Room: Exhibit Hall | Forum 4
Purpose: The main aim of this research is to model the interplay effect caused by number of parameters and minimize this effect by proper selection of these parameters for SBRT of liver tumors.
Methods: Ten patients of liver tumors, treated using VMAT technique for SBRT, were selected retrospectively. The dosimetric error due to interplay effect has been measured with micro ionization chamber (0.015cmÂ³) in a Quasar phantom with acrylic insert when quasar phantom programmed with the patient respiratory waveform. The effect due to patient breaths per minute (BPM), amplitude of respiration, fractional dose, relative degree of modulation (RDoM) of treatment plans because of different energy, degree of modulation (DoM) because of plan complexity and high dose rate (DR) with flattening filter free (FFF) beam has been measured
Results: The final equations have been modeled from 300 combinations of all the proposed parameters using multivariate regression analysis in jupyter notebook using python language. The mean dose error with standard deviation observed due to BPM, amplitude, RDM, fractional dose, DOM and high DR of 6 FFF and 10 FFF beam is -6.78 Â± 1.24%; -7.20 Â± 1.73%; -7.54 Â± 1.63%; -10.54 Â± 3.22%; -9.28 Â± 1.09%; -13.37 Â± 1.07% and -14.77 Â± 1.27% respectively
Conclusion: By choosing proper values of the parameters using the multivariate equations, dose error can be minimizing to 3 %. If patient BPM is more than 25 and amplitude of tumor motion less than 6mm, then dose error is reduced to 6 % for one fraction in SBRT and noticeable dose error is observed with DR 2200 MU/min FFF beam when fractional dose is >12 Gy/fraction.