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Effects of breathing variation on gating window internal target volume in respiratory gated radiation therapy a)
Author(s) -
Cai Jing,
McLawhorn Robert,
Read Paul W.,
Larner James M.,
Yin Fangfang,
Benedict Stanley H.,
Sheng Ke
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 - 10.1118/1.3457329
Subject(s) - imaging phantom , breathing , gating , radiation therapy , nuclear medicine , margin (machine learning) , medicine , radiology , computer science , anatomy , physiology , machine learning
Purpose: To investigate the effects of breathing variation on gating window internal target volume (ITV GW)in respiratory gated radiation therapy. Method and Materials: Two‐dimensional dynamic MRI (dMRI) of lung motion was acquired in ten volunteers and eight lung cancer patients. Resorted dMRI using 4DCT acquisition method (RedCAM) was generated for selected subjects by simulating the image rebinning process. A dynamic software generated phantom (dSGP) was created by moving a solid circle (to mimic the “tumor”) with dMRI‐determined motion trajectories. The gating window internal target area (ITA GW, 2D counterpart ofITV GW) was determined from both RedCAM and dSGP/dMRI. Its area( A ) , major axis( L 1 ) , minor axis( L 2 ) , and similarity( S )were calculated and compared. Results: In the phantom study of 3 cm tumor, measurements of theITA GWfrom dSGP ( A = 10.0 ± 1.3cm 2 , L 1 = 3.8 ± 0.4 cm , and L 2 = 3.3 ± 0.1 cm ) are significantly( p < 0.001 )greater than those from RedCAM ( A = 8.5 ± 0.7cm 2 , L 1 = 3.5 ± 0.2 cm , and L 2 = 3.1 ± 0.1 cm ). Similarly, the differences are significantly greater( p < 0.001 )for the 1 cm tumor ( A = 1.9 ± 0.5cm 2 , L 1 = 1.9 ± 0.4 cm , and L 2 = 1.3 ± 0.1 cm in dSGP; A = 1.3 ± 0.1cm 2 , L 1 = 1.5 ± 0.2 cm , and L 2 = 1.1 ± 0.1 cm in RedCAM). In patient studies, measurements of theITA GWfrom dMRI ( A = 15.5 ± 8.2cm 2 , L 1 = 5.0 ± 1.1 cm , and L 2 = 3.8 ± 1.2 cm ) are also significantly greater( p < 0.05 )than those from RedCAM ( A = 13.2 ± 8.5cm 2 , L 1 = 4.3 ± 1.4 cm , and L 2 = 3.7 ± 1.2 cm ). Similarities were 0.9 ± 0.1 , 0.8 ± 0.1 , and 0.8 ± 0.1 in the 3 cm tumor phantom, 1 cm tumor phantom, and patient studies, respectively. Conclusion:ITV GWcan be underestimated by 4DCT due to breathing variations. An additional margin may be needed to account for this potential error in generating aPTV GW. Cautions need to be taken when generatingITV GWfrom 4DCT in respiratory gated radiation therapy, especially for small tumors( < 3 cm )with a large motion range( > 1 cm ) .