Hypothyroidism following radiotherapy for head and neck cancer

Incidence and complications of hypothyroidism postlaryngectomy: A systematic review and meta-analysis

BACKGROUND

Hypothyroidism is common postlaryngectomy and is associated with laryngectomy-specific complications. The objective of this study is to determine the incidence and predictors of hypothyroidism postlaryngectomy and its associated complications.

METHODS

Systematic review, data extraction, and meta-analyses were performed following the PRISMA protocol. Six databases were searched for studies reporting on postlaryngectomy thyroid status with incidence, risk factors, management, or complications.

RESULTS

Fifty-one studies with 6333 patients were included. The pooled incidence of postlaryngectomy hypothyroidism is 49% (CI 42%-57%). Subgroup analysis showed postlaryngectomy hypothyroidism rates significantly correlated with hemithyroidectomy and radiotherapy. Patients who underwent laryngectomy, hemithyroidectomy, and radiotherapy had a 65% (CI 59%-71%) rate of hypothyroidism; laryngectomy and hemithyroidectomy 46% (CI 33%-60%); laryngectomy and radiotherapy 26% (CI 19%-35%); and laryngectomy alone 11% (CI 4%-27%) (p < 0.001).

CONCLUSIONS

Laryngectomized patients with partial thyroidectomy or radiation therapy are at significant risk of postoperative hypothyroidism. Evidence-based protocols for early detection and (prophylactic) treatment should be established.

Primary Hypothyroidism in Patients Exposed to Therapeutic External Beam Radiation: Non-randomized Comparative Study

Background Cancer patients are not routinely assessed for thyroid function after external beam radiotherapy (EBRT) to the neck, despite hypothyroidism being a known side effect of EBRT. So, this study aimed to assess the incidence of hypothyroidism after therapeutic external beam radiotherapy to the neck and to determine the time for the development of hypothyroidism. Methodology A non-randomized prospective comparative study was done at a tertiary care center from April 2018 to September 2020. Any cancer patients who were euthyroid before radiotherapy and are planned to receive EBRT to the neck were included as cases, whereas controls were selected from the patients who were euthyroid before radiotherapy and were planned to receive EBRT to the site other than the neck. A total of 100 participants in each case and control group were selected. Data were collected on participants' age, gender, primary tumor site, treatment modality, total radiation dose along with concurrent chemoradiation regimens. Details of blood chemistry including thyroid hormone levels were collected during the pre-radiation phase and post-radiation phase. After the completion of radiotherapy, both the patients and controls were followed up periodically at three months, six months, nine months, 12 months, and finally at 15 months post-radiation. Data were analyzed and interpreted to pursue defined objectives by using tables and graphs using Microsoft Excel and IBM SPSS, version 26.0 (Armonk, NY: IBM Corp.). The chi-square test was applied to find out the association of different variables with the development of hypothyroidism. P-values<0.05 were considered significant throughout. Results According to our findings, the incidence of hypothyroidism following external beam radiotherapy to the neck where radiation portals included a portion or the entire thyroid gland was 16% and 4%, when the radiation given to sites other than neck region. The difference in incidence between the case and control groups was found to be statically significant (p<0.05). However, it was found that age, gender, the primary tumor site, total radiation dose, and treatment modality had no significant effects on hypothyroidism development. The median time duration to become hypothyroid after EBRT was 12 months. Conclusions The monitoring of thyroid function should become a part of routine follow-up procedures in all cancer patients who receive neck radiation as part of their treatment.

Determining the Occurrence of Hypothyroidism Following Treatment With Radiation Therapy in Head and Neck Carcinoma Patients and the Associated Role of Risk Factors and Dose-Volume Histograms: A Prospective Study

Background

Head and neck carcinomas are one of the most common malignancies in developing countries including India. Most patients are treated with radiotherapy. Although post-radiotherapy hypothyroidism is a known complication, data regarding its incidence and factors influencing it are scarce. This study aimed to determine the incidence of post-radiotherapy hypothyroidism in head and neck carcinoma patients treated with radiotherapy and the factors influencing it.

Methodology

Patients with head and neck carcinomas treated with radiotherapy as one of the modalities were included in this study. Thyroid function tests were done, and quality of life questionnaires were completed before treatment and during follow-up. Dose-volume histogram (DVH), demographic data, and disease-related parameters were compared.

Results

Out of the 95 patients screened, 14 were found to be hypothyroid prior to the commencement of radiotherapy and were excluded. With a median follow-up duration of 34 weeks, 29.6% developed hypothyroidism, with 19% developing it in the first year. On univariate and multivariate analysis of the DVH of the thyroid gland, volume receiving 50 Gy (V50), dose received to 50% volume (D50), and the mean dose (more than 50 Gy) were found to be significantly associated with hypothyroidism.

Conclusions

Hypothyroidism is a significant comorbid factor in Indian patients with head and neck carcinomas. The incidence of post-radiotherapy hypothyroidism is significant and occurs early compared to the western population leading to significant deterioration in the quality of life. Parameters such as the volume of the thyroid gland, V50, D50, and mean dose to the thyroid gland influence the incidence of hypothyroidism. The use of appropriate constraints can significantly prevent radiotherapy-induced hypothyroidism.

Functional and biochemical changes in the thyroid gland following exposure to therapeutic doses of external beam radiotherapy in the head-and-neck cancer patients

Context

Majority of the head-and-neck cancers are locoregionally advanced at the time of diagnosis. Hence, radiotherapy (RT) portals will invariably cover the whole neck and thus, the thyroid gland which may lead to its dysfunction.

Aims

The purpose of this study is to identify the functional and biochemical changes in the thyroid gland following RT to the neck using single-photon emission computed tomography-computed tomography (SPECT-CT) and thyroid function tests (TFTs).

Subjects and Methods

In this prospective study, 45 patients of the head-and-neck cancer, receiving RT with or without chemotherapy were investigated. Baseline TFTs and thyroid scans (on SPECT-CT) were done, and the same were repeated at the completion of RT, at 3 and 6 months.

Results

All patients received a minimum of 30 Gy to the whole neck. Baseline TFTs and thyroid scans were normal. None of them developed hypothyroidism clinical or subclinical (C/S) at the completion of RT. Six patients developed hypothyroidism (four subclinical, two clinical) at 3 months of the completion of treatment. At 6 months of follow-up 14 patients (31.1%) developed hypothyroidism (ten subclinical, four clinical) with P≤ 0.01. All patients having clinical or subclinical hypothyroidism had decreased uptake on thyroid scan. Patients having decreased uptake on thyroid scan only, with normal TFTs and no symptoms of hypothyroidism were zero at the completion of RT, 1 at 3 months follow-up, and seven at 6 months follow-up.

Conclusions

Hypothyroidism (C/S) is an under-recognized but significant complication of therapeutic doses of RT to the neck. In our study, we recognized hypothyroidism as early as 3 months following the completion of RT. Hence, tests to evaluate functional and biochemical changes in the thyroid gland should be instituted as early as 3 months following RT.

