ABSTRACT
Objective:To compare the differences in the delineation of the gross tumor volume (GTV) and lymph nodes of nasopharyngeal carcinoma (NPC) patients using computerized tomography (CT), magnetic resonance imaging (MRI), and 18F-fluorodeoxyglucose positron emission tomography/computed tomography ( 18F-FDG PET/CT), and to investigate the optimal standard uptake value (SUV; relative to the MRI-based delineation) for the automatic delineation of GTV using PET. Methods:A total of 53 NPC patients proposing to receive radiotherapy were selected for this study. The CT, MRI, and PET images of each patient were obtained before radiotherapy. Then GTV and positive lymph nodes were delineated on these three types of images. They were individually named GTV MRI, GTV CT, GTV PET2.5 (SUV=2.5), Lymph MRI, Lymph CT, and Lymph PET2.5 and compared. The GTV ∩2.5 (overlapped GTV) was obtained through the alignment of MRI and PET/CT images. Meanwhile, GTV was delineated on PET images using thresholds of SUV=4.0, 4.5, 5.0, and 5.6, obtaining GTV PET4.0, GTV PET4.5, GTV PET5.0, and GTV PET5.6. Then their volume and Dice similarity coefficients (DSCs) were compared. Results:Compared to GTV MRI, GTV CT decreased by 1.73% ( P>0.05) and GTV PET2.5 increased by 21.34% ( t=-3.52, P < 0.05) in the three types of images. The volume of Lymph PET2.5 was 1.61 and 1.87 times the volume of Lymph MRI and Lymph CT, respectively ( t=-4.12, -5.18; P< 0.05). The volume of high-SUV lymph nodes was 4.07 times the volume of lymph nodes with low SUVs or SUV=0 ( t=5.50, P< 0.05) on PET images. The DSC between GTV PET4.0and GTV MRI was 0.78 ± 0.27, which was lower than that between GTV PET2.5 and GTV MRI (0.84 ± 0.18). However, GTV PET4.0 approximated to GTV ∩2.5 ( P>0.05). Conclusions:Compared to CT and 18F-FDG PET/CT, MRI shows more accurate boundaries of GTV and lymph nodes. When 18F-FDG PET/CT was adopted to automatically delineate GTV, the GTV delineated using SUV=4.0 was closer to GTV MRI.
ABSTRACT
Intensity-modulated radiotherapy (IMRT) is gradually replacing conventional radiation therapy and has become the mainstream radical treatment for patients with nasopharyngeal carcinoma (NPC). IMRT can conform and increase radiation doses to tu-mor-associated regions as well as decrease exposure doses and volumes on normal organs and tissues to avoid damage on critical or-gans. Aside from system and setup errors, other factors, such as the gradual reduction of the primary NPC lesion and the decrease in vol-ume of involved neck lymph nodes as well as body weight loss and changes in the head and neck shape during IMRT, may cause devia-tions in the radiation doses and volume delivered to the NPC targets and the organs at risk. These factors may affect the accuracy of IMRT. Several researchers have attempted to correct such deviations during IMRT for NPC patients by using adaptive radiotherapy (ART). The results indicate that ART is feasible to a certain degree and can correct the deviations, including decrease in tumor volume, body weight loss, and changes in head and neck shape of NPC patients.
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ObjectiveTo study the CT values of certain phantoms scanned by various CT scanners with dissimilar parameters.Methods The CT values of tissue equivalent inserts was measured in the TM164 and CIRS-062 phantom scanned by TOSHIBA AQUILIONTM,SIEMENS SOMATOMTMSENSATIONTM 64 and SIEMENS SOMATOMTM SENSATIONTM OPEN with different voltages,currents and slice thicknesses and then the corresponding CT-to-density curves was compared. Results There are no significant differences of CT values with various currents and slice thicknesses and also for low atom number materials scanned by different scanners with various tube voltages.The CT values of high atom number materials have obvious differences scanned with tube voltage,the maximum is about 400 HU.There are also significant differences between CT-density curves of two phantoms in the range from soft tissues to dense bone,the maximum is up to 500 HU.ConclusionsCT-density curves were highly affected by materials of phantoms,scanners and tube voltages.It is necessary to measure the curve with a comfortable phantom and certain scanner to assure the accuracy for dose calculation for treatment planning system.
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75).The mean score for ability to cat in public was 72,mean of 70 for normality of diet,and 92 for understand- ability of speech.Conclusion Concurrent chemoradiotherapy for advanced tongue base cancer achieved satisfactory long-term tumor control and oropharyngeal function preservation.