Quantifying interobserver variation in target definition in palliative radiotherapy.

Area of Science:

• Radiation Oncology
• Medical Imaging
• Treatment Planning

Background:

• Accurate target and field definition is crucial for effective radiotherapy.
• Variability in planning can lead to suboptimal treatment outcomes.
• Three-dimensional (3D) volume-based planning aims to improve upon traditional two-dimensional (2D) field-based methods.

Purpose of the Study:

• To compare interobserver and intraobserver variability in target and field definition between 3D volume-based and 2D field-based radiotherapy planning.
• To assess the impact of different planning approaches on coverage and potential misses.

Main Methods:

• Five radiation oncologists evaluated 9 standardized palliative care cases (bone metastases, lung cancer, abdominal/pelvic soft tissue).
• Observers created treatment fields using both 2D field-based and 3D volume-based planning.
• Variability was quantified using percent overlap, under-coverage, and over-coverage.

Main Results:

• Interobserver variability was similar for both 2D (76% overlap) and 3D (74% overlap) planning.
• Intraobserver comparison showed 78% overlap, 22% over-coverage, and 41% under-coverage.
• Two-dimensional planning resulted in significantly more under-coverage for bone metastases (33%) compared to other sites (16%), suggesting a higher risk of geographic misses.

Conclusions:

• Clinically significant interobserver and intraobserver variability exists in palliative radiotherapy, regardless of whether 2D field-based or 3D volume-based planning is used.
• Two-dimensional planning poses a greater risk of under-coverage and geographic misses, particularly for bone metastases.
• Further research is needed to develop strategies for reducing planning variability in radiotherapy.