Radiopharmacokinetics of radioiodine in the parotid glands after the administration of lemon juice

The EANM guideline on radioiodine therapy of benign thyroid disease

This document provides the new EANM guideline on radioiodine therapy of benign thyroid disease. Its aim is to guide nuclear medicine physicians, endocrinologists, and practitioners in the selection of patients for radioiodine therapy. Its recommendations on patients' preparation, empiric and dosimetric therapeutic approaches, applied radioiodine activity, radiation protection requirements, and patients follow-up after administration of radioiodine therapy are extensively discussed.

Effect of recombinant human thyroid stimulating hormone on long-term salivary gland dysfunction in thyroid cancer patients treated with radioactive iodine. A systematic review

Adjuvant radioactive iodine (RAI) is administered to thyroid cancer patients following thyroidectomy for remnant tissue ablation and metastatic disease management. Patients are prepared with thyroid hormone withdrawal (THW) or recombinant human thyroid stimulating hormone (rhTSH). Long-term salivary gland dysfunction (LT-SGD) is a common, dosage-dependent, RAI adverse effect. Although rhTSH preparation seems to reduce LT-SGD, this effect could be due to lower RAI activity generally used in rhTSH-prepared patients. Therefore, this meta-analysis investigated the effect of preparation type on LT-SGD development. Literature search (PubMed, Medline, EmBase, Cochrane, Web of Science, LILACS, Google Scholar) was performed four times (January-November 2022) and studies reporting LT-SGD incidence ≥1 year after RAI in patients prepared with rhTSH/THW were identified. The LT-SGD risk ratio (RR) was estimated with various models considered for sensitivity analysis (fixed-effect, random-effects, study-quality adjusted, publication-bias adjusted, individual-patient-data meta-analysis adjusted for RAI). Subgroup analysis according to RAI activity (<3.7/≥3.7 GBq) also was performed. Literature search resulted in five studies (321 rhTSH, 632 THW patients). The pooled RRs according to various models were 0.65 (95% confidence interval -95CI, 0.49-0.86; fixed-effect); 0.62 (95CI, 0.38-1.02; random-effects); 0.72 (95CI, 0.54-0.96; quality adjusted); 0.76 (95CI, 0.58-0.99; publication-bias adjusted); 0.0.80 (95CI, 0.55-1.14; individual-patient-data meta-analysis). The pooled RRs stratified for RAI activity were 0.26 (95CI, 0.05-1.30) for <3.7 GBq; 0.75 (95CI, 0.57-0.98) for ≥3.7 GBq. The number of patients needed to be prepared with rhTSH to prevent one case of LT-SGD ranged between seven and thirty-seven. There is moderate-quality scientific evidence that rhTSH preparation may consistently protect salivary gland function.

Optimal administration time of vitamin C after 131I therapy in differentiated thyroid cancer based on propensity score matching

Objectives

This study aimed to investigate the protection of the salivary glands by vitamin C administration at 2 and 24 h after an initial treatment using iodine-131 (131I) in patients with differentiated thyroid cancer (DTC) and examined the optimal administration time of vitamin C to protect the salivary glands from radiation injury.

Method

The clinical data of patients with differentiated thyroid carcinoma who had been treated with 131I in the Department of Nuclear Medicine in Shanxi Bethune Hospital from January 2014 to December 2020 were retrospectively analyzed. The propensity score matching method was adopted to match patients who received the administration of vitamin C at 2 h with those receiving administration at 24 h. A total of 230 pairs/460 patients were enrolled in the study. The chi-squared (χ2) or Fisher's exact test was used to compare the indicators representing the incidence of salivary gland injury between the two groups.

Results

The incidence of salivary gland injury (17.39%) with acidic substances at 2 h was lower compared with administration at 24 h (26.96%). The incidence of acute salivary gland injury (15.22%) and chronic salivary gland injury (26.09%) in the 24-h group were higher than those in the 2-h group (4.78% and 18.26%, respectively). The differences in the left submandibular gland concentrate index and right submandibular gland concentrate index were statistically significant before and after treatment in both the 2 and the 24-h groups; these functions had been impaired after treatment.

Conclusions

Following treatment with 131I, the protective effect of acidic substances administered at 2 and 24 h on the salivary glands were different. The incidence of salivary gland injury in the 2 h acid stimulation group was lower than in the 24 h acid stimulation group. The present study revealed that 131I treatment did cause some injury to the salivary glands and that the protective effect of administering vitamin C at 2 and 24 h may be limited. Accordingly, protection against salivary gland injury should be conducted using comprehensive measures.

