SU-E-J-68: An Optical Image Guidance System: To Detect Arbitrarily Attached Markers Behind a Full Facemask

Area of Science:

• Medical Physics
• Radiotherapy
• Image Guidance

Background:

• Patient setup errors in radiotherapy can lead to inaccurate radiation delivery.
• Reproducibility of external marker positions behind facemasks is crucial for precise patient alignment.
• Existing optical image guidance systems face challenges with marker placement consistency.

Purpose of the Study:

• To develop an improved optical image guidance system for managing inter-fractional setup errors.
• To address the challenge of marker position reproducibility using arbitrary-point-to-plane registration.
• To enhance the accuracy and robustness of patient positioning in radiotherapy.

Main Methods:

• Infra-red reflecting markers were attached to arbitrary positions on a head phantom's face.
• A calibrated stereo camera system reconstructed 3D marker coordinates using the direct linear transform (DLT) algorithm.
• Point-to-plane registration with the contractive projection point (CPP) algorithm was used for fine registration after initial rough registration.

Main Results:

• The mean target registration error (TRE) for arbitrarily attached markers was 1.24 ± 0.32 mm.
• The combination of rough and fine registration demonstrated fast and robust performance.
• The system validated accuracy through intentional phantom movements with known translation parameters.

Conclusions:

• The proposed arbitrary-point-to-plane registration method effectively manages setup errors associated with external markers behind facemasks.
• This approach eliminates daily errors in attaching external markers to specific positions.
• The system offers a more reliable solution for patient alignment in radiotherapy treatments.