Reconstruction of organ dose for external radiotherapy patients in retrospective epidemiologic studies

Abstract

Organ dose estimation for retrospective epidemiological studies of late effects in radiotherapy patients involves two challenges: radiological images to represent patient anatomy are not usually available for patient cohorts who were treated years ago, and efficient dose reconstruction methods for large-scale patient cohorts are not well established. In the current study, we developed methods to reconstruct organ doses for radiotherapy patients by using a series of computational human phantoms coupled with a commercial treatment planning system (TPS) and a radiotherapy-dedicated Monte Carlo transport code, and performed illustrative dose calculations. First, we developed methods to convert the anatomy and organ contours of the pediatric and adult hybrid computational phantom series to Digital Imaging and Communications in Medicine (DICOM)-image and DICOM-structure files, respectively. The resulting DICOM files were imported to a commercial TPS for simulating radiotherapy and dose calculation for in-field organs. The conversion process was validated by comparing electron densities relative to water and organ volumes between the hybrid phantoms and the DICOM files imported in TPS, which showed agreements within 0.1% and 2%, respectively. Second, we developed a procedure to transfer DICOM-RT files generated from the Eclipse system directly to a Monte Carlo transport code, X-ray Voxel Monte Carlo (XVMC) for more accurate dose calculations. Third, to illustrate the performance of the established methods, we simulated a whole brain treatment for the 10-year-old male phantom and a prostate treatment for the adult male phantom. Radiation doses to selected organs were calculated using the Eclipse and XVMC, and compared to each other. Organ average doses from the two methods matched within 7%, whereas maximum and minimum point doses differed up to 45%. The dosimetry methods and procedures established in this study will be useful for the reconstruction of organ dose to support retrospective epidemiological studies of late effects in radiotherapy patients.

A Review of Radiotherapy-Induced Late Effects Research after Advanced Technology Treatments

“…At least one commercial TPS offers an electron Monte Carlo algorithm ( 90 , 91 ). There has been effort to combine the commercial TPS and calibrated fast Monte Carlo codes to provide organ dose calculations in both in-field and out-of-field regions for epidemiological studies ( 92 ). The Monte Carlo method has been an invaluable research tool for studying therapeutic and stray radiation exposures.…”

Pediatric Normal Tissue Effects in the Clinic (PENTEC): An International Collaboration to Analyse Normal Tissue Radiation Dose–Volume Response Relationships for Paediatric Cancer Patients

“…Even when the treatment fields were designed to include the entire structure, such as vertebral bodies, this target may not have received a uniform dose simply because of the rapid dose fall-off of electron and orthovoltage beams commonly used before the 1980s. In a minority of cases, the organ dose has been retrospectively reconstructed based on computational phantoms of varying complexity aided by a review of patient treatment records [10,11]. These tend to be the basis for large-scale epidemiology studies that group organ doses into wide bins.…”

Automatic radiotherapy plan emulation for 3D dose reconstruction to enable big data analysis for historically treated patients

“…The lack of a 3D anatomical image, i.e., computed tomography (CT), of patients precludes direct 3D dose calculation on CT as is performed routinely for currently treated patients [5]. To deal with the absence of 3D anatomical images of historically treated patients, dose reconstruction methods have been developed [6][7][8]. These methods provide 3D dose estimations by emulating the historical treatment on a 3D patientresembling surrogate anatomy, e.g., computational phantoms [6].…”

“…Studies have been published on how to match/select a surrogate phantom/CT scan that could best resemble the historical patients' anatomy [12][13][14]. Furthermore, the last step can also be automated, by scripting the dose calculation algorithms in a treatment planning system (TPS) or by using other out-of-field dose estimation algorithms [8,15]. The bottleneck that prevents performing dose reconstruction on a large scale is the intermediate step of RT plan emulation.…”