The Effect of Total Fields' Area and Dose Distribution in Step and Shoot IMRT on Gamma Passing Rate Using OCTAVIUS ۴D-۱۵۰۰ Detector Phantom

Introduction: Quality assurance is necessary for every IMRT plan.‎Octavius ۴D-۱۵۰۰ detector phantom is ‎one of the new phantoms for ‎determining the treatment plan quality‎.‎ This study aimed to examine the IMRT plans using the ‎Octavius ۴D-۱۵۰۰‎ ‎to determine if ‎it is a reliable, ‎dependable, and durable.  Material and Methods: IMRT QA conducted for ۳۰ cases: HN and pelvis. The Monaco TPS used for treatment planning. The treatment plans ‎were then applied ‎to the Octavius ۴D-۱۵۰۰ phantom (virtually and actually), ‎‎the γ-index was calculated in VeriSoft program to evaluate the IMRT plans. Results: Significant differences were observed between the ‎‎‎measured and calculated dose distributions for HN and pelvic plans, while the treatment ‎sites did not affect the GP rate. The results of the global Gp ‎ were higher than the local GP, ‎regardless of the study criteria. The ‎HN plans ‎showed a more significant difference ‎than the pelvic plans. The HN plans, ‎a ‎strong significant correlation was found between the total ‎fields’area and %GP in both global ‎‎and local analyses, while in the pelvic plans, there was only a significant association with the ‎local %GP. Conclusion: The measured dose distributions significantly different from calculated distributions. The relationship between the ‎‎fields’ ‎ area ‎and ‎‎‎%GP was inverse. In the HN plans, a ‎significant correlation found between the total ‎‎fields’ ‎area ‎and %GP in both global and ‎local, while only local %GP in the pelvic plans was significant correlation. Overall, the Octavius ۴D-۱۵۰۰ detector phantom ‎might be applicable for ‎assessing the QA of IMRT plans.

Keywords:

Gamma Passing Rate , Dose Distribution , Intensity Modulated Radiotherapy , Quality Assurance