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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 â‚‹ 0.038) in the IMRT plans and 0.031 (range, 0.016 â‚‹ 0.043) in the RA plans. The CLs of low point dose in the avoidance structures were 0.028 (range, 0.024 â‚‹ 0.039) in the IMRT plans and 0.029 (range, 0.017 â‚‹ 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 â‚‹ 8.6) in the IMRT plans and 4.84 (range, 1.5 â‚‹ 8.8) in the RA plans. The CLs in the low dose region were 5.04 (range, 1.2 â‚‹ 7.4) and 4.2 (range, 1.8 â‚‹ 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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