Correlation between IQM Signal, Gamma Index and Dose-Volume-HistogramAOU Careggi Florence, University of Florence


Do changes in IQM signal correlate with other metrics, such as the Gamma passing rate and DVH Variations when introducing a small delivery error?

IQM Monitor
Gamma Index
Dose-Volume-Histogram

Treatment delivery error #1: Dose

changes of 1MU, 2Mu and 3MU per beam
introducing dose changes of
0.8% – 2.5% for H&N plan, 1.4% – 4.2% for Prostate plan and 0.4% – 1.3% for APBI plan.

H&N Plan
Prostate Plan
TPBI Plan

Treatment delivery error #2: Geometry

changes of 1mm in leaf bank positions
single bank shift by 1mm and beam position shift by 1mm

Single Bank Error
Field Shift

Results

IQM Sensitivity for small treatment delivery errors

IQM is able to detect all treatment delivery errors

IQM signal correlation with 2D Gamma (1%/1mm, 10%, local approach)

2D Gamma correlation

IQM signal correlation with PTV DVH

Correlation with PTV D95

IQM signal correlation with OAR DVH (rectum in prostate case)

Correlation with Rectum V50
Rectum DVH
Correlation Rectum V70

IQM detects all small dose and geometry related treatment delivery errors with
clinically sufficient sensitivity

The IQM signal shows a good correlation with other metrics (Gamma pass rate, DVH) used to quantify the deviations
between expected and actually delivered dose distribution