Comparison of two dosimetric systems for quality assurance in a clinical treatment scenario for brain radiotherapy:...

Advanced radiotherapy techniques such as single-isocenter volumetric modulated arc therapy (VMAT) and simultaneous integrated boost (SIB-VMAT) require precise quality assurance (QA) due to their complexity and sensitivity to geometric and dosimetric uncertainties, especially for multi-target configurations.

To evaluate and compare two dosimetric systems-a diode array and a polymer gel dosimeter-for quality assurance in single-isocenter multi-target VMAT and SIB-VMAT plans through 3D gamma index and statistical agreement analysis.

A diode array system (Delta⁴-Scandidos, Uppsala, Sweden) and a 3D printed phantom (Prime-RTsafe, Athens, Greece) embedded with in-house polymer gel were utilized. The treatment plans for VMAT and SIB-VMAT were created using the Monaco treatment planning system (TPS) and irradiations were performed with the Elekta Infinity linear accelerator with a 6-MV photon beam on both Prime and Delta⁴. Analyses of the irradiated gels were performed using a 1.5T clinical MRI system. Additionally, 3D gamma indexes and Bland-Altman analyses were conducted to evaluate the agreement between relative doses from MRI-derived gel data and diode array's detector measurements.

Diode array system achieved gamma passing rates (GPRs) >99%, while polymer gel showed >95% GPR for both irradiation plans. Bland-Altman analysis indicated minimal bias (mean difference: 0.1%) and narrow limits of agreement (-1.9% to 2.2%), confirming good consistency between the two dosimetric methods for both plans delivered.

Acceptable agreement between the two systems was observed. Both demonstrated complementary capabilities, making both essential tools for ensuring precision in advanced radiotherapy techniques. The polymer gel system offers more detailed insights compared to the diode array method, showing increased sensitivity in challenging cases that involve small targets at greater distances from the isocenter.