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

An Assessment of Enhancement Patterns in Abnormal Parathyroid Glands on Three-Phase CT Imaging

Background Four-dimensional computed tomography (4DCT) is increasingly used in the investigation of primary hyperparathyroidism. The objective of this study was to identify and analyse the usefulness of different enhancement patterns on 4DCT to improve its sensitivity. Methodology Retrospective data were collected on 100 glands. A consultant head and neck radiologist measured the Hounsfield units (HU) of the parathyroid gland and surrounding normal thyroid tissue in the pre-contrast, arterial and venous phases. Each gland was grouped according to the enhancement pattern, and the percentage change in HU was also calculated between the three phases. Results Thirty-five parathyroid glands demonstrated enhancement higher than the thyroid gland in the arterial phase and lower in the delayed phase and were placed into group A. Four parathyroid glands demonstrated enhancement higher than the thyroid gland in the arterial phase and also higher in the delayed phase and were placed into group B. Fifty-nine parathyroid glands demonstrated enhancement lower than the thyroid gland in the arterial phase and also lower in the delayed phase and were placed into group C. Two parathyroid glands demonstrated enhancement lower than the thyroid gland in the arterial phase and higher in the delayed phase and were placed into group D. Conclusions This study demonstrated that the classically described enhancement pattern of the parathyroid gland is not always present or the most frequent, thereby showing that the enhancement pattern cannot be relied upon in isolation. Instead, a thorough understanding of anatomy, embryology and possible ectopic gland locations is essential.

An Underestimated Toxicity Radiation-Induced Hypothyroidism in Patients Multimodally Treated for Breast Cancer

Radiation therapy is part of the therapeutic arsenal for breast cancer, whether it is adjuvant treatment after lumpectomy or radical mastectomy, or it is used as a palliative option in the case of metastatic or recurrent disease. Significant advances in diagnostic and therapeutic stratification of breast cancers have significantly prolonged survival, even in the metastatic stage. Exposure of patients during the course of the disease in a multidisciplinary therapeutic approach including chemotherapy, hormone therapy, targeted anti-HER therapies or CDK4/6 inhibitors had led to improved survival but with the price of additional toxicity. Among them, hypothyroidism is a well-known consequence of external radiation therapy, especially in the case of cervical region irradiation, including supraclavicular and infra-clavicular nodal levels. In this situation, the thyroid gland is considered as an organ at risk (OAR) and receives a significant dose of radiation. Subclinical hypothyroidism is a common endocrine disorder characterized by elevated TSH levels with normal levels of FT4 (free T4) and FT3 (free T3), and as a late effect, primary hypothyroidism is one of the late effects that significantly affects the quality of life for patients with breast cancer receiving multimodal treatment. Hypothyroidism has a significant impact on quality of life, most often occurring as late clinical toxicity, secondary to thyroid irradiation at doses between 30 and 70 Gy. Dose-volume parameters of irradiation, gland function at the beginning of the treatment and associated systemic therapies may be factors that alter thyroid radio-sensitivity and affect thyroid gland tolerance. In the case of head and neck tumor pathology, in which doses of >50 Gy are routinely used, the thyroid gland is generally considered as an OAR, the rate of radio-induced hypothyroidism being estimated at rates of between 20% and 52%. For breast cancer, the thyroid is often neglected in terms of dosimetry protection, the rate of late dysfunction being 6–21%.

Research progress of radiation-induced hypothyroidism in head and neck cancer

This paper reviews the factors related to hypothyroidism after radiotherapy in patients with head and neck cancer to facilitate the prevention of radiation-induced hypothyroidism and reduce its incidence. Hypothyroidism is a common complication after radiotherapy in patients with head and neck cancer, wherein the higher the radiation dose to the thyroid and pituitary gland, the higher the incidence of hypothyroidism. With prolonged follow-up time, the incidence of hypothyroidism gradually increases. Intensity modulated radiotherapy should limit the dose to the thyroid, which would reduce the incidence of hypothyroidism. In addition, the risk factors for hypothyroidism include small thyroid volume size, female sex, and previous neck surgery. The incidence of radiation-induced hypothyroidism in head and neck cancer is related to the radiation dose, radiotherapy technique, thyroid volume, sex, and age. A prospective, large sample and long-term follow-up study should be carried out to establish a model of normal tissue complications that are likely to be related to radiation-induced hypothyroidism.

