Reconstitution of internal target volumes by combining four-dimensional computed tomography and a modified slow computed tomography scan in stereotactic body radiotherapy planning for lung cancer

Abstract

BackgroundTo evaluate the volumetric and geometric differences in the ITVs generated by four-dimensional (4D) computed tomography (CT), a modified slow CT scan, and a combination of these CT methods in lung cancer patients treated with stereotactic body radiotherapy (SBRT).MethodsBoth 4D CT and modified slow CT using a multi-slice CT scanner were performed for SBRT planning in 14 patients with 15 pulmonary targets. Volumetric and geometric analyses were performed for (1) ITVall, generated by combining the gross tumor volumes (GTVs) from all 8 phases of the 4D CT; (2) ITV2, generated by combining the GTVs from 2 extreme phases of the 4D CT; (3) ITVslow, derived from the GTV on the modified slow CT scan; (4) ITVall+slow, generated by combining ITVall and ITVslow; and (5) ITV2+slow, generated by combining ITV2 and ITVslow. Three SBRT plans were performed using 3 ITVs to assess the dosimetric effects on normal lung caused by the various target volumes.ResultsITVall (11.8 ± 8.3 cm3) was significantly smaller than ITVall+slow (12.5 ± 8.9 cm3), with mean values of 5.8% for the percentage volume difference, and a mean of 7.5% of ITVslow was not encompassed in ITVall. The geometric coverages of ITV2 and ITVslow for ITVall were 84.7 ± 6.6% and 76.2 ± 9.3%, respectively, but the coverage for ITVall increased to 90.9 ± 5.9% by using the composite of these two ITVs. There were statistically significant increases in the lung-dose parameters of the plans based on ITVall+slow compared to the plans based on ITVall or ITV2+slow. However, the magnitudes of these differences were relatively small, with a value of less than 3% in all dosimetric parameters.ConclusionsDue to its ability to provides additional motion information, the combination of 4D CT and a modified slow CT scan in SBRT planning for lung cancer can be used to reduce possible errors in true target delineation caused by breathing pattern variations.

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

“…202 It was noted that the largest difference amongst the ITV methods was seen for small targets exhibiting large motion amplitudes. Another method to minimize ITV uncertainties was proposed by Jang et al 211 by combining the ITV from a 4D-CT scan together with an ITV generated from a modified slow-CT scan to generate a composite ITV, which they found to be more robust to breathing irregularities for lung SBRT planning.…”

Partial and Full Arc Volumetric Modulated Arc Therapy in Lung Cancer Stereotactic Body Radiotherapy with Different Definitions of Internal Target Volume Based on 4D CT

“…This is not a minor deviation considered the small tumor volume of SBRT lung patients as declared in other study [30]. A percent volume difference of 15.3% ± 6.6% between ITV 2phases and ITV all had also been reported [31]. However, these volumetric differences did not result in significant dosimetric deviations.…”

A Feasibility Study of Tumor Motion Estimate With Regional Deformable Registration Method for 4-Dimensional Radiation Therapy of Lung Cancer

“…As illustrated in this work and others elsewhere, 12,13,16,29 the estimation of tumor motion using 4DCT is solely dependent on the accuracy of the deformable registration. A well-known problem in image registration and contour segmentation studies is the lack of quantitative validation.…”

“…It provides spatial-temporal information of patient's anatomy that can be utilized for better breathing control. As opposed to conventional treatment techniques where treatment planning and delivery were conducted in a static manner, 4D radiation therapy [15][16][17] would be adopted as a standard strategy in the future. Under this scenario, knowing precisely intrafractional anatomy change becomes important.…”