Target Contour Consistency During Magnetic Resonance-Guided Online Adaptive Stereotactic Body Radiation Therapy.

PURPOSE

Adaptive magnetic resonance-guided stereotactic body radiation therapy (MRgSBRT) requires expeditious recontouring of target volumes based on daily anatomy. Contouring of the gross tumor volume (GTV) is frequently performed by covering radiation oncologists who may be less familiar with the case than the primary physician (PP). The objective of this study is to determine consistency in GTV contouring between PP and covering physician (CP) and to analyze the effect of resources to support accurate GTV delineation.

METHODS AND MATERIALS

Between 2021 and 2023, 59 patients underwent 302 fractions of MRgSBRT at our institution. GTVs were analyzed for the effect of 3 different types of contouring support resources: (a) number of slices of the original GTV, (b) external software displaying original GTV contours, and (c) alerting if GTVs differed > 10% from the original. Differences between physicians and contouring support resources were analyzed for different tumor sites and fractions using 2-tailed test and analysis of variance.

RESULTS

One hundred nineteen out of 302 (39.4%) MRgSBRT treatments were supervised by a CP. The difference in the mean absolute percent volume change of GTV compared with original GTV for PPs (11.1%) versus CPs (4.6%) across all treatment fractions was statistically significant ( = .00006). Significant differences were observed for pancreas (12.8% vs 5.0%, = .03), liver (13.0% vs 4.0%, = .007), and lymph nodes (12.4% vs 2.1%, = .004) with larger volume differences for PPs. No significant differences were observed for tumors of the prostate (3.7% vs 3.6%) and adrenal glands (9.7% vs 12.2%). No significant GTV differences between the 3 contouring support techniques were observed.

CONCLUSIONS

Our results show larger GTV changes by PPs for most tumor sites with little impact from contouring support resources. Observed differences might be related to higher contouring confidence of PPs who are more familiar with the case. Further investigation into enhancing contouring support methods is warranted.