# Evaluation of multileaf collimator driving accuracy in helical rotational irradiation system: Quantitative analysis of leaf open time during treatment

## TL;DR

This study evaluates the accuracy of a device's leaf movement during radiation treatment by comparing planned and actual leaf open times across different treatment sites.

## Contribution

A simple method for quantitatively analyzing MLC leaf open time during treatment is proposed.

## Key findings

- The average leaf open time attainment rate across all patients was 94.56 ± 2.37%.
- SBRT treatment plans showed the highest average attainment rate at 98.39 ± 0.57%.
- The standard deviation of attainment rates varied significantly by treatment site.

## Abstract

The Radixact treatment system is equipped with a delivery analysis feature. This feature enables dose reconstruction using the patient's treatment‐planning computed tomography scans and allows verification of the multileaf collimator (MLC) performance before and during treatment. In the Radixact system, the opening time of the MLC leaves is determined based on the treatment plan.

This study aimed to evaluate MLC driving accuracy by assessing the MLC leaf open time (LOT) during treatment.

Using Delivery Analysis version 2.3, we compared the treatment plan LOT with the LOT measured during treatment to determine the average and one standard deviation (%) of the LOT attainment rate. The analysis included comparisons of treated sites across 39 cases: nine prostate, eight pelvic, seven head, six chest, five head and neck (H&N), and four stereotactic body radiation therapy (SBRT) treatment plans.

The average and one standard deviation (%) of the LOT attainment rate for all patients on treatment was 94.56 ± 2.37. The values of each site were as follows: prostate, 95.93 ± 0.68; pelvis, 93.37 ± 2.16; head, 95.05 ± 1.99; chest, 97.61 ± 0.78; H&N, 92.44 ± 1.32; and SBRT, 98.39 ± 0.57. The treatment plans with the lowest attainment rates for each site were as follows: prostate, 95.19 ± 0.39; pelvis, 90.59 ± 0.16; head, 92.20 ± 0.15; chest, 95.76 ± 0.04; H&N, 90.55 ± 0.30; and SBRT, 97.32 ± 0.07. The plans with the largest one standard deviation (%) per site were as follows: prostate, ± 0.97; pelvis, ± 0.26; head, ± 0.57; chest, ± 0.23; H&N, ± 0.30; and SBRT, ± 0.07.

We proposed a simple method for quantitatively analyzing the LOT of an MLC. The average LOT attainment rate and its standard deviation varied by treatment site. Since the standard deviation differed by plan, the LOT attainment rate during treatment should be carefully monitored.