to infer photon fluence deviations, then "forward-projected" as dose deviations at patient test points.
• The method was validated using the 2D-ARRAY729 and VeriSoft5.0 software in prostate and head and neck (H&N) regions, with simulated Gamma-Index failures (3mm/3%).

Main Results:

• A good consistency was observed between the relative dose deviations predicted from the 2D-ARRAY evaluations and those calculated directly within the patient.
• The proposed rescaling method effectively translates array-detected Gamma-Index failures into patient dose deviations.

Conclusions:

• The developed rescaling method, coupled with visualization tools, provides a valuable approach for re-evaluating patient dose deviations when Gamma-Index failures occur during IMRT verification.
• This technique enhances the clinical interpretability of IMRT verification results by directly assessing potential dose errors in the patient.