Hypothyroidism in Head and Neck Squamous Cell Carcinoma Patients Receiving Radiotherapy With or Without Immune Checkpoint Inhibitors

OBJECTIVES/HYPOTHESIS

Hypothyroidism is a relatively common complication of head and neck squamous cell carcinoma (HNSCC) treatment. The objective of this study was to determine whether the addition of programmed death ligand-1 (PD-1) or programmed death ligand-1 (PD-L1) inhibition (anti-PD-1/PD-L1 therapy) to standard treatment increases the risk of hypothyroidism in HNSCC.

STUDY DESIGN

Retrospective Cohort.

METHODS

This is a retrospective, single institutional cohort study. Patients who received radiotherapy (RT) for HNSCC were identified in the electronic medical record. Patient factors collected include age, sex, body mass index (BMI), smoking status, alcohol use, Charlson comorbidity index, and HNSCC treatment records. The rate of hypothyroidism for patients with HNSCC receiving RT (+/- chemotherapy and surgery) (RT group, n = 101) was compared to that of HNSCC patients receiving RT (+/- chemotherapy and surgery) + anti-PD-1/PD-L1 therapy, either concurrently or after RT (RT + anti-PD-1/PD-L1 group, n = 38).

RESULTS

There was no significant difference in the rate of clinical or subclinical hypothyroidism between the two groups. Multinomial logistic regression found no significant difference in hypothyroidism based on age, sex, or BMI.

CONCLUSIONS

The addition of anti-PD-1/PD-L1 therapy to standard HNSCC treatment does not significantly increase the risk of developing hypothyroidism.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:E2413-E2419, 2021.

Thyroid Dysfunction Following Management of Non-thyroid Head and Neck Cancers

Head and neck cancers are one of the commonest malignancies in India. Majority of cases of head and neck malignancy undergo chemoradiation with or without surgery. Thyroid bears the brunt in terms of either excision or the gland tends to get irradiated and fibrosed. In either scenario the functionality of gland is lost leading to hypothyroidism and other clinical manifestations. It tends to get subclinical and goes unnoticed. To identify the occurrence of clinical and subclinical hypothyroidism among head and neck cancer patients receiving radiation to the neck and to justify routine use of thyroid function tests during follow up. It was a prospective non randomized control study of 100 patients of head and neck cancer receiving radiotherapy for duration of 1 year. Thyroid stimulating hormone and T3 and T4 estimations were done at baseline and at 3 and 9 months following radiotherapy. Out of 100 patients, 72 (72%) were males and 28 (28%) were females. All the patients received radiation to the neck to a dose of > 30 Gy. 35 patients received concurrent chemotherapy. 11 patients were found to have subclinical hypothyroidism while 32 patients developed significant clinical hypothyroidism (P value of 0.001). Thus a total of 43 patients developed radiation induced hypothyroidism. 20 of the 32 patients who developed clinical hypothyroidism were in the age group of 41-50 years. 11 of 32 patients who developed clinical hypothyroidism received chemoradiation while rest 21 received radiotherapy alone. Mean period for developing radiation induced hypothyroidism was 4.5 months. Hypothyrodism (clinical or subclinical) is an under recognised morbidity of external radiation to the neck which is seen following a minimum dose of 30 Gy to the neck. Recognising hypothyroidism (clinical or subclinical) early and treating it prevents thyroid dysfunction related complications. Hence, thyroid function tests should be made routine during follow up in all patients undergoing radiotherapy.

The Relationship Between Occupational Exposure to Low-dose Ionizing Radiation and Changes in Thyroid Hormones in Hospital Workers

BACKGROUND

The effects of ionized radiation on the thyroid have been extensively studied. However, most studies have focused on high-dose radiation received accidentally or through therapy, and few were on low-dose occupational exposure.

METHODS

Using a retrospective cohort study design, we collected health examination reports from employees who worked on jobs with occupational exposure to radiation at a hospital to evaluate possible changes in the serum thyroid hormones and determine whether there is a dose-response effect. After excluding those with diseases that may affect thyroid function and who were pregnant at any given examination during the study periods we followed the remaining 326 workers for 12 years and evaluated the associations between radiation exposure and changes in serum thyroid hormones using the generalized estimating equation for repeated measures. Data from an external comparison cohort were used to adjust for changes over time.

RESULTS

We observed declines in triiodothyronine (T3) and thyroxine (T4) over the study period, but not in thyroid-stimulating hormone (TSH). In addition, we found negative dose-response relationships between exposure duration and declines in the serum levels of T3 (a change of -0.037 ng/ml/year after adjusting for sex and age at the beginning of follow-up; 95% confidence interval [CI] = -0.042, -0.032 ng/ml/year) and T4 (-0.115 µg/dl/year; 95% CI = -0.140, -0.091 µg/dl/year). We also observed an increase in the TSH level (0.683 µIU/ml/year; 95% CI = 0.151, 1.214 µIU/ml/year) after the ninth year of follow-up.

CONCLUSIONS

We concluded that despite low exposure doses, occupational exposure to ionizing radiation in healthcare workers still may be associated with the declines in the serum levels of T3 and T4.

The Benefit of Adjuvant Radiation in Surgically-Treated T1-2 N1 Oropharyngeal Squamous Cell Carcinoma

Importance

The benefit of adjuvant radiation in surgically treated T1‐2N1 oropharyngeal cancer without adverse pathologic features remains unclear

Objectives

To compare population‐level survival outcomes in surgically‐treated T1‐2N1 oropharyngeal squamous cell carcinoma (OPSCC) with and without the use of adjuvant radiation.

Study Design

Retrospective population‐based study using the Surveillance, Epidemiology, and End Results (SEER) registry data from 1998–2011.

Setting

Population‐level study.

Participants

Patients with T1‐2N1 OPSCC treated with surgical resection and neck dissection with or without adjuvant radiation.

Intervention(s) for Clinical Trials or Exposure(s) for observational studies

The use of postoperative adjuvant radiation.

Main Outcome(s) and Measures

Overall and disease‐specific survival.

Results

Radiation was utilized in 74% of patients and was positively associated with extracapsular extension and well‐differentiated histology. The use of radiation was associated with improved mean overall survival (124 v. 108 months, p=0.023) and a non‐significant increase in mean disease‐specific survival (138 v. 131 months, p=0.053).

Conclusions and Relevance

The use of adjuvant radiation is associated with improved survival in surgically‐treated T1‐2N1 squamous cell carcinoma of the oropharynx with unknown HPV status.

Level of Evidence

IV

AMERICAN ASSOCIATION OF CLINICAL ENDOCRINOLOGISTS AND AMERICAN COLLEGE OF ENDOCRINOLOGY POSITION STATEMENT ON THYROID DYSFUNCTION CASE FINDING

Hypothyroidism and hyperthyroidism can be readily diagnosed and can be treated in a safe, cost-effective manner. Professional organizations have given guidance on how and when to employ thyroid-stimulating hormone testing for the detection of thyroid dysfunction. Most recently, the United States Preventive Services Task Force did not endorse screening for thyroid dysfunction based on a lack of proven benefit and potential harm of treating those with thyroid dysfunction, which is mostly subclinical disease. The American Association of Clinical Endocrinologists (AACE) is concerned that this may discourage physicians from testing for thyroid dysfunction when clinically appropriate. Given the lack of specificity of thyroid-associated symptoms, the appropriate diagnosis of thyroid disease requires biochemical confirmation. The Thyroid Scientific Committee of the AACE has produced this White Paper to highlight the important difference between screening and case-based testing in the practice of clinical medicine. We recommend that thyroid dysfunction should be frequently considered as a potential etiology for many of the nonspecific complaints that physicians face daily. The application and success of safe and effective interventions are dependent on an accurate diagnosis. We, therefore, advocate for an aggressive case-finding approach, based on identifying those persons most likely to have thyroid disease that will benefit from its treatment.

