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SU‐E‐T‐93: A Comparison of Out‐Of‐Field Dose and Its Constituent Components for 6MV Flattened and 7MV Unflattened Photon Beam
Author(s) -
Sigamani Ashokkumar,
Raj Arunai Nambi,
Sinha SN,
Yadav Girigesh,
Raman Kothanda,
Thiyagarajan Rajesh,
Bhushan Manindra
Publication year - 2013
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 - 10.1118/1.4814528
Subject(s) - field size , field (mathematics) , collimator , imaging phantom , nuclear medicine , materials science , analytical chemistry (journal) , physics , medicine , chemistry , optics , mathematics , chromatography , pure mathematics
Purpose: A Comparison of out‐of‐field dose and its constituent components for 6MV Flattened and 7MV unflattened Photon Beams Methods: The flattening filter and primary collimator are the major sources of producing the scattered radiation. The out‐of‐field photon dose, Sc,p, Sc and Sp were measured with CC 13 chamber for square open fields from 5 × 5 cm 2 to 30 × 30 cm 2 using IBA blue phantom and solid phantom as a function of distance from central axis and field size at depth of maximum for respective photon energies. Scatter radiation, which predominantly contributes to peripheral dose at larger distance from the field edge, was measured using a CC 13 ionization chamber. Results: All the values of Sc,p and Sc are normalized to 10 × 10 cm 2 field size. The measured values of Sc,p for 6MV‐FB and 7MV‐UFB varies from 0.9437 to 1.0651 and 0.9690 to 1.0283 respectively. The Sc values for 6MV‐FB maximum (max.) 2.1 percent lesser than 7MV‐UFB for up to 10 ×10 cm 2 field size and 6MV‐FB max.1.7 percent higher than the 7MV‐UFB for above 10 × 10cm 2 field size. Out of field dose is max.42.0 percent higher for 6MV‐FB compare to 7MV‐UFB at 25 cm from the field edge for up to 10 × 10 cm 2 field size and max.50.39 percent reduced dose for 7MV‐UFB for above 10 × 10 cm 2 . Out of field dose is max.70.0 percent reduced for 7MV‐UFB compare to 6MV‐FB above 50 cm away from the field edge for up to 10 × 10 cm 2 field size and max.68 percent reduced dose for 7MV‐UFB for above 10 × 10 cm 2 . Conclusion: 7MV‐UFB may be advantageous by reduced out‐of‐field dose compare to 6MV‐FB, but differences are small in absolute terms.