Rapid innovations in radiation therapy techniques have resulted in an urgent need for risk projection models for second cancer risks from high-dose radiation exposure, because direct observation of ...the late effects of newer treatments will require patient follow-up for a decade or more. However, the patterns of cancer risk after fractionated high-dose radiation are much less well understood than those after lower-dose exposures (0.1-5 Gy). In particular, there is uncertainty about the shape of the dose-response curve at high doses and about the magnitude of the second cancer risk per unit dose. We reviewed the available evidence from epidemiologic studies of second solid cancers in organs that received high-dose exposure (>5 Gy) from radiation therapy where dose-response curves were estimated from individual organ-specific doses. We included 28 eligible studies with 3434 second cancer patients across 11 second solid cancers. Overall, there was little evidence that the dose-response curve was nonlinear in the direction of a downturn in risk, even at organ doses of ≥60 Gy. Thyroid cancer was the only exception, with evidence of a downturn after 20 Gy. Generally the excess relative risk per Gray, taking account of age and sex, was 5 to 10 times lower than the risk from acute exposures of <2 Gy among the Japanese atomic bomb survivors. However, the magnitude of the reduction in risk varied according to the second cancer. The results of our review provide insights into radiation carcinogenesis from fractionated high-dose exposures and are generally consistent with current theoretical models. The results can be used to refine the development of second solid cancer risk projection models for novel radiation therapy techniques.
To review the reports of subsequent neoplasms (SNs) in the Childhood Cancer Survivor Study (CCSS) cohort that were made through January 1, 2006, and published before July 31, 2008, and to discuss the ...host-, disease-, and therapy-related risk factors associated with SNs.
SNs were ascertained by survivor self-reports and subsequently confirmed by pathology findings or medical record review. Cumulative incidence of SNs and standardized incidence ratios for second malignant neoplasms (SMNs) were calculated. The impact of host-, disease-, and therapy-related risk factors was evaluated by Poisson regression.
Among 14,358 cohort members, 730 reported 802 SMNs (excluding nonmelanoma skin cancers). This represents a 2.3-fold increase in the number of SMNs over that reported in the first comprehensive analysis of SMNs in the CCSS cohort, which was done 7 years ago. In addition, 66 cases of meningioma and 1,007 cases of nonmelanoma skin cancer were diagnosed. The 30-year cumulative incidence of SMNs was 9.3% and that of nonmelanoma skin cancer was 6.9%. Risk of SNs remains elevated for more than 20 years of follow-up for all primary childhood cancer diagnoses. In multivariate analyses, risks differ by SN subtype, but include radiotherapy, age at diagnosis, sex, family history of cancer, and primary childhood cancer diagnosis. Female survivors whose primary childhood cancer diagnosis was Hodgkin's lymphoma or sarcoma and who received radiotherapy are at particularly increased risk. Analyses of risk associated with radiotherapy demonstrated different dose-response curves for specific SNs.
Childhood cancer survivors are at a substantial and increasing risk for SNs, including nonmelanoma skin cancer and meningiomas. Health care professionals should understand the magnitude of these risks to provide individuals with appropriate counseling and follow-up.
Abstract
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.
A pooling of nine cohort studies of childhood external radiation exposure revealed a linear increase in risk of thyroid cancer and reaffirmed the “as low as reasonably achievable” principal for pediatric low dose radiation.
Although incidence of colorectal cancer (CRC) in the United States has declined in recent years, rates remain higher in men than in women and the male‐to‐female incidence rate ratio (MF IRR) ...increases progressively across the colon from the cecum to the rectum. Rates among races/ethnicities other than Whites or Blacks have not been frequently reported. To examine CRC rates by sex across anatomic subsite, age and racial/ethnic groups, we used the National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) program for cases diagnosed among residents of 13 registries during 1992–2006. Incidence rates were expressed per 100,000 person‐years and age‐adjusted to the 2000 US Standard Population; MF IRR and 95% confidence intervals were also calculated. Among each racial/ethnic group, the MF IRR increased fairly monotonically from close to unity for cecal cancers to 1.81 (Hispanics) for rectal cancers. MF IRRs increased with age most rapidly for distal colon cancers from <1.0 at ages <50 years to 1.4–1.9 at older ages. The MF IRR for rectal cancers also rose with age from about 1.0 to 2.0. For proximal cancer, the MF IRR was consistently <1.5; among American Indian/Alaska Natives, it was <1.0 across all ages. The MF IRRs for CRC vary markedly according to subsite and age but less by racial/ethnic group. These findings may partially reflect differences in screening experiences and access to medical care but also suggest that etiologic factors may be playing a role.
