The impact of IMRT and proton radiotherapy on secondary cancer incidence

Strahlenther Onkol. 2006 Nov;182(11):647-52. doi: 10.1007/s00066-006-1534-8.


Background and purpose: There is concern about the increase of radiation-induced malignancies with the application of modern radiation treatment techniques such as intensity-modulated radiotherapy (IMRT) and proton radiotherapy. Therefore, X-ray scatter and neutron radiation as well as the impact of the primary dose distribution on secondary cancer incidence are analyzed.

Material and methods: The organ equivalent dose (OED) concept with a linear-exponential and a plateau dose-response curve was applied to dose distributions of 30 patients who received radiation therapy of prostate cancer. Three-dimensional conformal radiotherapy was used in eleven patients, another eleven patients received IMRT with 6-MV photons, and eight patients were treated with spot-scanned protons. The treatment plans were recalculated with 15-MV and 18-MV photons. Secondary cancer risk was estimated based on the OED for the different treatment techniques.

Results: A modest increase of 15% radiation-induced cancer results from IMRT using low energies (6 MV), compared to conventional four-field planning with 15-MV photons (plateau dose-response: 1%). The probability to develop a secondary cancer increases with IMRT of higher energies by 20% and 60% for 15 MV and 18 MV, respectively (plateau dose-response: 2% and 30%). The use of spot-scanned protons can reduce secondary cancer incidence as much as 50% (independent of dose-response).

Conclusion: By including the primary dose distribution into the analysis of radiation-induced cancer incidence, the resulting increase in risk for secondary cancer using modern treatment techniques such as IMRT is not as dramatic as expected from earlier studies. By using 6-MV photons, only a moderate risk increase is expected. Spot-scanned protons are the treatment of choice in regard to secondary cancer incidence.

Publication types

  • Comparative Study

MeSH terms

  • Dose-Response Relationship, Radiation
  • Humans
  • Incidence
  • Male
  • Models, Theoretical
  • Neoplasms, Radiation-Induced / epidemiology*
  • Phantoms, Imaging
  • Probability
  • Prostatic Neoplasms / diagnostic imaging
  • Prostatic Neoplasms / radiotherapy*
  • Proton Therapy*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted
  • Radiotherapy, Conformal*
  • Radiotherapy, Intensity-Modulated* / adverse effects
  • Relative Biological Effectiveness
  • Risk Factors
  • Scattering, Radiation
  • Tomography, X-Ray Computed


  • Protons