Robust treatment planning for intensity modulated radiotherapy of prostate cancer based on coverage probabilities.
OBJECTIVE
To evaluate an optimization approach where coverage probabilities are incorporated into the optimization of intensity modulated radiotherapy (IMRT) to overcome the problem of margin definition in the case of overlapping planning target volume and organs at risk.


METHODS
IMRT plans were generated for three optimization approaches: based on a planning CT plus margin (A), on prostate and rectum contours from five pre-treatment CT plus margin (B), and on coverage probabilities (C). For approach (C), the probability of organ occupation was computed for each voxel from five pre-treatment CTs and the population distribution of systematic setup error and it was used as local weight in the costfunctions. Monte Carlo simulations of treatment courses were used to compute the probability distribution of prostate and rectal wall equivalent uniform dose (EUD).


RESULTS
Treatment simulations showed best and most robust results for prostate and rectal wall EUD within the population for (C). For (A) the rectal wall EUD was on average about 1.5 Gy greater than in (C), while the prostate EUD was lower than those from (C) for most of the patients for (B) (especially for those with great organ motion).


CONCLUSIONS
The incorporation of coverage probabilities as local weights allows for dose escalation as well as improved rectal sparing and results in a safer and more robust IMRT treatment.
Baum
Christoph
C
Sektion für Biomedizinische Physik, Universitätsklinik für Radioonkologie, Universität Tübingen, Germany. christoph.baum@gmx.de
Alber
Markus
M
Birkner
Mattias
M
Nüsslin
Fridtjof
F
D003198:Computer Simulation; D006801:Humans; D008297:Male; D008962:Models, Theoretical; D009010:Monte Carlo Method; D011336:Probability; D011467:Prostate / Q000000981:diagnostic imaging; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D012007:Rectum / Q000000981:diagnostic imaging; D012062:Relative Biological Effectiveness; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed