Journal of Associated Medical Sciences (Jan 2018)
Volumetric and dosimetric comparison of helical tomotherapy treatment planning using different strategies of four dimensional computed tomography images for target volume definition in non-small cell lung cancer patients
Abstract
Background: Four-dimensional computed tomography (4DCT) images were used to generate internal target volume (ITV) in lung cancer. However, the drawback is time consumed to delineate all sets of CT scans. Maximum intensity projection (MIP) and select phases of 4DCT datasets were used to reduce time consumed to delineate the ITV. Objectives: To compare the volume of ITV and dosimetric parameters of planning target volume (PTV) based on three different 4DCT datasets in non-small cell lung cancer (NSCLC) patients of helical tomotherapy treatment planning. Material and methods: The 4DCT image datasets of 7 patients diagnosed with stage I-III NSCLC were used. All gross target volumes (GTVs) were delineated by the same radiation oncologist in 3 different 4DCT datasets (10 phases, 3 phases, and MIP image) using Oncentra Master Plan v.4.3 contouring software. PTV10phases, PTV3phases and PTVMIP were generated and treatment planning were performed. From PTVs contour, volume and ratio of ITV as well as matching index (MI) were compared. Helical tomotherapy planning was done for each PTV then dosimetric parameters for PTVs and organs at risk (OARs) were evaluated. Statistical analysis was performed using Pair t- test and a p<0.05 was considered to be statistically significant. Results: Mean volume of ITVs were 64.09±63.05 cc, 60.40±60.99 cc, 59.85±60.23 cc for ITV10phases, ITV3phases and ITVMIP, respectively. The ITV3phases and ITVMIP were significantly smaller than the ITV10phases (p<0.05). The mean ratios between ITV3phases and ITV10phases and between ITVMIP and ITV10phases were 0.93 and 0.92, respectively. The mean MI between ITV3phases and ITV10phases and between ITVMIP and ITV10phases were 0.90 and 0.87, respectively. For the mean MI and the mean ratios of ITVs, there was no significant difference between ITV3phases versus ITV10phases and ITVMIP versus ITV10phases. For dosimetric parameters of PTVs, the average V95 of PTV10phases, PTV3phases and PTVMIP were 99.51%, 99.65% and 99.68%, respectively. The average V107 of PTV10phase, PTV3phases and PTVMIP were 0.24%, 0.22% and 0.23%, respectively. About OARs dose, only statistically significant difference was found in the Ipsilateral lung dose (V20 and V30) of PTV10phases and PTVMIP. Conclusion: MIP images are reliable for creating ITVs in early stage patients. The 3 phases images data sets are reliable for generating ITVs for all stages of NSCLC in which tumor moves straightforward superoinferior (SI) direction and that tumor deformation during breathing are minimal. Dosimetric parameters of all 3 PTVs generated by using 3 different ITV definitions are similar.
