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Improving Health Through Medical Physics
The objective of this Special Session (SS-06), organized by the AAPM International Educational Activities Committee, was to present and discuss state-of-the-art technological developments in medical imaging and therapeutical interventions with a specific focus on their impact on patient safety. Topics tackled novel dosimetry techniques in radiotherapy and imaging, including interventional radiology; robotic assistance in image-guided surgery; advanced combined therapy and imaging approaches in external beam treatments and in theranostics, and quantitative molecular imaging biomarker research. The speakers described innovative technologies, emphasized their benefits and recommended prevention or mitigation of potential adverse effects to ensure improved patient safety. The session ended with a discussion exploring ways on how to move the medical physics field forward.
SS-06 Expanding Horizons of Medical Physics: Patient Safety and Beyond
Chairs: Cari Borrás, Robert Jeraj
ID: 1580
Novel approaches to patient dosimetry measurements in radiotherapy and interventional radiology: The role of in vivo dosimetry.
Part 1 Radiotherapy

The dosimetric quantity in Radiation Therapy is absorbed dose to water (TG 51 or TRS 398). Today, the ionization chambers are calibrated in terms of absorbed dose to water, which is used in treatment planning systems (TPS). Some modern day TPS are moving toward Monte Carlo or Boltzman calculations to determine dose in different tissues. This novel approach has been limited by the calculation time. However, in certain cases, it becomes very important to be able to calculate with different tissue types. A reference ionization chamber must be used for absolute measurements in radiation therapy. The characteristics of the ionization chamber are important to consider for precise and accurate measurements. The introduction of small fields for treatment has resulted in important considerations for correct measurements. Other detectors, such as TLD, diamonds, semiconductors, and scintillators,h ave been introduced as alternative means of measurement. The most important consideration is the size of the detector relative to the field to be measured. Each of these detectors must be compared against an ionization chamber as the standard. There are small ionization chambers but sometimes their characteristics can be questionable. So it is important that the ionization chamber to be used has well known characteristics. Brachytherapy applications as part of Radiation therapy require knowledge of the source being used. Generally the dosimetric quantity in use is air kerma strength with the TG 43 protocol. The dosimetric quantity for electronic brachytherapy is air kerma and a modification of the TG 43 protocol is used. The clinic must measure the sources with a calibrated well chamber. Generally, the dose is short range but again different tissue types should be taken into consideration as appropriate.
Larry DeWerd
ID: 1662
Novel approaches to patient dosimetry measurements in radiotherapy and interventional radiology: The role of in vivo dosimetry.
Part 2.

Absorbed dose determination in patients undergoing radiological procedures has two main purposes: ensuring that patient doses are commensurate with the medical purpose of the procedure and obtaining dose-effect relationships for epidemiological studies. Given the harmful tissue (deterministic) effects they may cause, fluoroscopically-guided interventions, named here interventional radiology (IR) procedures, require the most accurate patient dose determination. Dosimetric quantities applicable to IR are incident air kerma (Kai), entrance surface air kerma (Kae), air kerma area product (PKA), and the reference point air kerma Ka,r. Kai, Kae and Ka,r can be measured with calibrated ion chambers or solid state dosimeters; PKA, with either a KAP meter or an ion chamber and film. In modern angiographic systems, cumulative Ka,r and PKA are routinely determined, displayed, stored and transferred electronically. To check their accuracy, the systems need to be calibrated before being put into clinical use. Whilst these dose metrics are very useful for the determination of and the comparison with Diagnostic Reference Levels (DRL), they are not patient doses. Surface patient doses can be determined from Kae measurements by application of the appropriate dose-to-air kerma ratios. However, because of the often-overlapping radiation beams in IR procedures, measurements at specific points may miss the peak doses. Therefore, it is necessary to obtain dose distributions for the patient's most exposed regions, which for IR procedures is the skin. Calibrated silver halide or radiochromic films placed on or around the patient at the entrance of the radiation beams permit determination of the peak dose to the skin and to other critical organs such as the eye lens. Various film arrangements for cardiology and neuroradiology procedures will be presented. How the method could be used to assess the accuracy of the organ doses estimated by the new DICOM Patient Radiation Dose Structured Report will be explored.
Cari Borrás
ID: 1728
Electronic recording of radiography, fluoroscopy and computed tomography dose metrics: When should they be included in the patient chart?
Dose metrics generated by medical imaging devices are useful in guiding proper use of equipment, adjusting acquisition protocols, providing feedback for operators, and for comparing practices. They also contribute to setting representative exam-specific Diagnostic Reference Levels (DRLs). In certain circumstances, because dose metrics are only peripherally related to patient dose, the values are potentially misleading. Dose metric quantities applicable to projection radiography and fluoroscopy include entrance surface air kerma (Ka,e), incident air kerma (Ka,i), incident air kerma at the patient entrance reference point (Ka,r), and kerma area product (PKA). For computed tomography (CT), dose metric values include volume CT dose index (CTDlvol) and dose-length product (DLP). All dose metric indicators, Ka,e, Ka,i, Ka,r, PKA, CTDlvol, and DLP should have calibrations verified for each type of equipment, and should ideally be sent to a radiation dose management system (RDMS) for evaluation, accumulation and retention of ionizing radiation events. Dose-metric values must be included in the EHR/interpretive report when local, regional, or national laws require such documentation (for example, California 2012 CT reporting law). While this can be helpful to identify overuse, a negative impact could be denial of appropriate and justified exams. Misinterpretation of dose metric information by physicians or patients can result in inaccurate under- or over-estimates of patient dose without sufficient knowledge of the details. Recent approval of the DICOM Patient Radiation Dose Structured Report (P-RDSR) and its implementation should provide improvements in patient-specific characterization of radiation doses. In this presentation, event recording of dose metric values for each modality by an RDMS is discussed, including benefits and pitfalls that can occur. Estimating patient doses with use of dose metric values and/or the P-RDSR by a medical physicist and identifying potential actionable findings to be included in the patient chart are considered.
