Abstract
BackgroundLarge tumor motion often leads to larger treatment volumes, especially the lung tumor located in lower lobe and adhered to chest wall or diaphragm. The purpose of this work is to investigate the impacts of planning target volume (PTV) margin on Stereotactic Body Radiotherapy (SBRT) in non-small cell lung cancer (NSCLC).MethodsSubjects include 20 patients with the lung tumor located in lower lobe and adhered to chest wall or diaphragm who underwent SBRT. Four-dimensional computed tomography (4DCT) were acquired at simulation to evaluate the tumor intra-fractional centroid and boundary changes, and Cone-beam Computer Tomography (CBCT) were acquired during each treatment to evaluate the tumor inter-fractional set-up displacement. The margin to compensate for tumor variations uncertainties was calculated with various margin calculated recipes published in the exiting literatures.ResultsThe means (±standard deviation) of tumor centroid changes were 0.16 (±0.13) cm, 0.22 (±0.15) cm, and 1.37 (±0.81) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor edge changes were 0.21 (±0.18) cm, 0.50 (±0.23) cm, and 0.19 (±0.44) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor set-up displacement were 0.03 (±0.24) cm, 0.02 (±0.26) cm, and 0.02 (±0.43) cm in RL, AP, and SI directions, respectively. The PTV margin to compensate for lung cancer tumor variations uncertainties were 0.88, 0.98 and 2.68 cm in RL, AP and SI directions, which were maximal among all margin recipes.Conclusions4DCT and CBCT imaging are appropriate to account for the tumor intra-fractional centroid, boundary variations and inter-fractional set-up displacement. The PTV margin to compensate for lung cancer tumor variations uncertainties can be obtained. Our results show that a conventional 1.0 cm margin in the SI plane dose not suffice to compensate the geometrical variety of the tumor located in lower lobe and adhered to chest wall and diaphragm.
Highlights
Large tumor motion often leads to larger treatment volumes, especially the lung tumor located in lower lobe and adhered to chest wall or diaphragm
The maximum were 0.88, 0.98 and 2.68 cm in RL, AP and SI directions, which were calculated with the recipe by van Herk et al Discussion It is reported [29] that the tumor movement in lung is not related to patient height, weight, cancer stage and lung function, and these issues were not included in this study
We evaluated changes in tumor motion magnitude and set-up error by Four-dimensional computed tomography (4DCT) scan at planning and Cone-beam Computer Tomography (CBCT) scan at treatment and calculated the margins to compensate for these changes [16, 17]
Summary
Large tumor motion often leads to larger treatment volumes, especially the lung tumor located in lower lobe and adhered to chest wall or diaphragm. The purpose of this work is to investigate the impacts of planning target volume (PTV) margin on Stereotactic Body Radiotherapy (SBRT) in non-small cell lung cancer (NSCLC). The stereotactic body radiation therapy (SBRT) is a new technology which can effectively improve the treatment effect of lung cancer. Li et al Radiation Oncology (2016) 11:152 margin (IM) and set-up margin (SM) should be included in the PTV to compensate geometrical uncertainties including tumor centroid movement [10], tumor boundary [11, 12] and set-up displacement, especially in SBRT. The tumor boundary displacement merely discussed about margin calculation previously. It would be assessed in present study
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