Assessment of late side effect development risk in jawbones of patients receiving head and neck radiotherapy

In this study, the predictability of the risk of developing late side effects of ionizing radiation on bone tissue such as osteopenia, osteoporosis, radiation fracture, and radionecrosis, in the lower jawbones of patients receiving head and neck radiotherapy (RT) was investigated using computed tomographic (CT) Hounsfield Unit (HU) values. The study sample consisted of recorded information on treatment and follow-up and radiographic images of 27 patients who received RT with a diagnosis of head and neck cancer in the Radiation Oncology Clinic between 2014-2018. The volumes of interest(VOIs) were generated on CT-simulator (CT-SIM) images used in treatment planning. VOIs were transferred to the CT and positron emission tomography-CT (PET-CT) images obtained during follow-up by the image registration process. The HU values of the regions of the mandible exposed to the specified dose ranges were measured by these VOIs. To compare the HU values from radiographic images obtained from different devices, deviations from device to device were corrected by calculating a conversion parameter. The HU values of images acquired before treatment and during follow-up were compared and the change in HU values was revealed. In our study; no decrease in HU values was observed over time within the VOI groups. However, the whole mandibular HU scores were found to decrease during the follow-up intervals '3-6' and '12 -24' after RT. The effect of dose was found very close to the statistical significance threshold (Pillai's Trace Statistics=3.53, p=0.055) in the interaction model between the change in measured HU values of the mandible over time and the radiation dose to which the mandible was exposed. The limitations of our research stem from its retrospective nature. With a new prospectively planned study, a larger sample and representative results can be obtained. In this respect, our research is a preliminary study of future prospective studies.