Varalakshmi Bandaru

124I Positron Emission Tomography Versus 131I Planar Imaging in the Identification of Residual Thyroid Tissue and/or Metastasis in Patients Who Have Well-Differentiated Thyroid Cancer

BACKGROUND AND OBJECTIVE (124)I emits a positron and can be imaged with a positron emission tomography (PET) scanner. The objective of this study was to compare the ability of diagnostic (124)I PET images versus (131)I planar whole-body imaging in detecting residual thyroid tissue and/or metastatic well-differentiated thyroid cancer (WDTC). METHODS Patients were recruited prospectively for this study who (i) had WDTC, (ii) were suspected of having metastatic WDTC, and (iii) were referred for (131)I whole-body dosimetry. The prescribed activity was 1-2 mCi (37-74 MBq) and 1.7 mCi (62.9 MBq) for (131)I and (124)I, respectively. For each image, one blinded reader (D.V.N.) categorized every focus of (131)I and (124)I radioiodine uptake as 1 = definite physiological uptake/artifact, 2 = most likely physiological uptake/artifact, 3 = indeterminate, 4 = residual thyroid tissue/metastases in the neck/bed, 5 = most likely metastases, or 6 = definite metastases. Foci categorized as 4, 5, or 6 were considered positive. When available, foci categorized as 4, 5, or 6 were correlated with other diagnostic studies. RESULTS Of the 25 patients, 8 patients (32%) had more positive foci on (124)I images than on (131)I, of which 3 patients to date have had metastases confirmed in one or more of the additional positive (124)I foci. (124)I demonstrated the same number of foci as on (131)I in 16 patients (14 with no positive foci, and 2 with two positive and five positive foci each). One patient had one additional positive focus on (131)I not seen on (124)I, which has not yet been confirmed as a metastasis. A total of 97 positive foci were identified on either (124)I or (131)I. (124)I identified 49 positive foci not seen with (131)I, and (131)I identified one positive focus not seen with (124)I. CONCLUSION Relative to (131)I planar whole-body imaging, (124)I PET identified as many as 50% more foci of radioiodine uptake suggestive of additional residual thyroid tissue and/or metastases in as many as 32% more patients who had WDTC.

Salivary Gland Protection with Sialagogues: A Case Study

BACKGROUND To decrease the severity and frequency of radiation sialoadenitis, postponement of the use of sialagogues has been proposed for the first 24 hours after (131)I treatment for well-differentiated thyroid cancer. One proposed mechanism is that sialagogues increased salivation and salivary blood flow resulting in greater radioiodine uptake in the salivary glands-a rebound effect. This case study demonstrates no rebound effect. METHODS A 33-year-old woman with well-differentiated thyroid cancer desired to know whether she would have a rebound effect if she used sialagogues during the 24-hour period after her (131)I treatment. Salivary images of the parotid glands were initiated 2 hours after the administration of (131)I for her whole body scan. Lemon juice was administered. Background corrected time-activity curves were obtained for both parotid glands. The potential reduction in radiation absorbed dose to the parotid glands secondary to the administration of lemon juice was calculated. RESULTS The time-activity curves demonstrated that the (131)I in the right and left parotid glands decreased rapidly after lemon juice by 87% and 83%, respectively, with return to pre-lemon juice levels by 30 and 13 minutes in the right and left parotid glands, respectively. However, at no time during the 1 hour of imaging did the uptake in either parotid gland significantly exceed the pre-lemon juice levels of activity. The potential reduction of radiation absorbed dose to the parotid glands secondary to the use of lemon juice ranged from as much as 30% to 67%. CONCLUSION This case study demonstrates 1) an approach to assess whether an individual patient will have increased or decreased radioiodine uptake in the salivary glands after administration of sialagogues without the administration of any additional radioiodine, 2) a decrease of radioiodine uptake in the salivary glands after lemon juice without a rebound effect, and 3) a potential reduction of radiation absorbed dose with administration of sialagogues.

Radiopharmacokinetics of Radioiodine in the Parotid Glands After the Administration of Lemon Juice

BACKGROUND The ability of sialagogues to increase or decrease radiation induced-sialoadenitis and/or xerostomia after therapeutic administration of ¹³¹I is controversial. To evaluate this we measured the radiopharmacokinetics of ¹²³I in the parotid glands (PGs) after its administration of lemon juice (LJ). METHODS A retrospective review was performed on all patients who had a salivary gland scan performed before ¹³¹I therapy between July 2008 and April 2009 at the Washington Hospital Center. Two hours after ¹²³I was given orally, dynamic scintigraphy was initiated. Five milliliters of LJ was given 5 minutes later. Then, the patient was imaged for 1 hour (phase 1) at which point the sequence was repeated (phase 2). Twenty-three patients were studied. For each PG, the presence or absence of uptake was assessed, and based on background corrected counts, the mean, range, and standard deviation were determined for multiple radiopharmacokinetic parameters such as (i) percent radioiodine washout, (ii) time from LJ administration to re-accumulation of radioiodine to pre-LJ activity, and (iii) percent reduction in radiation absorbed dose to the PGs if LJ had been re-administered at the time the radioiodine activity re-accumulated to the pre-LJ activity. RESULTS The mean  ± one standard deviation and range for percent washout were 84%  ± 18% (35%-100%) and 83%  ±  21% (37%-100%) in phase 1 and 2, respectively. The times from LJ to re-accumulation of the radioiodine to the pre-LJ activity were 21  ± 10 minutes (4-45 minutes) and 40  ± 14 minutes (12-62 minutes) for phase 1 and 2, respectively. The estimated percent reduction in radiation absorbed dose to the PGs following the first and second administration of LJ was 37%  ± 14% (13%-93%) and 47% ± 16% (21%-97%), respectively. CONCLUSIONS The washout of radioiodine from the PGs is rapid but transient. Early repeat administration may result in continued and cumulative reduction of radiation absorbed dose in the PGs.