The influence of saliva flow stimulation on the absorbed radiation dose to the salivary glands during radioiodine therapy of thyroid cancer using 124I PET(/CT) imaging.

PURPOSE: A serious side effect of high-activity radioiodine therapy in the treatment of differentiated thyroid cancer is radiogenic salivary gland damage. This damage may be diminished by lemon-juice-induced saliva flow immediately after 131I administration. The aim of this study was to assess the effect of chewing lemon slices on the absorbed (radiation) doses to the salivary glands. METHODS: Ten patients received (pretherapy) 124I PET(/CT) dosimetry before their first radioiodine therapy. The patients underwent a series of six PET scans at 0.5, 1, 2, 4, 48 and ≥96 h and one PET/CT scan at 24 h after administration of 27 MBq 124I. Blood samples were also collected at about 2, 4, 24, 48, and 96 h. Contrary to the standard radioiodine therapy protocol, the patients were not stimulated with lemon juice. Specifically, the patients chewed no lemon slices during the pretherapy procedure and neither ate food nor drank fluids until after completion of the last PET scan on the first day. Organ absorbed doses per administered 131I activity (ODpAs) as well as gland and blood uptake curves were determined and compared with published data from a control patient group, i.e. stimulated per the standard radioiodine therapy protocol. The calculations for both groups used the same methodology. RESULTS: A within-group comparison showed that the mean ODpA for the submandibular glands was not significantly different from that for the parotid glands. An intergroup comparison showed that the mean ODpA in the nonstimulation group averaged over both gland types was reduced by 28% compared to the mean ODpA in the stimulation group (p=0.01). Within each gland type, the mean ODpA reductions in the nonstimulation group were statistically significant for the parotid glands (p=0.03) but not for the submandibular glands (p=0.23). The observed ODpAs were higher in the stimulation group because of increased initial gland uptake rather than group differences in blood kinetics. CONCLUSION: The 124I PET(/CT) salivary gland dosimetry indicated that lemon juice stimulation shortly after 131I administration in radioiodine therapy increases the absorbed doses to the salivary glands.

Optimized 124I PET dosimetry protocol for radioiodine therapy of differentiated thyroid cancer.

UNLABELLED: Iodine kinetics and lesion dose per administered 131I activity (LDpA) of differentiated thyroid cancer metastases were determined using 124I PET. These data were analyzed to derive an optimized dosimetry protocol. METHODS: We evaluated the time-activity-concentration curves of 37 lesions in 17 patients who had undergone thyroidectomies. LDpA determination involved 124I PET images acquired at 4, 24, 48, 72, and 96 h after intake of a capsule containing 20-40 MBq of 124I. A combination of a linear and a monoexponential or a monoexponential function only parameterized the time-activity-concentration curves. The LDpAs, calculated using data from all 5 PET time points, served as reference. The lesions were classified into 3 groups, according to potential for cure with 131I therapy: low (< or =5 Gy GBq(-1); n = 14), medium (between 5 and 10 Gy GBq(-1); n = 9), or high LDpAs (>10 Gy GBq(-1); n = 14). Using the reference approach, the differences in the empiric kinetic parameters within the LDpA groups were evaluated. The reference LDpAs were compared with those derived from only 2, 3, or 4 PET data points and from 1 adapted 2-point approach. Lin's concordance correlation coefficient (rho c) and the mean absolute percentage deviation in LDpAs were used to assess agreement between simplified and reference approaches. RESULTS: The effective 124I half-life, linear activity-concentration rate (alpha), and 24-h activity concentration (CpA) (the latter 2 per administered 124I activity) differed significantly among the LDpA groups (P < 0.05). LDpAs correlated with 24-h CpAs (r = 0.94, P < 0.001). Using the 4-, 24-, and 96-h measurements, a rho c value of greater than or equal to 0.90 was found, and the mean absolute percentage deviation was less than or equal to 16%. Similar statistical values were obtained for the adapted approach, which was based on 24- and 96-h PET data points only. CONCLUSION: Lesion classification into LDpA groups was feasible using a single PET scan at approximately 24 h. Because of the highly variable kinetics, 1 additional measurement at approximately 96 h was needed to obtain a sufficiently reliable LDpA estimate. The adapted 24-96-h approach appears to be the optimal 124I protocol and is a reliable simplification of the 5-point protocol.