Hypothyroidism in patients treated with radiotherapy for head and neck carcinoma: standardised long-term follow-up study

OBJECTIVE

Hypothyroidism is a common complication when radiotherapy is part of the treatment for head and neck tumours. This study aimed to show the incidence of hypothyroidism and possible risk factors in these patients.

METHODS

Factors related to the population, tumour, treatment and occurrence of hypothyroidism were analysed in 241 patients diagnosed with head and neck carcinoma.

RESULTS

Approximately 53 per cent of patients were diagnosed with radiation-induced hypothyroidism. Its occurrence was related to: tumour location, laryngeal surgery type, neck dissection type, post-operative complications, cervical radiotherapy and radiotherapy unit type (linear particle accelerator or telecobalt therapy technology).

CONCLUSION

Control of thyroid function should be standardised for several years after treatment, particularly in patients with risk factors, such as those treated with telecobalt therapy, those with post-operative complications and for whom the thyroid parenchyma is included in the irradiated area (laryngeal or pharyngeal location and bilateral cervical radiation).

Sonographic appearance of thyroid glands in patients treated with intensity-modulated radiotherapy or conventional radiotherapy for nasopharyngeal carcinoma

BACKGROUND

This study aimed to investigate the sonographic appearances of the thyroid glands in nasopharyngeal carcinoma (NPC) patients whose cervical lymph nodes were treated with conventional radiotherapy (RT) or intensity-modulated radiotherapy (IMRT). The post-RT sonographic appearances of the thyroid glands in NPC patients were also correlated with the thyroid function.

METHODS

One hundred and three NPC patients who had completed RT of cervical lymph nodes using the anterior cervical field, 30 NPC patients who had completed RT of cervical lymph nodes using IMRT, and 61 healthy subjects were included in the study. Thyroid glands were sonographically assessed for their size, echogenicity, vascularity, and internal architecture. Thyroid function tests were also performed on each subject.

RESULTS

In comparison with the patients with abnormal thyroid function, the thyroid glands of the patients with normal thyroid function tended to be homogeneous and to have greater volume and echogenicity index (p < 0.05). Compared with those of the healthy subjects, the thyroid glands of patients previously treated with IMRT and those treated with the anterior cervical field showed significantly lower thyroid volume, lower incidence and number of nodules, and higher vascularity index (p < 0.05).

CONCLUSIONS

The patient's history of previous RT should be taken into consideration in the sonographic examination of the thyroid gland post-RT. © 2014 Wiley Periodicals, Inc. J Clin Ultrasound 43:210-223, 2015.

Thyroid dysfunction after intra-arterial chemotherapy for hypopharyngeal and laryngeal cancer

OBJECTIVE

Hypothyroidism is a late side effect after curative radiotherapy in the head and neck region. Superselective intra-arterial chemotherapy (SSIAC), when combined with radiation (SSIAC-R), shows higher control potential for locally advanced head and neck cancers, which is attributable to a delivery of higher concentrations of chemotherapeutic agents. However, it could enhance damages in the normal tissues. Hypothyroidism is a late adverse effect after curative radiotherapy in the head and neck region. This study focuses on the toxic effect of treatment modality for thyroid function.

METHODS

A retrospective analysis was performed to examine patients' thyroid function after SSIAC-R for laryngeal and hypopharyngeal cancer.

RESULTS

Hypothyroidism was observed in 21 (77.8%) of 27 patients receiving SSIAC-R, 4 (33.3%) of 12 patients treated with radiation alone, and 7 (41.1%) of 17 who underwent systemic chemoradiotherapy. The number of administered vessels significantly correlated with the incidence of developing hypothyroidism among SSIAC-R treated patients (P=0.03).

CONCLUSION

Concurrent setting of SSIAC with radiation significantly raises the possibility of hypothyroidism. Therefore, monitoring late complications of therapeutic procedures is essential during follow-up visits.

Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association

OBJECTIVE

Hypothyroidism has multiple etiologies and manifestations. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions. This paper describes evidence-based clinical guidelines for the clinical management of hypothyroidism in ambulatory patients.

METHODS

The development of these guidelines was commissioned by the American Association of Clinical Endocrinologists (AACE) in association with American Thyroid Association (ATA). AACE and the ATA assembled a task force of expert clinicians who authored this article. The authors examined relevant literature and took an evidence-based medicine approach that incorporated their knowledge and experience to develop a series of specific recommendations and the rationale for these recommendations. The strength of the recommendations and the quality of evidence supporting each was rated according to the approach outlined in the American Association of Clinical Endocrinologists Protocol for Standardized Production of Clinical Guidelines-2010 update.

RESULTS

Topics addressed include the etiology, epidemiology, clinical and laboratory evaluation, management, and consequences of hypothyroidism. Screening, treatment of subclinical hypothyroidism, pregnancy, and areas for future research are also covered.

CONCLUSIONS

Fifty-two evidence-based recommendations and subrecommendations were developed to aid in the care of patients with hypothyroidism and to share what the authors believe is current, rational, and optimal medical practice for the diagnosis and care of hypothyroidism. A serum thyrotropin is the single best screening test for primary thyroid dysfunction for the vast majority of outpatient clinical situations. The standard treatment is replacement with L-thyroxine. The decision to treat subclinical hypothyroidism when the serum thyrotropin is less than 10 mIU/L should be tailored to the individual patient.

Incidence of primary hypothyroidism in patients exposed to therapeutic external beam radiation, where radiation portals include a part or whole of the thyroid gland

INTRODUCTION

Hypothyroidism is a known consequence of external-beam radiotherapy to the neck encompassing a part or whole of the thyroid gland. In this non-randomized prospective study, we have tried to evaluate the response of the thyroid gland to radiation by assessing thyroid function before irradiation and at regular intervals after irradiation.

AIMS AND OBJECTIVES

THE AIM OF THIS STUDY WERE TO ASSESS IN THE CANCER PATIENTS, WHO WERE EXPOSED TO THE THERAPEUTIC EXTERNAL BEAM RADIATION, WHERE RADIATION PORTALS INCLUDE A PART OR WHOLE OF THE THYROID GLAND: the incidence of primary hypothyroidism, the time required to become hypothyroid, any relation between the total dose for the development of hypothyroidism, and whether there are any patient or treatment-related factors that are predictive for the development of hypothyroidism, including the use of concurrent chemotherapy.

MATERIALS AND METHODS

This non-randomized, prospective study was conducted for a period of 2 years in which thyroid function was assessed in 59 patients (cases) of head and neck cancer, breast cancer, lymphoma patients and other malignancies, who had received radiotherapy to the neck region. 59 euthyroid healthy patients (controls) were also taken, who had not received the neck irradiation. These patients/controls were assessed periodically for 2 years.

