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SU‐FF‐T‐330: Modeling Skin Collimation Using Electron Pencil‐Beam Redefinition Algorithm
Author(s) -
Chi P,
Hogstrom K,
Starkschall G,
Antolak J,
Boyd R
Publication year - 2005
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 - 10.1118/1.1998059
Subject(s) - collimated light , pencil (optics) , imaging phantom , dosimetry , optics , beam (structure) , materials science , physics , linear particle accelerator , dose profile , nuclear medicine , laser , medicine
Purpose: To modify the pencil‐beam redefinition algorithm (PBRA) to model skin collimation and to verify that the modified PBRA can accurately calculate dose in the presence of skin collimation for both electron fixed and arced beams. Method and Materials: The PBRA continuously redefines pencil beams at equally spaced depth. For pencil beam pixels fully (partially) shielded by skin collimation further propagation of all (a portion) of the pencil beam is terminated. The accuracy of the modified PBRA for skin collimation (10‐mm thick lead) was verified at 10 and 15 MeV. Fixed beam measurements were performed using a scanning diode detector in water: air gap is 32 cm, field size is 20×6 cm 2 , and skin collimation is at ±5.0 cm. Arced beam measurements were performed in a cylindrical, plastic phantom (ρ=13.5 cm) using film dosimetry: arc angle is ± 45°, skin collimation edge is at ± 30°, and field size is 5×20 cm 2 . Results: Fixed beam: For 10 MeV, the calculations and measurements agreed within 2% in the low dose‐gradient region (Dose>90% and Dose <10%) and within 2 mm distance to agreement (DTA) in the high dose‐gradient region (10%