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An attenuation integral digital imaging technique for the treatment portal verification of conventional and intensity‐modulated radiotherapy
Author(s) -
Guan Huaiqun
Publication year - 2010
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3447729
Subject(s) - imaging phantom , fluence , optics , attenuation , detector , image guided radiation therapy , medical imaging , dosimetry , physics , nuclear medicine , computer science , medicine , artificial intelligence , laser
Purpose To propose an attenuation integral digital imaging (AIDI) technique for the treatment portal verification of conventional and intensity‐modulated radiotherapy (IMRT). Methods In AIDI technique, an open in air fluence imageI oand a patient fluence image I were acquired under the same exposure. Then after doing the dark field correction for both theI oand I , the AIDI image was simply calculated as log ( I o / I ) , which is the attenuation integral along the ray path from the x‐ray source to a detector pixel element. Theoretical analysis for the low contrast detection and the contrast to noise ratio (CNR) of AIDI was presented and compared to those for the fluence imaging. With AIDI, the variation of x‐ray fluence and the variation of individual detector pixel's response can be automatically compensated without using the flood field correction. Results The AIDI image for a contrast detail phantom demonstrated that it can efficiently suppress the background structures such as the couch and generate better visibility for low contrast objects with megavoltage x rays. The AIDI image acquired for a Catphan 500 phantom using a 60° electronic dynamic wedge field also revealed more contrast disks than the fluence imaging did. Finally, AIDI for an IMRT field of a head/neck patient successfully displayed the anatomical structures underneath the treatment portal but not shown in fluence imaging. Conclusions For IMRT and high degree wedge beams, direct imaging using them is difficult because their photon fluence is highly nonuniform. But AIDI can be used for the treatment portal verification of these beams.