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Evaluation On Dosimetric Effects of Irregular Motion During 4DCT Scanning Using a Self-Developed Lung Phantom

R Zhao*1, H Wei1, X He2, (1) Shanghai Pulmonary Hospital and Tongji University School of Medicine,Shanghai, CN,(2)Ruijin Hospital and Shanghai Jiaotong University School of Medicine,Shanghai, CN


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

Room: AAPM ePoster Library

Purpose: breathing patterns of lung cancer patients are very complex, exhibiting considerable diversity even within the same patient. It should be noted that intrafraction variability in motion is significantly larger than interfraction motion variability. For mobile targets, 4DCT is a standard procedure for incorporating tumor motion in treatment planning. However, 4DCT cannot directly address the intrafractional motion problem. It is urgent to evaluate dosimetric effects caused by irregular motion systematically when patient received a stereotactic radiotherapy treatment.
Methods: measure the effects of irregular intrafraction variability in motion, a realistic self-developed lung phantom is required. The motion amplitude lengths and periods of the phantom can be configured by the control system respectively. In the configuration of the phantom motion, the motion amplitude lengths ranged from 10 mm to 25 mm and the frequencies of the platform were set at 3 s/cycle to 5 s/cycle. A GE CT scanner was used for the 4DCT scans.
Results: discrepancies increase with increasing irregular intrafractional motion. The target (3 cm diameter) exceeded 5% volumetric differences for the breath patterns of higher amplitude motion and constant respiratory cycle. Finally, irregular intrafractional motion will degrade the dose distribution seriously.
Conclusion: is sensitive to deviations in the respiratory pattern and intrafractional breathing motion might cause unwanted deviations between the planned and the delivered dose distributions for patients with poor pulmonary function. Knowledge of the disadvantages of dosimetric effects enables individualized optimisation of the radiotherapy treatment.


Phantoms, Radiation Dosimetry



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