# Establishment of a Novel Method for Dose Distribution Verification in Stereotactic Radiosurgery (SRS) Using General Semiconductor Array Detectors

## TL;DR

This paper introduces a cost-effective method for verifying radiation dose accuracy in SRS using standard detectors and couch movement, achieving results comparable to expensive film methods.

## Contribution

A novel patient-specific QA method for SRS using general semiconductor array detectors and couch movement to achieve film-like accuracy.

## Key findings

- RMSE decreased with narrower virtual detector spacing, reaching film-level accuracy at 1 mm spacing.
- γ pass rates at 5 mm spacing were comparable to radiochromic film for all tolerances.
- The method eliminates the need for high-resolution detectors or disposable film, reducing costs and labor.

## Abstract

Stereotactic radiosurgery (SRS) involves steep dose gradients and small irradiation fields, which makes ensuring irradiation accuracy extremely important. While general semiconductor array detectors are reusable and cost-effective, their wide detector spacing results in insufficient spatial resolution.

The aim of this study is to establish a novel patient-specific quality assurance (PSQA) method for single-isocenter multiple-target SRS volumetric modulated arc therapy (SIMT-SRS-VMAT) that can evaluate dose distribution with the same accuracy as radiochromic film by virtually narrowing the detector spacing by combining measurement with a general semiconductor array detector and translational movement of the treatment couch.

Single-field plans with a single target and SIMT-SRS-VMAT plans with two targets were created for 1 cm lesions. Measurements using MapCHECK2 (Sun Nuclear, Melbourne, FL, USA) were combined with couch movement to synthesize measurement data at virtual detector spacings of 5, 4, 3, 2, and 1 mm. Root mean square error (RMSE) was used to evaluate profile shape accuracy, and γ analysis was used to evaluate dose distribution agreement.

At virtual detector spacings of 10 mm, 5 mm, 4 mm, 3 mm, 2 mm, 1 mm, and with radiochromic film, the RMSE values in SIMT-SRS-VMAT were 8.02% ± 0.34%, 2.16% ± 0.07%, 1.60% ± 0.08%, 1.48% ± 0.17%, 1.32% ± 0.10%, 1.38% ± 0.03%, and 1.25% ± 0.02%, respectively. The RMSE decreased as the detector spacing narrowed, resulting in profile shapes comparable to those obtained with radiochromic film. In γ analysis, setting the virtual detector spacing to 5 mm enabled analysis covering the entire dose range, and the γ pass rate was comparable to EBT4 (Ashland Inc., Wayne, NJ, USA) for all tolerances.

This study established a novel method of verification of dose distribution with the same accuracy as film, combining measurement with a general semiconductor array detector and translational movement of the treatment couch. With this approach, specialized high-resolution SRS array detectors and disposable radiochromic film are not needed, making SRS PSQA less costly and manpower-intensive.