(Saturday, 4/7/2018)
Room: Foyer
Purpose: To evaluate the feasibility of using surface guided imaging system for patient positioning as an alternative of cone-beam computed tomography(CBCT) and for motion tracking during the treatment in Lateral(L/R),Longitude(S/I),and Vertical(A/P) directions.
Methods: A total of 97 fractions from 4 patients underwent 3DCRT and IMRT in Elekta VersaHD were randomly selected.The margins expanded from the targets were from 5 mm to 10 mm.Before each fraction,patients were aligned with 3-point subcutaneous tattoos and the planned shifts were implemented manually by the therapists.A CatalystHD surface mapping system was firstly used to capture the patient’s fractional setup error.The kV-CBCT was acquired immediately following to adjust for any residual corrections.The differences between the setup errors obtained from CatalystHD and CBCT were retrospectively compared.Patients’ motions were monitored during the treatment and recorded as a total of 15449 tracking points by the CatalystHD.The ranges of motions were statistically analyzed.
Results: The average differences between the setup errors obtained from CatalystHD and CBCT were -2.0±3.6 mm,-0.9±4.6 mm,-1.4±5.2 mm,and -2.8±2.8 mm for L/R,S/I,A/P,and 3D shift vectors,respectively.The ratios of the difference less than 10 mm were 97.9%,99.0%,94.8%, and 100% for L/R,S/I, A/P,and 3D shift vectors,respectively.The ratios of the motion more than 5 mm were 0.7%,2.6%,4.1%,and 11.0% for L/R,S/I,A/P,and 3D shift vectors,respectively.The average motions were -0.2±1.4 mm,0.1±1.7 mm,-0.4±2.2 mm,and 2.4±2.0 mm for L/R,S/I,A/P,and 3D shift vectors,respectively.The maximum motions for L/R,S/I,A/P directions were 8.1 mm,10.3 mm,and 11.4 mm,respectively.3D shift vectors showed good correlations with treatment time(R=0.91).
Conclusion: This study shows that CatalystHD can be a periodical alternative of CBCT for esophagus patient setup if the target has a margin larger than 10 mm.Special cautions should be taken for the case with a smaller margin.The intra-fractional motions vary and have significant deviations,which should be monitored during the treatment.To use a small margin for the target, the treatment time should be reduced.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by Elekta AB, Stockholm, Sweden
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