Detector Response in the Dosimetry of Small Modulated Arc Fields: An Experimental Study
J Larraga-Gutierrez*, O Garcia-Garduno, J Herrera-Gonzalez, National Institute of Neurology & Neurosurgery, Mexico City, Mexico
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PO-GePV-T-233 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To assess the response of three radiation detectors for the dosimetry of small modulated arc fields (VMAT)
Methods: A set of VMAT plans were designed with spherical targets, each with diameters of: 8.0, 3.0, 2.5, 2.0, 1.5, 1.0, and 0.5 cm on an anthropomorphic phantom. The dose prescription was set to 4.0 Gy for all the lesions. The treatment plan and dose delivery were performed in Eclipse 15.6 and TrueBeam STx (Varian USA), respectively. Three radiation detectors were used to measure the detector signals for each VMAT plan: microDiamond, Semiflex, and PinPoint 3D from PTW-Freiburg. The detectors' signals were normalized to the target of 8.0 cm in diameter. Also, the dose was measured using radiochromic film (EBT-XD, Ashland) for the same VMAT plans. The film was used to reduce the impact of the TPS to calculate the same dose to each target by correcting the detectors' signals for the dose differences.
Results: The dose correction factors measured with radiochromic film for each target were between 1.00 to 1.06 relative to the dose measured for the 8.0 cm target. These factors were applied to the detectors' signals to correct for non-uniformities of TPS dose calculations for each target, which calculated doses ranged from 4.1 to 4.3 Gy. The normalized detector response was found between 1.00 to 0.884, 1.00 to 1.07, and 1.0 to 0.986 for Semiflex, microDiamond and PinPoint 3D detectors, respectively. A response different from unity was found for field sizes < 2.0 cm.
Conclusion: A detector's response close to 1.0 (within 1%) was found for field sizes > 2.0 in accordance with previous findings in modulates fields. However, further research must be carried out to understand the detector response in small modulated fields for correct dosimetry in SRS/SBRT/SABR.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by "Fondo Sectorial de Investigacion en Salud y Seguridad Social" of the National Council of Research and Technology (CONACYT) with the grant A3-S-37057.
Keywords
Ionization Chamber, Small Fields, Dosimetry
Taxonomy
TH- External Beam- Photons: Small field experimental dosimetry
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