Cancer epidemiology articles often point out that cancer rates tend to be higher among males than females yet rarely is this theme the subject of investigation.
We used the Surveillance, Epidemiology ...and End Results program data to compute age-adjusted (2000 U.S. standard population) sex-specific incidence rates and male-to-female incidence rate ratios (IRR) for specific cancer sites and histologies for the period 1975 to 2004.
The 10 cancers with the largest male-to-female IRR were Kaposi sarcoma (28.73), lip (7.16), larynx (5.17), mesothelioma (4.88), hypopharynx (4.13), urinary bladder (3.92), esophagus (3.49), tonsil (3.07), oropharynx (3.06), and other urinary organs (2.92). Only 5 cancers had a higher incidence in females compared with males: breast (0.01), peritoneum, omentum, and mesentery (0.18), thyroid (0.39), gallbladder (0.57), and anus, anal canal, and anorectum (0.81). Between 1975 and 2004, the largest consistent increases in male-to-female IRR were for cancers of the tonsil, oropharynx, skin excluding basal and squamous, and esophagus, whereas the largest consistent decreases in IRR were for cancers of the lip and lung and bronchus. Male-to-female IRRs varied considerably by age, the largest increases of which were for ages 40 to 59 years for tonsil cancer and hepatocellular carcinoma. The largest decreases in male-to-female IRR by age, meanwhile, were for ages 30 to 49 years for thyroid cancer, ages >70 years for esophageal squamous cell carcinoma, and ages >30 years for lung and bronchus cancer.
These observations emphasize the importance of sex in cancer etiopathogenesis and may suggest novel avenues of investigation.
The objective of this study was to estimate solid cancer risk attributable to long‐term, fractionated occupational exposure to low doses of ionizing radiation. Based on cancer incidence for the ...period 1950–1995 in a cohort of 27,011 Chinese medical diagnostic X‐ray workers and a comparison cohort of 25,782 Chinese physicians who did not use X‐ray equipment in their work, we used Poisson regression to fit excess relative risk (ERR) and excess absolute risk (EAR) dose–response models for incidence of all solid cancers combined. Radiation dose reconstruction was based on a previously published method that relied on simulating measurements for multiple X‐ray machines, workplaces and working conditions, information about protective measures, including use of lead aprons, and work histories. The resulting model was used to estimate calendar year‐specific badge dose calibrated as personal dose equivalent (Sv). To obtain calendar year‐specific colon doses (Gy), we applied a standard organ conversion factor. A total of 1,643 cases of solid cancer were identified in 1.45 million person‐years of follow‐up. In both ERR and EAR models, a statistically significant radiation dose–response relationship was observed for solid cancers as a group. Averaged over both sexes, and using colon dose as the dose metric, the estimated ERR/Gy was 0.87 (95% CI: 0.48, 1.45), and the EAR was 22 per 104PY‐Gy (95% CI: 14, 32) at age 50. We obtained estimates of the ERR and EAR of solid cancers per unit dose that are compatible with those derived from other populations chronically exposed to low dose‐rate occupational or environmental radiation.
What's new?
High doses of radiation can increase cancer risk. However, less is known about the effects of chronic, long‐term exposure to low doses of radiation, such as that experienced by X‐ray technicians. In this study, the authors estimated the total radiation dose received by more than 27,000 Chinese medical workers, over a period of 30 years. They found that the risk for solid cancers increased significantly as cumulative radiation exposure increased. These results have important implications for the development of radiation‐safety precautions.
The majority of childhood cancer patients now achieve long-term survival, but the treatments that cured their malignancy often put them at risk of adverse health outcomes years later. New cancers are ...among the most serious of these late effects. The aims of this review are to compare and contrast radiation dose-response relationships for new solid cancers in a large cohort of childhood cancer survivors and to discuss interactions among treatment and host factors.
