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"In vivo dosimetry in external beam photon radiotherapy: Requirements and future directions for research, development, and clinical practice"
Igor Olaciregui-Ruiza,⁎, Sam Beddarb, Peter Greerc, Nuria Jornetd, Boyd McCurdye, Gabriel Paiva-Fonsecaf, Ben Mijnheera, Frank Verhaegenf
Journal: phiRO Physics and Imaging in Radiation Oncology
External beam radiotherapy with photon beams is a highly accurate treatment modality, but requires extensive quality assurance programs to confirm that radiation therapy will be or was administered appropriately. In vivo dosimetry (IVD) is an essential element of modern radiation therapy because it provides the ability to catch treatment delivery errors, assist in treatment adaptation, and record the actual dose delivered to the patient.
However, for various reasons, its clinical implementation has been slow and limited. The purpose of this report is to stimulate the wider use of IVD for external beam radiotherapy, and in particular of systems using electronic portal imaging devices (EPIDs). After documenting the current IVD methods, this report provides detailed software, hardware and system requirements for in vivo EPID dosimetry systems in order to help in bridging the current vendor-user gap. The report also outlines directions for further development and research. In vivo EPID dosimetry vendors, in collaboration with users across multiple institutions, are requested to improve the understanding and reduce the uncertainties of the system and to help in the determination of optimal action limits for error detection. Finally, the report recommends that automation of all aspects of IVD is needed to help facilitate clinical adoption, including automation of image acquisition, analysis, result interpretation, and reporting/documentation. With the guidance of this report, it is hoped that widespread clinical use of IVD will be significantly accelerated.
Here you can find the paper in phiRO Physics and Imaging in Radiation Oncology: DOI
In order to prevent future misinterpretations, a concise definition of IVD in the scope of EBRT is provided in the Methods section. According to this definition, point detectors placed on the patient’s skin in the treatment field such as thermoluminescent detectors, silicon diodes, metal-oxide semiconductor field-effect transistors, optically stimulated luminescence dosimeters, and electronic portal imaging devices (EPIDs) [4,5] are the main commercially available IVD methods. Due to the limitations of point detectors for large-scale implementation of IVD in modern EBRT, the emphasis of this report lies on EPID-based IVD (EIVD) systems.
IVD is a radiation measurement that is acquired while the patient is being treated containing information related to the absorbed dose in the patient. This definition implies that an IVD system must be able to capture errors due to equipment failure, errors in dose calculation, patient positioning errors, and patient anatomy changes.
The definition excludes all ‘transmission dosimetry’ methods that capture only the accelerator exit dose/energy fluence (or related quantities or metrics) before the beam reaches the patient, even if these are combined with a cone beam computed tomography (CBCT) image acquired right before treatment delivery. Using an accelerator log file, even in combination with a CBCT image, is also not considered IVD. The aforementioned systems can, however, complement IVD methods. Also, the comparison of an EPID image made during a specific fraction of a patient treatment with a reference EPID image, e.g., of the first fraction, may miss dose errors present in the reference image and is therefore a constancy check but not in vivo dosimetry. While such methods can be valuable tools for patient-specific QA, they are currently not categorized as IVD.