ABSTRACT
Objective To analyze setup errors and guide the calculation of margins from clinical target volume (CTV) and planning target volume (PTV) in esophageal cancer patients treated with tomothcrapy by the MVCT image-guided system.Methods Sixty-four esophageal canccr patients trcated with tomotherapy in our hospital in 2016 were randomly selected.MVCT images were acquired after patients' positioning and co-registered with KVCT images.The setup errors of x,y,and z translations and roll rotation were analyzed with the t-test or one-way ANOVA.Meanwhile,PTV margin was calculated based on the formula of M =2.5 Σ + 0.7δ Results According to the formula,the CTV-PTV margins in the x,y and z directions are slightly different between cancers located in the cervical,upper thoracic,middle thoracic,and lower thoracic segments.In patients with upper thoracic esophageal cancer,the average setnp error in the yaxis was lower when the head-neck-shoulder thermoplastic film fixation was used than when somatic thermoplastic film fixation (P=0.000);the setup errors of z-axis with somatic thermoplastic film fixation in the fifth and sixth weeks were slightly less than those in the first several weeks (P =0.036);the setup errors acquired by three image registration patterns were similar (x-axis P=0.868,y-axis P=0.491,z-axis P=0.169,roll P=0.985).Conclusions In the treatment of patients with esophageal cancer,the setup errors are large,but the MVCT in the TOMO HD system can greatly reduce the setup errors,ensuring the accuracy of each treatment.It is further recommended that in clinical practice,different CTV-PTV margins should be used for the treatments of esophageal cancers located in different segments.Patients with upper thoracic esophageal cancer are advised to use the head-neck-shoulder thermoplastic film fixation.
ABSTRACT
Objective To quantitatively investigate the image quality and dose calculation accuracy of megavoltage computed tomography (CT) in helical tomotherapy.Methods The megavoltage CT was used to scan the Cheese phantom,and the geometric accuracy of images,noise,image uniformity,spatial resolution,density-CT value conversion,and dose calculation accuracy were analyzed and compared with conventional kilovoltage CT.Results The geometric accuracy of megavoltage CT images was within 2 mm in three directions.The megavoltage CT was inferior to kilovoltage CT in terms of image noise,uniformity,and spatial resolution.The dose-volume histogram (DVH) in dose reconstruction based on CT images was well consistent with DVH in the kilovohage CT plan.Conclusions The megavoltage CT can obtain images with accurate geometric dimensions and has a low imaging dose and accurate dose calculation,which meets clinical requirements.
ABSTRACT
Objective To investigate the intensity modulated radiation therapy (IMRT) planning optimization method to reduce the additional dose resulting from megavoltage cone-beam CT (MVCBCT) imaging for nasopharyngeal carcinoma IMRT treatment. Methods MVCBCT images collection process was simulated using XiO treatment planning system. The mean doses of MVCBCT ( DMVCBCT ) were calculated in gross tumor volume ( GTV), clinical target volume ( CTV ) and risk at organ or tissue using 27. 4 cm× 27.4 cm portal radiation 8 MU,5 MU (A,C) and 27.4 cm× 15.0 cm portal radiation 8 MU,5 MU (B,D). The dose correct factor of MVCBCT (CFMVCBCT) according to IMRT TPS and DMVCBCT ,but CFMVCBCT plus MVCBCT imaging process for radiotherapy planning optimization. The paired t-test was play for A∶ B,C∶ D,A∶ C,B∶ D of DMVCBCT. Results The DMVCBCT and CFMVCBCT of A, B, C, D were 7. 78,5. 78,4. 88,3.55 cGy ( A∶ C, t =24.41,P＜0.01) and 0.993 -0.997 in GTV,with 7.88,6.95,4.88,4.38 cGy (A∶ B,A∶ C,B∶ C,t=3. 85, -31.82, -8.52, all P＜0. 01) and 0.992 -0.996 in CTV1 ,with 8.28,6.67,5. 17,4. 17 cGy (A ∶B,A∶C,B∶C,B∶D,t=6.41 -18.24,all P＜0. 01) and 0.991 -0.996 in CTV2;with 6.88,5.00,4.28,3. 50 cGy ( A∶ B, A∶ C,t = 2. 83,11.03, all P ＜ 0. 05 ) and 0. 989 - 0. 995 in spinal cord, with 7.88,7. 38,4. 95,4. 62 cGy and 0. 984 -0. 990 in left parotid, with 8. 67,0. 28,5. 33,0. 28 cGy and 0. 963 -0. 999 in left optic nerve,with 9. 17,0.22,5.72,0. 17 cGy and 0.821 -0.997 in left eye lens,with 6.95,2. 17,4. 38,1.38 cGy and 0. 987 -0. 997 in brain stem, with 7.78,0.45,4. 95,0. 28 cGy and 0. 978 -0. 999 ( A ∶ B,A∶ C,B∶ C,B∶ D for five organ or tissue,t =5. 06 -335. 16 ,all P ＜0. 01 ) in optic chiasm. Conclusions The MVCBCT imaging process resulted in radiation doses to patient. The impact of MVCBCT image acquired dose on IMRT treatment plan for NPC was eliminated by a compensation method.