Thyroid Cancer Following Childhood Low-Dose Radiation Exposure: A Pooled Analysis of Nine Cohorts.

Context: The increased use of diagnostic and therapeutic procedures that involve radiation raises concerns about radiation effects, particularly in children and the radiosensitive thyroid gland. Objectives: Evaluation of relative risk (RR) trends for thyroid radiation doses <0.2 gray (Gy); evidence of a threshold dose; and possible modifiers of the dose-response, e.g., sex, age at exposure, time since exposure. Design and Setting: Pooled data from nine cohort studies of childhood external radiation exposure and thyroid cancer with individualized dose estimates, ≥1000 irradiated subjects or ≥10 thyroid cancer cases, with data limited to individuals receiving doses <0.2 Gy. Participants: Cohorts included the following: childhood cancer survivors (n = 2); children treated for benign diseases (n = 6); and children who survived the atomic bombings in Japan (n = 1). There were 252 cases and 2,588,559 person-years in irradiated individuals and 142 cases and 1,865,957 person-years in nonirradiated individuals. Intervention: There were no interventions. Main Outcome Measure: Incident thyroid cancers. Results: For both <0.2 and <0.1 Gy, RRs increased with thyroid dose (P < 0.01), without significant departure from linearity (P = 0.77 and P = 0.66, respectively). Estimates of threshold dose ranged from 0.0 to 0.03 Gy, with an upper 95% confidence bound of 0.04 Gy. The increasing dose-response trend persisted >45 years after exposure, was greater at younger age at exposure and younger attained age, and was similar by sex and number of treatments. Conclusions: Our analyses reaffirmed linearity of the dose response as the most plausible relationship for "as low as reasonably achievable" assessments for pediatric low-dose radiation-associated thyroid cancer risk.

Is outdoor work associated with elevated rates of cerebrovascular disease mortality? A cohort study based on iron-ore mining.

BACKGROUND: A cohort study that examined iron ore mining found negative associations between cumulative working time employed underground and several outcomes, including mortality of cerebrovascular diseases. In this cohort study, and using the same group of miners, we examined whether work in an outdoor environment could explain elevated cerebrovascular disease rates. METHODS: This study was based on a Swedish iron ore mining cohort consisting of 13,000 workers. Poisson regression models were used to generate smoothed estimates of standardized mortality ratios and adjusted rate ratios, both models by cumulative exposure time in outdoor work. RESULTS: The adjusted rate ratio between employment classified as outdoor work ≥25 years and outdoor work 0-4 years was 1.62 (95 % CI 1.07-2.42). The subgroup underground work ≥15 years deviated most in occurrence of cerebrovascular disease mortality compared with the external reference population: SMR (0.70 (95 % CI 0.56-0.85)). CONCLUSIONS: Employment in outdoor environments was associated with elevated rates of cerebrovascular disease mortality. In contrast, work in tempered underground employment was associated with a protecting effect.

Thyroid Cancer after Childhood Exposure to External Radiation: An Updated Pooled Analysis of 12 Studies.

Studies have causally linked external thyroid radiation exposure in childhood with thyroid cancer. In 1995, investigators conducted relative risk analyses of pooled data from seven epidemiologic studies. Doses were mostly <10 Gy, although childhood cancer therapies can result in thyroid doses >50 Gy. We pooled data from 12 studies of thyroid cancer patients who were exposed to radiation in childhood (ages <20 years), more than doubling the data, including 1,070 (927 exposed) thyroid cancers and 5.3 million (3.4 million exposed) person-years. Relative risks increased supralinearly through 2-4 Gy, leveled off between 10-30 Gy and declined thereafter, remaining significantly elevated above 50 Gy. There was a significant relative risk trend for doses <0.10 Gy (P < 0.01), with no departure from linearity (P = 0.36). We observed radiogenic effects for both papillary and nonpapillary tumors. Estimates of excess relative risk per Gy (ERR/Gy) were homogeneous by sex (P = 0.35) and number of radiation treatments (P = 0.84) and increased with decreasing age at the time of exposure. The ERR/Gy estimate was significant within ten years of radiation exposure, 2.76 (95% CI, 0.94-4.98), based on 42 exposed cases, and remained elevated 50 years and more after exposure. Finally, exposure to chemotherapy was significantly associated with thyroid cancer, with results supporting a nonsynergistic (additive) association with radiation.

