Clinical Implementation of a Model-Based In Vivo Dose Verification System for Stereotactic Body Radiation Therapy-Volumetric Modulated Arc Therapy Treatments Using the Electronic Portal Imaging Device.

To report findings from an in vivo dosimetry program implemented for all stereotactic body radiation therapy patients over a 31-month period and discuss the value and challenges of utilizing in vivo electronic portal imaging device (EPID) dosimetry clinically. From December 2013 to July 2016, 117 stereotactic body radiation therapy-volumetric modulated arc therapy patients (100 lung, 15 spine, and 2 liver) underwent 602 EPID-based in vivo dose verification events. A developed model-based dose reconstruction algorithm calculates the 3-dimensional dose distribution to the patient by back-projecting the primary fluence measured by the EPID during treatment. The EPID frame-averaging was optimized in June 2015. For each treatment, a 3%/3-mm γ comparison between our EPID-derived dose and the Eclipse AcurosXB-predicted dose to the planning target volume (PTV) and the ≥20% isodose volume were performed. Alert levels were defined as γ pass rates <85% (lung and liver) and <80% (spine). Investigations were carried out for all fractions exceeding the alert level and were classified as follows: EPID-related, algorithmic, patient setup, anatomic change, or unknown/unidentified errors. The percentages of fractions exceeding the alert levels were 22.6% for lung before frame-average optimization and 8.0% for lung, 20.0% for spine, and 10.0% for liver after frame-average optimization. Overall, mean (± standard deviation) planning target volume γ pass rates were 90.7% ± 9.2%, 87.0% ± 9.3%, and 91.2% ± 3.4% for the lung, spine, and liver patients, respectively. Results from the clinical implementation of our model-based in vivo dose verification method using on-treatment EPID images is reported. The method is demonstrated to be valuable for routine clinical use for verifying delivered dose as well as for detecting errors.

McCowan PM ，Asuni G ，Van Uytven E ，VanBeek T ，McCurdy BM ，Loewen SK ，Ahmed N ，Bashir B ，Butler JB ，Chowdhury A ，Dubey A ，Leylek A ，Nashed M ... -  《-》

An in vivo dose verification method for SBRT-VMAT delivery using the EPID.

McCowan PM ，Van Uytven E ，Van Beek T ，Asuni G ，McCurdy BM ... -  《-》

Validation of a method for in vivo 3D dose reconstruction for IMRT and VMAT treatments using on-treatment EPID images and a model-based forward-calculation algorithm.

Van Uytven E ，Van Beek T ，McCowan PM ，Chytyk-Praznik K ，Greer PB ，McCurdy BM ... -  《-》

Overview of 3-year experience with large-scale electronic portal imaging device-based 3-dimensional transit dosimetry.

To assess the usefulness of electronic portal imaging device (EPID)-based 3-dimensional (3D) transit dosimetry in a radiation therapy department by analyzing a large set of dose verification results. In our institution, routine in vivo dose verification of all treatments is performed by means of 3D transit dosimetry using amorphous silicon EPIDs. The total 3D dose distribution is reconstructed using a back-projection algorithm and compared with the planned dose distribution using 3D gamma evaluation. Dose reconstruction and gamma evaluation software runs automatically in our clinic, and analysis results are (almost) immediately available. If a deviation exceeds our alert criteria, manual inspection is required. If necessary, additional phantom measurements are performed to separate patient-related errors from planning or delivery errors. Three-dimensional transit dosimetry results were analyzed per treatment site between 2012 and 2014 and the origin of the deviations was assessed. In total, 4689 of 15,076 plans (31%) exceeded the alert criteria between 2012 and 2014. These alerts were patient-related and attributable to limitations of our back-projection and dose calculation algorithm or to external sources. Clinically relevant deviations were detected for approximately 1 of 430 patient treatments. Most of these errors were because of anatomical changes or deviations from the routine clinical procedure and would not have been detected by pretreatment verification. Although cone beam computed tomography scans yielded information about anatomical changes, their effect on the dose delivery was assessed quantitatively by means of 3D in vivo dosimetry. EPID-based transit dosimetry is a fast and efficient dose verification technique. It provides more useful information and is less time-consuming than pretreatment verification measurements of intensity modulated radiation therapy and volumetric modulated arc therapy. Large-scale implementation of 3D transit dosimetry is therefore a powerful method to guarantee safe dose delivery during radiation therapy.

Mijnheer BJ ，González P ，Olaciregui-Ruiz I ，Rozendaal RA ，van Herk M ，Mans A ... -  《-》

In aqua vivo EPID dosimetry.

Wendling M ，McDermott LN ，Mans A ，Olaciregui-Ruiz Í ，Pecharromán-Gallego R ，Sonke JJ ，Stroom J ，van Herk M ，Mijnheer BJ ... -  《MEDICAL PHYSICS》