Does thyroid-sparing total laryngectomy decrease the risk of hypothyroidism?

BACKGROUND

Thyroid lobectomy is recommended with total laryngectomy for laryngeal cancer in the National Comprehensive Cancer Network ('NCCN') guidelines. However, it is associated with a 32-89 per cent risk of hypothyroidism, with or without adjuvant radiotherapy.

OBJECTIVE

The study aimed to determine whether preserving the whole thyroid, compared to a single lobe, does indeed significantly lower the incidence of hypothyroidism in the setting of total laryngectomy.

METHOD

A retrospective study was conducted at Groote Schuur Hospital in Cape Town, South Africa.

RESULTS

Eighty-four patients met the inclusion criteria. The overall incidence of hypothyroidism was 45.2 per cent. The incidence of hypothyroidism was significantly reduced in patients who underwent thyroid-sparing total laryngectomy compared to hemithyroidectomy (p = 0.037). Adjuvant radiotherapy was associated with a higher incidence of hypothyroidism (p = 0.001).

CONCLUSION

Thyroid-preserving laryngectomy should be advocated in carefully selected patients with advanced laryngeal carcinoma, as it reduces the incidence of hypothyroidism.

Effect of dose constraint on the thyroid gland during locoregional intensity-modulated radiotherapy in breast cancer patients

The aim of the present study was to compare radiation dose received by thyroid gland using different radiotherapy (RT) techniques with or without thyroid dose constraint (DC) for breast cancer patients. Computerized tomography (CT) image sets for 10 patients with breast cancer were selected. All patients were treated originally with opposite tangential field-in field (FinF) for the chest wall and anteroposterior fields for the ipsilateral supraclavicular field. The thyroid gland was not contoured on the CT images at the time of the original scheduled treatment. Four new treatment plans were created for each patient, including intensity-modulated radiotherapy (IMRT) and helical tomotherapy (HT) plans with thyroid DC exclusion and inclusion (IMRT_DC(-) , IMRT_DC(+) , HT_DC(-) , and HT_DC(+) , respectively). Thyroid DCs were used to create acceptable dose limits to avoid hypothyroidism as follows: percentage of thyroid volume exceeding 30 Gy less than 50% (V₃₀  < 50%) and mean dose of thyroid (TD_mean ) ≤ 21 Gy. Dose-volume histograms (DVHs) for TD_mean and percentages of thyroid volume exceeding 10, 20, 30, 40, and 50 Gy (V₁₀ , V₂₀ , V₃₀ , V₄₀ , and V₅₀ , respectively) were also analyzed. The D_mean of the FinF, IMRT_DC(-) , HT_DC(-) , IMRT_DC(+) and HT_DC(+) plans were 30.56 ± 5.38 Gy, 25.56 ± 6.66 Gy, 27.48 ± 4.16 Gy, 18.57 ± 2.14 Gy, and 17.34 ± 2.70 Gy, respectively. Median V₃₀ values were 55%, 33%, 36%, 18%, and 17%, for FinF, IMRT_DC(-) , HT_DC(-) , IMRT_DC(+) , and HT_DC(+) , respectively. Differences between treatment plans with or without DC with respect to D_mean and V₃₀ values were statistically significant (P < 0.05). When thyroid DC during breast cancer RT was applied to IMRT and HT, the TD_mean and V₃₀ values significantly decreased. Therefore, recognition of the thyroid as an organ at risk (OAR) and the use of DCs during IMRT and HT planning to minimize radiation dose and thyroid volume exposure are recommended.

