Quantitative characterization of tomotherapy MVCT dosimetry

Journal Article · Tue Oct 01 00:00:00 EDT 2013 · Medical Dosimetry

DOI:https://doi.org/10.1016/J.MEDDOS.2013.02.009· OSTI ID:22262824

Chen, Mingli ^[1]; Chao, Edward ^[2]; Lu, Weiguo ^[1]

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1. 21st Century Oncology, Madison, WI (United States)
2. Accuray Inc., Madison, WI (United States)

Megavoltage computed tomography (MVCT) is used as image guidance for patient setup in almost every tomotherapy treatment. Frequent use of ionizing radiation for image guidance has raised concern of imaging dose. The purpose of this work is to quantify and characterize tomotherapy MVCT dosimetry. Our dose calculation was based on a commissioned dose engine, and the calculation result was compared with film measurement. We studied dose profiles, center dose, maximal dose, surface dose, and mean dose on homogeneous cylindrical water phantoms of various diameters for various scanning parameters, including 3 different jaw openings (of nominal value J4, J1, and J0.1) and couch speeds (fine, normal, and coarse). The comparison between calculation and film measurement showed good agreement. In particular, the thread pattern on the film of the helical delivery matched very well with calculation. For the J1 jaw and coarse imaging mode, the maximum difference between calculation and measurement was about 6% of the center dose. Calculation on various sizes of synthesized phantoms showed that the center dose decreases almost linearly as the phantom diameter increases, and that the fine mode (couch speed of 4 mm/rotation) received twice the dose of the normal mode (couch speed of 8 mm/rotation) and 3 times that of the coarse mode (couch speed of 12 mm/rotation) as expected. The maximal dose ranged from 100% to ∼200% of the center dose, with increasing ratios for larger phantoms, smaller jaws, and faster couch speed. For all jaw settings and couch speeds, the mean dose and average surface dose vary from 95% to 125% of the center dose with increasing ratios for larger phantoms. We present a quantitative dosimetric characterization of the tomotherapy MVCT in terms of scanning parameters, phantom size, center dose, maximal dose, surface dose, and mean dose. The results can provide an overall picture of dose distribution and a reference data set that enables estimation of CT dose index for the tomotherapy MVCT.

• OSTI ID: 22262824
• Journal Information: Medical Dosimetry, Vol. 38, Issue 3; Other Information: Copyright (c) 2013 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0958-3947
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
COMPUTERIZED TOMOGRAPHY
CT-GUIDED RADIOTHERAPY
DOSIMETRY
PHANTOMS
RADIATION DOSE DISTRIBUTIONS
RADIATION DOSES