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Characterization of Recombination Effects in a Liquid Ionization Chamber Used for the Dosimetry of a Radiosurgical Accelerator
Published on: May 9, 2014
Comparing dose in the build-up region between compensator- and MLC-based IMRT.
Khosrow Javedan1, Geoffrey G Zhang, Sarah Hoffe
1Radiation Oncology, Moffitt Cancer Center, Tampa, FL 33612, USA.
Journal of Applied Clinical Medical Physics
|September 8, 2012
Summary
Compensator-based intensity-modulated radiation therapy (IMRT) significantly reduces surface dose compared to multileaf collimator (MLC)-based IMRT. This technique offers improved patient comfort and treatment efficacy by minimizing dose in the critical build-up region.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Dosimetry
Background:
- The dose in the build-up region is a critical factor in intensity-modulated radiation therapy (IMRT), impacting patient comfort and treatment outcomes.
- Excessive surface dose can lead to treatment interruptions, while insufficient dose may cause tumor repopulation and local treatment failure.
- Comparing different IMRT delivery techniques is essential for optimizing radiation therapy protocols.
Purpose of the Study:
- To investigate and compare the build-up dose characteristics of compensator-based IMRT and multileaf collimator (MLC)-based IMRT.
- To quantify the dose contribution in the shallow build-up region for both IMRT techniques.
- To evaluate the impact of beam hardening from brass compensators on surface dose.
Main Methods:
- Measured build-up dose (1-5 mm depth) using an ionization chamber for compensator-based and MLC-based IMRT delivered by a Varian Trilogy linear accelerator.
- Designed and utilized a step-wise solid brass compensator and programmed step-and-shoot MLC fields to achieve similar dose profiles at 10 cm depth.
- Employed Monte Carlo simulations to model the brass compensator and MLC fields, validating measured dose profiles.
Main Results:
- Compensator-based IMRT demonstrated up to 7% lower build-up dose compared to MLC-based IMRT, attributed to beam hardening effects in the brass compensator.
- Low-energy electrons contributed 22% to the dose at 1 mm depth for compensator IMRT, versus 15% for MLC IMRT.
- Measured and simulated dose profiles for both techniques were matched within ±1.5% at the isocenter depth of 10 cm.
Conclusions:
- Compensator-based IMRT delivers a reduced dose in the build-up region, potentially enhancing patient comfort and reducing side effects.
- The observed reduction in surface dose is primarily due to the beam hardening effect of the brass compensator.
- This study provides valuable dosimetric data for optimizing IMRT techniques to improve treatment delivery and patient outcomes.
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