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A Fast and Optimized Patient-Specific Quality Assurance Method for Helical Tomotherapy Total Body Irradiation Using a 2-D Array Detector

J Fang

J Fang1*, X Zhang1 , Q Yue2 , G Narayanasamy1 , J Penagaricano1 , L Peacock1 , S Maraboyina1 , F Xia1 , S Morrill1 , (1) University of Arkansas for Medical Sciences, Little Rock, AR, (2) First Affiliated Hospital of Kunming Medical University, Kunming, Yunnan


SU-I-GPD-T-301 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Develop a fast and optimized patient-specific delivery quality assurance (DQA) method for total body irradiation (TBI) patients treated with helical tomotherapy (HT) and evaluate this method by comparing it with traditional TBI DQA methods.

Methods: Ten HT TBI patients with upper body length ranging from 87.6 cm to 113.1 cm were selected for this study. Three DQA plans were generated using PTW Octavius 729 ion chamber array phantom to cover three locations - head and neck (HN), chest-abdomen, and pelvis, which represent the most dose inhomogeneity locations along the body. For the planning of each DQA, the center of the detector was aligned with the red laser, which has a longitudinal distance of 40 cm, 8 cm, and -24 cm from the green laser. Only one treatment plan was required to deliver three DQA plans. For the HN DQA, the detector was initially aligned with the green laser and the couch was moved 40 cm towards the gantry. The beam was manually terminated whenever the dose map covered the entire detector. The measured dose was compared with the calculated plan dose using gamma analysis. Continuous deliveries generated from previous incomplete procedures were performed with 8/-24 cm couch movements for the chest-abdomen and pelvic plans.

Results: The average TBI dose verification time was significantly reduced to 25.1 minutes, compared to 41.2 minutes of the traditional method. The detector with predefined couch movements completely covered all patients’ critical parts in the body. The mean passing rate for 3 mm distance-to-agreement and 5% dose difference gamma criteria was 98.4%±1.5%, 97.1%±2.3%, and 98.1%±1.2% for HN, chest-abdomen, and pelvic plans. The measured absolute dose at the center ion chamber of the detector was higher than calculated dose by 3.8%±1.1%.

Conclusion: Our optimized patient-specific DQA method provides efficient and informative quality assurance for HT TBI.

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