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A Patient Plan Verification Confidence Limits Been Founded for TOMOTHERAPY HDA Type Machine

T Pang*, L Yu, B Yang, J Qiu, Peking Union Medical College Hospital, Beijing, 11CN,

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Before the TOMOTHERAPY HDA type machine been used in clinical, the treatment planning system, delivery system and measure system must be test carefully and a patient plan verification confidence limits level should be created for future quality assuranceuse.


Methods:
We created IMRT plans for most usual clinal disease which follow AAPM TG119 work. Every disease site, we made IMRT plans with difference delivery modes (helical and Direct), jaw modes (fix and dynamic) and field widths (1cm, 2.5cm and 5.0cm). We measured point dose and plane dose and compare them with which from IMRT plans. The confidence limits by the formulation CL= mean+1.96SD. The CL formulation makes 95% of measure results fall within the CL limits. The plane dose gamma analysis criteria were 3% dose difference and 3mm DTA with 10% of max dose threshold.

Results:
For helical delivery mode, the mean difference was 0.44% and the standard deviation was 0.01, so the confidence limit for target volume points was 2.43%.By the same way, TOMO Direct delivery mode plans was 2.72%. The CL level for OAR Points doses in TOMO Helical delivery mode was 3.96%, TOMO Direct delivery mode plans about OAR points was 5.86%. The plane dose verification confidence limits for helical delivery mode was 2.08% and Tomo Direct delivery mode plans plane dose confidence limits was 3.07%.

Conclusion: We test most usual clinical sites and get the difference confidence limits for different delivery modes. All measured plans results were fall with in CL region. And for points, more 98% of measured points were fall within their CL regions. Our CL regions were comparable with AAPM TG119 recommend values.We founded our action levels as: 5% difference for target volume points and 7% for QAR points. This work will be very helpful for our quality assurance work in future.

Download ePoster [PDF]

Keywords

Tomotherapy, Quality Assurance, Acceptance Testing

Taxonomy

IM- Radiation Dose and Risk: General (Most Aspects)

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