(Tuesday, 7/16/2019) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 2
Purpose: Despite the common use of MRI on radiosurgery (SRS) treatment planning, there is no established standard protocol for brain MR acquisition for the purposes of SRS treatment planning. There is variability in MR protocols across practices, including variable slice thicknesses ranging from 1 to 3 mm. The purpose of this work is to determine the impact of slice thickness on the contoured volumes of brain metastases (BMs).
Methods: The 10 most recent patients treated at our institution for brain metastases with gamma knife were analyzed. The planning MRI for each patient was originally acquired at 1 mm slice thickness for clinical treatment planning and delivery. The MRIs were resampled to 2 mm and 3 mm slice thickness by averaging in the slice direction. BMs were delineated by an experienced radiation oncologist on the 1 mm, 2 mm, and 3 mm resampled MRIs within Gammaplan treatment planning system.
Results: A total of 49 BMs were found on the scans with 1 mm slices. On 2 mm slice MRIs, 2 BMs were overcalled (noted to be blood vessels on 1 mm) and 2 were missed. Compared with the 1mm slice MR plan, contours on the 2 mm slices were larger by a mean volume of 0.007 cm³ [range: -0.61 cm³ and 0.15 cm³](p=0.64). On the 3 mm slice MRIs, 3 BMs were missed, and 1 was overcalled. On average, the volume of the contours drawn on the 3 mm scans were larger than the 1 mm scans by a mean volume of 0.08 cm³ [range: 1.41 cm³ and -0.19 cm³] (p=0.021).
Conclusion: In this study, delineation of targets on MRIs with slice thickness greater than 1 mm resulted in both over calling and missing tumors. Standard protocols should be thoughtfully developed and recommended to ensure quality treatment at all institutions.
Keywords
Not Applicable / None Entered.
Taxonomy
IM/TH- MRI in Radiation Therapy: MRI for treatment planning
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