ABSTRACT
Objective:To estimate the renal absorbed dose in the treatment of neuroendocrine tumors using 177Lu-DOTA-TATE and to assess the radiation safety and guide the treatment. Methods:The dosimetric calculations of patients treated with 177Lu-DOTA-TATE were carried out based on planar images of single photon emission computed tomography (SPECT). The regions of interest (ROIs) of the whole body and kidneys were delineated and converted into activity. Accordingly, the time-activity curves of the ROIs were obtained. The effective half-lives and cumulative activity of ROIs were calculated through the fitting of a single exponential equation of the ROIs. Then the absorbed doses were calculated based on the medical internal radiation dosimetry (MIRD) formalism. Results:A total of 11 patients with neuroendocrine tumors received 18 cycles of treatments with 177Lu-DOTA-TATE. The effective half-lives of 177Lu-DOTA-TATE in the whole body and kidneys were 20.0-99.8 h and 38.2-75.2 h, respectively, with an average of (57.3 ± 21.4) h and (53.1 ± 12.5) h, respectively. The renal absorbed doses of 177Lu-DTA-TATE were 0.25-1.48 mGy/MBq, with an average of (0.90 ± 0.31) mGy/MBq. The minimum and maximum renal absorbed doses in a single treatment cycle were 1.8 Gy and 9.6 Gy, respectively, while the maximum renal absorbed dose in multiple treatment cycles was 21.7 Gy. Conclusions:The renal absorbed doses in the treatment of neuroendocrine tumors using 177Lu-DOTA-TATE were estimated. The result indicate that the renal absorbed doses were lower than the tolerable dose limits. This study is expected to guide the precise treatment of neuroendocrine tumors.
ABSTRACT
Objective:To estimate the induced radioactive 56Mn and its level of iron in heavy concrete shielding wall due to neutron activation during tumor proton therapy. Methods:A Geant4 program was adopted to build the model of a heavy concrete shielding wall in a proton therapy room, simulate secondary neutrons generated by 245 MeV proton beam irradiating water phantom. The statistical distribution of radionuclide 56Mn in shielding wall was calculated. The shielding wall was layered every 10 cm thickness, the dose equivalent rate of radionuclide 56Mn in the first three shielding walls was calculated. Results:Under the maximum beam irradiation conditions (1.872 × 10 10), the number of radionuclide 56Mn in the first three layers of shielding walls are 3.10×10 8, 1.60×10 8, 9.33×10 8. The ambient dose equivalent rate at a distance of 1 m from the treatment room are 2.13×10 -3, 8.82×10 -4, 9.10×10 -4 μSv/h, and the total ambient dose equivalent rate for the first three layers was 3.92× 10 -3 μSv/h. Conclusions:During proton therapy, the shielded walls near the central axis of the beam produce more induced radioactivity. The induced radioactivity produced by the neutron-activated iron element at the ahead of the shielding wall is the strongest, and decreases exponentially as the thickness of the shield wall increases.The induced radioactivity in front of the shielding wall of proton therapy room should be concerned.