A comparison between standard methods and structural nested modelling when bias from a healthy worker survivor effect is suspected: an iron-ore mining cohort study.

OBJECTIVES: Iron-ore miners are exposed to extremely dusty and physically arduous work environments. The demanding activities of mining select healthier workers with longer work histories (ie, the Healthy Worker Survivor Effect (HWSE)), and could have a reversing effect on the exposure-response association. The objective of this study was to evaluate an iron-ore mining cohort to determine whether the effect of respirable dust was confounded by the presence of an HWSE. METHODS: When an HWSE exists, standard modelling methods, such as Cox regression analysis, produce biased results. We compared results from g-estimation of accelerated failure-time modelling adjusted for HWSE with corresponding unadjusted Cox regression modelling results. RESULTS: For all-cause mortality when adjusting for the HWSE, cumulative exposure from respirable dust was associated with a 6% decrease of life expectancy if exposed ≥15 years, compared with never being exposed. Respirable dust continued to be associated with mortality after censoring outcomes known to be associated with dust when adjusting for the HWSE. In contrast, results based on Cox regression analysis did not support that an association was present. CONCLUSIONS: The adjustment for the HWSE made a difference when estimating the risk of mortality from respirable dust. The results of this study, therefore, support the recommendation that standard methods of analysis should be complemented with structural modelling analysis techniques, such as g-estimation of accelerated failure-time modelling, to adjust for the HWSE.

Validity of the Swedish Rectal Cancer Registry for patients treated with major abdominal surgery between 1995 and 1997.

BACKGROUND: Founded in 1995, the Swedish Rectal Cancer Registry (SRCR) is frequently used for rectal cancer research. However, the validity of the registry has not been extensively studied. This study aims to validate a large amount of registry data to assess SRCR quality. MATERIAL AND METHODS: The study comprises 906 patients treated with major abdominal surgery registered in the SRCR between 1995 and 1997. SRCR data for 14 variables were scrutinized for validity against the medical records. Kappa's and Kendall's correlation coefficients for agreement between SRCR data and medical records data were calculated for 13 variables. RESULTS: For 11 variables, concerning the tumor, neoadjuvant therapy, the surgical procedure, local radicality and TNM stage, data were missing in 5% or less of the registrations; for the remaining three variables, anastomotic leakage, local and distant recurrence, data were missing in 13-38%. For the variables surgery performed or not and type of surgical procedure, no data were missing. Erroneous registrations were found in less than 10% of all variables; for the variables preoperative chemotherapy and surgery performed or not, all registrations were correct. For the variables concerning neoadjuvant therapy, local radicality according to the surgeon as well as the pathologist and distant metastasis, the false-positive or -negative registrations were equally distributed, and for the variables rectal washout, rectal perforation, anastomotic leakage and local recurrence there was a discrepancy in distribution. The correlation coefficient for 12 variables ranged from 0.82 to 1.00, and was 0.78 for the remaining variable. CONCLUSION: The validity of the SRCR was good for the initial three registry years. Thus, research based on SRCR data is reliable from the beginning of the registry's use.

Reduced mortality rates in a cohort of long-term underground iron-ore miners.

