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SU‐GG‐T‐128: Rapid Dose Calculation for Dose Per MU Verification of IMRT Fields
Author(s) -
Zhu T,
Karunamuni R,
Finlay J,
Bjarngard B
Publication year - 2008
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 - 10.1118/1.2961880
Subject(s) - imaging phantom , collimated light , quality assurance , physics , convolution (computer science) , monitor unit , photon , nuclear medicine , dosimetry , field (mathematics) , optics , mathematics , computer science , medicine , laser , external quality assessment , pathology , machine learning , artificial neural network , pure mathematics
Purpose: We have developed a fast algorithm to calculate patient specific 2D distribution of absolute dose per MU (D/MU) for megavoltage photon beams. Method and Materials: To calculate D/MU correctly, one has to perform the scatter‐integration with proper weights to account for the primary fluence distribution. In our PC‐based MU‐calculation program, the ratio of scatter‐to‐primary dose, D s /D p , for a 2‐D non‐uniform field is calculated as: SPR ( x , y , d ) =∫ x∫ yIM ( x ′ , y ′ ) IM ( x , y ) ⋅ a ( d + d 0 ) 2w ( r + d + d 0 ) 2⋅ 2 π rdx ′ dy ′ , with r = ( x − x ′ ) 2 + ( y − y ′ ) 2and IM ( x , y ) = ∑ i ƒ MU ip i( x ′ , y ′ ) is the 2D intensity profile within the IMRT field, p i is 1 inside field and 0 outside field collimation for segment field i of the IMRT field. This convolution is calculated using a Fast Fourier Transform. The parameters a, w , and d 0 characterize the phantom scatter properties and can be determined from measured PDD . Results: SPR can be calculated on an Intel Pentium 2.8GHz PC for 0.5‐cm grid size in less than 0.1 second for a 80×80 grid covering 40 × 40 cm 2 . For IMRT patients examined, the standard deviation of all comparisons is 1.5±3.9%. Conclusion: This algorithm is ideally suitable for calculating patient‐specific MU for quality assurance of patient specific IMRT fields for photon beams. The major attraction is the fast speed, which allows potential real‐time applications.