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IMRT and RapidArc Commissioning of Truebeam Linear Accelerator Using Gafchromic EBT3 Film


N Wen

N Wen*, B Zhao, K Barton, K Chin, J Kim, C Liu, I Chetty, Henry Ford Health System, Detroit, MI

SU-E-T-126 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The study is to establish confidence limits (CLs) for both IMRT and RapidArc (RA) of all five photon energies (6X, 10X, 15X, 6XFFF, 10XFFF) of a TrueBeam system based on TG119 Guideline.

Methods:Both IMRT and RA plans were created in solid water phantom. The test plans were representative of normal clinical treatment sites including AP/PA fields, bands, multiple target, prostate, head & neck, easy and hard C-shape. A high dose point in the PTV and a low dose point in the critical organ were measured with ion chamber. The percentage difference was defined as [(measured dose ₋ plan dose)/Prescription dose]. Planar dose distributions were also measured in the high and low dose regions with EBT3 films. The confidence limit was set to have 95% of the measured data fall within the tolerance. It was defined as (mean + 1.96 σ) for point dose measurement and [(100₋mean) + 1.96 σ] for passing gamma criteria of 3%/3mm.

Results:The CLs of high dose point in the target were 0.031 (range, 0.024 ₋ 0.038) in the IMRT plans and 0.031 (range, 0.016 ₋ 0.043) in the RA plans. The CLs of low point dose in the avoidance structures were 0.028 (range, 0.024 ₋ 0.039) in the IMRT plans and 0.029 (range, 0.017 ₋ 0.047) in the RA plans. The CLs of passing 3%/3mm gamma criteria in the high dose region were 6.28 (range, 1.4 ₋ 8.6) in the IMRT plans and 4.84 (range, 1.5 ₋ 8.8) in the RA plans. The CLs in the low dose region were 5.04 (range, 1.2 ₋ 7.4) and 4.2 (range, 1.8 ₋ 8.3) in the IMRT plans.

Conclusion:We have established the CLs values to access the overall accuracy to ensure the high precision of IMRT and RA delivery. They were all within the values published in TG119.

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