Stability of A-150 plastic ionisation chamber response over a  30-y period

Kroc, Thomas; Lennox, A.J.

doi:10.1093/rpd/ncm126

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“…For shallower depths, the computationally more expensive method based on the MCNP +F6 tally are needed to accurately model dose in the buildup region. The IC-17 dose-response functions and methods reported in this paper are also relevant to the other neutron therapy (Lee et al 2001, Tsuda et al 2004, Kroc and Lennox 2007 and accelerator facilities that use the IC-17 for absolute and relative dose measurements.…”

Section: Discussionmentioning

confidence: 98%

“…The absolute calibration protocol is detailed in the AAPM Report 7 (AAPM Task Group 18 1987) and Mijnheer et al (1987). The IC-17 has been used in many other neutron therapy facilities for absolute dosimetry (Lee et al 2001, Tsuda et al 2004, Kroc and Lennox 2007 and meets the recommendations of the International Commission on Radiation Units and Measurement (Allisy et al 1989). We also use the IC-17 for TMR measurements and measurements of output factors and wedge factors.…”

Section: Mcnp6 Model Of the Ic-17 With Te Fill Gasmentioning

confidence: 99%

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Dosimetric characteristics of the University of Washington Clinical Neutron Therapy System

et al. 2018

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The University of Washington (UW) Clinical Neutron Therapy System (CNTS), which generates high linear energy transfer fast neutrons through interactions of 50.5 MeV protons incident on a Be target, has depth-dose characteristics similar to 6 MV x-rays. In contrast to the fixed beam angles and primitive blocking used in early clinical trials of neutron therapy, the CNTS has a gantry with a full 360° of rotation, internal wedges, and a multi-leaf collimator (MLC). Since October of 1984, over 3178 patients have received conformal neutron therapy treatments using the UW CNTS. In this work, the physical and dosimetric characteristics of the CNTS are documented through comparisons of measurements and Monte Carlo simulations. A high resolution computed tomography scan of the model 17 ionization chamber (IC-17) has also been used to improve the accuracy of simulations of the absolute calibration geometry. The response of the IC-17 approximates well the kinetic energy released per unit mass (KERMA) in water for neutrons and photons for energies from a few tens of keV up to about 20 MeV. Above 20 MeV, the simulated model 17 ion chamber response is 20%-30% higher than the neutron KERMA in water. For CNTS neutrons, simulated on- and off-axis output factors in water match measured values within ~2% ± 2% for rectangular and irregularly shaped field with equivalent square areas ranging in a side dimension from 2.8 cm to 30.7 cm. Wedge factors vary by less than 1.9% of the measured dose in water for clinically relevant field sizes. Simulated tissue maximum ratios in water match measured values within 3.3% at depths up to 20 cm. Although the absorbed dose for water and adipose tissue are within 2% at a depth of 1.7 cm, the absorbed dose in muscle and bone can be as much as 12 to 40% lower than the absorbed dose in water. The reported studies are significant from a historical perspective and as additional validation of a new tool for patient quality assurance and as an aid in ongoing efforts to clinically implement advanced treatment techniques, such as intensity modulated neutron therapy, at the UW.

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Section: Discussionmentioning

confidence: 98%