Potential impacts of circulatory diseases on the radiation health detriment: a first appraisal

1. Potential impacts of circulatory diseases on the radiation health detriment: a first appraisal Thierry SCHNEIDER The 3rd Workshop on Science and Values in Radiological Protection Decision Making and the 6th Asian Regional Conference on the Evolution of the System of Radiological Protection Tokyo, 6th-8thNovember, 2012

2. Context • Risk of circulatory diseases already mentioned in ICRP Publication 8 in 1965! • Recent publications of epidemiological studies show significant increase for both mortality and incidence • The debate during the Second Science and Values seminar, organised in December 2009, pointed out the interest for a preliminary assessment of the potential quantitative impact on the radiation health detriment • ICRP Publication 118 on Tissue Reaction Effects

3. Objective of the preliminary assessment • Assessing the excess risk of circulatory diseases for two assumptions: • Late tissue reaction effect with a threshold at 0.5 Gy (on the basis of ICRP Publication 118) • Linear no-threshold extrapolation of excess relative risk to low doses (on the basis of available epidemiological studies) • Discussing the potential consequences on ICRP health detriment

4. Health detriment • Radiation health detriment: introduced in 1973 by ICRP in its Publication 22 and adopted in its general recommendations in 1977 (Publication 26) • Defined as: « The total harm to health experienced by an exposed group and its descendants as a result of the group’s exposure to a radiation source. » (ICRP Pub. 103) • Directly derived from the LNT model • A key role in the implementation of the ICRP radiation protection system: justification, optimisation and limitation principles

5. Meaning of the health detriment • A risk-indicator, including mortality, morbidity, life expectancy and severity of the diseases • Dedicated to risk management • Based on available and current scientific knowledge • Including value judgements • Evolving with time to take into account new knowledge 5

6. Late tissue reaction and threshold for circulatory diseases (1) • ICRP Publication 118 on Tissue Reaction Effects suggests that: • “Absorbed dose threshold for circulatory disease may be as low as 0.5 Gy to the heart or brain” • “0.5 Gy may lead to approximately 1% of individuals developing the disease in question (i.e. cardiovascular and cerebrovascular diseases) > 10 years after exposure” • “It is unclear from available evidence whether or not the threshold is the same for acute, fractionated, and chronic exposures” • “The threshold dose is assumed to be the same for all three types of exposures” (acute, fractionated, and chronic) • “Particular emphasis should be placed on optimisation”

7. Late tissue reaction and threshold for circulatory diseases (2) • Assuming simple assumption for risk calculation leads to: • 1% of effects (mortality + morbidity) per 0.5 Gy • Assuming around 20% for the lethality fraction for circulatory diseases (according to French data) • Without information on the dose-effect relationship, we can considered that the risk could be estimated in the range of: • 0.2 % of fatal effects per 0.5 Gy (if applied to circulatory diseases) • 0.4 % of fatal effects per 0.5 Gy (if applied separately to cardio & cerebrovascular diseases)

8. Assuming a LNT relationship for circulatory diseases • Calculations performed, using the ASQRAD code (co-developed by CEPN and HPA in 1996) with following assumptions: • Life Span Study (LSS) for circulatory diseases (Shimizu et al., BMJ, 2010): • With constant excess relative risk (ERR) • Multiplicative model with 10 y latency and DDREF = 2 • UNSCEAR 2000 model for cancer and leukaemia • “Population exposure” based on mortality rates for FRANCE (2007) • Sensitivity analysis: • UK population (2008) • Mayak cohort (ERR for internal exposure for heart diseases) • Introduction of lethality fraction (France 2006)

9. Preliminary results for mortality (1) • Results for mortality (population exposure) - Excess lifetime risk of deaths for France 2007

10. Preliminary results for mortality (2) • Excess deaths for 100,000 persons - 2007 French population - Effective dose = 1 Sv – Distribution for both male and female

11. Estimates for the contribution to detriment • Estimated increase of detriment for circulatory diseases weighted with years of life lost: 11 % including : • Heart diseases: 9 % • Cerebrovascular diseases: 2 % • Total radiation health detriment for whole population : • Current value (ICRP Publication 103): 5.7 10-2 per Sv • Potential value including circulatory diseases: 6.3 10-2 per Sv

12. Sensitivity analysis

13. Preliminary conclusions (1) • Results to be considered with caution • Similar values for Late tissue reaction simple risk calculations (for dose > 0.5 Gy) and excess risk of death estimated for France with LSS: • 0.2 to 0.4 . 10-2 per 0.5 Gy for late tissue reaction • 0.7 . 10-2 per 0.5 Sv for lifetime excess death associated with circulatory diseases (France + LSS) • 0.3 . 10-2 per 0.5 Sv for the detriment associated with circulatory diseases (France + LSS) • Larger differences between late tissue reaction, simple risk calculations, and upper calculations for detriment (UK + Mayak)

14. Preliminary conclusions (2) • Need to further investigate: • LNT calculations: • Calculations for different populations, risk models and incidence data (see Little et al. EHP, Nov. 2012) • Excess death ranging from 2.5 %/Sv to 8.5 %/Sv • Consistent with our analysis • Assumptions adopted for the extrapolation of the calculation to low dose and dose rate and to the lifelong risk for the whole population • Application of the optimisation principle for late tissue reactions with threshold