Medical Physics Seminar – Monday, October 12, 2020
Calibrating dynamic clinical photon treatments closer to treatment conditions: recent developments in plan-class specific reference field linear accelerator dosimetry
Vimal Desai, Ph.D.
Radiation Oncology Physics Resident
Department of Human Oncology
University of Wisconsin School of Medicine and Public Health
Radiation detectors are used to precisely and accurately determine the absorbed dose to water under a specific set of reference conditions and are critically important for determining the absorbed dose to the patient. Due to the advent of intensity modulated radiation therapy, however, actual clinical treatments are often far removed from reference field conditions. For highly modulated patient-specific deliveries, it can be difficult to determine the absorbed dose to water without the use of additional plan- and detector-specific corrections, and these corrections can be difficult and time-consuming to establish. The plan-class specific reference (pcsr) field concept was conceived as part of a 2008 IAEA-AAPM collaboration with the goal of efficiently bridging the gap between reference field conditions and modulated treatment deliveries through the use of intermediate calibration fields which would be representative of a subset of treatments. This seminar will cover the background, recent developments, and remaining challenges pertaining to the clinical implementation of the pcsr field concept.
Short question that the work is attempting to answer: “Can we effectively bring calibration conditions of linear accelerators closer to actual patient deliveries using intermediate calibration fields in the form of plan-class specific reference fields?â€
Short answer: Establishing pcsr fields or a methodology for generating them has historically proven to be difficult because of the large amounts of representative data required even for a single institution and the heavy computation and measurement resources required to establish detector- and plan-specific corrections. Recent work has provided more insight into relevant plan metrics through statistical analysis and clustering strategies and has also established a large number of plan-specific corrections to guide pcsr field development or alternative strategies such as case-by-case corrections.