A review on the dosimetrical and radiobiological prediction of radiation-induced hypothyroidism in radiation therapy of head-and-neck cancer, breast cancer, and Hodgkin’s lymphoma survivors

A review on the radiobiological modeling of radiation-induced hypothyroidism after radiation therapy of head-and-neck cancers, breast cancer, and Hodgkin’s lymphoma is presented. The current review is based on data relating to dose-volume constrains and normal tissue complication probability (NTCP) as a function of either radiobiological or (pre)treatment-clinical parameters. Also, these data were explored in order to provide more helpful criteria for radiobiological optimization of treatment plans involving thyroid gland as a critical normal organ.

Validation of previously reported predictors for radiation-induced hypothyroidism in nasopharyngeal cancer patients treated with intensity-modulated radiation therapy, a post hoc analysis from a Phase III randomized trial

This study aimed to validate previously reported dosimetric parameters, including thyroid volume, mean dose, and percentage thyroid volume, receiving at least 40, 45 and 50 Gy (V40, V45 and V50), absolute thyroid volume spared (VS) from 45, 50 and 60 Gy (VS45, VS50 and VS60), and clinical factors affecting the development of radiation-induced hypothyroidism (RHT). A post hoc analysis was performed in 178 euthyroid nasopharyngeal cancer (NPC) patients from a Phase III study comparing sequential versus simultaneous-integrated boost intensity-modulated radiation therapy. RHT was determined by increased thyroid-stimulating hormone (TSH) with or without reduced free thyroxin, regardless of symptoms. The median follow-up time was 42.5 months. The 1-, 2- and 3-year freedom from RHT rates were 78.4%, 56.4% and 43.4%, respectively. The median latency period was 21 months. The thyroid gland received a median mean dose of 53.5 Gy. Female gender, smaller thyroid volume, higher pretreatment TSH level (≥1.55 μU/ml) and VS60 < 10 cm3 were significantly associated with RHT in univariate analyses. Only pretreatment TSH ≥ 1.55 μU/ml and VS60 < 10 cm3 were significant predictors in multivariate analysis. Our results suggested that patients with pretreatment TSH ≥ 1.55 μU/ml should be cautious about the risk of RHT. The VS60 ≥ 10 cm3 is recommended for treatment planning.

Development of a normal tissue complication probability (NTCP) model for radiation-induced hypothyroidism in nasopharyngeal carcinoma patients

BACKGROUND

The objectives of this study were to build a normal tissue complication probability (NTCP) model of radiation-induced hypothyroidism (RHT) for nasopharyngeal carcinoma (NPC) patients and to compare it with other four published NTCP models to evaluate its efficacy.

METHODS

Medical notes of 174 NPC patients after radiotherapy were reviewed. Biochemical hypothyroidism was defined as an elevated level of serum thyroid-stimulating hormone (TSH) value with a normal or decreased level of serum free thyroxine (fT4) after radiotherapy. Logistic regression with leave-one-out cross-validation was performed to establish the NTCP model. Model performance was evaluated and compared by the area under the receiver operating characteristic curve (AUC) in our NPC cohort.

RESULTS

With a median follow-up of 24 months, 39 (22.4%) patients developed biochemical hypothyroidism. Gender, chemotherapy, the percentage thyroid volume receiving more than 50 Gy (V50), and the maximum dose of the pituitary (Pmax) were identified as the most predictive factors for RHT. A NTCP model based on these four parameters were developed. The model comparison was made in our NPC cohort and our NTCP model performed better in RHT prediction than the other four models.

CONCLUSIONS

This study developed a four-variable NTCP model for biochemical hypothyroidism in NPC patients post-radiotherapy. Our NTCP model for RHT presents a high prediction capability.

TRIAL REGISTRATION

This is a retrospective study without registration.

