ABSTRACT
The aim of this work was to study the feasibility of proton radiography (pRad) as a patient-specific range compensator (RC) quality assurance (QA) tool and to validate its clinical utility by performing QA on RCs having three kinds of possible defects. In order to achieve pRad for a single EBT film, proton beam currents were modulated with new weighting factors, maximizing the linearity of optical-density-to-thickness ratio. Two RCs, examined to be accurately manufactured as planned, were selected to estimate the feasibility of our pRad. The optical densities of the EBT film on which the RC was irradiated with the modulated proton beam were digitized to pixel values (pv) and then converted to thickness using a thickness-pv calibration curve. The thickness information on the pRad was compared with plan data that had been extracted from treatment planning system. The mean thickness difference (TD) over the flat RC regions was calculated as 0.39 mm, and the standard deviation as 0.22 mm, and the proton scattering effect was analyzed by step phantom measurement. Even proton scattering effected a TD of over 1 mm in the large gradient region, the percentage of pixels over the acceptance criterion was only within 1.11% and 3.49%, respectively, when a 1 mm distance to agreement tolerance limit was applied. The QA results for both precisely and imprecisely manufactured RCs demonstrated the high potential utility and clinical applicability of the pRad-based RC QA tool.
Subject(s)
Proton Therapy , Radiography/methods , Algorithms , Calibration , Computer Simulation , Film Dosimetry/methods , Humans , Phantoms, Imaging , Quality Control , Radiography/instrumentation , Radiotherapy Dosage , Radiotherapy Planning, Computer-Assisted , Reproducibility of Results , Scattering, RadiationABSTRACT
Strong mode selection through an enhanced interferential coupling effect was observed in a thin dielectric-coated layered cylindrical microcavity laser. The strong coupling effect was induced owing to an enhanced reflectivity of around 50% at the dielectric-coated inner boundary of a fused silica capillary filled with a dye-doped liquid. At an optimized coating thickness of about 0.4 microm, the lasing peaks appeared only at the wavelengths corresponding to the constructive interference condition, whereas those from a bare capillary were weakly modulated.
