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The Impact of Jaw Positioning Errors for Dynamic Jaw Delivery in Tomotherapy

Z Hu*, K Zhang, K Men, J Dai, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital,Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, BeijingCN,


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

Room: AAPM ePoster Library

Purpose: To evaluate the dosimetric impact of jaw positioning errors and to determine the QA tolerances of such errors for helical tomotherapy with TomoEDGE dynamic jaw delivery.

Methods: Dosimetric impact of delivery errors in jaw start position and jaw speed were evaluated by introducing these errors into ten prostate treatment plans created with TomoEDGE dynamic jaw technique in tomotherapy. Each error type was simulated independently for both the front jaw and the back jaw. Dose-volume histograms and dose metrics differences were compared between error-introduced and original plans to evaluate the clinical significance. A 3D gamma analysis was also performed to compare dose distributions to determine the machine QA tolerances of each error type.

Results: There is a linear correlation of errors in jaw start position with dose delivered to the planning target volume (PTV) and organs at risk (OARs). Errors in back jaw speed can also lead to significant dosimetric changes. To maintain the passing rate = 95% with a criterion of a dose difference and DTA of 3%/2mm would require that errors in jaw start position and back jaw speed be within ±1% of field width and ±2% from the planned value, respectively. In contrast, error in front jaw speed has little impact on dose distributions. In this work, even errors of ±5% in front jaw speed resulted in negligible dosimeric changes for both PTV and OARs.

Conclusion: This work indicates potential dosimetric changes due to jaw positioning errors in tomotherapy dynamic jaw delivery and establish a framework to determine the machine QA tolerances for a given disease. Adequate quality assurance programs should be performed to assess errors in jaw start position and back jaw speed as they tend to be more impactful than errors in front jaw speed.


Quality Assurance, Tomotherapy, Dosimetry


TH- External Beam- Photons: tomotherapy

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