RESULTS

The incidence of hypothyroidism after external beam radiation therapy (EBRT) to neck where radiation portals include part or whole of the thyroid gland was 16.94%, seven cases had subclinical hypothyroidism (11.86%) and three cases had clinical hypothyroidism (5.08%). Mean time for development of hypothyroidism was 4.5 months. There was no effect of age, gender, primary tumor site, radiation dose and chemotherapy, whether neoadjuvant or concurrent with the development of hypothyroidism.

CONCLUSION

In summary, we found that thyroid dysfunction is a prevalent, yet easily treatable source of morbidity in patients undergoing radiation therapy to neck where radiation portals include a part or whole of the thyroid gland.

Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association

BACKGROUND

Hypothyroidism has multiple etiologies and manifestations. Appropriate treatment requires an accurate diagnosis and is influenced by coexisting medical conditions. This paper describes evidence-based clinical guidelines for the clinical management of hypothyroidism in ambulatory patients.

METHODS

The development of these guidelines was commissioned by the American Association of Clinical Endocrinologists (AACE) in association with American Thyroid Association (ATA). AACE and the ATA assembled a task force of expert clinicians who authored this article. The authors examined relevant literature and took an evidence-based medicine approach that incorporated their knowledge and experience to develop a series of specific recommendations and the rationale for these recommendations. The strength of the recommendations and the quality of evidence supporting each was rated according to the approach outlined in the American Association of Clinical Endocrinologists Protocol for Standardized Production of Clinical Guidelines-2010 update.

RESULTS

Topics addressed include the etiology, epidemiology, clinical and laboratory evaluation, management, and consequences of hypothyroidism. Screening, treatment of subclinical hypothyroidism, pregnancy, and areas for future research are also covered.

CONCLUSIONS

Fifty-two evidence-based recommendations and subrecommendations were developed to aid in the care of patients with hypothyroidism and to share what the authors believe is current, rational, and optimal medical practice for the diagnosis and care of hypothyroidism. A serum thyrotropin is the single best screening test for primary thyroid dysfunction for the vast majority of outpatient clinical situations. The standard treatment is replacement with L-thyroxine. The decision to treat subclinical hypothyroidism when the serum thyrotropin is less than 10 mIU/L should be tailored to the individual patient.

How common is hypothyroidism after external radiotherapy to neck in head and neck cancer patients?

PURPOSE

To identify the occurrence of clinical and subclinical hypothyroidism among head and neck cancer patients receiving radiation to the neck and to justify routine performing of thyroid function tests during follow-up.

MATERIALS AND METHODS

This is a prospective nonrandomized study of 45 patients of head and neck cancer, receiving radiotherapy (RT). Thyroid stimulating hormone and T4 estimations were done at baseline and at 4 months and 9 months following RT.

RESULTS

Of the 45 patients, 37(82.2 %) were males and eight (17.8 %) were females. All patients received radiation to the neck to a dose of >40Gy. 35.6% received concurrent chemotherapy. Two patients underwent prior neck dissection. Fourteen patients (31.1%) were found to have clinical hypothyroidism (P value of 0.01). Five (11.1%) patients were found to have subclinical hypothyroidism with a total 19 of 45 (42.2%) patients developing radiation-induced hypothyroidism. Nine of 14 patients with clinical hypothyroidism were in the age group of 51 to 60 years (P=0.0522). Five of 16 patients who received chemoradiation and nine of 29 who received RT alone developed clinical hypothyroidism. Above 40 Gy radiation dose was not a relevant risk factor for hypothyroidism.

CONCLUSION

Hypothyroidism (clinical or subclinical) is an under-recognized morbidity of external radiation to the neck which is seen following a minimum dose of 40 Gy to neck. Recognizing hypothyroidism (clinical or subclinical) early and treating it prevents associated complications. Hence, thyroid function tests should be made routine during follow-up.

Evaluation of multiple-atlas-based strategies for segmentation of the thyroid gland in head and neck CT images for IMRT

Segmenting the thyroid gland in head and neck CT images is of vital clinical significance in designing intensity-modulated radiation therapy (IMRT) treatment plans. In this work, we evaluate and compare several multiple-atlas-based methods to segment this structure. Using the most robust method, we generate automatic segmentations for the thyroid gland and study their clinical applicability. The various methods we evaluate range from selecting a single atlas based on one of three similarity measures, to combining the segmentation results obtained with several atlases and weighting their contribution using techniques including a simple majority vote rule, a technique called STAPLE that is widely used in the medical imaging literature, and the similarity between the atlas and the volume to be segmented. We show that the best results are obtained when several atlases are combined and their contributions are weighted with a measure of similarity between each atlas and the volume to be segmented. We also show that with our data set, STAPLE does not always lead to the best results. Automatic segmentations generated by the combination method using the correlation coefficient (CC) between the deformed atlas and the patient volume, which is the most accurate and robust method we evaluated, are presented to a physician as 2D contours and modified to meet clinical requirements. It is shown that about 40% of the contours of the left thyroid and about 42% of the right thyroid can be used directly. An additional 21% on the left and 24% on the right require only minimal modification. The amount and the location of the modifications are qualitatively and quantitatively assessed. We demonstrate that, although challenged by large inter-subject anatomical discrepancy, atlas-based segmentation of the thyroid gland in IMRT CT images is feasible by involving multiple atlases. The results show that a weighted combination of segmentations by atlases using the CC as the similarity measure slightly outperforms standard combination methods, e.g. the majority vote rule and STAPLE, as well as methods selecting a single most similar atlas. The results we have obtained suggest that using our contours as initial contours to be edited has clinical value.

Risk factors for radiation-induced hypothyroidism: a literature-based meta-analysis

BACKGROUND

A systematic overview and meta-analysis of studies reporting data on hypothyroidism (HT) after radiation therapy was conducted to identify risk factors for development of HT.

METHODS

Published studies were identified from the PubMed and Embase databases and by hand-searching published reviews. Studies allowing the extraction of odds ratios (OR) for HT in 1 or more of several candidate clinical risk groups were included. A meta-analysis of the OR for development of HT with or without each of the candidate risk factors was performed. Furthermore, studies allowing the extraction of radiation dose-response data were identified for a meta-analysis of the dose-response curve.

RESULTS

Female gender (OR = 1.6; 95% confidence interval [CI], 1.3-1.9; P < .00001), surgery involving the thyroid gland (OR = 8.3; 95% CI, 5.7-12.0; P < .00001), or other neck surgery (OR = 1.7; 95% CI, 1.16-2.42; P = .006) were associated with a higher risk of HT. Caucasians were at higher risk of HT than African Americans (OR = 4.8; 95% CI, 2.8-8.5; P < .00001). The data showed association between lymphangiography and HT but with evidence of publication bias. There was a radiation dose-response relation with a 50% risk of HT at a dose of 45 Gy but with considerable variation in the dose response between studies. Chemotherapy and age were not associated with risk of HT in this analysis.

CONCLUSIONS

Several clinical risk factors for HT were identified. The risk of HT increases with increasing radiation dose, but the specific radiation dose response varies between the studies. The most likely cause of this heterogeneity is differences in follow-up between studies.

