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SIRiiM International Society for Radiation Medicine, Immunity and Immunomodulation

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Radiation immunity

Low-dose ionizing radiation modulates inflammation rather than killing tissue. That statement is not a treatment claim. It is the reason SIRiiM exists.

A discontinuous dose–response

Radiation at doses far below those used to treat cancer — typically fractions of a gray rather than tens of grays — acts through immunological pathways and the behaviour of endothelial cells, leukocytes and macrophages. The DEGRO consensus on radiotherapy of non-malignant disorders reviews that experimental basis.1

The effect is not linear. Across leukocyte–endothelial adhesion, adhesion-molecule and cytokine expression, apoptosis induction, and macrophage and neutrophil behaviour, the immunomodulatory signal peaks somewhere around 0.3–0.7 Gy and falls off on either side — a window empirically identified in clinical practice before the mechanism was described.2

A peak is a finding. A smooth toxicological gradient would have been easier to ignore.

The mechanism is real. That is not the same as the treatment working.

In cancer, a small late risk is set against a lethal disease. In a boil, a flare of psoriasis, or a pneumonia that most patients survive, the arithmetic is completely different — and it is the arithmetic, not the mechanism, that decides whether a treatment should exist. SIRiiM will not collapse those two sentences.

The COVID-19 lesson

When COVID-19 pneumonia overwhelmed critical care in 2020, whole-lung low-dose radiation was proposed on exactly the reasoning above. Historical pneumonia series and a modern adaptive-response literature made the idea look less exotic than it sounded. Trials opened. A joint NCI / NCRP / NIAID workshop declined either to endorse or refute the approach, and published a framework for how such studies should be run.3

Single-arm and matched-control studies looked encouraging, including prospective work that reported improved oxygenation and inflammatory-marker shifts after a single whole-lung treatment.4

The randomised, double-blind trial did not. Ventilated patients randomised to 1 Gy whole-lung LDRT or sham irradiation showed no difference in ventilator-free days, and 28-day survival was identical at 63.6% in both arms. Whole-lung LDRT failed to improve clinical outcomes in that setting.5

Governing lesson. Uncontrolled data on an inflammatory illness that fluctuates on its own will look like a treatment effect whether or not one exists. Every future indication SIRiiM considers has the same shape COVID-19 pneumonia had in early 2020: a real mechanism, a desperate need and encouraging uncontrolled reports.

What SIRiiM will study next

Related work on the radiation adaptive response spans oncology, neurodegenerative disease, pandemic response and space medicine, and reaches the same conclusion each time: the phenomenon is real, the mechanism is incompletely elucidated, and the field lacks standardised protocols.6

  • Which immune pathways carry the 0.3–0.7 Gy peak — and whether they can be produced or blocked pharmacologically.
  • Whether that window is the same across tissues and diseases.
  • Which inflammatory conditions have a risk–benefit arithmetic that could justify irradiating a non-malignant disease at all.
  • Shared protocols, endpoints and a venue for negative results — the job of IJRM-SSS.

Continue with the abscopal effect, the arthritis indication, or the PCP immunity tutorial.

Informational Society education, not medical advice. Low-dose radiation for infections, including COVID-19 pneumonia, is investigational and belongs only in an appropriate clinical-trial or compassionate-use setting.

References

  1. Reichl B, Block A, Schäfer U, et al. DEGRO practical guidelines for radiotherapy of non-malignant disorders: part I. Strahlenther Onkol. 2015;191(9):701–709. doi:10.1007/s00066-015-0865-8
  2. Rödel F, Frey B, Manda K, et al. Immunomodulatory properties and molecular effects in inflammatory diseases of low-dose x-irradiation. Front Oncol. 2012;2:120. doi:10.3389/fonc.2012.00120
  3. Prasanna PG, Woloschak GE, DiCarlo AL, et al. Low-dose radiation therapy (LDRT) for COVID-19: benefits or risks? Radiat Res. 2020;194(5):452–464. doi:10.1667/RADE-20-00211.1
  4. Hess CB, Nasti TH, Dhere VR, et al. Immunomodulatory low-dose whole-lung radiation for patients with coronavirus disease 2019–related pneumonia. Int J Radiat Oncol Biol Phys. 2021;109(4):867–879. doi:10.1016/j.ijrobp.2020.11.049
  5. Papachristofilou A, Finazzi T, Blum A, et al. Low-dose radiation therapy for severe COVID-19 pneumonia: a randomized double-blind study. Int J Radiat Oncol Biol Phys. 2021;110(5):1274–1282. doi:10.1016/j.ijrobp.2021.02.054
  6. Kanani A, Krasowska J, Fornalski KW, et al. Adaptive response: a scoping review of its implications in medicine, space exploration, and beyond. Dose Response. 2025;23(3). doi:10.1177/15593258251360051