The Response of Tissues to Very Low Doses per Fraction: A Reflection of Induced Repair?
The linear-quadratic (LQ) equation is now used widely to model and predict the increase in total dose with decreasing dose per fraction needed for an isoeffective response to radiotherapy in normal tissues and tumors (Joiner 1989). This relationship reflects the gradual decrease in radiation effectiveness with lowered doses due to these doses being further and further back “on the shoulder” of the underlying survival curve for the cells at risk. Although there has been some indication in experimental studies in vivo that the LQ model can underpredict radiation response to doses per fraction in the range 1–2 Gy relative to higher doses per fraction, this appears to be due to incomplete repair between successive doses (Thames et al. 1988). Alternatively, studies on pig skin have suggested that the LQ model can overpredict radiation effect in the range 2–6 Gy, but this has been attributed to a combination of cellular repopulation and cell cycle redistribution affecting net tissue response (Hopewell and van den Aardweg 1991). Thus for doses greater than 1 Gy per fraction, the LQ model describes the radiation response of normal tissues reasonably well.
KeywordsFractionation Oncol Parkin Beryllium Rhabdomyosarcoma
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- Hopewell JW, van den Aardweg GJMJ (1991) Studies of dose-fractionation on early and late responses in pig skin: a reappraisal of the importance of the overall treatment time and its effects on radiosensitization and incomplete repair. Int J Radiat Oncol Biol Phys 21: 1441–1450PubMedCrossRefGoogle Scholar
- Joiner MC (1989) The dependence of radiation response on the dose per fraction. In: McNally NJ (ed) The scientific basis for modern radiotherapy. British Institute of Radiology, London, pp 20–26 (BIR Report 19 )Google Scholar
- 19.Marples B, Joiner MC (1992) The response of V79 cells to low radiation doses: evidence of enhanced sensitivity of the whole cell population. Radiat Res (in press)Google Scholar
- Parkins CS, Fowler JF (1986) The linear quadratic fit for lung function after irradiation with X-rays at smaller doses per fraction than 2 Gy. Br J Cancer 53 [Suppl VII]: 320–323Google Scholar