Nomogram for radiation-induced hypothyroidism prediction in nasopharyngeal carcinoma after treatment

OBJECTIVE

The aim of this study was to develop a nomogram for radiation-induced hypothyroidism (RHT) prediction.

METHODS

We collected data from 164 patients with nasopharyngeal carcinoma (NPC) in our previous prospective study. Biochemical hypothyroidism was defined as a serum thyroid-stimulating hormone level greater than the normal value. We collected both clinical and dose-volume factors. A univariate Cox regression analysis was performed to identify RHT risk factors. Optimal predictors were selected according to the least absolute shrinkage and selection operator (LASSO). We then selected the Cox regression models that best balanced the prediction performance and practicability to build a nomogram for RHT prediction.

RESULTS

There were 38 (23.2%) patients who developed RHT, and the median follow-up was 24 months. The univariate Cox regression analysis indicated that gender, minimum dose, mean dose (D_mean) and V₂₅-V₆₀ [V_x (%), the percentage of thyroid volume receiving >x Gy] of the thyroid were significantly associated with RHT. The variables of gender, receiving chemotherapy or not (chemo), D_mean and V₅₀ were selected using the LASSO analysis. A nomogram based on a three-variable (gender, chemo and V₅₀) Cox regression model was constructed, and its concordance index was 0.72. Good accordance between prediction and observation was showed by calibration curves in the probability of RHT at 18, 24 and 30 months.

CONCLUSION

This study built a nomogram for RHT in NPC survivors by analyzing both clinical and dose-volume parameters using LASSO. Thus, the individual dose constraint could be achieved in a visual format. Advances in knowledge: This study used LASSO to more accurately address the multicollinear problem between variables. The resulting nomogram will help physicians predict RHT.

Toxicity profile and early clinical outcome for advanced head and neck cancer patients treated with simultaneous integrated boost and volumetric modulated arc therapy

Background

Shortening the overall treatment time without increasing acute reactions is one of the major aims in radiotherapy for head and neck cancer (HNC). Volumetric modulated arc therapy (VMAT) with Simultaneous Integrated Boost (SIB) showed improvements in outcome and pattern of toxicity. Patients with stage III-IV HNC treated with VMAT-SIB have been analysed, and doses were correlated to limiting structures and toxicity.

Methods

One hundred two patients treated from December 2008 to August 2014 were analysed. Patients were treated with VMAT (RapidArc) and SIB in 33 fractions for a total dose of 69.96 and 54.45Gy, respectively. For organs at risk, D_{1/3 V}, D_{1/2 V}, D_{2/3 V}, the mean dose, V_D with D = 10,20,30,40,50,70 Gy were analysed. For targets, D_98%, D_2%, and V_95%, V_107%, conformity and homogeneity indexes were calculated. Toxicity was graded according to CTCAE3.

Results

Oral cavity V_30Gy, V_40Gy, and V_70Gy, were found correlated with mucosal toxicity grading. Concerning salivary glands, significant was only D_2/3V for one of the two parotids. Almost all analysed parameters of the inferior constrictor muscle were significant while no correlations were found for middle and superior constrictors. With median follow-up of 19 months, Overall Survival (OS) at 3 and 5 years was 83 % ± 4 % and 73 % ± 10 %. Mean OS was 51 ± 3 months. Disease Free Survival (DFS) at 3 and 5 years was 71 % ± 7 %, and 34 % ± 16 %. Mean DFS was 43 ± 3 months.

Conclusions

RapidArc technology and SIB with 1.65 and 2.12Gy/fraction for 33 fractions showed a good toxicity profile and encouraging trend for OS and DFS for patients with stage III-IV HNC.

The dosimetric impact of supraclavicular nodal irradiation on the thyroid gland in patients with breast cancer

PURPOSE

The thyroid is not routinely considered an organ at risk in supraclavicular (SC) nodal radiation therapy (RT) for breast cancer. We compared the dosimetric impact of the following 2 RT planning techniques on the thyroid: (1) conventional single anterior field to encompass the SC nodal volume defined clinically; and (2) 3-dimensional conformal radiation therapy (3DCRT) planning to encompass the computed tomography (CT)-contoured SC nodal volume.