The incidence of thyroid dysfunction following radiotherapy for early stage carcinoma of the larynx

External beam radiotherapy is currently the commonest form of treatment for early laryngeal cancer (T1/2) and thyroid dysfunction is a well recognised complication of this treatment. Overt hypothyroidism is a specific clinical disorder which in most patients will be recognized and treated. The problems associated with subclinical hypothyroidism (elevated TSH with normal T4), however, are only now being recognized and their management is to some extent still controversial. The aims of our study are to determine the incidence of clinical and subclinical hypothyroidism in those who have been treated solely with curative radiotherapy for early laryngeal cancer. We performed a retrospective observational study encompassing all patients who underwent curative radiotherapy for T1/T2 laryngeal cancer between 1998 and 2002. 33 patients were identified (mean 66.85 years, range 48-93). 19 patients had T1 lesions (58%), 14 had T2 lesions (42%) and 27 were N0 (82%). 23 patients were euthyroid post treatment (70%), 2 became overtly hypothyroid (6%) and 8 developed subclinical hypothyroidism (24%). There was no association between tumour stage (p = 0.97), nodal stage (p = 0.46) and thyroid status, however, there was an association between increasing age and deteriorating thyroid function (p = 0.01). Our study showed that of patients with early laryngeal cancers treated solely with curative radiotherapy 24% developed subclinical hypothyroidism and 6% were overtly hypothyroid (Elevated TSH and reduced T4). We feel patients should receive regular thyroid function testing following completion of treatment and should be adequately counselled on the risk of thyroid dysfunction following radiotherapy at pre-treatment visits.

Thyroid dysfunction in patients treated with radiotherapy for neck

PURPOSE

The aim of the present study was to retrospectively evaluate the early and late changes in thyroid dysfunction after radiation therapy for head and neck cancer either with or without surgery.

PATIENTS AND METHODS

Sixty-three patients receiving neck irradiation including the thyroid gland were recruited in the study. Thirty-six patients had undergone either a functional or radical neck dissection, and radiotherapy was the primary treatment in 27 patients.

RESULTS

Of 63 patients, 24 (38%) were diagnosed with hypothyroidism (HT), 8 (12.7%) with clinical HT, and 16 (25.4%) with subclinical HT. The median time to the development of clinical HT was 15 months (range, 0-36 months) and subclinical HT was 3 months (range, 0-24 months). Eleven (17.5%) of the patients were diagnosed with subclinical hyperthyroidism. The median time to the development of the subclinical hyperthyroidism was 0 months (completion of radiation therapy) (range, 0-3 months). Univariate analyses of age, smoking history, neck RT dose, clinical stage, concurrent chemotherapy, and surgery failed to identify a clinically relevant risk factor for HT. Univariate analysis of clinical HT revealed that the elevated pre-radiation therapy thyroid-stimulating hormone level was significant factor (P = 0.021).

CONCLUSION

HT associated with head and neck irradiation. We recommend that thyroid function should be evaluated periodically in patients who have undergone neck radiation.

Hypothyroidism as a consequence of intensity-modulated radiotherapy with concurrent taxane-based chemotherapy for locally advanced head-and-neck cancer

PURPOSE

To conduct a retrospective review of 168 consecutively treated locally advanced head-and-neck cancer (LAHNC) patients treated with intensity-modulated radiotherapy (IMRT)/chemotherapy, to determine the rate and risk factors for developing hypothyroidism.

METHODS AND MATERIALS

Intensity-modulated radiotherapy was delivered in 33 daily fractions to 69.3 Gy to gross disease and 56.1 Gy to clinically normal cervical nodes. Dose-volume histograms (DVHs) of IMRT plans were used to determine radiation dose to thyroid and were compared with DVHs using conventional three-dimensional radiotherapy (3D-RT) in 10 of these same patients randomly selected for replanning and with DVHs of 16 patients in whom the thyroid was intentionally avoided during IMRT. Weekly paclitaxel (30 mg/m(2)) and carboplatin area under the curve-1 were given concurrently with IMRT.

RESULTS

Sixty-one of 128 evaluable patients (47.7%) developed hypothyroidism after a median of 1.08 years after IMRT (range, 2.4 months to 3.9 years). Age and volume of irradiated thyroid were associated with hypothyroidism development after IMRT. Compared with 3D-RT, IMRT with no thyroid dose constraints resulted in significantly higher minimum, maximum, and median dose (p < 0.0001) and percentage thyroid volume receiving 10, 20, and 60 Gy (p < 0.05). Compared with 3D-RT, IMRT with thyroid dose constraints resulted in lower median dose and percentage thyroid volume receiving 30, 40, and 50 Gy (p < 0.005) but higher minimum and maximum dose (p < 0.005).

CONCLUSIONS

If not protected, IMRT for LAHNC can result in higher radiation to the thyroid than with conventional 3D-RT. Techniques to reduce dose and volume of radiation to thyroid tissue with IMRT are achievable and recommended.

Thyroid Dysfunction after Combined therapy for Laryngeal Cancer: A Prospective Study

Objective

The purpose of this study was to assess the incidence of the thyroid dysfunction in a group of patients treated with laryngectomy and radiotherapy for larynx cancer and to analyze the risk factors related to the development of hypothyroidism.

Study Design

This was a prospective study conducted in a tertiary center hospital.

Subjects and Methods

Thyroid function tests have been applied to 75 patients treated with surgery and radiotherapy preoperatively, before radiotherapy, and postoperatively. Risk factors have been analyzed by carrying out a multivariate analysis.

Results

All the patients were men with the mean age of 59.4 and an average follow-up of 28.6 months. The incidence of hypothyroidism was 49.3 percent. The average time to detection of hypothyroidism was 6 months after the completion of treatment. Radiotherapy dose, type of laryngectomy, extent of neck dissection, implementation of thyroid lobectomy, and presence of thyroiditis in specimens were risk factors for thyroid dysfunction.

Conclusions

It is important to check the thyroid function periodically in these patients especially with risk factor to obtain early diagnosis and appropriate treatment.

Hypothyroidism when the thyroid is included only in the low neck field during head and neck radiotherapy

OBJECTIVE

The minimum dose required to electively irradiate all of part of the low neck for squamous cell carcinoma of the oropharynx is 50 Gy in 25 fractions or its radiobiological equivalent. The purpose of our study is to determine the incidence of hypothyroidism when the thyroid is treated only in the low-neck radiotherapy (RT) field to approximately 50 Gy.

METHODS AND MATERIALS

390 patients with oropharyngeal carcinoma received RT between 1990 and 2000, had no prior thyroid disease or surgery, and had RT involving the standard anterior low-neck field including the thyroid with a dose equivalent to 50 Gy at 2Gy/fx with or without a boost to a portion of the field to 60 to 70 Gy. The end point was hypothyroidism defined as thyroid stimulating hormone (TSH) above the upper limit of the normal range.

RESULTS

As we did not routinely monitor TSH during this study, it was obtained in 169 of 390 patients. Median follow-up on all 390 patients was 6.1 years. The incidence of hypothyroidism was calculated for 2 groups: 169 patients with TSH data and the total population of 390 patients. For both analyses, patients were censored at last follow-up if the TSH level was normal, or if TSH was not checked. The incidence of hypothyroidism at 5 years was 31% for all 390 patients and 54% for the subset of 169 patients with TSH data. Adjuvant chemotherapy and/or planned neck dissection may be associated with a small increased risk of hypothyroidism.

CONCLUSIONS

Including the thyroid in the low-neck field to 50 Gy results in hypothyroidism in 30% to 50% of patients at 5 years, suggesting that the threshold for this complication is <50 Gy.

