Abstract
Temporal and spatial anatomic changes caused by respiration during radiation treatment delivery can lead to discrepancies between prescribed and actual radiation doses. The present paper documents a study to construct a respiratory‐motion‐simulating, four‐dimensional (4D) anatomic and dosimetry model for the study of the dosimetric effects of organ motion for various radiation treatment plans and delivery strategies. The non‐uniform rational B‐splines (NURBS) method has already been used to reconstruct a three‐dimensional (3D) VIP‐Man (“visible photographic man”) model that can reflect the deformation of organs during respiration by using time‐dependent equations to manipulate surface control points. The EGS4 (Electron Gamma Shower, version 4) Monte Carlo code is then used to apply the 4D model to dose simulation. We simulated two radiation therapy delivery scenarios: gating treatment and 4D image‐guided treatment. For each delivery scenario, we developed one conformal plan and one intensity‐modulated radiation therapy plan. A lesion in the left lung was modeled to investigate the effect of respiratory motion on radiation dose distributions. Based on target dose–volume histograms, the importance of using accurate gating to improve the dose distribution is demonstrated. The results also suggest that, during 4D image‐guided treatment delivery, monitoring of the patient's breathing pattern is critical. This study demonstrates the potential of using a “standard” motion‐simulating patient model for 4D treatment planning and motion management.PACS numbers: 87.53.Bn, 87.53.Kn, 87.53.Tf, 87.53.Wz, 87.57.Gg, 89.80.+h
Highlights
17 Zhang et al.: Development of a geometry-based respiratory...in anatomic sites such as the thoracic cavity and the abdomen, predominantly because of respiratory motion
30 such tomographic models representing various ages and both sexes have been reported to date.[23]. The International Commission on Radiological Protection has recommended a programmatic shift from stylized models to tomographic models in radiation protection dosimetry.[24,25,26,27,28,29] In 2000, we reported the development of an adult male model named VIP-Man (“visible photographic man”).(30) That model was based on anatomic color images of the Visible Man from the Visible Human Project.[31,32] The original image resolution of the Visible Man was 0.33×0.33 mm, and the slice thickness was 1 mm, which allowed for small and radiosensitive structures to be identified and modeled, including skin, eye lenses, and red bone marrow.[30]. Fig. 1(a) shows a slice of the original Visible Human cryosectioned color image for the chest region
Using the detailed procedures described so far, we developed and tested a geometrybased respiratory-motion-simulating patient model for radiation dosimetry that uses Monte Carlo methods
Summary
17 Zhang et al.: Development of a geometry-based respiratory...in anatomic sites such as the thoracic cavity and the abdomen, predominantly because of respiratory motion. To account for temporal and spatial anatomic changes during radiation treatment, a means to specify organ and tumor motion in real time is desirable. This information needs to be incorporated into the radiation therapy planning process and to accurately reflect target and normal anatomic motion during subsequent radiation dose deliveries. This goal has only recently been formulated in the field of radiation oncology, and it has not yet been clinically implemented.[5] With the advent of so-called 4D computed tomography (CT), accounting for target changes is becoming possible in routine applications.[10]
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