SU‐E‐T‐135: 3D Dose Distribution Measurement with a New TLD Sheet

Abstract

Purpose: To evaluate the feature of a TLD sheet for dose distribution measurements of photon and electron beams Method and Materials:3D dose distributions from 10×10 cm2 to 20 × 20 cm2 field sizes for photon and electron beams were measured using a TLD sheet, which has 40 × 40 cm2 dimension and 0.3 mm thickness. Its density and effective atomic number are 1.0 g/cm3 and 7.4, respectively. Before the measurements of dose distributions, the irradiation was done to calibrate the response of each TLD sheet. The read out temperature was 180 °C and generated light was detected with a CCD camera which has 1024 × 1024 pixels (FLIML 1001E‐2, Finger Lakes Instrument). Results: Dose profiles were obtained as smooth curve after the calibration. Measured PDD with the TLD sheet well reproduced the results with ionization chamber, except for the surface region. The measured dose with TLD at surface is around 20%, which is lower more than 20% comparing to the dose with ionization chamber. The 3D dose distribution with TLD sheet shows that the low dose region has isotropic form at surface. We demonstrated the prostate IMRT dose distribution also. The result reproduces the calculated result of treatment planning system qualitatively. Conclusion: It is shown that the TLD sheet has the potential to measure the 3D dose distribution including low dose at surface. For the IMRT dose distribution, the measured result with TLD qualitatively reproduces the calculated dose distribution. For a quantitative comparison with TPS dose calculation, we need to improve the TLD feature.