Alterations in Oral Microbiota of Differentiated Thyroid Carcinoma Patients With Xerostomia After Radioiodine Therapy

BACKGROUND AND AIMS

Oral xerostomia remains one of the most common complications of differentiated thyroid carcinoma patients (DTC) after radioiodine therapy (RAI). Environmental factors in the etiology of xerostomia are largely unknown. We aimed to characterize the oral microbiota signatures and related biological functions associated with xerostomia and identify environmental factors affecting them.

METHODS

Saliva was collected from 30 DTC patients with xerostomia (XAs), 32 patients without xerostomia (indicated as non-XAs) following RAI after total thyroidectomy, and 40 healthy people (HCs) for 16S rRNA sequencing analysis.

RESULTS

The oral microbiota of XAs and non-XAs exhibited significant differences in α and β diversities and bacterial taxa. The abundance of porphyromonas, fusobacterium, and treponema_2 were significantly higher in XAs, while the abundance of the streptococcus was lower in the microbiota of non-XAs. Fusobacterium, and porphyromonas were negatively correlated with unstimulated/stimulated whole salivary secretion (USW)/(SWS), while fusobacterium, porphyromonas, and treponema_2 genera levels were positively associated with cumulative radioiodine dose. PICRUSt2 and BugBase suggested a significant difference in the expression of potentially_pathogenic, anaerobic, gram_negative, the arachidonic acid metabolism, and lipopolysaccharide (LPS) biosynthesis between XAs and non-XAs, possibly interdependent on radioiodine-induced inflammation. NetShift analysis revealed that porphyromonas genus might play as a key driver during the process of xerostomia. Five genera effectively distinguished XAs from non-XAs (AUC = 0.87).

CONCLUSION

Our study suggests for the first time that DTC patients with xerostomia after RAI display microbiota profiles and associated functional changes that may promote a pro-inflammatory environment. Dysbiosis of the oral microbiota may contribute to exacerbating the severity of xerostomia. Our results provide a research direction of the interaction mechanism between oral microbiota alteration and the progress of xerostomia.

The effect of eating on the uptake of PSMA ligands in the salivary glands

Rationale

PSMA-directed therapy for metastatic prostate cancer is gaining adoption as a treatment option. However, accumulation of ¹⁷⁷Lu/²²⁵Ac-PSMA in the salivary glands remains a problem, with risk of dose-limiting xerostomia and potentially severe effect on the quality of life. Gustatory stimulation is an approach that has commonly been used in radioactive iodine therapy to reduce accumulation in the salivary glands. However, based on theoretical differences in biodistribution, it was hypothesized that this could potentially lead to adverse increased toxicity for PSMA-ligand therapy. The primary objective of this work was to determine if gustatory stimulation by eating an assortment of sweet/fatty/acidic foods during the biodistribution phase of [¹⁸F]DCFPyl could result in a clinically relevant (> 30%) change in the uptake of the tracer in the salivary glands.

Methods

10 patients who already received a whole-body [¹⁸F]DCFPyl PET/CT scan for evaluation of prostate cancer, underwent a repeat (intervention) PET/CT scan within a month of the first (control) scan. During the intervention scan, patients chose from an assortment of sweet/fatty/acidic foods, which they then chewed and swallowed for a period of time starting 1 min before tracer administration to 10 min thereafter. Data from both scans were analyzed by placing VOIs on the major salivary glands and segmenting them using relative thresholds.

Results

A slight increase in PSMA uptake in the parotid glands was observed on the intervention scan when compared to the baseline scan (+ 7.1% SUL_mean and + 9.2% SUL_max, p < 0.05). No significant difference in PSMA uptake in the submandibular glands was seen.

Conclusions

Eating only slightly increases uptake of [¹⁸F]DCFPyl in the parotid glands. We nonetheless recommend refraining from gustatory stimulation during the administration and early biodistribution phase of radionuclide therapy with PSMA-ligands to reduce the risk of avoidable additional toxicity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13550-021-00838-y.

