What is the role of dosimetry in patients with advanced thyroid cancer?

PURPOSE OF REVIEW: Pretreatment dosimetry prior to I-131 treatment for patients with advanced differentiated thyroid cancer will provide critical information for optimizing dosing regimen for effectiveness and safety. The review briefly summarizes relevant information and updates the current advances. RECENT FINDINGS: I-124 positron emission tomography-computed tomography (PET-CT) with anatomical cross-section imaging provides a better assessment of lesional dosimetry in contrast to traditional I-131 whole body scan with planar imaging. The introduction of Thyrogen (Genzyme, Cambridge, Massachusetts, USA) primed dosimetry also provides an easy way to stimulate the uptake of iodine without prolonged withdrawal of thyroid hormone, although the impact of reducing lesional dosimetry requires attention and further investigation. Lower radioactivities of I-131 could provide similar outcomes in treatment of intermediate risk patients with thyroid cancer compared with traditional high doses. Despite a wide range of lesional doses being noted using fixed 100 mCi radioactivities of I-131, no dose-effective relationship can be established because of an overwhelming success in ablation. SUMMARY: Pretreatment dosimetry remains important to optimize the I-131 treatment dosages for patients with advanced or metastatic thyroid cancer, elderly patients with renal insufficiency or patients with renal failure. Modern I-124 PET-CT and Thyrogen may provide further improvement of this assessment although these advances may require further validation.

Recombinant human thyroid-stimulating hormone as an alternative for thyroid hormone withdrawal in thyroid cancer management.

PURPOSE OF REVIEW: The purpose of the review is to summarize the current findings of using recombinant human thyroid-stimulating hormone (rhTSH, also known as Thyrogen) as adjuvant stimulation for diagnostic monitoring, thyroid remnant ablation, and treatment of metastatic thyroid cancer. RECENT FINDINGS: A negative Thyrogen-stimulated thyroglobulin level has a negative predictive value of up to 98.5%. Therefore, it is unnecessary to repeat a Thyrogen-stimulated thyroglobulin level in the surveillance of patients with a negative result. There are no significant differences found in the rate of recurrence or persistent disease between Thyrogen-assisted and thyroid hormone withdrawal-ablated patient groups. Studies have shown that rapid clearance of excess radioiodine from the body in the euthyroid state with Thyrogen stimulation has significantly reduced whole body radiation exposure as compared with the hypothyroid state in withdrawal patients. SUMMARY: Thyrogen-assisted diagnosis and radioiodine ablation of thyroid remnant provide a reliable tool in the management of thyroid cancer without sacrificing patient quality of life. We believe that the use of Thyrogen for radioiodine treatment of metastatic thyroid cancer may also provide a better option due to its rapid preparation time and safety. Further prospective studies are required for the assessment of long-term outcomes.

Contemporary imaging for thyroid cancer.

Thyroid nodules are extremely common in the adult population of the United States, and the incidence of thyroid cancer continues to increase. Preoperative ultrasonography is a crucial component of the work up of thyroid nodules. Recent studies evaluating (18)F-2-fluoro-2-deoxy-D-glucose-positron-emission-tomography, with or without simultaneous computed tomography imaging, are encouraging for its potential utility in thyroid cancer in patients who have an elevated serum thyroglobulin level and a negative (131)I scan.

Low-dose P32 therapy in essential thrombocythemia.

We present a case of an 85-year-old woman with medically refractory essential thrombocythemia and subsequent venous thrombosis. She received conservative phosphorus-32 sodium phosphate therapy for 3 mCi, approximately half the usual dose. One month later, she received a second intravenous phosphorus-32 treatment of 3.5 mCi. She responded successfully to both treatments with drops in her platelet count and experienced no adverse effects. Our case is noteworthy in the effectiveness from a conservative dose while avoiding hematologic complications.

Determining the Minimal Required Radioactivity of 18F-FDG for Reliable Semiquantification in PET/CT Imaging: A Phantom Study.

UNLABELLED: In pursuit of as-low-as-reasonably-achievable (ALARA) doses, this study investigated the minimal required radioactivity and corresponding imaging time for reliable semiquantification in PET/CT imaging. METHODS: Using a phantom containing spheres of various diameters (3.4, 2.1, 1.5, 1.2, and 1.0 cm) filled with a fixed (18)F-FDG concentration of 165 kBq/mL and a background concentration of 23.3 kBq/mL, we performed PET/CT at multiple time points over 20 h of radioactive decay. The images were acquired for 10 min at a single bed position for each of 10 half-lives of decay using 3-dimensional list mode and were reconstructed into 1-, 2-, 3-, 4-, 5-, and 10-min acquisitions per bed position using an ordered-subsets expectation maximum algorithm with 24 subsets and 2 iterations and a gaussian 2-mm filter. SUVmax and SUVavg were measured for each sphere. RESULTS: The minimal required activity (±10%) for precise SUVmax semiquantification in the spheres was 1.8 kBq/mL for an acquisition of 10 min, 3.7 kBq/mL for 3-5 min, 7.9 kBq/mL for 2 min, and 17.4 kBq/mL for 1 min. The minimal required activity concentration-acquisition time product per bed position was 10-15 kBq/mL⋅min for reproducible SUV measurements within the spheres without overestimation. Using the total radioactivity and counting rate from the entire phantom, we found that the minimal required total activity-time product was 17 MBq⋅min and the minimal required counting rate-time product was 100 kcps⋅min. CONCLUSION: Our phantom study determined a threshold for minimal radioactivity and acquisition time for precise semiquantification in (18)F-FDG PET imaging that can serve as a guide in pursuit of achieving ALARA doses.

