SU‐E‐J‐172: A Quantitative Assessment of Lung Tumor Motion Using 4DCT Imaging Under Conditions of Controlled Breathing in the Management of Non‐Small Cell Lung Cancer (NSCLC) Using Stereotactic Body Radiation Therapy (SBRT)

Abstract

Purpose:To study breathing related tumor motion amplitudes by lung lobe location under controlled breathing conditions used in Stereotactic Body Radiation Therapy (SBRT) for NSCLC.Methods:Sixty‐five NSCLC SBRT patients since 2009 were investigated. Patients were categorized based on tumor anatomic location (RUL‐17, RML‐7, RLL‐18, LUL‐14, LLL‐9). A 16‐slice CT scanner [GE RT16 Pro] along with Varian Realtime Position Management (RPM) software was used to acquire the 4DCT data set using 1.25 mm slice width. Images were binned in 10 phases, T00 being at maximum inspiration ' T50 at maximum expiration phase. Tumor volume was segmented in T50 using the CT‐lung window and its displacement were measured from phase to phase in all three axes; superiorinferior, anterior‐posterior ' medial‐lateral at the centroid level of the tumor.Results:The median tumor movement in each lobe was as follows: RUL= 3.8±2.0 mm (mean ITV: 9.5 cm3), RML= 4.7±2.8 mm (mean ITV: 9.2 cm3), RLL=6.6±2.6 mm (mean ITV: 12.3 cm3), LUL=3.8±2.4 mm (mean ITV: 18.5 cm3), ' LLL=4.7±2.5 mm (mean ITV: 11.9 cm3). The median respiratory cycle for all patients was found to be 3.81 ± 1.08 seconds [minimum 2.50 seconds, maximum 7.07 seconds]. The tumor mobility incorporating breathing cycle was RUL = 0.95±0.49 mm/s, RML = 1.35±0.62 mm/s, RLL = 1.83±0.71 mm/s, LUL = 0.98 ±0.50 mm/s, and LLL = 1.15 ±0.53 mm/s.Conclusion:Our results show that tumor displacement is location dependent. The range of motion and mobility increases as the location of the tumor nears the diaphragm. Under abdominal compression, the magnitude of tumor motion is reduced by as much as a factor of 2 in comparison to reported tumor magnitudes under conventional free breathing conditions. This study demonstrates the utility of abdominal compression in reducing the tumor motion leading to reduced ITV and planning tumor volumes (PTV).