Phantom-Based Study on Testicular Dose Protection Using Different Thicknesses of Low-Melting-Point Lead Shields in Postoperative Radiotherapy for Seminoma
Li Zou, Huanhuan Fei, Wenlang Zhu, Haoyu Wang, Gang Zhou, Ye TianBackground
This phantom-based study evaluated the effects of low-melting-point lead shield thickness and field-edge distance on contralateral testicular dose.
Methods
A 3D-CRT plan was generated de novo on CT images of the SZMC-IV anthropomorphic phantom; no patient-derived imaging or treatment-plan data were used. A 0.6 cm 3 thimble ionization chamber measured dose per fraction at different field-edge distances without shielding and with 3, 5, 7, 10, and 15 mm lead shields. Measurement-derived normalized doses were fitted using an exponential model. The 36 Gy scenario was evaluated only by linear scaling.
Results
Normalized testicular dose decreased exponentially with increasing field-edge distance and shield thickness. For the nominal 26 Gy scenario, measurement-derived cumulative doses were 0.315 Gy with 3 mm shielding at 10 cm and 0.481 Gy with 7 mm shielding at 4 cm. For the hypothetical 36 Gy scenario, the measurement-based linearly scaled estimate was 0.432 Gy with 15 mm shielding at 4 cm. Excluding non-independent 36 Gy estimates, the RMSE was 0.074 Gy.
Conclusions
Customized low-melting-point lead shields can effectively reduce contralateral testicular scattered dose in a phantom-based seminoma radiotherapy setup. The dose reduction depends on both shield thickness and distance from the radiation field edge.