Thyroid Function Should Be Monitored Following Radiotherapy to the Low Neck

The purpose of this study was to determine whether the incidence of hypothyroidism following radiotherapy (RT) to the low neck is high enough to justify the routine monitoring of thyroid function in asymptomatic patients. A retrospective study of 504 patients with head and neck cancer whose RT fields included the thyroid gland was conducted. Patients were treated either with definitive or postoperative RT. Hypothyroidism was defined as a thyroid stimulating hormone (TSH) level > or =4.5 mIU/L, regardless of whether the patient had clinical symptoms. Of the 504 total patients, 206 had a serum TSH level checked at some point posttreatment. If we assume that patients who had no data did not have hypothyroidism, the actuarial freedom from hypothyroidism in the entire group was 78% at 5 years and 51% at 10 years. Of the 206 patients who had a documented posttreatment TSH, the actuarial freedom from hypothyroidism was 58% at 5 years and 26% at 10 years. Univariate analysis and multivariate analysis confirmed treatment modality to be a significant predictive factor. Definitive initial surgery that removed part of the thyroid gland increased the risk of developing hypothyroidism. Overall stage was also predictive on multivariate analysis. Head and neck irradiation results in biochemical hypothyroidism in at least 50% of patients. Thyroid function should be tested on a regular basis following RT to the low-neck region. Serum TSH should be checked every 6 months for the first 5 years and yearly thereafter. Thyroid hormone replacement should be initiated in any patient with a TSH of more than 4.5 mIU/L.

Long-term incidence of hypothyroidism after radiotherapy in patients with head-and-neck cancer

PURPOSE

To determine the long-term incidence of postirradiation hypothyroidism (HT) in patients with head-and-neck cancer.

METHODS AND MATERIALS

The incidence of overt HT was assessed prospectively in 391 patients with nonthyroid head-and-neck cancer admitted for radiotherapy (RT) consecutively between 1990 and 1996. Eighty-three patients were excluded from the analysis because of known thyroid disease before treatment (n = 27), no RT was given (n = 15), or inadequate follow-up (n = 41). Overt HT was defined as increased thyroid-stimulating hormone (TSH) in combination with decreased fT4/T4 or in combination with initiation of thyroxine replacement therapy.

RESULTS

With a median follow-up of 4.2 years (range, 3 months to 10.9 years) for 308 evaluable patients, the 5- and 10-year Kaplan-Meier actuarial risks of HT were 20% and 27%, respectively. The median time until development of HT was 1.8 years (3 months to 8.1 years). Multivariate analysis showed that patients with bilateral RT to the neck had a higher risk of HT in comparison with unilateral neck RT (relative hazard, 0.37; p = 0.02). The addition of surgery to RT increased the overall risk of HT (p < 0.001); and if surgery involved the thyroid gland, the relative hazard was 4.74 (p < 0.001). For an elevated pre-RT TSH value, the relative hazard was 1.58 (p < 0.001).

CONCLUSION

The incidence of overt HT after locoregional RT for nonthyroid head-and-neck cancer continues to increase with time, even after long-term follow-up. We recommend life-long TSH testing in these patients.

Radiotherapy-induced thyroid disorders

Despite their specific functional consequences, radiotherapy-induced thyroid abnormalities remain under-estimated and underreported. These sequelae may include primary or central hypothyroidism, thyroiditis, Graves' disease, euthyroid Graves' ophthalmopathy, benign adenomas, multinodular goitre and radiation-induced thyroid carcinoma. Primary hypothyroidism, the most common radiation-induced thyroid dysfunction, affects 20-30% of patients administered following curative radiotherapy to the neck region, with approximately half of the events occurring within the first 5 years after therapy. The relative risk of radiation-induced cancer (mainly well-differentiated tumours) is 15-53-fold higher than in non-irradiated population. The aetiology of radiation-induced thyroid injury includes vascular damage, parenchymal cell damage and auto-immune reactions. Total radiotherapy dose, irradiated volume of the thyroid gland, and the extent of prior thyroid resection are among the most important factors associated with the risk of hypothyroidism. The contribution of other treatment modalities (chemotherapy, endocrine therapy) as well as patient- and tumour-related factors is less clear. Reduction in radiation dose to the thyroid gland and hypothalamic/pituitary complex should be attempted whenever possible. New radiotherapy techniques, such as stereotactic radiosurgery, three-dimensional conformal irradiation, intensity modulated radiotherapy and proton therapy allow generally better dose distribution with lower dose to the non-target organs. The diagnostic approach to thyroid radiation injury includes baseline thyroid function assays in all patients undergoing thyroid or parasellar irradiation. Recommended follow-up procedures include at least annual evaluation with a history for symptoms of thyroid dysfunction, clinical examination, and measurement of thyroid hormones and thyrotropin. Management of overt hypothyroidism is based on hormone replacement therapy. Thyroid hormone therapy is also recommended in cases of subclinical hypothyroidism. Treatment of other radiation-induced thyroid disorders (thyroiditis, Graves' disease, thyroid cancer) is similar to that employed in spontaneously occurring conditions. Further improvements in radiotherapy techniques and progress in endocrine diagnostics and therapy may allow better prevention and management of radiation-related thyroid injury.

Thyroid Function Studies in Patients with Cancer of the Larynx: Preliminary Evaluation

OBJECTIVE: Our goal was to evaluate thyroid function before and after surgery only or radiotherapy plus surgery for laryngeal neoplasms.

STUDY DESIGN AND SETTING: The study group consisted of a total of 30 patients with laryngeal cancer (22 treated with surgery only and 8 treated with surgery plus radiotherapy) who were evaluated by ultrasensitive thyroid-stimulating hormone, free T4, and antithyroid antibodies both preoperatively and at 6 and 12 months after surgery.

RESULTS: All patients had normal thyroid function before treatment (1 patient had elevated antithyroid autoantibodies); after 1 year, 4 (13.34%) patients were hypothyroid. In 3 patients, it was sub-clinical (ie, elevated thyroid-stimulating hormone with normal free T4), and in 1 patient, it was symptomatic.

CONCLUSION: Our preliminary data suggest that hypothyroidism occurs in a small but substantial proportion of patients undergoing surgery with or without adjuvant radiotherapy for laryngeal cancer.

SIGNIFICANCE: Thyroid hormone dosing should be routinely included in the assessment of patients with laryngeal cancer, because it is simple and inexpensive and may allow the early diagnosis and management of hypothyroidism. (Otolaryngol Head Neck Surg 2003;129:733-8.)

Definitive radiotherapy for squamous carcinoma of the larynx

Definitive radiotherapy for T1 or T2 laryngeal carcinoma offers good local control and quality of voice. Recent clinical trials with hyperfractionated radiotherapy and concurrent chemoradiotherapy demonstrated improved rates of local control for advanced laryngeal cancer treated with primary radiotherapy and provides the opportunity for organ preservation. The use of amifostine and pilocarpine may prevent or ameliorate radiation-induced xerostomia. Recent advances in 3-D conformal radiotherapy and IMRT lead to a better dose distribution for sparing normal organs while treating target volumes with full dose.

