The impact of dose escalation on secondary cancer risk after radiotherapy of prostate cancer.
OBJECTIVE
To estimate secondary cancer risk due to dose escalation in patients treated for prostatic carcinoma with three-dimensional conformal radiotherapy (3D-CRT), intensity-modulated RT (IMRT), and spot-scanned proton RT.


METHODS
The organ equivalent dose (OED) concept with a linear-exponential, a plateau, and a linear dose-response curve was applied to dose distributions of 23 patients who received RT of prostate cancer. Conformal RT was used in 7 patients, 8 patients received IMRT with 6- and 15-MV photons, and 8 patients were treated with spot-scanned protons. We applied target doses ranging from 70 Gy to 100 Gy. Cancer risk was estimated as a function of target dose and tumor control probability.


RESULTS
At a 100-Gy target dose the secondary cancer risk relative to the 3D treatment plan at 70 Gy was +18.4% (15.0% for a plateau model, 22.3% for a linear model) for the 6-MV IMRT plan, +25.3% (17.0%, 14.1%) for the 15-MV IMRT plan, and -40.7% (-41.3%, -40.0%) for the spot-scanned protons. The increasing risk of developing a radiation-associated malignancy after RT with increasing dose was balanced by the enhanced cure rates at a larger dose.


CONCLUSIONS
Cancer risk after dose escalation for prostate RT is expected to be equal to or lower than for conventional 3D treatment at 70 Gy, independent of treatment modality or dose-response model. Spot-scanned protons are the treatment of choice for dose escalation because this therapy can halve the risk of secondary cancers.
Schneider
Uwe
U
Division of Medical Physics, Department of Radiation Oncology and Nuclear Medicine, Triemli Hospital, Zürich, Switzerland. uwe.schneider@psi.ch
Lomax
Antony
A
Besserer
Jürgen
J
Pemler
Peter
P
Lombriser
Norbert
N
Kaser-Hotz
Barbara
B
D003198:Computer Simulation; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D008297:Male; D008954:Models, Biological; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology*; D016016:Proportional Hazards Models; D011471:Prostatic Neoplasms / Q000150:complications / Q000453:epidemiology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000706:statistics & numerical data*; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors