RECORDS: Improved reporting of Monte Carlo radiation transport studies: Report of the AAPM Research Committee Task Group 268

© 2017 American Association of Physicists in Medicine. Studies involving Monte Carlo simulations are common in both diagnostic and therapy medical physics research, as well as other fields of basic and applied science. As with all experimental studies, the conditions and parameters used for Monte Carlo simulations impact their scope, validity, limitations, and generalizability. Unfortunately, many published peer-reviewed articles involving Monte Carlo simulations do not provide the level of detail needed for the reader to be able to properly assess the quality of the simulations. The American Association of Physicists in Medicine Task Group #268 developed guidelines to improve reporting of Monte Carlo studies in medical physics research. By following these guidelines, manuscripts submitted for peer-review will include a level of relevant detail that will increase the transparency, the ability to reproduce results, and the overall scientific value of these studies. The guidelines include a checklist of the items that should be included in the Methods, Results, and Discussion sections of manuscripts submitted for peer-review. These guidelines do not attempt to replace the journal reviewer, but rather to be a tool during the writing and review process. Given the varied nature of Monte Carlo studies, it is up to the authors and the reviewers to use this checklist appropriately, being conscious of how the different items apply to each particular scenario. It is envisioned that this list will be useful both for authors and for reviewers, to help ensure the adequate description of Monte Carlo studies in the medical physics literature.Postprint (published version

Inverse square corrections for FACs and WAFACs

Inverse square correction factors for wide-angle free-air chambers (WAFACs) and free-air chambers (FACs) for cylindrical, conical and square-prism detectors are required for determining the on-axis air kerma from measurements or Monte Carlo calculations made with these different shaped detectors. Values of air kerma measured with these detectors use an effective volume technique related to the inverse square correction factors. This paper presents these factors in a consistent framework and the relationships between them are made clear. Using Monte Carlo simulations, the various corrections and techniques are shown to be accurate within a statistical precision of about 0.04% or better with the exception of the published correction for square prism detectors which is shown to hold only for thin detectors which have an opening angle corresponding to the NIST and NRCC WAFAC primary standards. A more accurate correction for square prism detectors is presented which properly averages 1/d2 rather than d2 where d is the distance away from the source

TU‐C‐BRA‐01: Progress in Calculations of KQ for TG‐51

The calculated values of kQ in the TG‐51 protocol are based on analytic calculations which make use of various tabulated values of measured and calculated factors such as the water to air stopping‐power ratio, Pwall, Prepl and Pcel (for details see Ch 9 of the 2009 AAPM Summer School book, Med. Phys. Publishing, Madison, WI). Since the publication of TG‐51 there have been improved calculations of almost all the factors required in TG‐51. This talk will briefly review those improved calculations which are based on Monte Carlo calculations of ratios of the dose to the cavity of the ion chamber. However, with the development of the EGSnrc Monte Carlo system (Kawrakow, Med Phys 27(2000) 499) it became possible to accurately calculate the response of ion chambers, not just the ratios of the dose to the cavity. This made it possible to accurately do ab initio Monte Carlo calculations of kQ. As computers became faster per unit cost and clever variance reduction techniques for doing ion chamber calculations in complex geometries were implemented (Wulff et al, Med Phys 35(2008)1328) these calculations became both accurate and feasible (albeit with large clusters of computers). Values of kQ have been calculated this way for a total of 33 commonly used cylindrical ion chambers (Muir and Rogers, Med Phys 37(2010)5939). Detailed estimates of the systematic uncertainty in these calculations have been made and range between 0.6% and 1.0%, depending on the assumptions made. The largest component is the uncertainty (0.5%) in the assumed constancy with beam quality of (W/e)air, which relates the energy deposited in the cavity to the charge released in the air. In a detailed comparison of the calculated kQ values to the extensive high‐ quality measurements by McEwen (Med Phys 37(2010)2179), Muir et al (submitted, 2011) found the mean percentage differences between the calculations and the experiments are 0.08(0.17), 0.07(0.32) and 0.23(0.31) in 6, 10 and 25 MV beams respectively (bracketed values are rms deviations). These discrepancies are well within the stated uncertainties of the measurements (about 0.3% to 0.4%) and the calculations (about 0.3% to 0.4% ignoring W/e uncertainties and assuming correlated uncertainties in photon cross section). These comparisons can be used to set an upper limit of 0.4% on the variation of (W/e)air with beam quality between 60Co and 25 MV beams (95% confidence). More importantly, the close agreement with experiment gives confidence in the accuracy of the Monte Carlo calculated values of kQ with a 68% confidence uncertainty of between 0.4% and 0.5%. Learning Objectives 1. Understand the basis of calculated kQ values in the original TG‐51 protocol 2. Become aware of the improvements made in many of the required correction factors in the last decade 3. Understand how ab initio calculations of kQ are done 4. Understand the uncertainties involved in ab initio calculations of kQ