Comparison of 51Cr-EDTA and 99mTc-DTPA for glomerular filtration rate measurement.

PURPOSE: The production of 51Cr-labelled ethylenediaminetetraacetic acid (51Cr-EDTA), a validated and widely used radio-isotopic tracer for glomerular filtration rate (GFR) measurement in Europe, was recently halted by the manufacturer. Technetium-99m-diethylenetriaminepentaacetic acid (99mTc-DTPA) clearance has so far mostly been restricted to assessment of separate renal function by scintigraphy, but scarcely used and validated for GFR measurement. We compared the performances of 51Cr-EDTA and 99mTc-DTPA for GFR and extracellular fluid measurement. METHODS: In a multi-centre prospective study, 51Cr-EDTA and 99mTc-DTPA were simultaneously injected into 88 patients, and their urinary and plasma clearances, as well as their volumes of distribution, were measured during seven 30-min periods after a 90-min equilibrium time. RESULTS: Mean age was 52.2 ± 14.5 years, 59% were men. Urinary clearances of 51Cr-EDTA and 99mTc-DTPA were 64.1 ± 27.6 and 66.1 ± 28.0 mL/min, respectively, with a mean bias of 2.00 ± 2.25 mL/min, an accuracy within 10% of 95% [95% CI 91-99], and a coefficient of determination (R2) of 0.994. Plasma clearances of 51Cr-EDTA and 99mTc-DTPA were 66.1 ± 25.8 and 68.1 ± 26.6 mL/min, respectively, with a mean bias of 1.96 ± 3.32 mL/min, an accuracy within 10% of 91% [95% CI 85-97] and a R2 of 0.985. Distribution volumes were 17.3 ± 4.6 L for 51Cr-EDTA and 16.6 ± 4.6 L for 99mTc-DTPA (R2 0.930). CONCLUSION: The accuracy and precision of 99mTc-DTPA clearance, compared to 51Cr-EDTA clearance, was excellent for both urinary and plasma clearance methods, despite an approximate 2 mL/min overestimation, showing that the tracer is a reliable alternative to 51Cr-EDTA for GFR measurement.

Equivalent Dose Rate 1 Meter from Neuroendocrine Tumor Patients Exiting the Nuclear Medicine Department After Undergoing Imaging.

123I-metaiodobenzylguanidine (MIBG) and 111In-pentetrotide SPECT have been used for functional imaging of neuroendocrine tumors (NETs) for the last 2 decades. More recently, PET/CT imaging with 18F-FDG, 18F-fluorodihydroxyphenylalanine (FDOPA), and 68Ga somatostatin-receptor ligands in NETs has been expanding. A literature search could find no direct measurements of the dose rate from NET patients exiting the nuclear medicine department after undergoing PET/CT with 18F-FDOPA or 68Ga-DOTATOC, a somatostatin analog. Methods: We measured the dose rates from 93 NET patients on leaving the department after undergoing PET/CT or SPECT/CT in our centers. In total, 103 paired measurements of equivalent dose rate at 1 m (EDR-1m) from the sternum and urinary bladder were obtained. The detector faced the sternum or bladder and was 1 m away from and directly in front of the patient. The practice for exiting the department differed according to whether the patient had been referred for PET/CT or for SPECT/CT. PET/CT patients were discharged after imaging, whereas SPECT/CT patients left the department earlier, just after radiopharmaceutical injection. Results: The median administered activity was 122 MBq in 53 68Ga-DOTATOC PET/CT studies, 198 MBq in 15 18F-FDOPA PET/CT studies, and 176 MBq in 13 18F-FDG PET/CT studies. The corresponding median EDR-1m was 4.8, 9.5, and 8.8 µSv/h, respectively, facing the sternum, and 5.1, 10.1, and 9.5 µSv/h, respectively, facing the bladder. The median administered activity was 170 MBq in 12 111In-pentetreotide SPECT/CT studies and 186 MBq in 10 123I-MIBG SPECT/CT studies. The corresponding median EDR-1m was 9.4, and 4.9 µSv/h, respectively, at the level of the sternum, and 9.3 and 4.7 µSv/h, respectively, at the level of the bladder. The EDR-1m was less than 20 µSv/h in all patients. Thus, when exiting the nuclear medicine department, the NET patients injected with 68Ga-DOTATOC or 123I MIBG emitted an average EDR-1m roughly half that of patients injected with other radiopharmaceuticals. This finding is a complementary argument for replacing SPECT by PET somatostatin-receptor imaging. Conclusion: Our current practice of allowing patients to exit after PET/CT imaging or just after SPECT radiopharmaceutical injection appears to be safe from a radiation protection point of view. Restrictive advice is unnecessary for NET patients being discharged from the department.

Identification of a rectal subregion highly predictive of rectal bleeding in prostate cancer IMRT.

BACKGROUND AND PURPOSE: To identify rectal subregions at risks (SRR) highly predictive of 3-year rectal bleeding (RB) in prostate cancer IMRT. MATERIALS AND METHODS: Overall, 173 prostate cancer patients treated with IMRT/IGRT were prospectively analyzed, divided into "training" (n=118) and "validation" cohorts (n=53). Dose-volume histograms (DVHs) were calculated in three types of rectal subregions: "geometric", intuitively defined (hemi-rectum,…); "personalized", obtained by non-rigid registration followed by voxel-wise statistical analysis (SRRp); "generic", mapped from SRRps, located within 8×8 rectal subsections (SRRg). DVHs from patients with and without RB were compared and used for toxicity prediction. RESULTS: Training cohort SRRps were primarily within the inferior anterior hemi-rectum and upper anal canal, with 3.8Gy mean dose increase for Grade⩾1 RB patients. The SRRg, representing 15% of the absolute rectal volume, was located in 10 inferior-anterior rectal subsections. V18-V70 for SRRps and V58-V65 for SRRg were significantly higher for RB patients than non-RB. Maximum areas under the curve (AUCs) for SRRp and SRRg RB prediction were 71% and 64%, respectively. The validation cohort confirmed the predictive value of SRRg for Grade⩾1 RB. The total cohort confirmed the predictive value of SRRg for Grade⩾2 RB. Geometrical subregions were not RB predictors. CONCLUSION: The inferior-anterior hemi anorectum was highly predictive of RB.