Dose distribution measurements using luminol water during irradiation of high-energy X-rays from medical linear accelerators (LINAC)

Dose distribution measurements of high-energy X-rays from a medical linear accelerator (LINAC) in water are important for quality control (QC) of the system, and Cherenkov-light imaging is an efficient method for measuring the high-energy X-ray dose distribution. However, the depth profiles have an underestimated dose at increased depths due to the angular dependency of the Cherenkov light. Luminol water is a possible material for measuring the dose distribution by detecting the light emitted from the chemical reaction with the reactive hydroxyl radical (・OH) produced in water by irradiation. In this study, we used luminol water for dose distribution measurements of high-energy X-rays from a LINAC. Imaging of the light emitted from luminol water was conducted using a cooled charge-coupled device (CCD) camera during irradiation with 6 MV X-rays from a LINAC to the luminol water. Imaging of the Cherenkov light in water was also conducted by irradiating 6 MV X-rays to water for correcting the Cerenkov-light component produced in luminol water. The Cherenkov-light image was subtracted from that of the luminol water to derive a dose image. The light emission of luminol water was ∼3 times higher than that of Cherenkov light in water. By subtracting the Cherenkov-light image from the luminol-water image, we could obtain an image that was identical to the dose distributions. The difference in the relative dose distribution was within −0.4% for the corrected image while that of the Cherenkov-light image was −7.9%. The multiple irradiations of luminol water with X-rays produced non-uniformity of emitted light, probably due to the production of hydrogen peroxide (H2O2) in water. We confirmed that imaging luminol water was promising for dose distribution imaging by correcting the Cherenkov-light component in the images. The non-uniformity of the emitted light by multiple irradiations in luminol water needs to be solved for more stable measurements.