Tony Seibert
ID: 1750
Optical surface imaging to improve the precision and accuracy of radiotherapy delivery
The advents of precise radiotherapy planning and delivery tools have necessitated the need for mitigating both interand intra-fraction patient motion uncertainties. Surface imaging (SI) allows users to view the patient's topography without ionizing radiation or invasive surrogate markers. Commercial SI systems read the patient position in the room in real time and compare it to the expected treatment position as dictated by the external surface, which is derived from the patient's planning CT scan. Detected deviations are potential surrogates for patient positioning error. This information is useful both during initial patient setup, as it can guide accurate and efficient positioning, and during treatment to ensure radiation is delivered only when the patient is in the correct position. The opportunity of direct and continuous patient surface tracking, without additional risk from increased imaging radiation dose and time-ontable, makes SI a valuable tool that is safe, efficient, and accurate. Aside from real time patient position monitoring, SI has shown potential for Stereotactic Body Radiotherapy (SBRT), pediatric treatments, Deep inspiration breath hold treatments, and Stereotactic radiosurgery (SRS). The use of SI for DIBH obviates the need for more invasive respiratory motion management techniques, such as active breath hold, while allowing for safe and accurate treatments. For SRS, these systems give patients the option of undergoing treatment with open-face masks without compromising precision of radiation delivery. However, as any other system, SI has its limitations. It only tracks external motion so any internal target movement independent of external surface motion is not detected. This technology was never meant to substitute internal imaging. Despite its limitations, SI has a positive impact on precise and safe radiotherapy delivery, and as its applications expand beyond the current use, its impact will only become greater.
Laura Padilla
ID: 873
Advances in intraoperative imaging, registration, and robotic assistance in surgery
Recent advances in intraoperative imaging offer the means to extend beyond conventional goals of geometric precision and surgical navigation to offer new capabilities to ensure accurate targeting, evaluate the quality of the surgical product, and detect suboptimal surgical constructs and/or complications in the operating room with opportunity to revise if necessary. Such advances include: new platforms for cone-beam CT (including mobile and fixed-room systems); algorithms for high-quality 3D image reconstruction with improved image quality and/or reduced radiation dose; 3D-2D image registration methods to annotate radiographic views with planning and navigation information; 3D-3D image registration methods to combine multi-modality image information in a manner that accounts for complex deformation; integration of imaging with robotic assistance to increase precision, safety, and workflow; and data-intensive approaches to improve planning and better predict (and minimize) variations in surgical outcome. Such approaches aim to improve patient safety, provide independent checks and decision support in the OR, streamline intraoperative workflow, and provide quality assurance to improve surgical outcomes and reduce the rate of revision surgeries.
Jeffrey Siewerdsen
ID: 926
Treatment Optimization in Theranostic Radionuclide Therapies
The administration of a tracer quantity of a tumor targeting agent in order to determine patient specific pharmacokinetics of the radiotracer prior to a therapeutic activity is the foundation of treatment planning for radionuclide therapies. In this presentation, different theranostic approaches will be discussed in which the treatment can be imaged pre and during therapy; thus providing quantitative feedback which can be used to intervene and alter the therapy. The examples presented will include: (i) the use of re-differentiation therapy with BRAF inhibitors in radioiodine management of thyroid cancer, (ii) The use of Lu-177 labeled peptides as theranostic agents to image and treat neuroendocrine cancers and (iii) the use of Zr-89 and 1-124 antibodies to study tumor uptake and assist in optimizing new targeting immunoconjugates. Theranostic strategies provide an opportunity for careful individualized radionuclide dosimetry to ensure that each patient achieves the maximum tumor dose safely within the tolerances of the dose limiting tissues.
John Humm
ID: 849
Quantitative molecular imaging biomarkers and how they impact patient safety
Quantitative imaging biomarkers (QIB) are gaining in importance, as they are pushing the application of imaging beyond qualitative (diagnostic) applications. They are essential for target definition or treatment response assessment. QIBs require quantification of the whole imaging chain from image acquisition, reconstruction as well as image analysis. QIBs also require detailed assessment of the uncertainties, which can in turn be used to define confidence intervals which define what changes in QIB signal can be deemed significant. These confidence intervals, typically defined through repetitive test/retest scanning, can be used to define clinically significant changes of disease response or progression. Furthermore, QIB need to go through the whole biomarker qualification/validation chain before they can be reliably used in clinics. Unfortunately, most of the QIB in use today, have not gone through proper biomarker qualification/validation steps. Improper use of QIBs beyond their proven validity severely affects patient safety. An example of the QIB based on NaF PET/CT scanning of metastatic prostate cancer to bone, including test/retest and clinical validation will be presented. Potential use of such validated QIBs to assess metastatic prostate disease and guide treatment decisions will be presented.
Robert Jeraj