Radiation dose distribution in medical physics applications

In this study, dosimetric calculations were made for the targeted radionuclide therapy and radiation dose distributions were investigated. For this purpose, Medical Internal Radiation Dosimetry, MIRD method has been chosen as an appropriate and effective method for clinical applications among different dosimetric methods. Dosimetric calculations were done by using planar whole body scintigraphic images of the patients treated with radionuclide. For calculations; patients with chemotherapy-resistant prostate cancer (mCRCP-metastatic castration-resistant prostate cancer) and treated with 177Lu PSMA were selected. In phantom simulation studies, OLINDA EXM 1.1 simulation program has been utilized. The doses absorbed by radiation-sensitive critical organs were calculated and the dose values obtained were compared with the limit values given by the ICRP. The absorbed doses per 100 mCi of activity were 2.88 ± 1.18 Gy for kidney, and 0.39 ± 0.17 Gy for liver. The liver dose was found to be below the ICRP limit values. When the absorbed renal doses were examined, it was seen that the total dose value approached the limit value after 4th treatment. The absorbed doses per 100 mCi of activity were 5.27 ± 2.75 Gy and 4.71 ± 2.73 Gy for parotid left and right salivary glands, 3.68 ± 1.58 for submandibular left and right salivary glands, 3.9 ± 1.66 Gy, for the left and right lacrimal glands, 11 ± 2.6 Gy and 8.1 ± 3.18 Gy, respectively. In the study, it was observed that the absorbed dose values in parotid, submandibular salivary glands and lacrimal glands were well above the renal dose values. For this reason, it has been suggested that salivary glands and lacrimal glands should be considered as critical organs for the radionuclide treatment. Because the anatomical structures, treatment performances and clinical responses of patients differ from each other, the importance of carrying out a patient-specific dosimetric study in radionuclide treatment has been emphasized.