Similar to early effects late effects have a period before they develop. Unlike early effects which are usually due to the turnover time of epithelial layers, late effect latency is due to numerous factors.
Latency of Deterministic Effects
Deterministic effects occur after a threshold dose and worsen as dose increases. Radiation may induces numerous cellular processes in response to damage of DNA (and possibly other proteins). The latency of late deterministic effects is dependent on:
- The type, lifespan and repopulation of parenchymal cells (in a similar way to the early deterministic effects in epithelial layers)
- The amount of damage to connective tissue cells such as endothelial cells and fibroblasts, their own lifespan and the effects of intercellular communication with cytokines.
Latency of Stochastic Effects
Stochastic effects include radiation carcinogenesis and hereditary effects.
For carcinogenesis, the average age to develop a radiation induced malignancy is between 68-70, although it may occur earlier in people exposed to radiation in children. Following the atomic bomb attacks on Japan, there was a latent period of about 5 - 7 years for the development of leukaemia with cases falling in frequency by 15 years. Solid tumours may have a latent period from 10 to 60 years. Rather than a 'latent period', Hall suggests that radiation may simply increase the rate of solid tumour risk in the population.
The latency of hereditary effects is at least as long as it takes for the individual to procreate. It may rake even longer if the hereditary effect is autosomal recessive in nature - it may only become apparent when the damaged gene is paired in a homozygous individual.