[Comparison of setup errors between two immobilization methods in prostate cancer radiotherapy based on cone-beam...

Area of Science:

• Radiation Oncology
• Medical Physics
• Prostate Cancer Treatment

Background:

• Accurate patient positioning is crucial for effective radical radiotherapy in prostate cancer.
• Interfractional setup errors can compromise treatment accuracy and efficacy.
• Optimizing immobilization techniques is essential for improving radiotherapy workflows.

Purpose of the Study:

• To compare interfractional setup errors between two fixation methods: lithotomy position with a full-body frame versus a conventional frame with a thermoplastic mask.
• To calculate clinical target volume (CTV) to planning target volume (PTV) margins for both methods.
• To optimize immobilization techniques and radiotherapy workflows for prostate cancer radical radiotherapy.

Main Methods:

• Retrospective analysis of 37 prostate cancer patients undergoing radical radiotherapy.
• Comparison of two immobilization groups: Group A (full-body frame, lithotomy) and Group B (conventional frame with thermoplastic mask).
• Daily cone-beam computed tomography (CBCT) image guidance and analysis of setup errors in X, Y, and Z directions.

Main Results:

• Significant differences in setup errors between the two groups (P < 0.01).
• Group B (thermoplastic mask) showed significantly reduced median absolute errors in X, Y, and Z directions compared to Group A.
• Lower setup error displacement within 0.5 cm was observed in Group B for X and Z directions.
• Calculated CTV-PTV margins were smaller for Group B across all directions.

Conclusions:

• Conventional carbon fiber fixators with thermoplastic masks significantly reduce setup errors in prostate cancer radiotherapy.
• The carbon fiber whole-body fixator in the lithotomy position resulted in larger setup errors.
• Further research and workflow optimization are needed to enhance positioning accuracy, especially for techniques requiring the lithotomy position.