The impact of IMRT and proton radiotherapy on secondary cancer incidence.
OBJECTIVE
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.


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).


CONCLUSIONS
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.
Schneider
Uwe
U
Division of Medical Physics, Department of Radiation Oncology and Nuclear Medicine, Triemli Hospital Zürich, 8063 Zürich, Switzerland. uwe.schneider@psi.ch
Lomax
Antony
A
Pemler
Peter
P
Besserer
Jürgen
J
Ross
Dieter
D
Lombriser
Norbert
N
Kaser-Hotz
Barbara
B
D004307:Dose-Response Relationship, Radiation; D006801:Humans; D015994:Incidence; D008297:Male; D008962:Models, Theoretical; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D019047:Phantoms, Imaging; D011336:Probability; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D061766:Proton Therapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated / Q000009:adverse effects; D012062:Relative Biological Effectiveness; D012307:Risk Factors; D012542:Scattering, Radiation; D014057:Tomography, X-Ray Computed; D011522:Protons
D011522:Protons