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The most recent reviews of accuracy requirements in radiation oncology were published in the 1990s, primarily in an era that was transitioning from 2-D to 3-D conformal radiation therapy (CRT). Since then, the technology associated with radiation oncology has changed dramatically. The combination of various forms of imaging for radiation therapy planning, treatment planning software, dose delivery technology including 4-D considerations as well as in-room daily image guidance has resulted in new perspectives on accuracy considerations. The underlying hypothesis for the use of these advanced technologies is that loco-regional control of cancer remains a significant barrier to cancer cure for many common cancers and that better dose distributions will translate into better outcomes. However, further clinical gain using these new technologies may be limited by single or compounded uncertainties associated with the entire treatment process. Thus, it is important to understand what factors should be considered in determining accuracy requirements as well as the realistic expectations of uncertainties that exist within the total treatment process. The need for accuracy is based on clinical requirements such as the steepness of dose-response curves, inherent heterogeneity in patient response to treatment, and the level of accuracy that is practically achievable. Statements on accuracy are dependent on the technology used and the reality of what is practically achievable and necessary. This review highlights some of the major differences between accuracy requirements as determined in the 2-D RT and 3-D CRT era versus the modern era of intensity modulated, image-guided, 4-D radiation therapy.

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Objectives: To determine the effective dose and CT dose index (CTDI) for a range of imaging protocols using the Sirona GALILEOS ® Comfort CBCT scanner (Sirona Dental Systems GmbH, Bensheim, Germany). Methods: Calibrated optically stimulated luminescence dosemeters were placed at 26 sites in the head and neck of a modified RANDO ® phantom (The Phantom Laboratory, Greenwich, NY). Effective dose was calculated for 12 different scanning protocols. CTDI measurements were also performed to determine the dose-length product (DLP) and the ratio of effective dose to DLP for each scanning protocol. Results: The effective dose for a full maxillomandibular scan at 42 mAs was 102 ± 1 mSv and remained unchanged with varying contrast and resolution settings. This compares with 71 mSv for a maxillary scan and 76 mSv for a mandibular scan with identical milliampere-seconds (mAs) at high contrast and resolution settings. Conclusions: Changes to mAs and beam collimation have a significant influence on effective dose. Effective dose and DLP vary linearly with mAs. A collimated maxillary or mandibular scan decreases effective dose by approximately 29% and 24%, respectively, as compared with a full maxillomandibular scan. Changes to contrast and resolution settings have little influence on effective dose. This study provides data for setting individualized patient exposure protocols to minimize patient dose from ionizing radiation used for diagnostic or treatment planning tasks in dentistry.

Purpose: To develop a portable scanner that demonstrates the principles of radiography and computed tomography (CT). Methods: The traditional methods for teaching the physics of medical imaging rely on lectures, followed by demonstrations on a clinical system that is not easily accessible or programmed for educational purposes. We have developed a scaled‐down portable CT imaging system suitable for interactive “real time” demonstrations using a laptop computer during a classroom or lab session. Our optical system uses light rays in lieu of x‐rays so that experiments can be conducted while posing no electrical or radiation hazards to instructors and students. The desk‐top CT imaging device will be supplied with a learning kit of experimental test phantoms, lab manuals, instructional videos, and specialized software that demonstrate 2D radiographic and 3D CT image reconstruction methods. These approaches are relevant to imaging systems used in digital diagnostic imaging and image‐guided therapy. Results: A low‐cost portable system (< $15,000) has been manufactured (http://www.deskcat.com/) to enrich the studentˈs learning experience and improve the retention of fundamental imaging concepts. Students learn about spatial resolution, contrast resolution, system linearity, image artifacts and they perform quantitative measurements in 3D space, using image visualization software tools and specialized test phantoms (7.2 cm diameter × 5.3 cm long). Early reaction from instructors and students alike has been very encouraging. Conclusions: This learning package should prove attractive to universities with medical physics programs in Departments of Physics, Medical Biophysics, or Biomedical Engineering, as well as Medical Schools with residency training programs (Medical Imaging, Radiation Oncology). The systemˈs modular nature allows extensions for future coverage of related topics such as nuclear and molecular SPECT imaging. Through future developments, it may also be possible to model the dose deposition patterns from intensity‐modulated radiotherapy beams using ultraviolet exposure of radiochromic gel volumes. This research was sponsored by the Ministry of Research and Innovation, Government of Ontario, Canada (ORDCF Grant, OCITS Project) and by Modus Medical Devices as the industry partner. We also thank The University of Western Ontario for providing funding through its “Fellowship for Teaching Innovation”. This supported one of the authors (RT) during a summer studentship.