In aqua vivo EPID dosimetry
- 22 December 2011
- journal article
- radiation measurement-physics
- Published by Wiley in Medical Physics
- Vol. 39 (1), 367-377
- https://doi.org/10.1118/1.3665709
Abstract
Purpose: At the Netherlands Cancer Institute—–Antoni van Leeuwenhoek Hospitalin vivo dosimetry using an electronic portal imaging device (EPID) has been implemented for almost all high‐energy photon treatments of cancer with curative intent. Lung cancer treatments were initially excluded, because the original back‐projection dose‐reconstruction algorithm uses water‐based scatter‐correction kernels and therefore does not account for tissue inhomogeneities accurately. The aim of this study was to test a new method, in aqua vivo EPID dosimetry, for fast dose verification of lung cancer irradiations during actual patient treatment. Methods: The key feature of our method is the dose reconstruction in the patient from EPID images, obtained during the actual treatment, whereby the images have been converted to a situation as if the patient consisted entirely of water; hence, the method is termedin aqua vivo. This is done by multiplying the measured in vivo EPID image with the ratio of two digitally reconstructed transmission images for the unit‐density and inhomogeneous tissue situation. For dose verification, a comparison is made with the calculated dose distribution with the inhomogeneity correction switched off. IMRT treatment verification is performed for each beam in 2D using a 2D γ evaluation, while for the verification of volumetric‐modulated arc therapy (VMAT) treatments in 3D a 3D γ evaluation is applied using the same parameters (3%, 3 mm). The method was tested using two inhomogeneous phantoms simulating a tumor in lung and measuring its sensitivity for patient positioning errors. Subsequently five IMRT and five VMAT clinical lung cancer treatments were investigated, using both the conventional back‐projection algorithm and the in aqua vivo method. The verification results of the in aqua vivo method were statistically analyzed for 751 lung cancer patients treated with IMRT and 50 lung cancer patients treated with VMAT. Results: The improvements by applying thein aqua vivo approach are considerable. The percentage of γ values ≤1 increased on average from 66.2% to 93.1% and from 43.6% to 97.5% for the IMRT and VMAT cases, respectively. The corresponding mean γ value decreased from 0.99 to 0.43 for the IMRT cases and from 1.71 to 0.40 for the VMAT cases, which is similar to the accepted clinical values for the verification of IMRT treatments of prostate, rectum, and head‐and‐neck cancers. The deviation between the reconstructed and planned dose at the isocenter diminished on average from 5.3% to 0.5% for the VMAT patients and was almost the same, within 1%, for the IMRT cases. The in aqua vivo verification results for IMRT and VMAT treatments of a large group of patients had a mean γ of approximately 0.5, a percentage of γ values ≤1 larger than 89%, and a difference of the isocenter dose value less than 1%. Conclusions: With thein aqua vivo approach for the verification of lung cancer treatments (IMRT and VMAT), we can achieve results with the same accuracy as obtained during in vivo EPID dosimetry of sites without large inhomogeneities.Keywords
This publication has 17 references indexed in Scilit:
- Simplifying EPID dosimetry for IMRT treatment verificationMedical Physics, 2011
- Quality assurance of volumetric modulated arc therapy: Evaluation and comparison of different dosimetric systemsMedical Physics, 2011
- 3D Dosimetric verification of volumetric-modulated arc therapy by portal dosimetryRadiotherapy and Oncology, 2010
- A simple backprojection algorithm for 3D in vivo EPID dosimetry of IMRT treatmentsMedical Physics, 2009
- Frameless Stereotactic Body Radiotherapy for Lung Cancer Using Four-Dimensional Cone Beam CT GuidanceInternational Journal of Radiation Oncology*Biology*Physics, 2008
- A literature review of electronic portal imaging for radiotherapy dosimetryRadiotherapy and Oncology, 2008
- Lessons from recent accidents in radiation therapy in FranceRadiation Protection Dosimetry, 2008
- 3D in vivo dose verification of entire hypo-fractionated IMRT treatments using an EPID and cone-beam CTRadiotherapy and Oncology, 2007
- Replacing Pretreatment Verification With In Vivo EPID Dosimetry for Prostate IMRTInternational Journal of Radiation Oncology*Biology*Physics, 2007
- Mid-ventilation CT scan construction from four-dimensional respiration-correlated CT scans for radiotherapy planning of lung cancer patientsInternational Journal of Radiation Oncology*Biology*Physics, 2006