Salivary and lacrimal dysfunction after radioactive iodine for differentiated thyroid cancer: American Head and Neck Society Endocrine Surgery Section and Salivary Gland Section joint multidisciplinary clinical consensus statement of otolaryngology, ophthalmology, nuclear medicine and endocrinology

BACKGROUND

Postoperative radioactive iodine (RAI) administration is widely utilized in patients with differentiated thyroid cancer. While beneficial in select patients, it is critical to recognize the potential negative sequelae of this treatment. The prevention, diagnosis, and management of the salivary and lacrimal complications of RAI exposure are addressed in this consensus statement.

METHODS

A multidisciplinary panel of experts was convened under the auspices of the American Head and Neck Society Endocrine Surgery and Salivary Gland Sections. Following a comprehensive literature review to assess the current best evidence, this group developed six relevant consensus recommendations.

RESULTS

Consensus recommendations on RAI were made in the areas of patient assessment, optimal utilization, complication prevention, and complication management.

CONCLUSION

Salivary and lacrimal complications secondary to RAI exposure are common and need to be weighed when considering its use. The recommendations included in this statement provide direction for approaches to minimize and manage these complications.

Poor patient compliance with instructions for continuous sialogogues after 131 I therapy

OBJECTIVES

To analyze the role of patient compliance as a factor in evaluating the effectiveness of continuous sialogogues to prevent salivary side effects from ¹³¹ I therapy in differentiated thyroid cancer patients.

METHODS

Differentiated thyroid cancer patients who were clinically scheduled for an ¹³¹ I therapy at MedStar Washington Hospital Center between 2012 and 2013 were given instructions for continuous sialogogues per standard clinical protocol. The prospective survey was given at multiple time points.

RESULTS

Ninety-nine patients consented to participate of whom 94 participants had complete data. The mean prescribed ¹³¹ I activity was 121 ± 50 mCi (4.5 ± 1.9 GBq), range 27.5-288 mCi (1.0-10.7 GBq ). Overall, only 10% (9/94) of patients were compliant with continuous sialogogues. Even though all patients took sialogogues on the first day of post-therapy, 17% of participants did not continuously take sialogogues during the first day, 60% during the first night, and 72% on the second day despite rigorous instructions to continue for two days.

CONCLUSION

Despite repetitive instructions to use sialogogues continuously, most patients (90%) were not compliant. In future studies, strict monitoring and evaluation of patient compliance will be crucial when assessing the effect of continuous versus intermittent or delayed initiation of sialogogues.

The effect of chewing-gum on dose rate of salivary gland in differentiated thyroid carcinoma patients treated with radioiodine

BACKGROUND

Although, different methods have been suggested on reducing salivary gland radiation after radioiodine administration, an effective preventive or therapeutic measure is still debated. To the best of our knowledge this is the second study that aimed to evaluate the effect of chewing-gum as a sialagogue on the radioiodine content of salivary gland, and radioiodine-induced symptoms of salivary gland dysfunction.

METHODS

Twenty-two patients who were referred to radioiodine therapy were randomized into chewing-gum (group A) and control (group B) groups. Anterior and posterior planar images including both head and neck were obtained 2, 6, 12, 24 and 48 hours after the administration of radioiodine in all patients and round regions of interest (ROI) were drawn for both left and right parotid glands with a rectangular ROI in the region of cerebrum as the background. All patients were followed once, 6 months after radioiodine administration via a phone call for subjective evaluation of symptoms related to salivary gland damage.

RESULTS

There was no significant difference between the two groups regarding the mean age, gender and initial iodine activity. The geometric mean of background-corrected count per administrated dose and acquisition time was calculated for bilateral parotid glands. This normalized parotid count showed a significant reduction in net parotid count in both groups during the first 48 hours after the radioiodine administration. However, no significant difference was found between the groups according to the amount and pattern of dose reduction in this time period.

CONCLUSIONS

This study revealed that chewing-gum had no significant effect on the radioiodine content of parotid glands during the first 48 hours after radioiodine administration. Also, no significant difference was found in the incidence of relevant symptoms after 6 months comparing both groups.

Early and late adverse effects of radioiodine for pediatric differentiated thyroid cancer

BACKGROUND

Radioiodine-131 (I131) therapy for differentiated thyroid cancer (DTC) is generally a safe and effective treatment, but it has some potential side effects, which have been well described in adults but less analyzed in children. Our aim was to describe early and late adverse events of radioactive I131 in pediatric patients.