Influence of various geometric factors on the iodine-131 uptake measurement for solitary thyroid nodules.

AIM: The influence of various geometric factors on I uptake measurements for solitary thyroid nodule was systematically investigated to derive an approach, based on routinely performed ultrasound examinations, to correct for the effect of geometric variations. METHODS: The influence of size, shape, and position of a thyroid nodule, neck-to-detector distance and neck curvature on the uptake value was analyzed with a three-dimensional model. Uptake measurements using a tissue-equivalent neck phantom were carried out to verify the calculated correction factors and also to check the influence of scatter. Sonograms of 92 patients with solitary nodules were analyzed to correct for geometric variations. RESULTS: The correction factors were independent of the size and shape of the nodule, and the activity distribution of the solitary nodules can be approximated by a point source. The correction factors were mainly determined by the nodular depth and by the accuracy of the neck-to-detector distance and were affected to a lesser extent by the lateral position of the nodule as well as the curvature of the neck. The effect of scatter can be neglected if the energy window largely excludes Compton scatter, as is the case in the I uptake measurement. The ultrasound-derived correction factors ranged from 0.85 to 1.25. CONCLUSION: The proposed approach is capable of correcting for the geometric variation for a solitary nodule and can be easily applied in routine clinics. The accuracy of absorbed dose in radioiodine therapy can be improved in particular for nodules located well beneath the neck surface.

Segmentation of PET volumes by iterative image thresholding.

UNLABELLED: The segmentation of metastatic volumes in PET is usually performed by thresholding methods. In a clinical application, the optimum threshold obtained from the adaptive thresholding method requires a priori estimation of the lesion volume from anatomic images such as CT. We describe an iterative thresholding method (ITM) used to estimate the PET volumes without anatomic a priori knowledge and its application to clinical images. METHODS: The ITM is based on threshold-volume curves at varying source-to-background (S/B) ratio acquired from a body phantom. The spheres and background were filled either with (18)F-FDG or Na(124)I ((124)I). These calibrated S/B-threshold-volume curves were used in estimating the volume by applying an iterative procedure. The ITM was validated with a PET phantom containing spheres and with 39 PET tumors that were discernable on CT by using whole-body (18)F-FDG (15 patients) and (124)I PET/CT (9 patients): The measured S/B ratios of the lesions were estimated from PET images, and their volumes were iteratively calculated using the calibrated S/B-threshold-volume curves. The resulting PET volumes were then compared with the known sphere inner volume and CT volumes of tumors that served as gold standards. RESULTS: Phantom data analysis showed that the S/B-threshold-volume curves of (18)F-FDG and (124)I were similar. The average absolute deviation (expressed as a percentage of the expected volume) obtained in the PET validation phantom was 10% for volumes larger than 1.0 mL; sphere volumes of 0.5 mL showed a significantly larger deviation. For patients, the average absolute deviation for volumes between 0.8 and 7.5 mL was about 9% (31 lesions), whereas volumes larger than 7.5 mL showed an average volume mismatch of 15% (8 lesions). CONCLUSION: The ITM sufficiently estimated the clinical volumes in the range of 0.8-7.5 mL; volumes larger than 7.5 mL showed greater deviations that were still acceptable. These findings are associated with the limitation of the ITM. The ITM is especially useful for lesions that are only visible on PET. As a consequence, the lesion dosimetry is feasible with sufficient accuracy using PET images only.

Economic image compression of output documentation of the most frequent examinations in nuclear medicine.

