Inter-observer variability of prostate delineation on cone beam computerised tomography images

Area of Science:

• Radiotherapy and Oncology
• Medical Imaging
• Radiation Oncology

Background:

• Image-guided radiotherapy (IGRT) relies on accurate target delineation.
• Cone beam computed tomography (CBCT) is increasingly used for soft tissue IGRT.

Purpose of the Study:

• To quantify inter-observer variability in prostate gland contouring on CBCT images.
• To assess the impact of this variability on radiotherapy planning and delivery.

Main Methods:

• Five genitourinary oncologists contoured prostate glands on five CBCT datasets.
• Variations in boundary delineation, isocenter placement, volume, and center of mass were measured.
• Finite element modeling was used to determine boundary definition variations.

Main Results:

• Average standard deviations for center of mass displacement were small (0.7-2.8 mm).
• Standard deviation for prostate volume determination was 8.93 cm³, with significant variability (3.98-19.00 cm³).
• Mean standard deviations for boundary displacements ranged from 1.8 mm to 3.6 mm.

Conclusions:

• Expert observers exhibited difficulty in defining the prostate peri-prostatic interface on CBCT.
• Inter-observer variability in prostate detection on CBCT is not prohibitive for soft tissue guidance.
• Rigorous training and protocol development are needed to mitigate potential systematic matching errors.