Estimation of Error in Maximal Intensity Projection-Based Internal Target Volume of Lung Tumors: A Simulation and Comparison Study Using Dynamic Magnetic Resonance Imaging

• Published in: International journal of radiation oncology, biology, physics Vol. 69; no. 3; pp. 895 - 902
• Main Authors: Cai, Jing, Ph.D, Read, Paul W., M.D., Ph.D, Baisden, Joseph M., M.D., Ph.D, Larner, James M., M.D, Benedict, Stanley H., Ph.D, Sheng, Ke, Ph.D
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.11.2007
• Subjects: Aged; Aged, 80 and over; CARCINOMAS; COMPARATIVE EVALUATIONS; COMPUTERIZED TOMOGRAPHY; ERRORS; FAILURES; Female; Four-dimensional computed tomography; HEALTH HAZARDS; Hematology, Oncology and Palliative Medicine; Humans; Internal target volume; Lung - diagnostic imaging; Lung Neoplasms - diagnostic imaging; Lung tumor motion; LUNGS; Magnetic resonance imaging; Magnetic Resonance Imaging - methods; Male; Maximal intensity projection; Middle Aged; Movement; NMR IMAGING; Observer Variation; PATIENTS; PHANTOMS; Phantoms, Imaging; Radiology; RADIOLOGY AND NUCLEAR MEDICINE; Respiration; SIMULATION; Tomography, X-Ray Computed - methods; Maximal intensity projection; Four-dimensional computed tomography; Magnetic resonance imaging; Lung tumor motion; Internal target volume
• ISSN: 0360-3016; 1879-355X
• DOI: 10.1016/j.ijrobp.2007.07.2322

Purpose To evaluate the error in four-dimensional computed tomography (4D-CT) maximal intensity projection (MIP)–based lung tumor internal target volume determination using a simulation method based on dynamic magnetic resonance imaging (dMRI). Methods and Materials Eight healthy volunteers and six lung tumor patients underwent a 5-min MRI scan in the sagittal plane to acquire dynamic images of lung motion. A MATLAB program was written to generate re-sorted dMRI using 4D-CT acquisition methods (RedCAM) by segmenting and rebinning the MRI scans. The maximal intensity projection images were generated from RedCAM and dMRI, and the errors in the MIP-based internal target area (ITA) from RedCAM (ε), compared with those from dMRI, were determined and correlated with the subjects' respiratory variability (ν). Results Maximal intensity projection-based ITAs from RedCAM were comparatively smaller than those from dMRI in both phantom studies (ε = −21.64% ± 8.23%) and lung tumor patient studies (ε = −20.31% ± 11.36%). The errors in MIP-based ITA from RedCAM correlated linearly (ε = −5.13ν − 6.71, r2 = 0.76) with the subjects' respiratory variability. Conclusions Because of the low temporal resolution and retrospective re-sorting, 4D-CT might not accurately depict the excursion of a moving tumor. Using a 4D-CT MIP image to define the internal target volume might therefore cause underdosing and an increased risk of subsequent treatment failure. Patient-specific respiratory variability might also be a useful predictor of the 4D-CT–induced error in MIP-based internal target volume determination.