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Comparison of Two Methods for Daily Dose Reconstruction of Volumetric Modulated Arc Therapy Treatments

J Grenier

J Grenier1, J Fontenot1,2, 1 Louisiana State University, Baton Rouge, LA, 2 Mary Bird Perkins Cancer Center, Baton Rouge, LA

TU-E-108-1 Tuesday 2:00PM - 3:50PM Room: 108

Purpose: To compare daily dose reconstruction of volumetric modulated arc therapy treatments using delivery log files from two sources: the treatment control system (TCS) and the record and verify (RV) system. The former has the advantage of automated operation from remote terminals while the latter has the advantage of better recording fidelity.

Methods: VMAT treatment plans from five prostate patients and five head and neck patients treated at our clinic were selected for this study. Each plan was delivered on an Elekta linear accelerator, and the resulting dose distribution was measured with a two-dimensional diode array. During delivery, positions of the gantry, multi-leaf collimator (MLC), and jaws were captured in the RV system and in the TCS through third party software. Following plan delivery, delivery parameters were imported to the treatment planning system and used to recalculate the dose delivered to the measurement phantom. Planar dose profiles were computed for the planned and reconstructed (RV and TCS) doses. Each of the planar doses were compared to the measured dose using the gamma metric with 3% dose difference and 3 mm distance to agreement.

Results: The average improvement over the agreement between the planned and measured doses was 0.2% ± 0.8% and 0.7% ± 0.6% for RV- and TCS-reconstructed doses for prostate cases, respectively; and -0.6% ± 0.7% and 0.3 ± 0.6% for head and neck cases, respectively. In other words, TCS-reconstruction improved agreement for both treatment sites while RV-reconstruction showed only slight improvement in prostate cases.

Conclusion: Dose reconstructed with TCS log files more closely reflects the delivered dose than does the original plan. Reconstruction with RV data shows similar potential, but time delays in the reporting of different parameters diminish its ability for plans requiring greater MLC movements.

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