BACKGROUND: Historically, working in iron-ore mines has been associated with an increased risk of lung cancer and silicosis. However, studies on other causes of mortality are inconsistent and in the case of cancer incidence, sparse. The aim of this study was to examine the association between iron-ore mining, mortality and cancer incidence. METHODS: A 54-year cohort study on iron-ore miners from mines in northern Sweden was carried out comprising 13,000 workers. Standardized rate ratios were calculated comparing the disease frequency, mortality, and cancer incidence with that of the general population of northern Sweden. Poisson regression was used to evaluate the association between the durations of employment and underground work, and outcome. RESULTS: Underground mining was associated with a significant decrease in adjusted mortality rate ratios for cerebrovascular and digestive system diseases, and stroke. For several outcomes, elevated standardized rate ratios were observed among blue-collar workers relative to the reference population. However, only the incidence of lung cancer increased with employment time underground (P < 0.001). CONCLUSIONS: Long-term iron-ore mining underground was associated with lower rates regarding several health outcomes. This is possibly explained by factors related to actual job activities, environmental exposure, or the selection of healthier workers for long-term underground employment.

A pooled analysis of thyroid cancer incidence following radiotherapy for childhood cancer.

Childhood cancer five-year survival now exceeds 70-80%. Childhood exposure to radiation is a known thyroid carcinogen; however, data are limited for the evaluation of radiation dose-response at high doses, modifiers of the dose-response relationship and joint effects of radiotherapy and chemotherapy. To address these issues, we pooled two cohort and two nested case-control studies of childhood cancer survivors including 16,757 patients, with 187 developing primary thyroid cancer. Relative risks (RR) with 95% confidence intervals (CI) for thyroid cancer by treatment with alkylating agents, anthracyclines or bleomycin were 3.25 (0.9-14.9), 4.5 (1.4-17.8) and 3.2 (0.8-10.4), respectively, in patients without radiotherapy, and declined with greater radiation dose (RR trends, P = 0.02, 0.12 and 0.01, respectively). Radiation dose-related RRs increased approximately linearly for <10 Gy, leveled off at 10-15-fold for 10-30 Gy and then declined, but remained elevated for doses >50 Gy. The fitted RR at 10 Gy was 13.7 (95% CI: 8.0-24.0). Dose-related excess RRs increased with decreasing age at exposure (P < 0.01), but did not vary with attained age or time-since-exposure, remaining elevated 25+ years after exposure. Gender and number of treatments did not modify radiation effects. Thyroid cancer risks remained elevated many decades following radiotherapy, highlighting the need for continued follow up of childhood cancer survivors.

Lung cancer risk and radon exposure in a cohort of iron ore miners in Malmberget, Sweden.

OBJECTIVES: Lung cancer caused by radon in miners is a well-known risk. However, the risk estimates vary between studies and between mines. We have studied the dose response-relationship in a Swedish iron ore mine where two other studies have previously reached different risk estimates. As this mine has relatively low radon levels, the results are highly relevant for risk estimation in non-uranium underground mines. METHODS: A new cohort of 5486 male workers employed from 1923 to 1996 was established. Cumulative radon exposures were assessed based on a large number of measurements, including reconstructions of historical conditions. 122 lung cancer cases occurred during the follow-up period of 1958-2000. RESULTS: The average cumulative exposure in underground workers was 32 kBq year/m(3) (65 working level months (WLM)), experienced over 14.6 years. The excess RR (ERR) per kBq year/m(3) was 0.046 (95% CI 0.015 to 0.077; 0.022 ERR/WLM). Confounding by quartz may affect these results but appears to account only for 10-20% of the risk. The results for squamous cell and small cell lung cancer were 0.049 and 0.072, respectively. However, no increased risk was observed for adenocarcinoma (0.000 ERR per kBq year/m(3), 95% CI -0.017 to 0.017). CONCLUSION: Our overall risk estimate is about half of that found in the first Malmberget study but twice that found in the same cohort in the previously published pooled analysis. Radon did not increase the risk for adenocarcinoma in the lung.

Lung cancer and exposure to quartz and diesel exhaust in Swedish iron ore miners with concurrent exposure to radon.

