Accuracy of radiation field alignment in clinical practice

Area of Science:

• Radiotherapy physics
• Medical imaging analysis
• Radiation oncology

Background:

• Accurate patient positioning is crucial for effective radiation therapy.
• Anatomical variations can occur between treatment sessions, potentially affecting dose delivery.
• Simulator and portal films are used to verify patient setup and treatment fields.

Purpose of the Study:

• To quantify treatment-to-treatment anatomical variations using portal films.
• To determine discrepancies between simulator and portal films across different treatment sites.
• To assess the impact of anatomical variations on radiation therapy accuracy.

Main Methods:

• Analysis of simulator and portal films from 71 patients.
• Retrospective and prospective analysis of film data.
• Comparison of sequential portal films to determine treatment-to-treatment variations.
• Comparison of simulator films with portal films to identify discrepancies.

Main Results:

• Treatment-to-treatment anatomical variations averaged 3 mm (standard deviation), independent of site and field shaping.
• Discrepancies between portal and simulator films were site-dependent, averaging 7.7 mm.
• The head and neck region showed the lowest discrepancy (3.5 mm), while the thorax exhibited the highest (9.2 mm).

Conclusions:

• Daily anatomical variations in radiation therapy are generally small (around 3 mm).
• Simulator-portal film discrepancies are larger and site-specific, highlighting the need for careful patient setup verification.
• These findings have implications for optimizing radiation therapy protocols and patient safety.