METHODS AND MATERIALS

The thyroid, SC nodal volumes, and organs at risk were contoured on the planning CT of 20 patients who received 50 Gy in 2-Gy daily fractions to the breast or chest wall, and SC nodes. Comparisons of dosimetric parameters between the techniques were performed: thyroid, mean and maximum dose, V5, V30, and V50 (percentage of thyroid receiving ≥5 Gy, ≥30 Gy, and ≥50 Gy, respectively); SC nodal volume, homogeneity index (HI, percentage volume receiving 95%-107% of prescribed dose); and maximum doses of spinal cord and brachial plexus. Anatomic characteristics that influenced the dose distributions were investigated.

RESULTS

The 3DCRT planning technique significantly increased all thyroid dosimetric measures (mean dose 17.2 Gy vs 26.7 Gy; maximum dose 48.5 Gy vs 51.9 Gy; V5 45.7% vs 64.9%; V30 33.7% vs 48%; and V50 0.6% vs 26.7%; P < .001). It improved HI for the SC nodal volumes (P < .001) but resulted in higher maximum doses to the spinal cord (6.1 Gy vs 30 Gy) and brachial plexus (43.2 Gy vs 51.4 Gy). The thyroid volume and depth of SC nodes did not influence the thyroid dose distribution. The depth of SC nodes impacted on the HI of SC nodal volumes in the conventional technique (P = .004).

CONCLUSIONS

The 3DCRT planning improved dosimetric coverage of the SC nodal volume but increased thyroid radiation doses. The potential adverse effects of incidental thyroid irradiation should be considered while improving dosimetric coverage in SC nodal irradiation for breast cancer.

Dose-volumetric parameters for predicting hypothyroidism after radiotherapy for head and neck cancer

OBJECTIVE

To investigate predictors affecting the development of hypothyroidism after radiotherapy for head and neck cancer, focusing on radiation dose-volumetric parameters, and to determine the appropriate radiation dose-volumetric threshold of radiation-induced hypothyroidism.

METHODS

A total of 114 patients with head and neck cancer whose radiotherapy fields included the thyroid gland were analysed. The purpose of the radiotherapy was either definitive (n = 81) or post-operative (n = 33). Thyroid function was monitored before starting radiotherapy and after completion of radiotherapy at 1 month, 6 months, 1 year and 2 years. A diagnosis of hypothyroidism was based on a thyroid stimulating hormone value greater than the maximum value of laboratory range, regardless of symptoms. In all patients, dose volumetric parameters were analysed.

RESULTS

Median follow-up duration was 25 months (range; 6-38). Forty-six percent of the patients were diagnosed as hypothyroidism after a median time of 8 months (range; 1-24). There were no significant differences in the distribution of age, gender, surgery, radiotherapy technique and chemotherapy between the euthyroid group and the hypothyroid group. In univariate analysis, the mean dose and V35-V50 results were significantly associated with hypothyroidism. The V45 is the only variable that independently contributes to the prediction of hypothyroidism in multivariate analysis and V45 of 50% was a threshold value. If V45 was <50%, the cumulative incidence of hypothyroidism at 1 year was 22.8%, whereas the incidence was 56.1% if V45 was ≥50% (P = 0.034).

CONCLUSIONS

The V45 may predict risk of developing hypothyroidism after radiotherapy for head and neck cancer, and a V45 of 50% can be a useful dose-volumetric threshold of radiation-induced hypothyroidism.

