RERF Report No. 5-16

Paper published in the Radiation Research§“Solid cancer incidence among the Life Span Study of atomic bomb survivors: 1958–2009”
Eric J. Grant, Alina Brenner, Hiromi Sugiyama, Ritsu Sakata, Atsuko Sadakane, Mai Utada, Elizabeth
K. Cahoon, Caitlin M. Milder, Midori Soda, Harry M. Cullings, Dale L. Preston, Kiyohiko Mabuchi,
Kotaro Ozasa
Radiat Res 2017 (187:1-25) (electronic version prior to print publication)(doi: 10.1667/RR14492.1)
Study Findings
This study showed that the incidence of all solid cancers was higher with increasing radiationdose, a finding that was similar to previous RERF reports that have explored this relationship. This
study investigated the radiation risks of all solid cancers in aggregate and updated the results with 11
additional years of follow-up since the last report. An important new aspect of this study was theinclusion of smoking in the risk analyses. Smoking is known to be a potent carcinogen but when
adjusting for its effects, the radiation risks of solid cancer occurrence were found to be unaffected.
Future studies will carefully investigate the risks in individual organs or organ systems.
Explanation
We conducted a study on the relationship between solid cancer incidence and radiation dose to
the colon among the Life Span Study (LSS) of atomic bomb survivors. Colon dose was chosenbecause the colon is a large, central organ and was considered representative of the whole-body
exposure received by the atomic bomb survivors. Data on solid cancer occurrence was collected fromthe Hiroshima and Nagasaki cancer registries during the follow-up period 1958–2009. Adjustment forsmoking was included in the analysis, and the data on smoking were collected from periodic mailsurveys and surveys conducted during clinical visits.
1. Study purpose
An important task of the long-term follow-up of the atomic bomb survivors is to document theoccurrence and risks of solid cancers. With aging, cancer is a common health affliction in anypopulation. In the atomic bomb survivors, cancer occurs more often with increasing radiation dosefrom the bombings. The purpose of this study was to quantify the risks from radiation exposure ofsolid cancer incidence. This is the third RERF report on the risks of solid cancer incidence.
2. Study methods
LSS cohort members in this study numbered 105,444 and included those who were alive with nocancer history as of January 1, 1958, and had a known radiation dose. First primary incident cancers
were identified through linkage with Hiroshima and Nagasaki cancer registries. Follow-up was carriedout through December 31, 2009. We used smoking history information based on mail and clinicalsurveys. Individual radiation doses to the colon were estimated for each cohort member using therevised DS02 dosimetry system (DS02R1). Risks of solid cancers as a function of radiation dose, sex,
pack-years of smoking*, age at exposure, and attained age were estimated using statistical models.
Estimates of risk were expressed as an excess relative risk (ERR).
ERR is reported as relative to another person without radiation exposure. As background rates ofcancers change rapidly with aging, relative risk must be indicated at a particular age. Further, since
age at the time of exposure also modifies the relative risk of contracting a cancer due to radiation, age
at exposure must also be specified. We reported radiation risks at 70 years for a person exposed at age
30. This practice is common with RERF results and is the same as the methodology used in ourprevious cancer incidence studies.
*When evaluating health impact of smoking, this index is used to indicate “tobacco consumption per
day x number of years of smoking.” In Japan, tobacco consumption per day is calculated as1

RERF Report No. 5-16

number of cigarettes; in the case of Western countries, consumption is typically indicated bynumber of packs (1 pack = 20 cigarettes).

3. Study results
A total of 22,538 incident first primary solid cancer cases were observed over the follow-up
period. In the 11 years since the last report, 5,918 new cases occurred. This figure represents 26% of
the total number of cases, reflecting the advanced age of the cohort.
(1) Linear dose response with and without adjustment for smoking
Using a sex-averaged, linear dose response relationship, the ERR per gray of radiation (ERR/Gy)
was 0.50 (i.e. 50% higher) before adjusting for smoking for a person aged 70 years and exposed at age30 years. After the adjustment, the ERR value was 0.47, indicating that smoking made almost nodifference in the radiation risk estimates.
(2) Sex-specific dose response
In women, a linear dose response described the data most accurately, with a 0.64/Gy ERR at
attained age 70 after exposure at age 30. For men, the ERR was 0.20 and the shape of the dose
response was curvilinear. Higher ERR values for women are common and are generally thought to bedue to the lower natural rates of solid cancers observed in women compared with men. However, thecurved dose response shape for cancer incidence data found in the men of this study had not beenpreviously observed.
Study SignificanceThis study showed that solid cancer risks remain elevated more than 60 years after radiation
exposure. For the first time in a major RERF report, we adjusted for smoking. While there was astrong risk of cancers due to smoking, the strength and shape of the radiation dose response was notaffected. Mathematical models developed by RERF that describe the radiation risks of cancers areused by many scientific groups around the world to help formulate radiation protection policies forworkers and the public. After 11 years of additional follow-up, the linear dose response estimate wasnearly unchanged from the value reported in our previous paper. However, the male dose response
exhibited a more curved response, which had not been previously observed. We are carefully
considering the causes of this change. This study considered all solid cancers in aggregate. We areworking on a series of additional studies that will investigate the dose response of specific organs andorgan systems.
The Radiation Effects Research Foundation has studied A-bomb survivors and their offspring in Hiroshimaand Nagasaki for around 70 years. RERF’s research achievements are considered the principal scientific basis
for radiation risk assessment by the United Nations Scientific Committee on the Effects of Atomic Radiation(UNSCEAR) and for recommendations regarding radiation protection standards by the InternationalCommission on Radiological Protection (ICRP). RERF expresses its profound gratitude to the A-bomb survivors
and survivors’ offspring for their cooperation in our studies.
§Radiation Research, which is an official monthly journal of the Radiation Research Society, publishes
original peer-reviewed papers and review articles on radiation effects and related issues in the fields ofphysics, chemistry, biology, and medicine. (Impact factor in 2015: 2.67)

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