Do low dose-rate bystander effects influence domestic radon risks?

[epirad@mchsi.com]

Int J Radiat Biol 2002 Jul;78(7):593-604  



Do low dose-rate bystander effects influence domestic 

radon risks?



Brenner DJ, Sachs RK.



Center for Radiological Research, Columbia University, 

630 West 168th Street, New York, NY 10032, USA.



PURPOSE: Radon risks derive from exposure of bronchio-

epithelial cells to high-linear energy transfer (LET) 

alpha-particles. alpha-particle exposure can result in 

bystander effects, where irradiated cells emit signals 

resulting in damage to nearby unirradiated bystander 

cells. This can result in non-linear dose-response 

relations, and inverse dose-rate effects. Domestic radon 

risk estimates are currently extrapolated from miner 

data, which are at both higher doses and higher dose-

rates, so bystander effects on unhit cells could play a 

large role in the extrapolation of risks from mines to 

homes. Therefore, we extend an earlier quantitative 

mechanistic model of bystander effects to include 

protracted exposure, with the aim of quantifying the 

significance of the bystander effect for very prolonged 

exposures. MATERIALS AND METHODS: A model of high-LET 

bystander effects, originally developed to analyse 

oncogenic transformation in vitro, is extended to low 

dose-rates. The model considers radiation response as a 

superposition of bystander and linear direct e It 

attributes bystander effects to a small subpopulation of 

hypersensitive cells, with the bystander contribution 

dominating the direct contribution at very low acute 

doses but saturating as the dose increases. Inverse dose-

rate effects are attributed to the replenishment of the 

hypersensitive subpopulation during prolonged 

irradiation. RESULTS: The model was fitted to dose- and 

dose-rate-dependent radon-exposed miner data, suggesting 

that one directly hit target bronchio-epithelial cell 

can send bystander signals to about 50 neighbouring 

target cells. The model suggests that a naive linear 

extrapolation of radon miner data to low doses, without 

accounting for dose-rate, would result in an 

underestimation of domestic radon risks by about a 

factor of 4, a value comparable with the empirical 

estimate applied in the recent BEIR-VI report on radon 

risk estimation. CONCLUSIONS: Bystander effects 

represent a plausible quantitative and mechanistic 

explanation of inverse dose-rate effects by high-LET 

radiation, resulting in non-linear dose-response 

relations and a complex interplay between the effects of 

dose and exposure time. The model presented provides a 

potential mechanistic underpinning for the empirical 

exposure-time correction factors applied in the recent 

BEIR-VI for domestic radon risk estimation.



> Thank you, Maury.  My brother and my first husband are both Korean War 

> veterans  .  It was truly the "forgotten war."

> 

> Ruth Weiner, Ph. D.

> ruthweiner@aol.com

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