Artifactual spinal metastases imaged by PET/CT: a case report.

A 55-y-old patient with multiple myeloma presented for restaging after chemotherapy and radiation. The patient had undergone vertebroplasty of multiple thoracic vertebrae because of painful compression fractures. The 18F-FDG PET images showed increased activity at the T8 and T10-T12 vertebral bodies. Comparison of the attenuation-corrected and non-attenuation-corrected images demonstrated that the activity was due to an artifact of attenuation correction. The CT scan correlated the sites of vertebroplasty to the 4 foci of increased uptake of 18F-FDG. The increasing use of vertebroplasty for malignant spinal fractures warrants vigilance for this artifact.

Using SUV as a guide to 18F-FDG dose reduction.

UNLABELLED: This article explores how one can lower the injected (18)F-FDG dose while maintaining validity in comparing standardized uptake values (SUVs) between studies. Variations of the SUV within each lesion were examined at different acquisition times. METHODS: Our protocol was approved by either the Human Investigation Committee or the Institutional Review Board. All 120 PET datasets were acquired continuously for 180 s per bed position in list mode and were reconstructed to obtain 30-, 60-, 90-, 120-, 150-, and 180-s-per-bed-position PET images with registration to a single set of nondiagnostic CT images. Qualitative assessment of the images was performed separately for correlation. The SUV measurements of each lesion were computed and normalized to the 180-s acquisition values to create a stabilization factor. These stabilization factors were used to demonstrate a predictable trend of stabilization over time. The variances of the stabilization factors over the entire dataset, composed of several tumor types over a range of sizes, were compared for each time point with the corresponding 150-s time point using a 2-sided F test, which has similar values to the 180-s time point. RESULTS: The variance of the data decreased with increasing acquisition time and with increasing dose but leveled off for sufficiently long acquisitions. CONCLUSION: Through the statistical analysis of SUVs for increasing acquisition times and visual evaluation of the plots, we developed and hereby propose an algorithm that can be used to seek the maximum reduction in administered (18)F-FDG dose while preserving the validity of SUV comparisons.

The utility of I-123 pretherapy scan in I-131 radioiodine therapy for thyroid cancer.

BACKGROUND: There is a growing belief that a pretherapy scan yields little or no additional information that would impact on radioiodine ablation dosing. In addition, there is some concern regarding on the stunning effect of a pretherapy scan, especially when I-131 radioisotope is used for imaging. We hypothesized that a pretherapy scan provides invaluable information on the amount of thyroid remnant, sometimes indicating the need for two-step I-131 ablation. It may also detect unsuspected local lymph node involvement or distant metastases, indicating the requirement for a higher I-131 dose after thyroidectomy. The aim of this study was to evaluate how effective pretherapy scans are for guiding I-131 therapy planning and augmenting information provided in the pathology reports for thyroidectomy specimens. METHODS: We reviewed 122 patients who underwent I-123 pretherapy scan and I-131 radioablation at Yale New Haven Hospital between January 2006 and August 2007. The percentage of neck uptake and whole-body images were acquired 24 hours following the administration of 51.8 MBq (1.4 mCi) of I-123 NaI. A 24-hour uptake of >3% was used as the cutoff to determine whether there was a greater than desired quantity of thyroid remnant, which would require a two-step treatment protocol. Furthermore, attention was paid to identifying cervical lymph nodes, which may not have presented themselves in the euthyroid state at the time of thyroidectomy. Additional clinical information provided by pretherapy scans was computed as percentages with 95% confidence intervals by using adjusted Wald intervals. RESULTS: Overall, the pretherapy scans provided additional critical information in 25% of the cases (31/122; 95% CI: 18%-34%). For cases demonstrating >3% uptake with midline lymph nodes, the pretherapy scan provided additional information in 50% of the cases (8/16; 95% CI: 28%-72%). CONCLUSIONS: Our study demonstrated that I-123 pretherapy scans provide valuable information with regard to unsuspected lymph nodes or distant metastases, indicating the requirement for a significantly higher I-131 dose, and unexpected large thyroid remnants, suggesting the need for two-step ablation. We should take advantage of stimulated pretherapy scans and adjust the treatment dosing accordingly.

Rapid correction of bone mass after parathyroidectomy in an adolescent with primary hyperparathyroidism.