METHODS

All consecutive patients ≤18 years treated for DTC in the period 1980-2015 were retrospectively analyzed for early and late side effects of radioiodine. Early side effects include nausea/emesis, radiation thyroiditis, sialadenitis, dry mouth, and transient bone marrow (BM) suppression. Late complications include permanent salivary gland dysfunction, permanent BM suppression, pulmonary fibrosis, second cancers, and fertility problems.

RESULTS

One hundred five pediatric patients were treated with I131 for DTC in our department for a total amount of 302 radioiodine treatments. In total, 127 early complications were recorded: 44 episodes of nausea/emesis; 30 sialoadenitis, 24 thyroiditis, 18 dry mouth, and 11 transient BM suppression. Early side effects were correlated with the amount of radioactivity administered in any treatment. Twelve children developed ≥1 late complication for a total of 20 complications: two permanent salivary gland dysfunction, four permanent BM suppression, five pulmonary fibrosis, four second malignancies, and five fertility alterations. Late events, except fertility alterations, were correlated with the number of therapies and cumulative activities of I131.

CONCLUSIONS

In conclusion, early side effects of I131 are associated with the amount of administrated activities of each treatment, while the late effects are correlated with the number of treatments and cumulative activities of radioiodine, except for fertility problems.

Recombinant Human Thyroid-Stimulating Hormone Versus Thyroid Hormone Withdrawal in 124I PET/CT-Based Dosimetry for 131I Therapy of Metastatic Differentiated Thyroid Cancer

Patients with metastatic differentiated thyroid cancer (DTC) may be prepared using either thyroid-stimulating hormone withdrawal (THW) or recombinant human thyroid-stimulating hormone (rhTSH) injections before ¹³¹I administration for treatment. The objective of this study was to compare the absorbed dose to the critical organs and tumors determined by ¹²⁴I PET/CT-based dosimetry for ¹³¹I therapy of metastatic DTC when the same patient was prepared with and imaged after both THW and rhTSH injections. Methods: Four DTC patients at MedStar Washington Hospital Center were first prepared using the rhTSH method and imaged by ¹²⁴I PET/CT at 2, 24, 48, 72, and 96 h after administration of approximately 30-63 MBq of ¹²⁴I. After 5-8 wk, the same patients were prepared using the THW method and imaged as before. The ¹²⁴I PET/CT images acquired as part of a prospective study were used to perform retrospective dosimetric calculations for ¹³¹I therapy for the normal organs with the dosimetry package 3D-RD. The absorbed doses from ¹³¹I for the lungs, liver, heart, kidneys, and bone marrow were obtained for each study (rhTSH and THW). Twenty-two lesions in 3 patients were identified. The contours were drawn on each PET image of each study. Time-integrated activity coefficients were calculated and used as input in OLINDA/EXM sphere dose calculator to obtain the absorbed dose to tumors. Results: The THW-to-rhTSH organ absorbed dose ratio averaged over 5 organs for the first 3 patients was 1.5, 2.5, and 0.64, respectively, and averaged over 3 organs for the fourth patient was 1.1. The absorbed dose per unit administered activity to the bone marrow was 0.13, 0.086, 0.33, and 0.068 mGy/MBq after rhTSH and 0.11, 0.14, 0.22, and 0.080 mGy/MBq after THW for each patient, respectively. With the exception of 3 lesions of 1 patient, the absorbed dose per unit administered activity of ¹³¹I was higher in the THW study than in the rhTSH study. The ratio of the average tumor absorbed dose after stimulation by THW compared with stimulation by rhTSH injections was 3.9, 27, and 1.4 for patient 1, patient 2, and patient 3, respectively. The ratio of mean tumor to bone marrow absorbed dose per unit administered activity of ¹³¹I, after THW and rhTSH, was 232 and 62 (patient 1), 12 and 0.78 (patient 2), and 22 and 11 (patient 3), respectively. Conclusion: The results suggest a high patient variability in the overall absorbed dose to the normal organs per MBq of ¹³¹I administered, between the 2 TSH stimulation methods. The tumor-to-dose-limiting-organ (bone marrow) absorbed dose ratio, that is, the therapeutic index, was higher in the THW-aided than rhTSH-aided administrations. Additional comparison for tumor and normal organ absorbed dose in patients prepared using both methods is needed before definitive conclusions may be drawn regarding rhTSH versus THW patient preparation methods for ¹³¹I therapy of metastatic DTC.

