Effects of breathing variation on gating window internal target volume in respiratory gated radiation therapy

• Published in: Medical physics (Lancaster) Vol. 37; no. 8; pp. 3927 - 3934
• Main Authors: Cai, Jing, McLawhorn, Robert, Read, Paul W., Larner, James M., Yin, Fang-fang, Benedict, Stanley H., Sheng, Ke
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01.08.2010
• Subjects: 4DCT; 60 APPLIED LIFE SCIENCES; Adult; Aged; COMPUTERIZED TOMOGRAPHY; dynamic MRI; Female; Humans; IMAGE PROCESSING; Imaging, Three-Dimensional - methods; internal target volume; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - radiotherapy; LUNGS; Magnetic Resonance Imaging - methods; Male; Middle Aged; NEOPLASMS; NMR IMAGING; PATIENTS; PHANTOMS; RADIOLOGY AND NUCLEAR MEDICINE; RADIOTHERAPY; Radiotherapy, Computer-Assisted - methods; Radiotherapy, Conformal - methods; Reproducibility of Results; residual tumor motion; RESPIRATION; respiratory gated radiation therapy; Respiratory Mechanics; Respiratory-Gated Imaging Techniques - methods; Sensitivity and Specificity; Tomography, X-Ray Computed - methods
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3457329

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 of ITV 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 the ITA GW from dSGP ( A = 10.0 ± 1.3   cm 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 ± 0.7   cm 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 ± 0.5   cm 2 , L 1 = 1.9 ± 0.4   cm , and L 2 = 1.3 ± 0.1   cm in dSGP; A = 1.3 ± 0.1   cm 2 , L 1 = 1.5 ± 0.2   cm , and L 2 = 1.1 ± 0.1   cm in RedCAM). In patient studies, measurements of the ITA GW from dMRI ( A = 15.5 ± 8.2   cm 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 ± 8.5   cm 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 GW can be underestimated by 4DCT due to breathing variations. An additional margin may be needed to account for this potential error in generating a PTV GW . Cautions need to be taken when generating ITV GW from 4DCT in respiratory gated radiation therapy, especially for small tumors ( < 3   cm ) with a large motion range ( > 1   cm ) .