[Study of setup margins in radiation therapy: how many verification times and patients are required].
BACKGROUND
The purpose of this research is to require suitable numbers of verification times and patients for calculating the setup margin (SM) in radiotherapy.


METHODS
1) This simulation was performed using the standard normal distribution random number. The simulation used the seven levels of verification from 5 to 35 in 5 steps, and 35 patients. 2) The setup error in prostate radiotherapy at three hospitals was analyzed. Systematic error and random error were calculated from each patient's average value and standard deviation. Furthermore, we used the formula of J Stroom to calculate SM. Suitable numbers of verification times and patients were obtained from statistical analysis of the simulated results.


RESULTS
1) In the results of our simulations using random number, SM converged on 1.0 to 1.3 mm, regardless of the number of patients, when there were more than 15 verification times; 2) The results of clinical data were slightly different from the standard normal distribution, and more than 15 verification times and over 15 patients were required.


CONCLUSIONS
In conclusion, calculation of the SM in radiotherapy required more than 15 verification times and over 15 patients.
Department of Medical Physics, Division of Health Sciences, Osaka University Graduate School of Medicine.
Mitsuhiro
M
Matsumoto
Seiichi
S
Ohta
Yoshimi
Y
Ohno
Yuji
Y
Ogata
D003198:Computer Simulation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000532:radiotherapy; D011878:Radiotherapy / Q000592:standards*