Program Information
Impact of Different Tumors-To-PTV Margins in the Management of Non-Small-Cell-Lung-Cancer (NSCLC) Being Treated Using Stereotactic Body Radiotherapy [SBRT]
H Malhotra*, J Keim , M Greene , D Mohatt , A Patel-Yadav , J Gomez , Roswell Park Cancer Institute, Buffalo, NY
Presentations
SU-K-FS1-12 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: Four Seasons 1
Purpose: Various techniques exist to incorporate lung tumor motion into treatment plans (10-phase ITV, MIP, Ave-IP, FB etc.). In this study, we attempt to see whether different image types & ITV-to-PTV margins yield equivalent volumes both numerically as well as spatially and their resulting dosimetric differences against using all 10-phases for SBRT treatment of NSCLC.
Methods: 4DCT & Free-breathing (FB) data from 17-lower lobe lung patients were analyzed. GTVs were contoured on FB-scan and in all 10-individual phases obtained by binning 4DCT data. While MIP & AIP CT data sets directly yielded ITVs, individual GTVs from all the 10-phases were summated to yield ITV using a BOOLEAN-OR operation. Except for FB-GTV where differential 10mm superior-inferior, 5mm axial, PTV margins was used, 5mm isotropic tumor-PTV margin was used elsewhere. Dice similarity coefficient (DSC) was used to analyze their spatial differences. Treatment plan was designed on the 10-phase PTV set which was then copied over to other structure sets with MLC conforming to the respective PTVs and normalized to ensure that 95% of the PTV gets 100% of the prescribed dose.
Results: Average PTV volumes (cm^3) were 56.1±51.4 [10-phases], 57.5±50.7 [Aug-FB], 54.1±47 [MIP], 51±44.1 [AIP] & 58.7±48.6 [FB]. The average movement vector was 9.5±0.06 mm. The DSC with respect to 10-phase gold standard were found to be 0.714±0.10 (FB), 0.814±0.059 (MIP), 0.805±0.053 (AIP) and 0.877±0.054 (Aug-FB). The PTV(%) coverage with respect to 10-phase plan was 100.3±2.7 [Aug-FB], 95.7±6.6 [MIP], 92.1±7.4 [AIP] & 86.2±27.7 [FB].
Conclusion: The PTVs generated from all the 4-methods yielded volumes which were numerically & spatially different and resulted into different coverage dosimetrically. Volumetrically, spatially & dosimetrically, Aug-FB PTV plans yielded the best conformality with 10 phase PTVs followed by MIP, AIP and the FB and may provide a best compromise in maximizing work-flow efficiency and dose delivery accuracy.
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