ESTRO 36 Abstract Book

S219 ESTRO 36 _______________________________________________________________________________________________

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For the patient error tests, PTV DVHs with MU errors correspond well to expectations. For OARs and MLC errors, trends are as expected but quantitative validation is more difficult (Table). Slab phantom results show that generally both systems accurately measure MU errors. Differences between 3DVH and pDVH are larger for MLC errors, especially for the conformal plans and OARs (Table). Comparing with the predictions, it appears that 3DVH tends to underestimate the effect of MLC errors, whereas pDVH performs more accurately (Table).

by experiment; to construct a realistic surrogate anatomy by using computational human phantoms; and to automatically contour major organs of interest on patient images. Material and Methods We employed XVMC computer code for Monte Carlo radiation transport with enhanced computation speed. We adjusted the virtual source models built in XVMC to match out-of-field dose profile measured in a water phantom. For the cases where patient images are not available, we converted a library of existing computational human phantoms with the range of age and body size in voxel format into Digital Imaging and Communications in Medicine (DICOM)-images by translating material composition and density to Hounsfield Unit. We then converted the organ structures in the voxel phantoms into DICOM-structures and tested the resulting DICOM phantoms with multiple treatment planning systems. Finally, for the cases where patient images may be available for a large number of patients, we developed methods to automatically contour the heart and its substructures, as a start, by using an atlas library derived from 60 adult male and female patients. Results First, the lateral dose profiles computed from XVMC and the water phantom matched well within 15% (<10 cm from field edge) and 40% (> 10 cm and <30 cm from the field edge)(Figure 1). Second, a set of DICOM-images and structures was generated from the pediatric and adult reference and non-reference phantom series (Figure 2). We validated the DICOM phantoms by comparing density and volume of selected organs between the original phantom and Eclipse showing a good agreement less than 5% and 0.1% for density and volume, respectively. Finally, we confirmed that the auto-contoured heart and manually-contoured heart for 30 adult male patients show the Dice coefficients up to 91% for the total heart and up to 84% for the left ventricle.

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Conclusion We developed a procedure to verify DVH measurements for individual patient QA. 3DVH has similar gamma results as 2D ArcCheck for clinical cases. Phantom studies however indicate that 3DVH can underestimate the dosimetric effect of MLC errors, where EPID based pDVH performs better. PV-0416 Novel methods for normal tissue dose in epidemiological studies of second cancer in radiotherapy C. Lee 1 , J.W. Jung 2 , C. Lee 3 , M.M. Mille 1 , E. Mosher 1 , C. Pelletier 2 , G. Kuzmin 1 1 National Cancer Institute, Division of Cancer Epidemiology and Genetics, Bethesda, USA 2 East Carolina University, Department of Physics, Greenville, USA 3 University of Michigan, Department of Radiation Oncology, Ann Arbor, USA Purpose or Objective Dose estimation of normal tissues located outside treatment beam fields is one of the crucial components in retrospective epidemiological studies of late effects in radiotherapy patients but there are three challenges. First, dosimetry methods for out-of-field normal tissues are not well established compared to in-field. Second, radiological images of patient anatomy are not commonly available. Third, even if patient images are available, contouring several normal organs of interest would take substantial effort for large-scale patient cohorts. We have developed computational solutions: to calculate normal tissue doses for out-of-field region, which was validated

Conclusion The computational methods established in this study will be useful for the reconstruction of normal tissue dose to