Hypothyroidism after a cancer diagnosis: etiology, diagnosis, complications, and management

Hypothyroidism is a common disease that is easily treated in the majority of cases, when readily diagnosed; however, presentation of an aggregate of its symptoms is often clinically overlooked or attributed to another disease and can potentially be lethal. Already prevalent in older women, its occurrence in younger patients is rising as a result of radiation therapy, radioactive iodine therapy, and newer antineoplastic agents used to manage various malignancies. The presence of nonspecific constitutional symptoms and neuropsychiatric complaints in cancer patients can be attributed to a myriad of other diagnoses and therapies. Thyroid dysfunction can be easily overlooked in cancer patients because of the complexity of cancer's clinical picture, particularly in the pediatric population. Underdiagnosis can have important consequences for the management of both hypothyroidism and the malignancy. At minimum, quality of life is adversely affected. Untreated hypothyroidism can lead to heart failure, psychosis, and coma and can reduce the effectiveness of potentially life-saving cancer therapies, whereas iatrogenic causes can provoke atrial fibrillation and osteoporosis. Consequently, the diagnosis and treatment of hypothyroidism in cancer patients are pertinent. We summarize the history, epidemiology, pathophysiology, clinical diagnosis, and management of hypothyroidism in cancer patients.

Hypothyroidism after primary radiotherapy for head and neck squamous cell carcinoma: normal tissue complication probability modeling with latent time correction

BACKGROUND AND PURPOSE

To develop a normal tissue complication probability (NTCP) model of radiation-induced biochemical hypothyroidism (HT) after primary radiotherapy for head and neck squamous cell carcinoma (HNSCC) with adjustment for latency and clinical risk factors.

PATIENTS AND METHODS

Patients with HNSCC receiving definitive radiotherapy with 66-68Gy without surgery were followed up with serial post-treatment thyrotropin (TSH) assessment. HT was defined as TSH >4.0mU/l. Data were analyzed with both a logistic and a mixture model (correcting for latency) to determine risk factors for HT and develop an NTCP model based on mean thyroid dose (MTD) and thyroid volume.

RESULTS

203 patients were included. Median follow-up: 25.1months. Five-year estimated risk of HT was 25.6%. In the mixture model, the only independent risk factors for HT were thyroid volume (cm(3)) (OR=0.75 [95% CI: 0.64-0.85], p<0.001) and MTD (Gy) (OR=1.12 [95% CI: 1.07-1.20], p<0.001). From the mixture NTCP-model individual dose constraints for a 25% risk of HT were 26, 38, 48 and 61Gy for thyroid volumes of 10, 15, 20 and 25cm(3), respectively.

CONCLUSIONS

Comparing the logistic and mixture models demonstrates the importance of latent-time correction in NTCP-modeling. Thyroid dose constraints in treatment planning should be individualized based on thyroid volume.

A prospective longitudinal study on endocrine dysfunction following treatment of laryngeal or hypopharyngeal carcinoma

OBJECTIVES

The incidences of hypo(para)thyroidism were assessed prospectively in 137 consecutive patients with laryngeal (84.7%) or hypopharyngeal (15.3%) carcinoma who were treated with surgery and/or radiotherapy between 2004 and 2006.

MATERIAL AND METHODS

Laboratory studies were performed in patients before primary or salvage treatment of a laryngeal or hypopharyngeal carcinoma and were repeated 6, 12, 18 and 24months after treatment. All patients were evaluated for the development of hypo(para)thyroidism, and the presence of autoantibodies. The association of hypothyroidism was analyzed against several patient parameters including tumor and treatment characteristics.

RESULTS

The incidence of hypothyroidism following treatment of laryngeal and hypopharyngeal carcinoma was 47.4%: 27.7% subclinical hypothyroidism and 19.7% clinical hypothyroidism. The median time to develop hypothyroidism was 10months. The incidence of hypoparathyroidism was 7.3%. Univariate analysis showed that patients with laryngectomy, hemithyroidectomy, neck dissection, paratracheal lymph node dissection and radiotherapy had a higher risk of developing hypothyroidism. Multivariate analysis showed laryngectomy, hemithyroidectomy, neck dissection and age to be predictive factors for the development of hypothyroidism. The combination of surgery and radiotherapy increased this risk. Hemithyroidectomy was the most important risk factor.

