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Validation of a Dose Verification Tool Using a Simplified Monte Carlo Method for Patient Quality Assurance

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S Mizutani

S Mizutani1*, K Hotta2 , H Baba2 , T Yamaguchi1 , T Mukawa1 , Y Aoki1 , T Miyashita3 , T Akimoto2 , (1) Sumitomo Heavy Industries,Ltd., Yokosuka-shi, Kanagawa, Japan, (2) National Cancer Center Hospital East, Kashiwa-shi, Chiba, Japan, (3) Sumitomo Heavy Industries,Ltd., Niihama-shi, Ehime, Japan


SU-I-GPD-T-134 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Patient Quality Assurance (QA) is always performed before treatment for the scanned proton therapy. Current patient QA commonly performs dosimetric verification on geometric phantom using 2D chamber. This current QA procedure has a big drawback. Setting up the phantom and doing dosimetric measurements are time consuming and labor intensive. We have developed a dose verification tool using the simplified Monte Carlo (SMC) method. We propose to computation-based approach using this developed tool to reduce the patient QA time.

Methods: Dosimetric verification using 2D chamber is not performed by the newly proposed QA procedure. First, we deliver the treatment plan without the phantom setup to obtain machine log files which record delivery information. The dose verification tool calculates the actual delivered dose distribution based on log files. In the newly patient QA, we compare the dose distribution calculated with log files and it from the TPS. To verify the accuracy of dose verification tool, we compared the dose distribution based on log files to measured dose distribution on the polyethylene phantom.

Results: While the 2D-gamma passing rate was 94% in distal fall-off region for the 2mm/3% criteria, agreement of overall dose distributions is quite good. And, the dose calculation followed by the log files takes an average 3 minutes, while the conventional measurement-based approach takes an average about 2 hours per irradiation field. The developed dose verification tool may be sufficiently applicable to new patient QA for the proton therapy.

Conclusion: We proposed to computation-based approach using dose verification tool followed by log files. This developed tool is fast and accurate dose calculation. The proposed procedure offers significant advantage in reducing the time needed for the patient QA and it is less labor-intensive. Therefore, we should replace experimental-based verification method to computation-based approach as soon as possible.

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