RATIONALE AND OBJECTIVES: In recent years, picture archiving and communication systems and electronic transfer of radiologic images using the digital imaging and communications in medicine file standard has become more widely employed in diagnostic radiology. It seems to be likely that nuclear medicine will be integrated within such systems. On the other hand, many departments possess older nuclear medicine equipment without digital output facilities. There is an increasing tendency to display and archive evaluated images ("save-screens," printouts) on nondedicated, inexpensive systems using file formats capable of data compression. This was the reason for examining the value of the JPEG format in this pilot study. MATERIALS AND METHODS: Fifty scanned planar bitmap images of the most frequent scintigraphic examinations (thyroid, bone, myocardium, lungs, and kidneys) were compared with JPEG format at different data compressions by two blinded observers. The visualization of details (eg, pathologic findings) is described for all these images as the visual appearance of the images and the storage capacity required. RESULTS: Relevant loss of clinical information did not occur up to compression factors of 0.75. A major decrease of subjective image quality was seen at compression factors >0.90. Compared with bitmap files, the use of these factors reduced the storage capacity required by 98% at a (JPEG-related) compression factor of 0.50, and 99% at a compression factor of 0.90. Compared with the GIF format, a reduction by 4.0-5.7 could be achieved. CONCLUSIONS: Use of the JPEG format can therefore be recommended to save costs of image transfer or archiving of standard planar scans for nuclear medical evaluation.

Relationship between cumulative radiation dose and salivary gland uptake associated with radioiodine therapy of thyroid cancer.

AIM: To estimate the individual absorbed dose to the parotid and submandibular salivary glands in radioiodine therapy and its dependence from the previous cumulative therapy. METHODS: Fifty-five patients with differentiated thyroid carcinoma after thyroidectomy received 1-21 GBq (131)I using single activities of 1-6 GBq. The patients were stratified according to the cumulative activities into low-activity (1-2 GBq), middle-activity (3-7 GBq), and high-activity groups (9-21 GBq). The time-activity curves over the respective salivary glands were derived from multiple static calibrated images measured for each patient up to 48 h after ingestion of the radioiodine therapy capsule with a gamma camera. Manually drawn regions of interests were used to determine the background activities and the activities arising from the salivary glands. The gland volumes were determined by ultrasonography using appropriate volume models. RESULTS: The median absorbed dose per administered activity of each single parotid and submandibular gland was about 0.15 Gy.GBq (range, 0.1-0.3 Gy.GBq(-1)) and 0.48 Gy.GBq(-1) (range, 0.2-1.2 Gy.GBq(-1)), respectively. The maximum uptake of both gland types was significantly lower for the high-activity than for the low-activity groups and correlated with the mean cumulative administered activity of the activity groups. CONCLUSION: The iodine uptake of salivary glands is significantly reduced, whereas the absorbed dose per administered (131)I activity was not significantly decreased during the course of therapy. Comparing the well-known dose-effect relationships in external radiation therapy, the absorbed dose per administered (131)I activity is too low to induce comparable radiation damage, suggesting an inhomogeneous distribution of (131)I in human salivary glands.

Burn injury by nuclear magnetic resonance imaging.

Nuclear magnetic resonance imaging has become a standard diagnostic procedure in clinical medicine and is well known to have hazards for patients with pacemaker or metallic foreign bodies. Compared to CT, the frequency of MRI examinations is increasing due to the missing exposure of the patients by X-rays. Furthermore, high-field magnetic resonance tomograph (MRT) with 3 T has entered clinical practice, and 7-T systems are installed in multiple scientific institutions. On the other hand, the possibility of burn injuries has been reported only in very few cases. Based on a clinical finding of a burn injury in a 31-year-old male patient during a routine MRI of the lumbar spine with standard protocol, the MR scanner was checked and the examination was simulated in an animal model. The patient received a third-degree burn injury of the skin of the right hand and pelvis in a small region of skin contact. The subsequent control of the MRI scanner indicated no abnormal values for radiofrequency (RF) and power. In the subsequent animal experiment, comparable injuries could only be obtained by high RF power in a microwave stove. It is concluded that 'tissue loops' resulting from a contact between hand and pelvis must be avoided. With regard to forensic aspects, the need to inform patients of such a minimal risk can be avoided if the patients are adequately positioned using an isolating material between the hands and pelvis. These facts must be emphasized more in the future, if high-field MRI with stronger RF gradients is available in routine imaging.