OBJECTIVES: Studies of underground miners have documented an increased risk of lung cancer mainly linked to radon exposure but possibly influenced by other concurrent exposures. METHODS: A cohort study was carried out in 8321 iron ore miners with low exposure to radon, employed in 1923-1998 and followed up for lung cancer in 1958-2000. Historical exposures to radon, crystalline silica and diesel exhaust were assessed. Data including exposure to radon, quartz and diesel exhaust from another mine with higher exposure to radon were reanalysed. RESULTS: Miners had increased risk for lung cancer (SIR 1.48 (95% CI 1.22 to 1.78), based on 112 cases during 227,000 person-years). The increased risk could not be explained by exposure to radon or diesel exhaust but was associated with exposure to crystalline silica: SIR 0.96 (0.53 to 1.62), 1.45 (1.10 to 1.87), 1.99 (1.31 to 2.90) and 1.77 (0.92 to 3.10) in groups with exposure to 0, 0-2, 2-5 and >5 mg years/m3, respectively. Reanalysis of data from the other mine indicated that quartz was a possible confounder in the analysis of relationship between radon and lung cancer. In the highest radon exposed group, the point estimate for the RR decreased from 5.65 to 3.90 when adjusting for concurrent exposure to quartz. CONCLUSIONS: Crystalline silica, a known carcinogen, probably affects lung cancer risk in iron ore miners. The main implication of the results is for interpretation of the dose-response curve for radon and lung cancer in underground iron ore miners. Since exposure to radon and quartz is often correlated, quartz exposure can be an important confounder.

Oncological outcome after incidental perforation in radical rectal cancer surgery.

PURPOSE: Identification of risk factors of poor oncological outcome in rectal cancer surgery is of utmost importance. This study examines the impact of incidental perforation on the oncological outcome. METHODS: Using the Swedish Rectal Cancer Registry, patients were selected who received major abdominal surgery for rectal cancer between 1995 and 1997 with registered incidental perforation. A control group was also selected for analysis of the oncological outcome after 5-year follow-up. Multivariate analysis was performed. Registry data were validated, and additional data were supplemented from medical records. RESULTS: After validation and exclusion of non-radically operated patients, 118 patients with incidental perforation and 155 controls in TNM stages I-III were included in the analysis. The rate of local recurrence (LR) [20% (23/118) vs. 8% (12/155) (p = 0.007)] was significantly higher among patients with perforation, whereas the rates of distant metastasis [27% (32/118) vs. 21% (33/155) (p = 0.33)] and overall recurrence (OAR) [35% (41/118) vs. 25% (38/155) (p = 0.087)] were not significantly different between the groups. Overall as well as cancer-specific 5-year survival rates were significantly reduced for the patients with perforation [44 vs. 64% (p = 0.002) and 66 vs. 80% (p = 0.026), respectively]. In the multivariate analysis, perforation was a significant risk factor of increased rates of LR and OAR as well as reduced 5-year overall and cancer-specific survival. CONCLUSIONS: Incidental perforation in rectal cancer surgery is an important risk factor of poor oncological outcome and should be considered in the discussion concerning postoperative adjuvant treatment as well as the follow-up regime.

The impact of hospital volume on surgical outcome in patients with rectal cancer.

PURPOSE: This study was designed to investigate, in a population-based setting, the surgical outcome in patients with rectal cancer according to the hospital volume. METHODS: Since 1995 all patients with rectal cancer have been registered in the Swedish Rectal Cancer Registry. Hospitals were classified, according to number treated per year, as low-volume, intermediate-volume, or high-volume hospitals (<11, 11-25, or >25 procedures per year). Postoperative mortality, reoperation rate within 30 days, local recurrence rate, and overall five-year survival were studied. For postoperative morbidity and mortality the whole cohort from 1995 to 2003 (n = 10,425) was used. For cancer-related outcome only, those with five-year follow-ups, from 1995 to 1998, were used (n = 4,355). RESULTS: In this registry setting the postoperative mortality rate was 3.6% in low-volume hospitals, and 2.2% in intermediate-volume and high-volume hospitals (P = 0.002). The reoperation rate was 10%, with no differences according to volume. The overall local recurrence rates were 9.4%, 9.3%, and 7.5%, respectively (P = 0.06). Significant difference was found among the nonirradiated patients (P = 0.004), but not among the irradiated patients (P = 0.45). No differences were found according to volume in the absolute five-year survival. CONCLUSION: Postoperative mortality and local recurrence in nonirradiated patients were lower in high-volume hospitals. No difference was seen between volumes in reoperation rates, overall local recurrence, or absolute five-year survival.

