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Reproducibility of field alignment in difficult patient positioning
R D Kortmann1, C F Hess, R Jany
1Department of Radiotherapy, University of Tübingen, Germany.
Summary
This study assessed radiation therapy field alignment accuracy in patients after hip replacement. Results show statistical fluctuations are more significant than initial setup errors, suggesting initial checks may not predict overall treatment accuracy.
Area of Science:
- Radiation Oncology
- Medical Imaging
- Radiotherapy Physics
Background:
- Accurate radiation therapy field alignment is crucial for effective treatment and minimizing off-target radiation exposure.
- Patients undergoing postoperative irradiation after total hip replacement present unique positioning challenges.
- Understanding and quantifying alignment discrepancies is essential for optimizing treatment delivery and patient safety.
Purpose of the Study:
- To quantitatively assess the accuracy of radiation therapy field alignment in patients with challenging positioning, specifically those receiving postoperative irradiation after total hip replacement.
- To evaluate linear and rotational discrepancies during the radiotherapy process for this patient cohort.
- To determine the significance of initial setup errors versus ongoing statistical fluctuations in treatment accuracy.
Main Methods:
- A cohort of 95 patients undergoing postoperative irradiation after total hip replacement was studied.
- Linear and rotational discrepancies were measured between simulation and the first verification film, as well as across five consecutive verification films.
- Statistical analysis was performed to assess the distribution and magnitude of these discrepancies.
Main Results:
- Linear discrepancies exhibited standard deviations of 4.0-8.0 mm, and rotational discrepancies showed standard deviations of 3.5-5 degrees.
- Deviations were consistent between the simulation-to-treatment machine transition and subsequent treatment verification films.
- Fifty percent and 95% of absolute differences were less than 5 mm and 15 mm, respectively, indicating predictable accuracy ranges.
Conclusions:
- Statistical fluctuations during treatment delivery are more impactful on field alignment accuracy than initial setup errors.
- A single initial verification film may not adequately predict the cumulative inaccuracies throughout the entire radiotherapy course.
- These findings can inform the prescription of appropriate safety margins for patients with difficult positioning, enhancing treatment precision.