Is the linear no-threshold (LNT) model relevant for radiotherapy?

Abstract

Initially considered as a kind of radiobiological law, the linear no-threshold (LNT) model, which by definition supports the absence of any threshold for cancer risk induction after irradiation, is nowadays more reasonably described as a pragmatic and prudent approach by the International Organizations. However, it remains today a dogma in radiological protection. Actually, this model had been essentially developed for the radiological protection of a general population against low, and sometimes very low, doses of irradiation. Radiation oncologists are dealing with a totally different situation since they deliver, on purpose, high doses of radiations in more or less limited volumes of the body of cancer patients, patients for whom no other alternatives do exist to get rid of their malignant tumors. Simultaneously, the radiation oncologists inevitably give low and even very low doses at distance from the so-called target volumes. In such a specific situation, what is the carcinogenicity of these low doses and the relevance of the LNT model in radiotherapy? Thus, this paper addresses three critical questions: 1) what is the risk acceptability of the radiation doses delivered by radiotherapy of malignant tumors? 2) what is the real carcinogenic risk of (very) low doses delivered at distance from the target volume? 3) are the clinical radiotherapy data, i.e., the number of second primary cancers, accumulated since more than a century, consistent with the LNT model? In conclusion, the LNT model appears to be poorly adapted to the high doses locally delivered to cancer patients and dramatically overestimates, in most cases, the risk of secondary radio-induced cancers. In fine, the real risk of the LNT model in radiotherapy would be to promote radiophobia in cancer patients and to see some of them turning away from a life-saving treatment.

Évaluation des risques en radioprotection : aller au-delà de la réponse du modèle linéaire sans seuil / Risk evaluation in radiological protection: going beyond the linear no-threshold model response

“…In this issue of Radioprotection, Jean-Marc Cosset uses the linear no-threshold model (LNT) to examine the assessment of the risks associated with radiotherapy (Cosset, 2022).…”

“…Among the numerous issues from Jean-Marc Cosset two points deserve much attention: if the LNT model is verified "nearly all radiotherapy patients ...should develop a radio-induced cancer" (Cosset, 2022). This is not clearly the case on the basis of clinical observations; effective dose expressed in mSv involves whole body doses or a weighted average of doses over the whole body whereas radiotherapy doses (but also medical diagnosis dose) are delivered to a small part of the body (targeting the tumor or the investigated organ).…”

“…Dans ce numéro de Radioprotection, Jean-Marc Cosset utilise le modèle linéaire sans seuil (LNT) pour s'interroger sur l'évaluation des risques liés à la radiothérapie (Cosset, 2022).…”

“…Parmi les nombreux problèmes soulevés par Jean-Marc Cosset, deux points méritent de s'y attarder : si le modèle LNT était vérifié, « presque tous les patients en radiothérapie... devraient développer un cancer radio-induit » (Cosset, 2022) ; ce n'est clairement pas le cas sur la base des observations cliniques ; la notion de dose efficace, exprimée en mSv, implique la prise en compte de doses au corps entier ou d'une moyenne pondérée des doses sur tout le corps alors que les doses de radiothérapie (mais aussi les doses de diagnostic médical) sont délivrées à une petite partie du corps ciblant la tumeur ou l'organe investigué.…”

Le retour d’expérience devrait être érigé en principe fondamental de la radioprotection / Experience feedback should be established as a fundamental principle of radiological protection

“…Other examples could be taken from publications of the last few months in Radioprotection: (i) the benchmark study of nuclear accident post-accidental management doctrines (Bertho et al, 2022), (ii) the relevance of the linear non-threshold model (LNT) for the assessment of the risks associated with radiotherapy (Cosset, 2022), (iii) the comparison of large-scale radiological emergency situations and COVID-19 regarding strategies used for mass testing of persons with biodosimetry and PCR respectively (Swartz et al, 2022).…”