(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: To evaluate the effect of field angle setting on the accuracy of the intensity modulated radiotherapy (IMRT) plan for patients with metal implants.
Methods: A CIRS phantom (Model 002H9K) with bilateral metal cylindrical steel inserts (2.5cm diameter) was scanned with the GE scanner, Two image series were reconstructed: uncorrected and MAR. In Monaco planning system, a 10cm×10cm square field with 100 MU was set up every 5 degrees from 0 to 360 degrees. Two kinds of IMRT plans (5 field and 7 field) were designed, each plan had 0, 1, or 2 fields whose incident paths passed through the metal area, and a total of 30 plans were designed. The average doses of point A, B and C on the central plane were calculated and measured, and the deviation of the calculated results was analyzed.
Results: In the uncorrected images and MAR images, when the incident path of the square field passes though the metal region, the dose calculation deviation will be 6.33%~86.27% and 6.10%~56.68%, respectively. When it does not pass through the metal region, the deviation is 2.29% and 1.56%, respectively. In 5-field IMRT plan, when the number of fields passing through the metal region is 0, 1, 2, respectively, the dose deviation is 2.97%, 8.64% and 13.87% in the uncorrected image, and 2.17%, 3.65% and 7.54% in the MAR image, respectively. For 7-field IMRT plan, the deviation is 2.42%, 6.28% and 10.92% in the uncorrected image, and 2.05%, 3.26% and 6.79% in the MAR image, respectively.
Conclusion: The incident path of the field passing through the metal region will significantly affect the accuracy of dose calculation. This effect can be improved by using MAR images, but even so, the presence of two or more such fields in the IMRT plan can result in clinically unacceptable dose deviations.
Funding Support, Disclosures, and Conflict of Interest: Suzhou Science and Technology Development Program, China, Grant Number: SS201642 Have no Conflict of Interest.
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