Activity estimation, bio-kinetic analysis and patient-specific dosimetry of 99mTc-Dimercaptosuccinic Acid (DMSA) in pediatric patients

Background: Renal scintigraphy with 99mTc labeled Dimercaptosuccinic acid (DMSA) has extensive clinical use in the diagnosis of renal pathophysiology including urinary tract infection (UTI) and parenchymal disorders. The main disadvantages of this examination is slightly higher radiation dose compared with other renal radiopharmaceuticals because time utilization may require a delay of 24 hours. Since children are more sensitive to ionizing radiation than adults, special care should be taken in the assessment of absorbed dose to evaluate the risk-benefit balance of the procedure. Monte Carlo (MC) simulation is known as the most accurate procedure for patient-specific radiation dosimetry. Therefore, the aim of this study was to estimate MC derived organ absorbed doses for children injected with 99mTc-DMSA.Methods: Ten child patients with genitourinary abnormalities were imaged using a series of planar, SPECT and MRI, after injection with 99mTc-DMSA. Patient specific organ segmentation was performed on MRI and used as input in GATE. Organs with substantial uptake included kidneys, bladder, and liver.Results: The mean organ absorbed dose coefficients (mGy/MBq) were 0.063, 0.058, 0.018, 0.016, 0.013 and 0.010 for the right kidney, left kidney, bones, urinary bladder wall, liver and gonads, respectively. The absorbed dose coefficients in the remainder of the body was 0.012 mGy/MBq.Conclusion: In this study the authors implemented an image based Monte Carlo method for patient-specific three-dimensional (3D) absorbed dose calculation. This study also demonstrates the possibility to obtain patient-specific attenuation map from MRI to be used for the simulations of radiation transport and energy deposition in phantom using Monte Carlo methods.