This review is based on previously published site-specific analyses for subsequent primary cancers of the brain, breast, thyroid gland, bone and soft tissue, salivary glands, and skin among 12,268 5-year childhood cancer survivors in the Childhood Cancer Survivor Study. Analyses included tumor site-specific, individual radiation dose reconstruction based on radiation therapy records. Radiation-related second cancer risks were estimated using conditional logistic or Poisson regression models for excess relative risk (ERR).
Linear dose-response relationships over a wide range of radiation dose (0-50 Gy) were seen for all cancer sites except the thyroid gland. The steepest slopes occurred for sarcoma, meningioma, and nonmelanoma skin cancer (ERR/Gy > 1.00), with glioma and cancers of the breast and salivary glands forming a second group (ERR/Gy = 0.27-0.36). The relative risk for thyroid cancer increased up to 15-20 Gy and then decreased with increasing dose. The risk of thyroid cancer also was positively associated with chemotherapy, but the chemotherapy effect was not seen among those who also received very high doses of radiation to the thyroid. The excess risk of radiation-related breast cancer was sharply reduced among women who received 5 Gy or more to the ovaries.
The results suggest that the effect of high-dose irradiation is consistent with a linear dose-response for most organs, but they also reveal important organ-specific and host-specific differences in susceptibility and interactions between different aspects of treatment.
Although exposure to moderate-to-high doses of ionizing radiation is the only established environmental risk factor for brain and CNS tumors, it is not clear whether this relationship differs across ...tumor subtypes, by sex or age at exposure, or at the low-to-moderate range of exposure. This systematic review summarizes the epidemiologic evidence on the association between ionizing radiation exposure and risk of brain/CNS tumors. Articles included in this review estimated radiation exposure doses to the brain and reported excess relative risk (ERR) estimates for brain/CNS tumors. Eight cohorts were eligible for inclusion in the analysis. Average age at exposure ranged from 8 months to 26 years. Mean dose to the brain ranged from 0.07 to 10 Gy. Elevated risks for brain/CNS tumors were consistently observed in relation to ionizing radiation exposure, but the strength of this association varied across cohorts. Generally, ionizing radiation was more strongly associated with risk for meningioma compared with glioma. The positive association between ionizing radiation exposure and risk for glioma was stronger for younger vs older ages at exposure. We did not observe an effect modification on the risk for meningioma by sex, age at exposure, time since exposure, or attained age. The etiologic role of ionizing radiation in the development of brain/CNS tumors needs to be clarified further through additional studies that quantify the association between ionizing radiation and risk for brain/CNS tumors at low-to-moderate doses, examine risks across tumor subtypes, and account for potential effect modifiers.
Childhood cancer survivors have an increased risk of secondary sarcomas. To better identify those at risk, the relationship between therapeutic dose of chemotherapy and radiation and secondary ...sarcoma should be quantified.
We conducted a nested case-control study of secondary sarcomas (105 cases, 422 matched controls) in a cohort of 14,372 childhood cancer survivors. Radiation dose at the second malignant neoplasm (SMN) site and use of chemotherapy were estimated from detailed review of medical records. Odds ratios (ORs) and 95% confidence intervals were estimated by conditional logistic regression. Excess odds ratio (EOR) was modeled as a function of radiation dose, chemotherapy, and host factors.
Sarcomas occurred a median of 11.8 years (range, 5.3-31.3 years) from original diagnosis. Any exposure to radiation was associated with increased risk of secondary sarcoma (OR = 4.1, 95% CI = 1.8-9.5). A dose-response relation was observed, with elevated risks at doses between 10 and 29.9 Gy (OR = 15.6, 95% CI = 4.5-53.9), 30-49.9 Gy (OR = 16.0, 95% CI 3.8-67.8) and >50 Gy (OR = 114.1, 95% CI 13.5-964.8). Anthracycline exposure was associated with sarcoma risk (OR = 3.5, 95% CI = 1.6-7.7) adjusting for radiation dose, other chemotherapy, and primary cancer. Adjusting for treatment, survivors with a first diagnosis of Hodgkin lymphoma (OR = 10.7, 95% CI = 3.1-37.4) or primary sarcoma (OR = 8.4, 95% CI = 3.2-22.3) were more likely to develop a sarcoma.
Of the risk factors evaluated, radiation exposure was the most important for secondary sarcoma development in childhood cancer survivors; anthracycline chemotherapy exposure was also associated with increased risk.
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