Introduction: Use of SPECT/CT data is the most accurate method for patient-specific internal DOSIMETRY when isotopes emit single gamma rays. The manual or semi-automatic segmentation of organs is a major obstacle that slows down and limits the patient-specific DOSIMETRY. Using digital phantoms that mimic patient’s anatomy can bypass the segmentation step and facilitate the DOSIMETRY process. In this study, the results of a patient-specific DOSIMETRY BASED on CT data and XCAT phantom, a flexible phantom with predefined organs, are compared.Methods: The DOSIMETRY results (S-value and SAF) were calculated for a patient with breast cancer who received Samarium- 153 ethylenediamine-N, N, N′, N′-tetrakis (methylenephosphonic acid (153 Sm-EDTMP). Biodistribution of activity was obtained from the SPECT scan. The anatomical data and attenuation map were extracted from CT as well as the XCAT phantom with different BMIs. GATE Monte-Carlo simulator was used to calculate the dose to different organs BASED on the activity distribution and segmented anatomy.Results: The whole body DOSIMETRY results are the same for both calculations BASED on the CT and XCAT with different BMIs; however for target organs, the differences between SAFs and S-values are high. In the spine, the clinically important target organ for Samarium therapy, the DOSIMETRY results obtained from phantoms with unmatched BMIs between XCAT phantom and CT are substantially different.Conclusion: We showed that ATLAS-BASED DOSIMETRY using XCAT phantom even with matched BMI may lead to considerable errors as compared to calculations BASED on patient’s own CT. For accurate DOSIMETRY results, calculations should be done using CT data.

Background: A new biological dosimeter BASED on methemoglobin level was developed in this study. Materials and Methods: Methemoglobin level in erythrocytes from mice subjected to g rays from a 60Co source was detected using the methemoglobin kit. The dose range was from 0.5 to 8 Gy and the dose rate was 0.5 Gy/min.Results: The results demonstrate that methemoglobin level increases with increasing dose. The detection limit BASED on methemoglobin has a lower limit of dose estimation of about 1 Gy. The high levels of methemoglobin are maintained for at least 28 days, and the maximal increase of methemoglobin observed occurs at about 30 min after g irradiation. The relationship between dosage and the increased methemoglobin level can be expressed by a linear quadra%c equation of y=-8.75x2+168.09x+32.66, with the correlation coefficient, r, equal to 0.96. The best suggested %me for blood collection is up to 1 day after g irradiation. The doses absorbed by mice as estimated from the use of the dose-response relationship were close to the blind doses of 1, 2, 4 and 8 Gy.Conclusion: Methemoglobin is a quick, simple, and precise biomarker for the early assessment of the absorbed dose in mice.

Background: Since 1984 MRI gel DOSIMETRY has been introduced as a potential technique for 3D DOSIMETRY. Most of the studies have measured R1 (1/T1) or R2 (1/T2) properties of the gel depending on the gel type. We have studied image intensity change in the Fricke gel by different MRI protocols. Materials and Methods: Gel Dosimeters contain 0.4 mM ferrous sulphate, 1 mM NaCl, 50 mM H2SO4 and 1% by weight agarose in distilled water. Prepared gels were poured in Plastic tube phantom and irradiated to a beam of Co-60 gamma rays. Imaging was performed by a 0.5T MRI system in the head coil with SE and GRE techniques.Results: Our results showed that linear response exists between the variations of image intensity with absorbed dose (1-15 Gy). Optimal imaging parameters should be defined locally according to the type of MRI scanner and exact composition of the gel. Gradient echo (GRE) imaging technique also have been studied in comparison with classic spin echo (SE) imaging technique which will be discussed in detail. Conclusions: Linearity of absorbed dose with intensity exists up to 15 Gy and can be used for MRI gel DOSIMETRY. Reduction of imaging time is achievable in image intensity technique so that it’s possible to image the gel in less than 20 minutes, which is critical to over-come the adverse ion-diffusion properties of the Fricke gel. Iran