Quality control in radiotherapy: the reduction of field placement errors

Area of Science:

• Radiation Oncology
• Medical Imaging
• Clinical Oncology

Background:

• Accurate radiation therapy delivery is crucial for effective cancer treatment, especially when targeting complex regions like para-aortic nodes.
• Infradiaphragmatic field placement for para-aortic nodal irradiation requires precise verification to ensure target coverage and minimize geographic misses.

Purpose of the Study:

• To assess the accuracy of complex infradiaphragmatic field placement for para-aortic node irradiation using treatment verification films.
• To identify and quantify errors in radiation field positioning and their impact on nodal coverage.
• To evaluate the effectiveness of practice changes in improving treatment accuracy.

Main Methods:

• A retrospective analysis of two patient series using 'blind' treatment verification films (VF).
• Comparison of sequential VFs against simulator plans to assess field position variations relative to anatomy and lymph nodes.
• Identification of missed nodes and classification of error types (lateral shift, field narrowing, rotation).

Main Results:

• Initial series showed 21% of VFs missed target nodes; subsequent practice modifications reduced this to 5.5% in the second series.
• Significant reduction in systematic lateral shift and rotation of posterior fields observed after discontinuing treatment through the couch.
• Key error factors identified: >6mm lateral shift, >7mm field narrowing, and >=2° rotation.

Conclusions:

• Routine clinical treatment verification films are essential for identifying and correcting systematic errors in radiation therapy.
• Implementing precise, standardized technical practices and correcting identified errors can eliminate subsequent nodal misses.
• Improved accuracy in radiation field placement enhances the efficacy of cancer treatment targeting para-aortic lymph nodes.