Quality Assurance of Simultaneous Treatment of Multiple Targets Planned with Mono Isocenter using three Dimensional Conformal Radiotherapy (3DCRT) Technique

Objective: The purpose of this study was to conduct quality assurance (QA) of plans of four patients having multiple metastatic lesions (targets) simultaneously treated with mono isocentric three dimensional conformal radiotherapy. Material and Methods: Patient geometry was simulated with two/three water equivalent phantom shaving ionization chamber (IC) sleeves (IC-1, IC-2 & IC-3 as if targets are in different locations of patient).QA plans were generated using mono isocenter technique with a dose prescription of 3.0 Gy to the targets for point dose verification. Plan evaluations was done using dose volume histogram (DVH) in terms of maximum, mean doses to target, conformity index (CI) and homogeneity index (HI). A two dimensional ion chamber array detector was used for fluence verification. Results: Calculated maximum dose (Gy), mean dose (Gy), CI and HI values with standard deviation around the targets in all QA plans were 3.09±0.02, 3.03±0.02, 0.96±0.03 and 0.04±0.03 respectively. Measured point doses to all lesions were within ±2.0% of the computed dose in all QA plans. A pass percentage of 97% was obtained with the set criteria of 3mm distance to agreement and 3% dose difference for fluence verification around the targets in QA plans. Conclusion: Treatment execution of multiple targets simultaneously with mono isocenter can reduce positional errors and delivery time.