In the case of dynamic radiotherapy plans, the fractionation schemes can have dosimetric
effects. Our goal was to define the effect of the fraction dose on the plan quality
and the beam delivery.Treatment plans were created for 5 early-stage lung cancer patients
with different dose schedules. The planned total dose was 60 Gy, fraction dose was
2 Gy, 3 Gy, 5 Gy, 12 Gy and 20 Gy. Additionally renormalized plans were created by
changing the prescribed fraction dose after optimization. The dosimetric parameters
and the beam delivery parameters were collected to define the plan quality and the
complexity of the treatment plans. The accuracy of dose delivery was verified with
dose measurements using electronic portal imaging device (EPID).The plan quality was
independent from the used fractionation scheme. The fraction dose could be changed
safely after the optimization, the delivery accuracy of the treatment plans with changed
prescribed dose was not lower. According to EPID based measurements, the high fraction
dose and dose rate caused the saturation of the detector, which lowered the gamma
passing rate. The aperture complexity score, the gantry speed and the dose rate changes
were not predicting factors for the gamma passing rate values.The plan quality and
the delivery accuracy are independent from the fraction dose, moreover the fraction
dose can be changed safely after the dose optimization. The saturation effect of the
EPID has to be considered when the action limits of the quality assurance system are
defined.
