ESTRO 2024 - Abstract Book

S4754

Physics - Quality assurance and auditing

ESTRO 2024

another, we can find the sensitivity of each detector from the array center to its periphery (relatively to the central detector #430), i.e. calculate the array calibration factor curve.

However, practice shows that if we use only 5 nearby central measurement points, we will get good results in terms of the sensitivity ratios of neighboring detectors, but for "longer" distances there may be an "error accumulation" effect in a positive or negative direction, especially if the accelerator output has some instability (Fig.2, A). To improve this, it is necessary to measure 2 more points in order to correct the calibration coefficient curve for the “long” distance array detectors. The correction function f =A-A*EXP (-B*C) was applied, where A=± max value of error to be corrected, B=0.03, C – crossplane coordinate (Fig. 2, B). This function use the results of profile measurements in 2 points with lateral coordinates ±63 mm, which gives the correct values of the ratios, for example, sensitivity#22/ sensitivity#41 for left side of the array and sensitivity#61/ sensitivity#42 for right side of the array.

To create an equidistant line of detectors on an array, it is necessary to simulate two additional detectors (#41-430 and #430-42, Fig. 1, A) with readings equal to the average values of their neighbors.

To be sure, that the accelerator output was constant during measurements, we start and complete investigation at the same point of lateral coordinate 0 mm, i.e. read-through profiles twice.

The measured detector readings (from .mcc files) imported into a prepared Excel file for quick calculations.

Figure 1. A- Seven lateral positions of the examined crossplane axis for profile measurement. B- Curves of readings of the detectors of the central matrix to explain the concept of calculating the relative sensitivity of the detectors.

Results: