Speaker
Description
Purpose Gamma index analysis and equipment are the most commonly used
methods and equipment for dosimetric control. Gamma index analysis is influenced
by multiple factors, and its accuracy is contingent upon various parameters and
variables. However, there has been limited research on how variations or errors in
dose delivery impact the results of gamma analysis, especially when conducted on
a faulty system. The purpose of this work is to determine Gamma Pass Rate (GPR)
consistency when across a dosimetric error and compare the different equipment
results. Method A total of 12 plans were selected. For each IMRT and VMAT plans dose
distribution measured with both electronic portal imaging device (EPID) and
MapCHECK 2 (MC2). 49 fields evaluated. These measurements are taken with 2
different output values (100 cGy = 100 MU / 104 cGy = 100 MU). %3/3mm and
gamma index > %95 used for the evaluation. Results All our measurements were pass at 100 cGy = 100 MU for the two
equipment. In case of 4% error (104 cGy = 100 MU), 38 fields were acceptable for
EPID and 15 fields were acceptable for MapCHECK 2. Many fields were acceptable
level even if there was an error in the dose. Conclusion It is important to realize the results of gamma index analysis are not
directly proportional to the decrease or increase at dose. Although the dose was
incorrect, the plans were found to be feasible. Also, the results may vary depending
on the equipment used. the presence of different results in each variable reduces
the reliability of the results. For this reason innovative approaches should be
investigated to improve results.
