Three-Dimensional Dose Verification of High-Dose-Rate (HDR) Flattening Filter Free (FFF) Radiation Therapy by Using NIPAM Gel Dosimetry

Abstract

Flattening filter free (FFF) beam exhibits higher dose rate, lower head scatter photons, and less treatment time for patient than that of a flattened beam. The profile shape of the FFF beam is considerably sharper than that of the flattened beam due to the lack of flattening filter. However, the dose accuracy irradiated by the FFF beam should be investigated. In this study, a square irradiation field with 30 × 30 mm 2 was used for the two beam modes, namely, FFF and flattened beams. A three-dimensional N-isopropylacrylamide gel dosimeter was adopted to measure the dose distribution. A gamma evaluation was performed to compare the measured dose with the treatment planning system calculated data with gamma evaluation criteria, i.e., 3% dose difference and 3 mm distance-to-agreement. In addition, the experiment was repeated three times to compare the passing rates of FFF and flattened beams.

Applying the N-isopropylacrylamide gel dosimeter to quantify dynamic dose effects: A feasibility study

“…They found that the dynamic dose response was similar to the static, and the average sensitivity difference of fixed and movement NIPAM was 0.001 s-1/Gy [7]. NIPAM gel dosimeters have also been used in static measurement, such as the study by Yao et al in 2019. The results confirm that NIPAM gel dosimeter can be used for dose measurement of modern radiation technology [8].…”

“…NIPAM gel dosimeters have also been used in static measurement, such as the study by Yao et al in 2019. The results confirm that NIPAM gel dosimeter can be used for dose measurement of modern radiation technology [8]. However, most studies assume that the target treatment area is fixed, or the measurement of the calibration tube, and does not study the dynamic dose effect caused by physiological movement.…”