2015 American Thyroid Association Management Guidelines for Adult Patients with Thyroid Nodules and Differentiated Thyroid Cancer: The American Thyroid Association Guidelines Task Force on Thyroid Nodules and Differentiated Thyroid Cancer

BACKGROUND

Thyroid nodules are a common clinical problem, and differentiated thyroid cancer is becoming increasingly prevalent. Since the American Thyroid Association's (ATA's) guidelines for the management of these disorders were revised in 2009, significant scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, researchers, and health policy makers on published evidence relating to the diagnosis and management of thyroid nodules and differentiated thyroid cancer.

METHODS

The specific clinical questions addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of task force members. Task force panel members were educated on knowledge synthesis methods, including electronic database searching, review and selection of relevant citations, and critical appraisal of selected studies. Published English language articles on adults were eligible for inclusion. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations for therapeutic interventions. We developed a similarly formatted system to appraise the quality of such studies and resultant recommendations. The guideline panel had complete editorial independence from the ATA. Competing interests of guideline task force members were regularly updated, managed, and communicated to the ATA and task force members.

RESULTS

The revised guidelines for the management of thyroid nodules include recommendations regarding initial evaluation, clinical and ultrasound criteria for fine-needle aspiration biopsy, interpretation of fine-needle aspiration biopsy results, use of molecular markers, and management of benign thyroid nodules. Recommendations regarding the initial management of thyroid cancer include those relating to screening for thyroid cancer, staging and risk assessment, surgical management, radioiodine remnant ablation and therapy, and thyrotropin suppression therapy using levothyroxine. Recommendations related to long-term management of differentiated thyroid cancer include those related to surveillance for recurrent disease using imaging and serum thyroglobulin, thyroid hormone therapy, management of recurrent and metastatic disease, consideration for clinical trials and targeted therapy, as well as directions for future research.

CONCLUSIONS

We have developed evidence-based recommendations to inform clinical decision-making in the management of thyroid nodules and differentiated thyroid cancer. They represent, in our opinion, contemporary optimal care for patients with these disorders.

Emptying effect of massage on parotid gland radioiodine content

BACKGROUND

To prevent salivary dysfunction in thyroid cancer patients who have undergone radioiodine ablation, massaging the parotid gland (PG) is presumed to be helpful for the removal of radioiodine. The purpose of this study was to evaluate the effect of PG massage in the removal of radioiodine from the PG.

METHODS

Forty-four patients (female, 38; 49.1 ± 11.0 years) who underwent total thyroidectomy followed by I-131 ablation were included in this prospective study. Three serial salivary gland scans were performed 2 h after administration of I-123 in thyroid hormone withdrawal status. The patients were divided into two groups. There was a 1-min (or 2-min) interval between the first and second scans for control, followed by the performance of PG massage for 1 min (or 2 min) between the second and third scans. Changes in uptakes were calculated between the first and second scans (control) and between the second and third scans (massage).

RESULTS

The mean change in uptake at the 1-min massage was 0.97 ± 11.27%, whereas that at the 1-min control was 11.54 ± 5.59% (P<0.001). The mean change in uptake at the 2-min massage was also significantly lower than that at the 2-min control (11.11 ± 6.97 vs. -0.85 ± 9.78%, P<0.001). However, no statistical difference was observed between the mean changes in uptake after 1- and 2-min massages (P=0.573).

CONCLUSION

PG massage reduced the radioiodine uptake in the PG, and the effect of PG massage for 1 min was comparable with that of PG massage for 2 min. PG massage can be applied to thyroid cancer patients who receive radioiodine therapy to reduce PG dysfunction.

Chewing-gum stimulation did not reduce the absorbed dose to salivary glands during radioiodine treatment of thyroid cancer as inferred from pre-therapy (124)I PET/CT imaging

Background

The goal of this prospective study was to estimate the absorbed (radiation) doses to salivary glands in radioiodine therapy of thyroid cancer under chewing-gum stimulation using ¹²⁴I positron emission tomography (PET)/computed tomography (CT) imaging.

Methods

Duplex ultrasonography was conducted in three test persons for visual comparison of the glandular blood flow with three different stimulation types (no stimulation, chewing tasteless gum base, sucking on lemon slices). Ten patients with newly diagnosed differentiated thyroid cancer received ¹²⁴I PET/CT dosimetry after thyroidectomy and prior to radioiodine therapy. Patients underwent a series of three ¹²⁴I PET/CT scans (4, 24, and ≥96 h after administration of 23 MBq ¹²⁴I). They were instructed to chew gum base (tasteless) approximately 20 min after ingesting the ¹²⁴I-containing capsule in the course of the first day. Absorbed doses per administered ¹³¹I activity to the salivary glands were calculated and compared with the previously published results of the lemon-juice stimulation and non-stimulation groups.