CONCLUSION

The incidence rate of hypothyroidism after treatment for laryngeal or hypopharyngeal cancer in this largest prospective study is high (47.4%), especially after combination treatment. Based on the intervals between treatment and the development of hypothyroidism, thyroid testing before treatment, every 3months during the first year, every 6months the second year and annually thereafter is recommended as screening procedure.

A prospective cohort study on radiation-induced hypothyroidism: development of an NTCP model

PURPOSE

To establish a multivariate normal tissue complication probability (NTCP) model for radiation-induced hypothyroidism.

METHODS AND MATERIALS

The thyroid-stimulating hormone (TSH) level of 105 patients treated with (chemo-) radiation therapy for head-and-neck cancer was prospectively measured during a median follow-up of 2.5 years. Hypothyroidism was defined as elevated serum TSH with decreased or normal free thyroxin (T4). A multivariate logistic regression model with bootstrapping was used to determine the most important prognostic variables for radiation-induced hypothyroidism.

RESULTS

Thirty-five patients (33%) developed primary hypothyroidism within 2 years after radiation therapy. An NTCP model based on 2 variables, including the mean thyroid gland dose and the thyroid gland volume, was most predictive for radiation-induced hypothyroidism. NTCP values increased with higher mean thyroid gland dose (odds ratio [OR]: 1.064/Gy) and decreased with higher thyroid gland volume (OR: 0.826/cm(3)). Model performance was good with an area under the curve (AUC) of 0.85.

CONCLUSIONS

This is the first prospective study resulting in an NTCP model for radiation-induced hypothyroidism. The probability of hypothyroidism rises with increasing dose to the thyroid gland, whereas it reduces with increasing thyroid gland volume.

Treatment outcome of nasopharyngeal carcinoma with retropharyngeal lymph nodes metastasis only and the feasibility of elective neck irradiation

OBJECTIVE

To investigate the outcome of nasopharyngeal carcinoma (NPC) with retropharyngeal lymph nodes (RLNs) metastasis only and evaluate the feasibility of elective neck irradiation.

MATERIALS AND METHODS

This is a retrospective study of 119 newly diagnosed non-metastatic NPC patients with RLNs metastasis only. All of them received definitive radiotherapy. Eighty nine patients received elective neck irradiation to levels II, III, VA and the rest received whole neck irradiation, including levels II-V.

RESULTS

The median follow-up was 36.6 months. The 5-year local recurrence-free survival (LFS), nodal recurrence-free survival (NFS), distant metastasis-free survival (DMFS) and overall survival (OS) was 81.4%, 92.7%, 91.8%, and 93.6%, respectively. Four patients developed nodal relapse and only one was out-of-field relapse. No significant difference of nodal recurrence was observed between elective neck irradiation and whole neck irradiation. IMRT or three-dimensional conformal radiotherapy (3D-CRT) showed a trend of improving regional control, compared with conventional two-dimensional radiotherapy (2D-RT) (p=0.074). In 2D-RT, a higher dose (>5600 cGy) to the upper neck showed a benefit of regional control(p=0.006). Multivariate analysis demonstrated that only the dose of upper neck was an independent prognostic factor of NFS.

CONCLUSIONS

Elective irradiation to levels II, III, VA was not inferior to whole neck irradiation for NPC patients with RLNs metastasis only. However, more evidences are needed to confirm the result. IMRT showed a trend of improving regional control. A higher dose of prophylactic radiation may be required for upper neck region in patients with RLNs metastasis.

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.

Radiation-induced hypothyroidism in head and neck cancer patients: a systematic review

PURPOSE

To review literature on the relationship between the dose distribution in the thyroid gland and the incidence of radiation-induced hypothyroidism in adults.

