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Inter-Comparison of Clinical Plans Created On Truebeam with Trilogy and Clinac

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M Sharma

M Sharma*, Y Wu , S Kim , Virginia Commonwealth University, Richmond, VA


SU-E-T-505 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The purpose of this study is to investigate the dosimetric differences in clinical treatment plans when machine parameters are switched from Varian Truebeam to older Varian models and vice-versa. This is used to determine the clinically-safe limits to directly transfer patients from Truebeam to Trilogy or Clinac.
Methods: Thirty-two patients with cancer of different treatment sites such as lung, head-and-neck, prostate and breast were studied. The clinically approved IMRT, VMAT or 3D conformal treatment plans were delivered either on Truebeam or Clinac/Trilogy. Keeping the monitor units, fraction size and other machine parameters the same, the plans were recomputed on a different Varian linear accelerator (e.g., Truebeam plans were recomputed on Trilogy and vice-versa). The plans comparison was done using the target D98 and normal organ D2, D10, D20, D30, D50 and D70 dose metrics.
Results: The per-fraction dose-difference in the PTV-D98 for all 32 patients varied from 0.01 to -0.06 Gy with median being -0.04 Gy. For a 2Gy/fraction treatment course, this would be maximum PTV-D98 dose-difference of 6 cGy/fraction or 30 cGy/5fractions. For organs-at-risks the maximum per-fraction dose-difference in D2, D5, D10, D20, D30, D50 and D70 between Truebeam and Trilogy/Clinac plans varied from 0.06 to -0.07 Gy with median being with -0.02 Gy. The 3D-CRT plans had relatively lower dose-difference in comparison to IMRT and VMAT plans. The dose computed on Truebeam was systematically lower than the dose computed on Trilogy/ Clinac.
Conclusions: For conventional fractionation schedules, assuming the maximum uncertainty of <2%, it is clinically safe to switch the treatment machine for 5 fractions. For hypo-fractionated treatments with higher dose per-fraction, plans may need to be revisited before switching the linear accelerator from Truebeam to Clinac/Trilogy or vice-versa.

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