Hypothyroidism: a frequent event after radiotherapy and after radiotherapy with chemotherapy for patients with head and neck carcinoma

BACKGROUND

The incidence of hypothyroidism was assessed retrospectively from a data base of 155 patients with head and neck carcinoma who were treated at the Cleveland Clinic Foundation between 1990 and 1997.

METHODS

One hundred patients were randomized between radiotherapy (RT) (66-72 grays in single daily fractions) and RT with concurrent chemotherapy (CT) using 5-fluorouracil and cisplatin. An additional 55 patients received RT and CT without randomization. Primary site surgery was performed for tumor persistence or recurrence and included a thyroidectomy in nine patients. These nine patients, along with three patients who had hypothyroidism prior to treatment, were excluded from the analysis. At regular intervals after the completion of treatment, all patients were evaluated for the development of hypothyroidism, defined as a serum thyroid-stimulating hormone (TSH) level > 5.5 microU/mL.

RESULTS

With a median follow-up for 143 evaluable patients of 4.4 years (range, 1.5-9.2 years), the 5-year Kaplan-Meier projected incidence rate of hypothyroidism was 48%, and the 8-year projected incidence rate was 67%. The median time to the development of hypothyroidism was 1.4 years (range, 0.3-7.2 years). The likelihood of developing hypothyroidism could not be predicted according to age, gender, primary site, tumor or lymph node status, overall stage, RT dosage to the primary site or to the neck, or inclusion of CT in the treatment plan. Only race proved predictive, with no African-American patients developing hypothyroidism (P = 0.02).

CONCLUSIONS

The authors conclude that the incidence rate of hypothyroidism after patients undergo RT for head and neck carcinoma is higher than generally reported and that TSH screening after treatment appears justified.

Hypothyroidism after radiotherapy for laryngeal cancer

PURPOSE

To investigate the incidence of hypothyroidism after radiotherapy of laryngeal cancer, including the possible factors that could predict the onset of hypothyroidism.

MATERIALS AND METHODS

We report this study on patients treated by radiotherapy as part of the treatment for laryngeal cancer in the Department of Oncology in Eastern Finland. Sixty-five males and seven females were treated with radiotherapy between 1974-1995.Thyroid function was determined by measuring serum thyroid stimulating hormone, and serum free thyroxine (FT4). The studied risk factors for hypothyroidism included age, treatment modalities, radiation dose and energy, height of the radiation field, and follow-up time.

RESULTS

Hypothyroidism was detected in 17 (24%) of the 72 patients. Hypothyroidism was clinically unsuspected in all but one patient. Hypothyroidism was more common, if the height of the radiation field was >/=7 cm, or the patient had been operated. Hypothyroidism was less common if less than a half of the thyroid bed was irradiated.

CONCLUSION

The detection of hypothyroidism clinically is difficult, and the rate of hypothyroidism warrants routine assessment of thyroid function after irradiation of laryngeal cancer.

Hypothyroidism after therapy for larynx and pharynx carcinoma

Early detection of local and regional recurrence is the main goal during follow-up of patients with larynx and pharynx cancer. Hypothyroidism occurring in those patients stays frequently undiagnosed as screening for hypothyroidism is not part of the routine follow-up. This study was performed to assess the prevalence of hypothyroidism in these patients. We included 120 patients (106 male, 14 female) with larynx or pharynx cancer treated more than 2 months earlier (mean = 41 months) in the study. Cancer treatment consisted of either surgery (n = 44), radiotherapy (n = 15), or surgery combined with postoperative radiotherapy (n = 61). In all patients, thyroid function studies (thyrotropin [TSH], free triiodothyronine [FT3], and free thyroxine [FT4]) were performed. Twenty-six of all patients (22%) were hypothyroid; in two patients hypothyroidism was diagnosed postoperatively and these two patients were on replacement therapy with thyroid hormones. The highest rate of hypothyroidism (34%) was present in patients treated with surgery combined with radiotherapy, whereas among patients treated with surgery only 7% were hypothyroid (p < 0.001). There was no difference in the duration of follow-up between therapy and inclusion in the study between those two groups. Two of 15 patients treated only with radiotherapy were diagnosed hypothyroid, but in this group the latency was shorter (p < 0.05). The results indicate that thyroid function studies should be routinely performed in the follow-up of head and neck cancer patients, especially if radiotherapy was part of the treatment.

[Late effects of ionizing radiations on the thyroid gland]

The thyroid is the purest endocrine gland in the body and is likely to produce clinically significant abnormalities after external radiotherapy. Functional clinical modifications after direct irradiation exceeding 30 Gy are essentially related to hypothyroidism which may be clinically overt or subclinical with normal serum free thyroxine levels and high thyrotropin concentrations; the risk of hyperthyroidism, silent thyroiditis and Hashimoto's disease is also increased. Secondary hypothyroidism related to irradiation of the hypothalamus and the pituitary gland may arise with doses over 40-50 Gy following treatment for brain and nasopharyngeal tumors--Morphological glandular modifications induced by radiotherapy are responsible for the appearance of benign adenomas, more rarely cystic degenerations and specially well differentiated papillary or follicular carcinomas among children and adults. After irradiation during childhood for benign or malignant tumors, thyroid cancers are more frequent, higher for younger children, and the relative excess risk is increased from 15.6-to 53-fold; tumors can belatedly occur, more than 35 years after initial therapy. Thereby, in order to limit excess morbidity, it is evident that long term supervision with careful clinical and biological evaluations is necessary for patients who previously received neck, upper mediastinum and pituitary radiation therapy.

Hypothyroidism after external radiotherapy for head and neck cancer

PURPOSE

To study the development of thyroid hypofunction in patients with head and neck cancers admitted for external radiotherapy.

METHODS AND MATERIALS

Between November 1990 and July 1996, thyroid function was measured in 264 consecutive patients, where the entire thyroid gland or part of it was included in the target volume. The time to development of hypothyroidism (HT) was calculated from the start of the radiotherapy.

RESULTS

The median follow-up period was 19 months. Seventeen patients (6%) developed elevated serum thyroid-stimulating hormone levels with depressed (free) thyroxine levels (i.e., clinical HT). Elevated serum thyroid-stimulating hormone level with normal (free) thyroxine levels (i.e., chemical HT) developed in 57 (22%). The median time to clinical HT was 15 months (range: 7 to 32). The median time to chemical HT was also 15 months (range: 2 to 28). The actuarial risk of developing clinical or chemical HT 3 years after treatment was 15 and 40%, respectively. The incidence of chemical HT was significantly higher (p = 0.041) when the whole thyroid was included in the target volume compared to patients where only part of the thyroid was irradiated. The same trend was seen as regards clinical HT (p = 0.063). For those 20 patients who underwent laryngectomy, there was an increased risk of both chemical and clinical HT (p = 0.011 and 0.019, respectively). Increasing age was associated with an increased risk of chemical HT (p = 0.001), but not of clinical HT (p = 0.553). Sex, tumor site, radiation dose, and combination of radiotherapy and chemotherapy were not significant factors for thyroid hypofunction.

CONCLUSION

Depressed thyroid function is common after external radiotherapy for cancers of the head and neck. Routine testing for possible thyroid hypofunction should be included in the follow-up procedures, even many years after end of radiotherapy.