MATERIAL AND METHODS

Articles were identified through a search in MEDLINE, EMBASE and the Cochrane Library. Approximately 2449 articles were screened and selected by inclusion- and exclusion criteria. Eventually, there were five papers that fulfilled the eligibility criteria to be included in this review.

RESULTS

The sample sizes of the reviewed studies vary from 57 to 390 patients. The incidence of hypothyroidism was much higher (23-53%) than would be expected in a non-irradiated cohort. There was a large heterogeneity between the studies regarding study design, estimation of the dose to the thyroid gland and definition of endpoints. In general, the relationship between thyroid gland volume absorbing 10-70Gy (V10-V70), mean dose (Dmean), minimal dose (Dmin), maximum dose (Dmax) and point doses with hypothyroidism were analysed. An association between dose-volume parameters and hypothyroidism was found in two studies.

CONCLUSIONS

Hypothyroidism is frequently observed after radiation. Although the results suggest that higher radiation doses to the thyroid gland are associated with hypothyroidism, it was not possible to define a clear threshold radiation dose for the thyroid gland.

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.

The shrinking thyroid: how does thyroid size change following radiation therapy for laryngeal cancer?

BACKGROUND AND PURPOSE

External beam radiation therapy (XRT) for head and neck cancer is known to induce hypothyroidism and cause morphologic changes in the thyroid gland. This retrospective study investigates change in the size of the thyroid gland detectable by CT after XRT for laryngeal cancer.

MATERIALS AND METHODS

The measured width of the thyroid lobes in 61 patients treated nonsurgically with XRT for laryngeal cancer between 2000 and 2003 on posttherapy CT was compared with that on pretherapy CT. Absolute and percentage changes in measured thyroid width following XRT were analyzed according to chemotherapy administration and posttherapy thyroid function.

RESULTS

Eighty-five percent (52/61) of patients had a decrease in the width of the thyroid gland. The average change in width measuring -4.7 mm and -13.8% (SD, 5.7 mm and 19.9%) occurred at an average of 758 days following completion of XRT (mean, 402-1534 days) and was significant (P = .002). Average change in width between hypothyroid patients (n = 19, -6.1 mm and -20.0% change) and euthyroid patients (n = 42, -4.1 mm and -11.1% change) was not significant (P = .20 absolute change and P = .11 percentage change). The average change in width between patients receiving chemotherapy (n = 31, -5.5 mm and -16.1% change) and patients not receiving chemotherapy (n = 30, -3.9 mm and -11.5% change) was not significant (P = .26 absolute change and P = .37 for percentage change).

CONCLUSIONS

Most nonsurgical patients receiving XRT for laryngeal cancer have a significant decrease in the width of their thyroid glands detected on CT. The average change in the size of the thyroid gland does not differ when development of hypothyroidism or chemotherapy administration are considered.

The need for patients' endocrine function vigilance following treatment of head and neck cancer

PURPOSE OF REVIEW

The aim of this article is to examine the need for screening of endocrine dysfunction following treatment of head and neck cancer.

RECENT FINDINGS

The incidence of occult hypothyroidism following treatment of head and neck cancer is high. Patients who develop hypothyroidism after treatment may have an increased survival compared with patients who did not become hypothyroid. Because of the growing body of evidence that supports a permissive role for thyroid hormone in the growth of certain solid tumours thyroid hormone replacement therapy may not be indicated in patients with subclinical hypothyroidism and prior or current cancer. Although the incidence of hypoparathyroidism after treatment for head and neck cancer is low, testing of serum calcium is easily performed during thyroid function evaluation. The incidence of hypopituitarism after irradiation of the nasopharynx or skull base is very high warranting regular evaluation of endocrine functions.

SUMMARY

Owing to the high incidence of endocrine dysfunction, all head and neck cancer patients who undergo treatment of the lower neck, nasopharynx or base of skull need regular endocrine evaluation during long-term follow-up to determine the need to start hormone replacement therapy and maintain optimal quality of life.