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Published on: May 9, 2014
Monte Carlo based IMRT dose verification using MLC log files and R/V outputs.
Wei Luo1, Jinsheng Li, Robert A Price
1Department of Radiation Oncology, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA. wei.luo@fccc.edu
This study introduces a Monte Carlo simulation method for Intensity-Modulated Radiation Therapy (IMRT) dose verification, using actual delivery data to validate both dose calculation and delivery accuracy. The method accurately assessed target dose but revealed significant underestimations in critical structures due to leaf position errors.
Area of Science:
- Medical Physics
- Radiation Oncology
- Computational Dosimetry
Background:
- Conventional Intensity-Modulated Radiation Therapy (IMRT) dose verification methods like film and ion chamber measurements have limitations in assessing patient-specific dose distributions.
- Monte Carlo (MC) simulations offer independent dose verification but traditionally validate only dose calculation accuracy, not actual plan delivery accuracy.
Purpose of the Study:
- To develop and validate a novel MC-based IMRT dose verification method that reconstructs patient dose distribution using actual beam data and Multi-Leaf Collimator (MLC) log files.
- To simultaneously validate both IMRT dose calculation and beam delivery accuracy.
Main Methods:
- Reconstruction of patient dose distribution using CT data, Record and Verify (R/V) system beam data, and MLC log files from actual dose delivery.
- Application of MC simulations to compare calculated dose with the original IMRT plan, incorporating actual delivery parameters.
- Definition and analysis of average leaf position error to correlate with dose deviations.
Main Results:
- MC simulations for eight IMRT prostate plans showed target dose consistency within 3.0% (with heterogeneity correction) and 2.0% (without) compared to CORVUS treatment plans.
- Significant dose underestimations were observed in critical structures, with up to 9.0% for bladder and 38.0% for rectum, despite leaf position errors contributing <2% to these specific structures.
- A linear correlation was found between target dose error and average leaf position error, indicating that a 0.2 mm average error can lead to a ~1.0% target dose error.
Conclusions:
- Log file-based MC simulations represent a valuable and efficient tool for IMRT quality assurance (QA), validating the actual dose delivered to the patient.
- The proposed method highlights potential inaccuracies in treatment planning systems and emphasizes the critical impact of MLC leaf position accuracy on dose delivery, particularly for organs at risk.
- Further investigation into MLC leaf position errors and their impact on dose distribution is warranted for improving IMRT accuracy and patient safety.
