The influence of output measurement time interval and tolerance on treatment dose deviation in photon external beam radiotherapy.
A method was developed to estimate the spread of treatment doses due to a given output measurement, time interval and action level in external photon beam radiotherapy. The method exploits empirical or simulated data of both output stability and the reproducibility of the absolute output measurements and relative constancy checks. The spread of an output and the probability that an output is outside the predefined tolerance limits were estimated for different quality control procedures of the output. The use of internationally recommended output measurement intervals of 3, 1 and 0.25 months together with an action level of +/-2% results in the out-of-tolerance probability up to 49%, 26% and 3%, respectively, while the output is kept within up to +/-5.5%, +/-4.0% and +/-2.0%, respectively. It was also found that the action level has more prominent relative influence than the measurement interval. The results suggest that similar treatment quality can be achieved by doubling the output measurement time interval and lowering the action level from +/-2% to +/-1.5% and the constancy check action level from +/-3% to +/-2%.
Kapanen
Mika
M
Radiation and Nuclear Safety Authority, STUK, Laippatie 4, 00881 Helsinki, Finland. mika.kapanen@hus.fi
Tenhunen
Mikko
M
Parkkinen
Ritva
R
Sipilä
Petri
P
Järvinen
Hannu
H
D000465:Algorithms; D006801:Humans; D010315:Particle Accelerators; D017785:Photons; D011336:Probability; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D011882:Radiotherapy, High-Energy / Q000379:methods*; D012984:Software; D013997:Time Factors