Effect of Detector Orientation and Influence of Jaw Position in the Determination of Small-field Output Factor with Various Detectors for High-energy Photon Beams.

Autor:	Godson HF; Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India., Manickam R; Department of Radiotherapy, Sri Shankara Cancer Hospital and Research Centre, Bengaluru, Karnataka, India., Ponmalar YR; Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India., Ganesh KM; Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India., Saminathan S; Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India., Chandraraj V; Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India., Kumar AS; Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India., George S; Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India., Raman A; Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bengaluru, Karnataka, India., Singh RR; Department of Radiation Oncology, Christian Medical College, Vellore, Tamil Nadu, India.
Jazyk:	angličtina
Zdroj:	Journal of medical physics [J Med Phys] 2024 Jan-Mar; Vol. 49 (1), pp. 73-83. Date of Electronic Publication: 2024 Mar 30.
DOI:	10.4103/jmp.jmp_148_23
Abstrakt:	Background: Accurate dose measurements are difficult in small fields due to charge particle disequilibrium, partial source occlusion, steep dose gradient, and the finite size of the detector. Aim: The study aims to determine the output factor using various detectors oriented in parallel and perpendicular orientations for three different tertiary collimating systems using 15 MV photon beams. In addition, this study analyzes how the output factor could be affected by different configurations of X and Y jaws above the tertiary collimators. Materials and Methods: Small field output factor measurements were carried out with three detectors for different tertiary collimating systems such as BrainLab stereotactic cones, BrainLab mMLC and Millennium MLC namely. To analyze the effect of jaw position on output factor, measurements have been carried out by positioning the jaws at the edge, 0.25, 0.5, and 1.0 cm away from the tertiary collimated field. Results: The data acquired with 15 MV photon beams show significant differences in output factor obtained with different detectors for all collimating systems. For smaller fields when compared to microDiamond, the SRS diode underestimates the output by up to -1.7% ± 0.8% and -2.1% ± 0.3%, and the pinpoint ion chamber underestimates the output by up to -8.1% ± 1.4% and -11.9% ± 1.9% in their parallel and perpendicular orientation respectively. A large increase in output factor was observed in the small field when the jaw was moved 0.25 cm symmetrically away from the tertiary collimated field. Conclusion: The investigated data on the effect of jaw position inferred that the position of the X and Y jaw highly influences the output factors of the small field. It also confirms that the output factor highly depends on the configuration of X and Y jaw settings, the tertiary collimating system as well as the orientation of the detectors in small fields. Competing Interests: There are no conflicts of interest. (Copyright: © 2024 Journal of Medical Physics.)
Databáze:	MEDLINE
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