Cancer in the Sami population of Sweden in relation to lifestyle and genetic factors.

The reindeer herding Sami of Sweden have low incidences of cancer. The aim of the present study was to investigate the cancer risk in a large cohort of Swedish Sami, containing Sami with different lifestyle and genetic Sami heritage. A cohort of 41,721 Sami identified in official national registers between 1960 and 1997, was divided into two sub-populations -- reindeer herding Sami (RS) and non-reindeer herding Sami (NRS). A demographically matched non-Sami reference population (NS) was used as standard when incidence and mortality ratios were calculated. Incidence and mortality data were obtained from the Swedish Cancer and Cause of Death Registers for the period 1961-2003. For Sami men, lower risks were found for cancers of the colon and prostate, and for malignant melanoma and non-Hodkins lymphoma, but higher for stomach cancer. The Sami women showed higher risks for cancers of the stomach and the ovaries, but lower risk for cancer of the bladder. The RS demonstrated lower relative cancer risks compared with the NRS. The lowest relative risk was found among the RS men, while the highest were observed among the NRS women. The RS men who had adopted a more westernized lifestyle showed a similar relative risk for prostate cancer as that of the NS living in the same region. Most of these differences in cancer risks could probably be ascribed to differences in lifestyle. It is concluded that the traditional Sami lifestyle contains elements, e.g. dietary contents and physical activity that may protect them from developing cancer.

Long-term follow-up study of mortality and the incidence of cancer in a cohort of workers at a primary aluminum smelter in Sweden.

OBJECTIVES: Previous studies on mortality and the incidence of cancer among workers at primary aluminum smelters have produced conclusive results indicating an elevated risk of bladder cancer. An increased risk of lung cancer has also been reported several times. The objective of this study was to examine mortality and the incidence of cancer at a Swedish aluminum smelter when different neighboring reference populations were used to evaluate any relationships to the length of employment. METHODS: A historical cohort--comprised of 2264 male nonoffice workers employed from 1942 on and tracked up to the year 2000--was examined. With the use of three reference populations for mortality and four for cancer incidence, standardized mortality and incidence ratios were calculated, together with hazard ratios derived from Cox regression models. RESULTS: This study showed an excess risk of mortality due to chronic obstructive lung disease, mental disorders, and diseases of the digestive system among the short-term workers. An elevated risk of cancer was found for the lungs, central nervous system, and esophagus. The highest lung cancer risk was observed for the workers employed for > or = 10 years in the factory when they were compared with the reference group from northern Sweden (standardized incidence ratio 1.99, 95% confidence ratio 1.21-3.07). CONCLUSIONS: The results support previous studies that demonstrated an excess risk of lung cancer, but, in contrast to the results of most studies, cancer of the central nervous system was also elevated. This study did not, however, verify an association between this type of exposure and cancer of the urinary organs.

Quality of life in patients with skeletal metastases of prostate cancer and status prior to start of endocrine therapy: results from the Scandinavian Prostate Cancer Group Study 5.