Postradiotherapy hypothyroidism: radiation dose response and chemotherapeutic radiosensitization at less than 40 Gy

To analyze our experience with iatrogenic hypothyroidism, we prospectively followed 84 patients, seen from 1984 to 1990, who had been diagnosed with either Hodgkin's disease (HD) or head and neck (H&N) carcinoma and subsequently treated with radiotherapy. Within these two diagnostic groups were subgroups whose treatment differed as to dose of therapeutic irradiation received or adjunctive use of chemotherapy. Approximately 50% of all patients and of each subgroup developed either clinical or subclinical hypothyroidism during follow-up. However, among the HD patients who received irradiation plus chemotherapy, a dose-response relationship below a threshold limit of dose received, probably 40 Gy, was observed.

Thyroid dysfunction following combined therapy for laryngeal carcinoma

The thyroid function of 27 patients who previously had carcinoma of the larynx treated by total laryngectomy with thyroid lobectomy was studied by measuring levels of thyroxine (T4) and thyroid stimulating hormone (TSH). Twenty-two of these patients also received external beam radiotherapy. Abnormal results were found in 45% (10 patients) of those who received combined therapy. Clinical hypothyroidism developed in two patients (9%) and subclinical hypothyroidism (elevated TSH) was seen in eight patients (36%). Eighty-eight per cent of those patients with subclinical hypothyroidism had low or low normal T4 levels. All the patients treated with surgery only had normal thyroid function. To prevent hypothyroidism and identify those at risk of developing hypothyroidism, post-operative testing of thyroid function should be carried out on a routine basis in patients receiving combined therapy for laryngeal cancer. In addition we recommend that patients with subclinical hypothyroidism who have had combined treatment should be treated with thyroxine to prevent the complications of this condition.

Thyroid dysfunction following radiotherapy for head and neck cancer

PURPOSE

To determine the frequency of hypothyroidism (both subclinical and clinical) following external beam radiotherapy to the whole of the thyroid gland in the treatment of squamous cell cancers of the head and neck.

METHODS AND MATERIALS

One hundred and four patients who had completed radiotherapy 30 days to 5 years earlier (84 patients) or who were scheduled for radiotherapy (20 patients) had a single measurement of serum-free thyroxine and thyroid stimulating hormone levels between August 1991 and May 1992.

RESULTS

None of the 20 patients assessed prior to treatment showed thyroid dysfunction. Twenty of 84 (23.8%) previously treated patients had subclinical (9.5%) or clinical (14.3%) hypothyroidism. By 5 years, up to 40% of patients may become hypothyroid. Thyroid underactivity was significantly more common in patients having both laryngectomy (including hemi-thyroidectomy) and radiotherapy compared to radiotherapy alone (p < 0.001). Hypothyroidism had not been suspected clinically in any patient tested.

CONCLUSION

In view of the frequency and potential morbidity of this complication, thyroid function testing should become a routine part of posttreatment follow-up for these patients.

Thyroid dysfunction after radiation therapy in head and neck cancer patients

INTRODUCTION

The reported incidence of hypothyroidism following surgery and/or radiation therapy for head and neck cancer varies widely. Most patients undergo thyroid lobectomy during laryngectomy. Standard radiation treatment portals often include the thyroid gland. The insidious development of hypothyroidism may be misdiagnosed. This study examines the incidence of thyroid dysfunction in the setting of head and neck cancer therapy.

MATERIALS AND METHODS

Thyroid function tests were performed on 100 consecutive patients treated in the head and neck tumor clinic. Statistical inferences on proportions were made using chi-square analysis.

RESULTS

Therapy included surgery only (10 patients), radiation therapy only (28 patients), and combined therapy (62 patients). These patients experienced thyroid dysfunction in 0%, 29%, and 45% of individuals respectively. These differences were statistically significant (P < .05). The highest rate of dysfunction (69%) was associated with patients undergoing laryngectomy and radiation therapy. When laryngectomy was not performed, thyroid dysfunction occurred in 28%.

CONCLUSION

The likelihood of thyroid dysfunction after radiation therapy is high particularly when combined with surgery in which thyroid lobectomy is performed and the contralateral lobe is potentially devascularized. These results suggest that radiation therapy is a primary factor in alteration of thyroid function. We recommend that routine thyroid function testing be part of follow-up of all head and neck cancer patients.

Irradiation-induced atherosclerosis: a factor in therapeutic planning

Early primary head and neck cancers (stages I and II) and occult metastatic neck disease have caused debate regarding the choice between surgery and irradiation. The arguments for each are reviewed with a new consideration: the acceleration and/or induction of carotid atherosclerosis in irradiated patients. We present clinical case reports (n = 9), a retrospective clinical evaluation for the occurrence of carotid atherosclerosis in irradiated head and neck cancer patients (n = 57) and a comparison study of the extent and distribution of atherosclerosis in irradiated (n = 29) and nonirradiated head and neck cancer patients controlled for age, blood pressure, and tobacco use. The results show that carotid atherosclerosis is found in a wider anatomic distribution and to a greater extent in irradiated than in nonirradiated patients. We conclude that carotid atherosclerosis is induced and/or accelerated by neck irradiation. The implications as they relate to choice of treatment, to pretreatment evaluations, and to long-term follow-up are discussed.

Hypothyroidism following combined treatment for hypopharyngeal and laryngeal carcinoma

The development of hypothyroidism following combined treatment for pharyngeal and laryngeal cancer has received little attention in the literature. We prospectively studied 32 patients over 4 years to determine the incidence of such hypothyroidism and to examine the effect of hemithyroidectomy associated with a combined treatment modality. All patients were men with pharyngeal or laryngeal squamous cell carcinomas and no prior history of thyroid disease. Treatment consisted of radical surgery (30 of 32 patients), followed by postoperative radiotherapy (31 patients). The results of thyroid function tests (free triiodothyronine, free thyroxine, and thyroid-stimulating hormone [TSH]) were all normal preoperatively; tests were repeated every 3 months after treatment. Elevation of TSH values in two successive blood samples was required to make a diagnosis of hypothyroidism. Of 12 patients who underwent hemithyroidectomy as part of total pharyngolaryngectomy and postoperative radiotherapy, 7 became hypothyroid a mean of 6 months after treatment. Twenty patients had similar combined treatment but without thyroid resection. Hypothyroidism developed a mean of 10 months after treatment in only four patients in this group (p less than 0.05). We conclude that hypothyroidism frequently develops following combined treatment for pharyngeal and laryngeal cancer even when thyroid resection has not been performed. Patients should be evaluated postoperatively and carefully monitored by means of serial thyroid function tests.

Thyroid-stimulating hormone levels after radiotherapy and combined therapy for head and neck cancer

Sixty-eight patients were studied prospectively with serial thyroid-stimulating hormone (TSH) levels after radiotherapy for head and neck neoplasms. Overall, 57% of the patients developed elevated TSH levels. Excluding patients with less than 2 years follow-up, 85% developed an elevated TSH. Ninety-two percent of patients treated with partial thyroidectomy and radiotherapy developed an elevated TSH. Most TSH elevations occurred within 1 year of treatment. The dose of radiotherapy used and the performance of hemithyroidectomy were related to the development of elevated TSH levels (p less than 0.05). The performance of radical neck dissection, gender, hyperfractionated radiotherapy and the use of chemotherapy were not related to the development of an elevated TSH (p greater than 0.05).