A novel edge gradient distance metric for automated evaluation of deformable image registration quality.

PURPOSE: To develop a new registration quality metric, based on the distance between image edges, for automated evaluation and comparison of DIR algorithms. METHODS: Canny filter is used to create binary gradient images from input images to be compared. A small subregion of one binary image is translated relative to the other. The translational distance maximizing overlap of edges in the subregion is the local edge gradient distance to agreement (EGDTA); repeating over all subregions provides an EGDTA map. The method was tested on phantom and pelvic CT images, by applying a known deformable vector field (DVF). The method was then applied to evaluate two DIR algorithms (SICLE and Demons) for pelvic CTs from five patients. Three SICLE variants were used: Grayscale-driven (G), Contour-driven (C), and Grayscale + Contour-driven (G + C). For each patient, a planning CT was registered to three repeat CTs using the above DIR algorithms. Mean EGDTA values in concentric ring regions of interest close to and far away from the pelvic organ contours were compared. RESULTS: EGDTA maps and imposed DVF deformations on phantom and CT images demonstrated agreement. In comparison of the three variants of SICLE: C had lower EGDTA values close to the pelvic organs, while G showed much better performance in the regions distant from the organs compared to C; and G + C registration exhibited the lowest or comparable EGDTA value among three variants. Demons achieved the lowest EGDTA values. CONCLUSIONS: The EGDTA metric shows potential as an automated means of evaluating and comparing DIR algorithms.

Dosimetric impact of range uncertainty in passive scattering proton therapy.

PURPOSE: The objective of this study was to investigate the dosimetric impact of range uncertainty in a large cohort of patients receiving passive scatter proton therapy. METHODS: A cohort of 120 patients were reviewed in this study retrospectively, of which 61 were brain, 39 lung, and 20 prostate patients. Range uncertainties of ±3.5% (overshooting and undershooting by 3.5%, respectively) were added and recalculated on the original plans, which had been planned according to our clinical planning protocol while keeping beamlines, apertures, compensators, and dose grids intact. Changes in the coverage on CTV and DVH for critical organs were compared and analyzed. Correlation between dose change and minimal distance between CTV and critical organs were also investigated. RESULTS: Although CTV coverages and maximum dose to critical organs were largely maintained for most brain patients, large variations over 5% were still observed sporadically. Critical organs, such as brainstem and chiasm, could still be affected by range uncertainty at 4 cm away from CTV. Coverage and OARs in lung and prostate patients were less likely to be affected by range uncertainty with very few exceptions. CONCLUSION: The margin recipe in modern TPS leads to clinically acceptable OAR doses in the presence of range uncertainties. However, range uncertainties still pose a noticeable challenge for small but critical serial organs near tumors, and occasionally for large parallel organs that are located distal to incident proton beams.

Inter-society standards for the performance of brachytherapy: a joint report from ABS, ACMP and ACRO.

PURPOSE: The proliferation of various brachytherapy modalities for different anatomical sites necessitates the creation of standards for brachytherapy. METHODS: A panel consisting of members of The American Brachytherapy Society (ABS), The American College of Medical Physics (ACMP) and The American College of Radiation Oncology (ACRO) developed standards for the clinical practice and quality assurance (QA) of brachytherapy. These were based upon their clinical experience and a review of the literature. RESULTS: Recommended practice standards are presented for clinical processes, treatment planning, equipment, facilities, QA, dose evaluation, dose specification, dose reporting, the training, and credentialing of personnel, and radiation control/safety/protection. Safe and efficacious performance of brachytherapy requires a highly structured QA program and carefully designed treatment delivery processes, as well as a coordinated effort amongst the team members. CONCLUSION: Standards for clinical brachytherapy are proposed. Practitioners are encouraged to use these standards to design and implement a consistent and efficacious brachytherapy program.