An end-to-end quality assurance procedure for pelvic VMAT using optically stimulated luminescence dosimeters and an anthropomorphic phantom.

BACKGROUND

Volumetric modulated arc therapy (VMAT) enables highly conformal pelvic dose delivery, but its clinical benefit depends on agreement between the Treatment Planning System (TPS) calculation and the dose actually delivered in anatomically realistic conditions.

PURPOSE: To experimentally validate VMAT dosimetric accuracy for cervical cancer using optically stimulated luminescence dosimeters (OSLDs) placed in an anthropomorphic female pelvic phantom.

MATERIALS AND

METHODS

A female pelvic phantom was CT-scanned. A dual-arc VMAT plan was created in Eclipse (v18) using the Acuros XB algorithm with heterogeneity correction. Fifty-three OSLDs were positioned across seven pelvic slices (28-34) spanning in-field, edge, peripheral, and out-of-field regions. Measured doses were compared to TPS values using a TG-119-style percent difference metric.

RESULTS

Overall agreement was clinically acceptable. The mean %Diff (OSL vs. TPS) was + 3.56% (range - 2.13% to + 6.93%). In-field doses showed the closest agreement (≤ 3%). Larger deviations occurred at the field edge (≈ 3.17%-6.93%), consistent with steep dose gradients. Peripheral and out-of-field locations generally remained within ~ 5%-7%, where scatter and low-dose modeling uncertainty dominate. Reproducibility was strong: SD_OSL values were < 5.2%, with mean SD of 2.63% (in-field), 4.34% (edge), 4.44% (peripheral), and 4.96% (out-of-field).

CONCLUSION

OSLD measurements in an anatomically realistic female pelvic phantom confirm that cervical cancer VMAT delivery is accurate and reproducible. These results support the reliability of Eclipse (v18) using the Acuros XB algorithm across high-dose, gradient, and low-dose regions.