Time-resolved versus time-integrated portal dosimetry: the role of an object’s position with respect to the isocenter in volumetric modulated arc therapy
| Autor: | Frank Verhaegen, Lotte E J R Schyns, Mark Podesta, Wouter van Elmpt, L. Persoon |
|---|---|
| Přispěvatelé: | Promovendi ODB, Radiotherapie, RS: GROW - R3 - Innovative Cancer Diagnostics & Therapy |
| Rok vydání: | 2016 |
| Předmět: |
Dose-volume histogram
medicine.medical_treatment VMAT Patient Positioning DVH metrics 030218 nuclear medicine & medical imaging 03 medical and health sciences 0302 clinical medicine Position (vector) medicine Animals Humans Dosimetry Radiology Nuclear Medicine and imaging Radiometry radiotherapy Physics Radiological and Ultrasound Technology business.industry Radiotherapy Planning Computer-Assisted Gamma ray Isocenter Radiotherapy Dosage Volumetric modulated arc therapy Radiation therapy Gamma analysis Gamma Rays 030220 oncology & carcinogenesis gamma analysis Cattle Radiotherapy Intensity-Modulated portal dosimetry Nuclear medicine business |
| Zdroj: | Physics in Medicine and Biology, 61(10), 3969-3984. IOP Publishing Ltd. |
| ISSN: | 1361-6560 0031-9155 |
| DOI: | 10.1088/0031-9155/61/10/3969 |
| Popis: | The aim of this work is to compare time-resolved (TR) and time-integrated (TI) portal dosimetry, focussing on the role of an object's position with respect to the isocenter in volumetric modulated arc therapy (VMAT). Portal dose images (PDIs) are simulated and measured for different cases: a sphere (1), a bovine bone (2) and a patient geometry (3). For the simulated case (1) and the experimental case (2), several transformations are applied at different off-axis positions. In the patient case (3), three simple plans with different isocenters are created and pleural effusion is simulated in the patient. The PDIs before and after the sphere transformations, as well as the PDIs with and without simulated pleural effusion, are compared using a TI and TR gamma analysis. In addition, the performance of the TI and TR gamma analyses for the detection of real geometric changes in patients treated with clinical plans is investigated and a correlation analysis is performed between gamma fail rates and differences in dose volume histogram (DVH) metrics. The TI gamma analysis can show large differences in gamma fail rates for the same transformation at different off-axis positions (or for different plan isocenters). The TR gamma analysis, however, shows consistent gamma fail rates. For the detection of real geometric changes in patients treated with clinical plans, the TR gamma analysis has a higher sensitivity than the TI gamma analysis. However, the specificity for the TR gamma analysis is lower than for the TI gamma analysis. Both the TI and TR gamma fail rates show no correlation with changes in DVH metrics. This work shows that TR portal dosimetry is fundamentally superior to TI portal dosimetry, because it removes the strong dependence of the gamma fail rate on the off-axis position/plan isocenter. However, for 2D TR portal dosimetry, it is still difficult to interpret gamma fail rates in terms of changes in DVH metrics for patients treated with VMAT. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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