Results

The sonograms in the three test persons showed that glandular blood perfusion by lemon-juice stimulation was clearly increased compared with non-stimulation or chewing of gum base. The sonogram comparison between the chewing-gum stimulation and non-stimulation demonstrated a minor increase of blood flow for the gum base-stimulated salivary glands. The mean ± standard deviation of the absorbed dose per activity under chewing-gum stimulation for the submandibular and parotid glands (within parentheses) was 0.22 ± 0.09 Gy/GBq (0.22 ± 0.08 Gy/GBq). Compared with the absorbed doses of the non-stimulation group, 0.24 ± 0.08 Gy/GBq (0.21 ± 0.05 Gy/GBq), those of the chewing-gum stimulation group showed no significant change (P > 0.60), but the absorbed doses of the lemon-juice stimulation group, 0.35 ± 0.14 Gy/GBq (0.33 ± 0.09 Gy/GBq), were significantly higher (P < 0.04) than those of the chewing-gum stimulation group.

Conclusions

The results suggest that salivary flow induced by chewing gum base does not cause a significant reduction of the salivary gland absorbed dose compared with that in the non-stimulation group. The increased blood flow appears to be a decisive factor causing the increased ¹³¹I absorbed doses in the lemon-juice stimulation group.

Initial radioiodine administration: when to use it and how to select the dose

All published guidelines on the use of radioactive iodine for the treatment of well-differentiated thyroid cancer agree that an individualized assessment of the risk of cancer-related mortality and of disease recurrence should direct the decision of whether radioiodine treatment is needed and how much to administer. At the author's institution, they mostly follow the American Thyroid Association's risk stratification system, with the addition of a category of very-low-risk patients that do not receive radioactive iodine.

Radioprotective agents for the prevention of side effects induced by radioiodine-131 therapy

Radioiodine 131 (131I) has been used worldwide for the ablation of remnant thyroidal tissue after surgery or as the first-line treatment for Graves’ disease. Although the use of 131I is becoming increasingly prevalent, there is evidence suggesting that this treatment is associated with side effects such as salivary gland dysfunction and an increased risk of leukemia. This article aims to review the potential use of radioprotective agents and the side effects induced by 131I therapy. Several synthetic and natural compounds have been investigated in preclinical and clinical studies. The protective agents reduced the toxicity of 131I, mainly in the salivary glands, and mitigated the genetic damage through different mechanisms. There are limited clinical studies evaluating the use of radioprotective agents in patients undergoing radioiodine therapy. However, lemon candies, lemon juice and sugarless chewing gum have been proposed to be beneficial for minimizing the side effects of radioiodine within the salivary glands.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Effect of parotid gland massage on parotid gland Tc-99m pertechnetate uptake

BACKGROUND

Salivary dysfunction is the most common side effect associated with (131)I therapy in patients with differentiated thyroid cancer. The purpose of this study was to evaluate the effect of parotid gland (PG) massage on radioisotope accumulation in the salivary gland.

METHODS

Sixty patients were included in this study. Using Tc-99m pertechnetate, two salivary scans were performed in all patients. In 30 patients, PG massage was performed between the two salivary gland scans, whereas in the other 30 patients no massage was performed between the two scans. Total counts of both PGs and accumulation ratios were calculated.

RESULTS

In the patients who received massage, no difference was observed between the mean PG counts of first and second images (8556.9±3333.4 count vs. 8598.3±3341.3 count, p=0.39). In the patients who did not receive massage, the mean PG count on second images was significantly higher than that on first images (8581.2±3618.0 count vs. 9096.4±3654.0 count, p<0.01). Mean accumulation ratio in the patients who received massage was significantly lower than in the patients who did not receive massage (0.5%±3.3% vs. 6.8%±3.8%, p<0.01). Further, among the patients who received massage there was a higher percentage of patients with a negative accumulation ratio than among the patients who did not receive massage (43.3% vs. 0%, p<0.01).

CONCLUSIONS

PG massage can reduce Tc-99m pertechnetate accumulation in the PG, and thus, should be helpful to prevent salivary damage associated with (131)I therapy.