Monitoring of Scattered Photons in Radiotherapy for Cavity Movement Detection in Human Body

• Published in: 2023 IEEE Nuclear Science Symposium, Medical Imaging Conference and International Symposium on Room-Temperature Semiconductor Detectors (NSS MIC RTSD) p. 1
• Main Authors: Kawarabayashi, J., Kawara, T., Fujiwara, T., Hagura, N.
• Format: Conference Proceeding
• Language: English
• Published: IEEE 04.11.2023
• Subjects: Gamma-rays; Linear particle accelerator; Phantoms; Radiation therapy; Semiconductor detectors; Semiconductor device measurement; X-rays
• ISSN: 2577-0829
• DOI: 10.1109/NSSMICRTSD49126.2023.10338429

Radiation therapy is one of the most commonly selected treatment for malignant tumors. Linac accelerator sends X-rays to cancerous tissue from outside of human body. However, the cancerous tissue changes its position in the body due to respiration, pulsation of the circulatory system, and movement of the intestinal tract. Thus, irradiation is performed while confirming the position of the tissues in the body. Although simple methods for monitoring the positional changes of cancer tissue due to the movement of the respiratory and circulatory systems have already been established, it is difficult to monitor the positional changes of cancer tissue due to the movement of the intestinal tract, especially the movement of the air cavity (void) in the intestinal tract without taking the CT. Therefore, we focused on scattered therapeutic X-rays and proposed an application of imaging with scattered X-rays to the detection of bowel movements. In our proposed method, the cancer tissue is regarded as the source of scattered X-rays because the therapeutic X-ray beam always penetrates through the cancer tissue, and a radiation detector is placed on the extension line connecting the cancer tissue and the intestinal void around the cancer tissue. To investigate the possibility of the above monitoring method, we irradiated a plastic phantom by a beam of gamma rays from cobalt-60 source. Spectrum of the scattered gamma rays was measured by a CdTe detector. We confirmed that the intensity of the scattered gamma rays changed by changing the position of the void at a depth of 0 cm to 5 cm from the phantom surface. This indicates that monitoring the intensity of scattered gamma rays can detect the movement of a 1 cm thick void in the phantom in this region. Next step of this study is to demonstrate the detection of void migration at deeper region using Linac X-rays, which are used in actual medical treatments.