OBJECTIVES: Prostate cancer (PC) is a highly lethal neoplastic disease affecting the physical, mental and social well-being of patients, i.e. their quality of life (QOL). Patients suffering from metastatic PC are faced with serious decisions regarding treatment strategies. Therefore, QOL information has become a crucial element of decision making in this group of patients. The first objective of this study was to describe QOL in a group of patients diagnosed with metastatic PC and skeletal metastases. At the time of evaluation the patients had not received any treatment but were evaluated before entering a study of androgen-modulating therapy (the Scandinavian Prostate Cancer Group study 5). The second objective was to identify demographic and disease-related factors affecting QOL. MATERIAL AND METHODS: A total of 917 patients with metastatic PC were evaluated using a well-described and validated questionnaire [European Organization for Research and Treatment of Cancer Quality-of-Life Questionnaire-C30 (EORTC QLQ-C30)]. The characteristics of the PC were noted, and simultaneously patients were evaluated with respect to use of analgesics, pain and performance status using a scoring system. Biochemical tests were performed when patients entered the study. A multivariate regression analysis was performed to analyse the correlations between QOL scores, patient demographics and disease-related data. RESULTS: The patients reported QOL scores significantly lower than those in the background population. Pain and fatigue were pronounced, whereas dyspnoea, insomnia, loss of appetite, constipation and diarrhoea were less prominent. Patients with high tumour grades, high PSPA scores (the sum of the pain score, the performance status and the use of analgesics) and those using analgesics had significantly lower QOL scores than the other patients. CONCLUSIONS: Patients with metastatic PC have reduced QOL. Our findings are in line with those of other studies of QOL among patients with this disease as evaluated by means of the EORTC QLQ-C30 questionnaire. Baseline data from studies like this provide important information when treatment modalities for PC are evaluated.

Causes of death in the Sami population of Sweden, 1961-2000.

BACKGROUND: Indigenous people often have a pattern of mortality that is disadvantageous in comparison with the general population. The knowledge on causes of death among the Sami, the natives of northern Scandinavia, is limited. The aim of the present study was to compare gender and cause specific mortality patterns for reindeer herding Sami, non-herding Sami, and non-Sami between 1961 and 2000. METHODS: A Sami cohort was constructed departing from a group of index-Sami identified as either reindeer herding Sami or Sami eligible to vote for the Sami parliament. Relatives of index-Sami were identified in the National Kinship Register and added to the cohort. The cohort contained a total of 41 721 people (7482 reindeer herding Sami and 34 239 non-herding Sami). A demographically matched non-Sami reference population four times as large, was compiled in the same way. Relative mortality risks were analysed by calculating standardized mortality ratios (SMRs). RESULTS: The differences in overall mortality and life expectancy of the Sami, both reindeer herding and non-herding, compared with the reference population were relatively small. However, Sami men showed significantly lower SMR for cancers but higher for external causes of injury. For Sami women, significantly higher SMR was found for diseases of the circulatory system and diseases of the respiratory system. An increased risk of dying from subarachnoid haemorrhage was observed among both Sami men and women. CONCLUSIONS: The similarities in mortality patterns are probably a result of centuries of close interaction between the Sami and the non-Sami, while the observed differences might be due to lifestyle, psychosocial and/or genetic factors.

Reproductive factors have low impact on the risk of different primary brain tumours in offspring.

OBJECTIVES: The aim of our study was to investigate whether reproductive factors influence the risk of primary brain tumours (PBT) in offspring. METHODS: Data on all deliveries in two Swedish counties from 1955 to 1990 were extracted from two birth registries. The follow-up period closed at the end of 1994, with subjects followed up to early middle age. Incidence rates of malignancy for 1958-1994 were obtained from the Swedish Cancer Registry. Standardised incidence ratios (SIR) and relative risks were calculated for astrocytomas, primitive neuroectodermal tumour, ependymoma and meningiomas in offspring. RESULTS: Few associations were detected. High birth weight indicated an increased risk for astrocytomas grade I and II for all primary brain tumours, and the risk was close to significance for astrocytomas grade I-II (SIR = 3.64; CI = 0.98-9.31). For children under 15 years of age the risk for astrocytomas grade I and II was further increased (SIR = 4.44; CI = 1.19-11.38). CONCLUSIONS: A consistent pattern of non-association indicated a low impact of intrauterine environment on the future development of primary brain tumours in offspring up to early middle age.

Population-based study of prostate-specific antigen testing and prostate cancer detection in clinical practice in northern Sweden.

