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Verification of setup errors in external beam radiation therapy using electronic portal imaging
K Krishna Murthy1, Zakiya Al-Rahbi, S S Sivakumar
1Department of Radiotherapy, National Oncology Center, the Royal Hospital, Muscat, Sultanate of Oman.
Journal of Medical Physics
|November 7, 2009
Summary
This study audited radiation therapy quality assurance, verifying treatment field positions to assess immobilization and reproducibility. Results show patient setup errors are site-specific but within acceptable limits, confirming treatment accuracy.
Area of Science:
- Radiation Oncology
- Medical Physics
- Quality Assurance in Healthcare
Background:
- Accurate patient positioning is crucial for effective radiation therapy.
- Immobilization techniques aim to improve treatment reproducibility.
- Quality assurance (QA) audits are essential for verifying treatment delivery accuracy.
Purpose of the Study:
- To audit quality assurance aspects of radiation therapy delivery.
- To verify treatment field positions and assess immobilization efficiency.
- To document the reproducibility of treatment delivery across different anatomical sites.
Main Methods:
- Retrospective analysis of 506 electronic portal imaging device (EPID) images from 60 patients (head and neck, breast, pelvis).
- Superimposition of portal images on reference images using Varian portal Vision software.
- Analysis of two-dimensional displacements and rotation to quantify patient setup errors.
Main Results:
- Mean deviations exceeding 3 mm were observed in 17.5% (breast), 11.25% (pelvis), and 7.5% (head and neck) of fields.
- Less than 0.83% of cases showed mean deviations greater than 5 mm.
- Average mean standard deviation along X and Y directions was below 2.65 mm, indicating high reproducibility.
Conclusions:
- Patient setup errors in radiation therapy are site-specific.
- Immobilization methods significantly enhance treatment reproducibility.
- The study confirms the accuracy and quality of radiation treatments delivered, with variations within acceptable clinical limits.
