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Determination Off-Axis Dosimetric Leaf Gap Using Optically Stimulated Luminescence Dosimeters and An Electronic Portal Imaging Device

Timothy P B Santosh*, Divyalakshmi J, Mohamathu Rafic K M, Amalan Sebastin, Sujith Christopher J, Jose Solomon Raj, Christian Medical College, Vellore, Tamil Nadu, India


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: explore the limitation in global modelling of the abutting leaf-end transmission with a single central axis (CAX) DLG value by investigating the dosimetric feasibility of using optically stimulated luminescence dosimeters (OSLD) and an electronic portal imaging device (EPID) for off-axis (OAX) dosimetric leaf gap (DLG) measurement.

Methods: Clinac 2100C/D linear accelerator equipped with the Millennium-120 Multileaf collimator (MLC) and aS1000 EPID was utilized for this study. The DLG values at CAX and ±1 cm OAX were measured using OSLD and validated using an ionization chamber dosimetry (ICD). The two-dimensional DLG map (2D DLG-EPID) was derived from the portal images of the DLG plan using a custom-developed software script that incorporated sliding aperture-specific correction factors.

Results: and DLG-ICD, though measured with diverse setup in different media, showed similar variation both at CAX and ±1 cm OAX positions. The corresponding DLG-EPID values derived using aperture specific correction were found to be in good agreement with DLG-OSLD and DLG-ICD. The 2D DLG-EPID map lends insight into the varying patterns of the DLG with respect to each leaf pair at any position across the field.

Conclusion: results of DLG-OSLD with DLG-ICD values have proven the efficacy of OSLD as an apposite dosimeter for DLG measurement. The 2D DLG-EPID map opens a potential pathway to accurately model rounded-leaf end transmission with discrete leaf-specific DLG values in a 2D dose space.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by an internal Fluid Research Grant (FG/9307/2/2015) from Christian Medical College, Vellore


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