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Stereotactic body radiation therapy patient specific quality assurance using a two-dimensional array at extended
Sotirios Stathakis1, Panayiotis Mavroidis, Ganesh Narayanasamy
1Department of Radiation Oncology, University of Texas Health Sciences Center at San Antonio, TX, USA.
Journal of B.U.ON. : Official Journal of the Balkan Union of Oncology
|September 30, 2015
Summary
This study shows extended Source to Surface Distance (SSD) measurements with a 2D detector array improve accuracy for patient-specific IMRT QA, especially for small targets like spinal tumors. This method enhances dose accuracy and efficiency in radiation therapy.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Quality Assurance
Background:
- Patient-specific quality assurance (QA) is crucial for accurate Intensity-Modulated Radiation Therapy (IMRT).
- Evaluating the accuracy of treatment planning systems (TPS) at extended Source to Surface Distances (SSDs) is important for clinical applications.
- Small and highly modulated fields present challenges in accurate dose verification.
Purpose of the Study:
- To evaluate the accuracy and efficiency of extended SSD measurements using a 2D detector array for patient-specific IMRT QA.
- To assess the impact of measurement setup on the accuracy of dose verification for small and complex radiation fields.
- To determine the suitability of the PTW Seven29 array for pre-treatment QA of IMRT plans.
Main Methods:
- Analyzed 38 treatment fields from five patients (liver, lung, brain, prostate, spine).
- Utilized the PTW Seven29 detector array and Eclipse v8.9 TPS for treatment planning and calculation.
- Performed measurements at an extended SSD of 215 cm on a NovalisTX linear accelerator.
- Evaluated results using gamma index passing rates with 2 mm distance to agreement (DTA) and 2% dose difference criteria, and also 2%/2mm.
Main Results:
- Gamma index passing rates with 2%/2mm criteria ranged from 90.8% to 100% (average 95.5%±3%).
- Detector array measurements closely matched calculated dose profiles, even for fields with multiple peaks and valleys.
- The accuracy of the Eclipse TPS at extended SSDs was within 1.0% using an ionization chamber.
Conclusions:
- Extended SSD measurements with a 2D detector array enhance sampling resolution for IMRT QA.
- This method is accurate and efficient for verifying doses in highly modulated small fields, crucial for patient-specific QA.
- The choice of IMRT QA device significantly impacts results, particularly for small targets like those in spinal treatments.
