CT simulation in nodal positive breast cancer

Area of Science:

• Radiation Oncology
• Medical Imaging
• Radiotherapy Physics

Background:

• Accurate matching of tangential and lymph node fields is crucial in nodal positive breast cancer irradiation.
• Current techniques vary based on available equipment and clinical context.
• CT simulation of non-monoisocentric techniques requires evaluation for accuracy and reproducibility.

Purpose of the Study:

• To evaluate the accuracy and reproducibility of CT simulation for non-monoisocentric tangential and lymph node field matching in breast cancer radiotherapy.
• To compare virtually adjusted field match parameters with mathematically derived parameters.
• To analyze coordinate transfer accuracy from CT simulator to conventional simulator.

Main Methods:

• Virtual adjustment of field match parameters at CT simulation.
• Comparison of virtual parameters with mathematical calculations.
• Analysis of coordinate transfer in 25 consecutive patients undergoing conventional simulation.
• Evaluation of patient positioning limitations due to CT gantry aperture.

Main Results:

• Virtually adjusted angles for coplanar field match corresponded with calculated angles.
• Mean isocenter displacement was 5.7 mm, with a total coordinate transfer uncertainty of 6.7 mm (1 SD).
• Patient set-up limitations, particularly steep arm abduction, led to significant matchline shifts (>1.0 cm) in 32% of patients.
• Technical limitations necessitated modifications to the virtual setup.

Conclusions:

• Virtual CT simulation enables precise, graphic definition of field match parameters.
• Technical limitations, primarily patient positioning, required modifications in 32% of cases.
• A hybrid technique combining virtual parameter adjustment with conventional simulation is currently employed for optimal field alignment.