Impact of Immobilization on Interfractional Errors for Upper Extremity Soft Tissue Sarcoma Radiation Therapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Orthopedic Oncology

Background:

• Upper extremity soft tissue sarcomas (STSs) present unique challenges in radiation therapy due to rare occurrence and mobile anatomy.
• Various patient positioning and immobilization strategies are employed to manage these challenges.

Purpose of the Study:

• To quantify interfractional setup errors in upper extremity STSs.
• To evaluate the effectiveness of different immobilization methods using cone-beam computed tomography (CBCT).

Main Methods:

• Seventeen patients with upper extremity STSs treated with daily CBCT guidance were analyzed.
• Immobilization methods included vacuum cradles with/without thermoplastic shells and no accessories.
• Interfractional positional discrepancies were quantified via automatic image registration.

Main Results:

• Significant interfractional errors, particularly rotational displacements, were observed across all immobilization methods.
• Repositioning rates varied: 18% (thermoplastic shell), 15% (vacuum cradle only), 6% (no accessory).
• Systematic error differences were significant (P < .05) between immobilization techniques.

Conclusions:

• Current immobilization strategies for upper extremity STSs demonstrate substantial interfractional errors.
• Improved immobilization techniques are crucial for accurate radiation therapy delivery in these cases.
• Limitations include a small study size and unequal extremity segment representation.