CONTEXT: Primary hyperparathyroidism is rare in children. Absence of specific symptoms and limited biochemical evaluation in children has led to lengthy delays in diagnosis with the potential for damage to the kidneys and skeleton. SETTING: The setting involved a private practice referral to a large tertiary care center. PATIENTS: Our patient is a 16-yr-old male presenting with gross hematuria, left flank pain, and right foot pain. INTERVENTION(S): A biochemical evaluation revealed hypercalcemia and elevated parathyroid hormone levels. Renal ultrasonography demonstrated bilateral nephrolithiasis. Parathyroid ultrasonography and dual-phase technetium-99m sestamibi scintigraphy revealed a parathyroid adenoma in the left mid/lower anterior thyroid bed. A 4.5-g adenoma was removed at parathyroidectomy. MAIN OUTCOME MEASURE(S): Bone mineral content and density performed by dual energy X-ray absorptiometry at the time of diagnosis and 1 yr after parathyroidectomy. RESULTS: The main outcome measurement is a dramatic (24%-whole body and 49.9%-left hip) increase in bone mineral density during the 1-yr interval. CONCLUSIONS: Delay in diagnosis of hyperparathyroidism is common in children, related to vague symptomatology and infrequent use of laboratory evaluations in children. Such delays lead to increased risk of osteoporotic fractures and kidney stones. This case illustrates the emergent need of diagnostic evaluation in children presenting with similar symptoms. We emphasize the importance of bone densitometry in children, which is not often considered as part of the standard evaluation in this age group. The remarkable increase in bone mineral density in the 1 yr after surgery attests to the plasticity of recovery of the growing skeleton.

Unusual case of amiodarone-induced thyrotoxicosis: "illicit" use of a technetium scan to diagnose a transiently toxic thyroid nodule.

OBJECTIVE: To present an unusual case of amiodarone-induced thyrotoxicosis (AIT) associated with an autonomously functioning thyroid nodule, which was detected by means of a technetium scan; review the existing literature regarding the association of AIT with autonomous thyroid nodules; and explore the use of radioisotope imaging studies in patients with AIT. METHODS: We describe a 62-year-old man with paroxysmal atrial fibrillation, receiving long-term amiodarone therapy, who was referred by his cardiologist for evaluation of abnormal thyroid function tests. He was found to have an unusual case of AIT, associated with an autonomously functioning thyroid nodule. RESULTS: Thyroid function studies obtained by the patient's cardiologist had shown a completely suppressed thyrotropin level and a free thyroxine level of 3.5 ng/dL. A 24-hour thyroid iodine 123 uptake and technetium Tc 99m pertechnetate scan revealed a "single, strong focus in the right thyroid lobe, with the rest of the thyroid gland...not well visualized." Thyroid ultrasonography disclosed a single, well-defined 1.5-cm solid nodule. Repeated thyroid function studies revealed a normal thyrotropin level of 2.87 micro IU/mL and a normal free thyroxine level of 2.4 ng/dL. The patient was managed conservatively with follow-up surveillance. CONCLUSION: Prospective studies should be performed to better ascertain the value of Tc 99m thyroid scanning in determining the cause of AIT. Until such studies have been completed, we suggest that nuclear studies are unlikely to be cost-effective for assessing all patients with AIT. One logical strategy would be to gain experience with scans in only those patients with known thyroid nodules, which have been detected during physical examination or by ultrasonography. The potential clinical utility of such an approach would be of considerable interest.

Reliability of lymphatic mapping after wide local excision of cutaneous melanoma.

BACKGROUND: Since the advent of sentinel lymph node (SLN) biopsy, patients with cutaneous melanoma have been referred to surgeons for consideration for SLN biopsy, sometimes even after the wide local excision (WLE) of the primary melanoma has been performed. This has raised the question of the reliability and validity of a lymphoscintigram performed for lymphatic mapping of the SLN after there has been anatomic rearrangement of the skin following the WLE of this primary melanoma. METHODS: We conducted a prospective study of 20 consecutive patients with cutaneous melanomas with thickness less than 1.00 mm, who volunteered to undergo preoperative and postoperative lymphatic mapping to determine if there were any changes in the lymph nodes that were identified following the WLE of the primary melanoma. Each of the patients had a resection with a minimum of 1.0 cm margin, and closure of their wounds with either transposition flap or double advancement flaps. RESULTS: Lymphatic mapping was clearly identified in all 20 patients. One patient declined to undergo postoperative lymphatic mapping. Postoperative lymphatic mapping performed in the remaining 19 patients 2-4 weeks following WLE was identical to the preoperative mapping in 13 patients (68%), showed additional lymph nodes in 4-5 patients (21-26%), and showed fewer lymph nodes in 1-2 patients (5-10%). CONCLUSIONS: Lymphatic mapping performed after a WLE of a primary cutaneous melanoma should be as reliable in identifying the SLN as a preoperative lymphatic mapping in 90% of the patients.