OBJECTIVE: The pattern of prostate-specific antigen (PSA) testing in clinical practice is largely unknown; it may be used either in asymptomatic men or in the work-up of men with urinary or other symptoms. The aim of this study was to investigate the pattern of PSA testing in clinical practice for men diagnosed with stage T1c prostate cancer in a region with no formal screening programme. MATERIAL AND METHODS: Using the Primary Prostate Cancer Register for Northern Sweden, all cases of stage T1c prostate cancer diagnosed between 1992 and 1999 in the city of Umeå were identified. The cause of PSA testing was assessed by examining the medical records. Men were categorized as asymptomatic, having lower urinary tract symptoms (LUTS) or having symptoms other than LUTS. Prospective registration of the cause of PSA testing in the entire region of Northern Sweden started in 2000. RESULTS: We found that in Umeå only 32/213 (15%) cases diagnosed with T1c prostate cancer were asymptomatic at the time of PSA testing, 55% of men had a PSA test as part of a work-up for LUTS and 30% had other symptoms. In 2000, 126 cases of stage T1c prostate cancer were diagnosed in the entire region and 20/126 (16%) of these men were asymptomatic. CONCLUSIONS: PSA testing was mostly used as a tool in the work-up of symptomatic patients in Umeå and also in the region of Northern Sweden. Further studies in other populations are needed.

Increased incidence of parathyroid adenomas following X-ray treatment of benign diseases in the cervical spine in adult patients.

OBJECTIVE: To determine whether or not exposure to ionizing radiation as an adult increases the risk of developing parathyroid adenomas. DESIGN AND PATIENTS: A cohort of 27 415 patients had received X-ray treatment to palliate pain originating from arthrosis and spondylosis from 1950 to 1964. In a subcohort of 8144 patients the cervical spine was the target, or one of the targets for the treatment. With the technique used it could be assumed that, as a rule, the parathyroid glands had been included in the treated volume. Patients with parathyroid adenomas were obtained from the Swedish Cancer Register from 1958 to 1995. The standardized incidence ratio (SIR) was calculated. RESULTS: The number of person-years at risk was 180 492 in the cohort exposed at the cervical spine, and 412 994 in the control cohort irradiated only at other sites. The calculated dose in the parathyroid region in the study cohort was about 1 Gy. The observed number of parathyroid adenomas in the study cohort was 22, and 24 in the control cohort. Expected numbers based on population data were 12.0 and 24.7, respectively, giving an SIR of 1.83 (95% CI 1.14-2.76) and 0.97 (CI 0.62-1.45), respectively. Mean age at exposure was 48.9 years (SD 10.2) and at diagnosis 71.5 years (SD 8.3). The time from exposure to diagnosis varied from 2 to 34 years (median 26 years). The excess relative risk was about 0.8 per Gy. CONCLUSION: Exposure to ionizing radiation to the cervical spine in adult age seems to be associated with an increased risk of developing parathyroid adenomas.

Thyroid cancer after X-ray treatment of benign disorders of the cervical spine in adults.

While there is very good epidemiological evidence for induction of thyroid cancer by radiation exposure in children, the risk for adults after exposure is still uncertain, especially when concerning relatively small radiation doses. A cohort of 27,415 persons which in 1950 through 1964 had received x-ray treatment for various benign disorders in the locomotor system (such as painful arthrosis and spondylosis) was selected from three hospitals in Northern Sweden. A proportion of this cohort, consisting of 8 ,44 persons (4,075 men and 4,069 women), had received treatment to the cervical spine and thereby received an estimated average dose in the thyroid gland of about 1 Gy. Standard incidence rates (SIR) were calculated by using the Swedish Cancer Register. In the cervical spine cohort, 22 thyroid cancers were found versus 13.77 expected (SIR 1.60, CI 1.00-2.42). The corresponding figures for women were 16 observed cases versus 9.60 expected cases (SIR 1.67: Cl 0.75-2.71). Most thyroid cancers (15 out of 22) were diagnosed > 15 years after the exposure. In the remaining part of the total cohort, i.e. those without cervical spine exposure, no increased risk of thyroid cancer was found (SIR 0.98, CI 0.64-1.38). The study strongly suggests that external radiation exposure of adults at relatively small doses increases the risk of thyroid cancer but also that this increase is very much lower than that reported after exposure in children.