Verification of patient-setup accuracy using a surface imaging system with steep measurement angle

Area of Science:

• Medical Physics
• Radiation Oncology
• Image Guidance

Background:

• Accurate patient positioning is critical in radiation therapy.
• Surface-guided radiation therapy (SGRT) offers a non-contact method for patient setup.
• Evaluating SGRT systems at non-standard installation angles is important for broader clinical adoption.

Purpose of the Study:

• To assess the accuracy of the Voxelan HEV-600 M/RMS SGRT device installed at a steep 74-degree camera view angle with the Radixact system.
• To compare the accuracy of Voxelan's surface setup (SS) against traditional laser setup (LS) using phantom experiments and patient data.

Main Methods:

• Phantom experiments were conducted to evaluate Voxelan's accuracy in translations and rotations against ground truth.
• Inter-fractional setup errors were compared between laser setup (LS) and surface setup (SS) in head and neck, chest, and pelvis patient cases.
• Setup errors were determined by comparing surface setup to bone matching using megavoltage computed tomography (MVCT) as the reference standard.

Main Results:

• Phantom experiments showed Voxelan's measured values to be within 1 mm and 1 degree of the true values.
• No significant difference in inter-fractional setup error was found between LS and SS across all patient cohorts (P > 0.05).
• Slight improvements in setup accuracy were noted for head and neck and chest cases with SS, while pelvis cases showed no improvement due to visualization challenges.

Conclusions:

• Surface setup using Voxelan at a 74-degree installation angle achieves accuracy comparable to or better than traditional laser setup.
• The Voxelan system, even at a steep angle, provides reliable patient positioning for radiation therapy.
• Further investigation may be needed for specific regions like the pelvis where surface visualization can be challenging.