[Guideline 'Imaging with ionizing radiation': risks, communication and shielding]. / Richtlijn 'Beeldvorming met ioniserende straling'.

The guideline 'imaging with ionizing radiation' provides information about the risks when using ionizing radiation and the communication thereabout. Because most radiological investigations are performed at one time, the chance of adverse effects, is small, even in children and pregnant women. In case of complex or multiple investigations, the medical physicist can be consulted to estimate the risks. The working group recommends using population diagrams when discussing possible risks. The working group recommends giving patients/caregivers room to express their concerns and questions. The working group advices using supporting material. The working group advocates the development of nationally uniform information material. If the patient/caregiver still has concerns, the working group recommends calling in experts such as radiologists, medical physicists, and radiographers.

Calibration of PET/CT scanners for multicenter studies on differentiated thyroid cancer with (124)I.

BACKGROUND: Studies on imaging of differentiated thyroid cancer (DTC) using (124)I often require a multicenter approach, as the prevalence of DTC is low. Calibration of participating scanners is required to obtain comparable quantification. As determination of a well-defined range of recovery coefficients is complicated for various reasons, a simpler approach based on the assumption that the iodine uptake is highly focal with a background that significantly lacks radioactivity might be more efficient. For each scanner, a linear conversion between known and observed activity can be derived, allowing quantification that can be traced to a common source for all scanners within one study-protocol. The aim of this paper is to outline a procedure using this approach in order to set up a multicenter calibration of PET/CT scanners for (124)I. METHODS: A cylindrical polyethylene phantom contained six 2-ml vials with reference activities of ~2, 10, 20, 100, 400, and 2000 kBq, produced by dilution from a known activity. The phantom was scanned twice on PET/CT scanners of participating centers within 1 week. For each scanner, the best proportional and linear fit between measured and known activities were derived and based on statistical analyses of the results of all scanners; it was determined which fit should be applied. In addition, a Bland-Altman analysis was done on calibrated activities with respect to reference activities to asses the relative precision of the scanners. RESULTS: Nine Philips (vendor A) and nine Siemens (vendor B) PET/CT scanners were calibrated in a time period of 3 days before and after the reference time. No significant differences were detected between the two subsequent scans on any scanner. Six fitted intercepts of vendor A were significantly different from zero, so the linear model was used. Intercepts ranged from -8 to 26 kBq and slopes ranged from 0.80 to 0.98. Bland-Altman analysis of calibrated and reference activities showed that the relative error of calibrated activities was smaller than that of uncalibrated activities. CONCLUSIONS: A simplified multicenter calibration procedure for PET/CT scans that show highly focal uptake and negligible background is feasible and results in more precise quantification. Our procedure can be used in multicenter (124)I PET scans focusing on (recurrent) DTC.

124I PET/CT to Predict the Outcome of Blind 131I Treatment in Patients with Biochemical Recurrence of Differentiated Thyroid Cancer: Results of a Multicenter Diagnostic Cohort Study (THYROPET).

UNLABELLED: Patients with suspected recurrence from differentiated thyroid carcinoma, based on an increased thyroglobulin (Tg) level and negative neck ultrasound (US), pose a clinical dilemma. Because standard imaging has a low yield identifying potential recurrence, blind (131)I treatment is often applied. However, a tumor-negative (131)I whole-body scintigraphy (WBS) prevails in 38%-50% of patients. We performed a prospective multicenter observational cohort study to test the hypothesis that (124)I PET/CT can identify the patients with a tumor-negative posttherapy (131)I WBS. METHODS: Our study was designed to include 100 patients with detectable Tg and a negative neck US, who were planned for blind (131)I therapy. All patients underwent (124)I PET/CT after administration of recombinant human thyroid-stimulating hormone. Subsequently, after 4-6 wk of thyroid hormone withdrawal patients were treated with 5.5-7.4 GBq of (131)I, followed by WBS a week later. The primary endpoint was the number of (131)I therapies that could have been omitted using the predicted outcome of the (124)I PET/CT, operationalized as the concordance of tumor detection by (124)I PET/CT, using post-(131)I therapy WBS as the reference test. The study would be terminated if 3 patients had a negative (124)I PET/CT and a positive posttherapy (131)I scan. RESULTS: After inclusion of 17 patients, we terminated the study preliminarily because the stopping rule had been met. Median Tg level at (131)I therapy was 28 µg/L (interquartile range, 129). Eight posttherapy WBS were negative (47%), all of which were correctly predicted by negative (124)I PET/CT. Nine posttherapy WBS showed iodine-avid tumor, of which 4 also had positive (124)I PET/CT findings. Sensitivity, specificity, negative predictive value, and positive predictive value of (124)I PET/CT were 44% (confidence interval [CI], 14%-79%), 100% (CI, 63%-100%), 62% (CI, 32%-86%), and 100% (CI, 40%-100%), respectively. Implementation of (124)I PET in this setting would have led to 47% (8/17) less futile (131)I treatments, but 29% of patients (5/17) would have been denied potentially effective therapy. CONCLUSION: In patients with biochemical evidence of recurrent differentiated thyroid carcinoma and a tumor-negative neck US, the high false-negative rate of (124)I PET/CT after recombinant human thyroid-stimulating hormone (124)I PET/CT as implemented in this study precludes its use as a scouting procedure to prevent futile blind (131)I therapy.