Dosimetric Validation of Volumetric Modulated Arc Therapy with Three 6MV Beam-Matched Linear Accelerators

Abstract

<br /> <strong><span style="font-size: small;">Background: </span></strong><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">To avoid inconvenience to patients due to linear accelerator down time in busy radio-therapy departments, treatment plans can be switched between linear accelerators provided that all exhibit the same same dosimetric characteristics. In other words linear accelerators should be beam-matched. </span></span><strong><span style="font-size: small;">Aim: </span></strong><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">The aim of this study </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">was to evaluate the clinical significance of beam-matching using VMAT plans. </span></span><strong><span style="font-size: small;">Materials and Methods: </span></strong><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">Dosimetric data with a 6MV beam from am Clinac 2100CD were taken as baseline values and other two units, a 2300CD and a </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">Unique Performance, were factory tuned in accordance. An analysis of PDD data was performed for different field sizes to evaluate energy matching. Beam profiles for field sizes of 10×10 cm</span></span><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;"><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;">2 </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">and 40 × 40 cm</span></span><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;"><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;">2 </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">at depths of 1.5 cm and 10 cm were analyzed. The relative output factor and MLC dosimetric properties were compared with each machine to determine variability among the different models. Thirty patients from our database were selected, ten each for head and neck, thorax and pelvis sites. VMAT plans were created in the Eclipse treatment planning system for a Clinac 2100 </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">CD for reference. and verification plans were created for each to compare point dose measurements. </span></span><strong><span style="font-size: small;">Results: </span></strong><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">The TPR </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">20/10 for 10 × 10 cm</span></span><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;"><span style="font-family: Times New Roman,Times New Roman; font-size: xx-small;">2 </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">was well matched, showing no energy differences. Deviation of all point dose measurements fell </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">within ±3%. Planar dose maps all showed greater than 95% of points with a passed area γ-value less than 1. </span></span><strong><span style="font-size: small;">Conclusion: </span></strong><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">Our study evaluation of beam matching with treatment planning modeling showed good agreement fior 6 MV beams </span></span><span style="font-family: Times New Roman,Times New Roman; font-size: small;"><span style="font-family: Times New Roman,Times New Roman; font-size: small;">across all three linear accelerators used in our clinical environment. </span></span>