| Objective:The aim of the study was to compre the positioning errors using the KV level cone beam CT(CBCT)images versus the 3D ultrasonic images in the radiotherapies for cervical cancer patients,to analyze the clinical applications and therapeutic efficacies of CBCT images and ultrasonic images in cervical cancer IGRT;moreover,we also wanted to compare the systematic errors and random errors within the gradation and between gradations of cervical cancer in IGRT through the positioning errors under three verification methods including the bone matching and gray matching of the CBCT 3D images as well as the volume matching of the Clarity ultrasonic 3D images,so as to propose the external boundary extension norms of the target volumes based on the above-mentioned three verification methods.Methods:This paper has collected 22 cases of cervical cancer patients diagnosed by pathology during the period from October 1,2018 till March 30,2020.The posture fixation and the CT simulated location were conducted respectively by the radiographers from our hospital;the clinical doctors delineated the anatomical structures of the target volumes,the nearby endangered tissues and other normal tissues on the CT simulated images;the radiotherapeutic physicists demanded according to the doses prescribed by the clinical doctors that: the prescribed doses of PTV were 50.4 Gy/28 f,1.8 Gy/f;while the radiotherapeutic plans were stipulated to calculate the doses of various target volumes and the exposure doses of the endangered tissues,wherein a plan was confirmed together with clinical doctors,followed by simulated verifications of the dosimetric accuracy and the executability of the treatment plan offline;finally,the radiotherapists conducted the resetting verification for the patients having passed the plan verification in the therapeutic center.Twenty-two cervical cancer patients were collected concurrently with their 3D ultrasonic images and CBCT images when the pre-treatment verification was conducted,to whom the calculations of the positioning errors were conducted respectively by use of three methods as the CBCT bone matching(Group A),the CBCT gray matching(Group C)and the volume matching of the ultrasonic images(Group B),with the displacement deviation values along the 3D directions(front-rear,left-right and head-feet directions)before each time of therapy recorded,the positioning errors under the above-mentioned three groups of methods for cervical cancer radiotherapy calculated and the statistic differences among these three groups analyzed,in order to further investigate the advantages and shortcomings as well as the application scopes of the cervical cancer radiotherapies using the ultrasonic image guidance and the CBCT image guidance respectively,and acquire the external boundary extension norms.Results:The erros from the three left-right direction groups were(-0.13±2.02)mm in Group A,(-2.0±2.66)mm in Group B,and(-0.03±2.07)mm in Group C;respectively.The errors from the three head-feet direction groups were(0.97±4.23)mm in Group A,(1.00±4.56)mm in Group B,and(1.33±4.08)mm in Group C;respectively.The errors from the three front-rear direction groups were(-1.9～1.0)mm in Group A,(-1.5～3.8)mm in Group B,and(-1.5～0.9)mm in Group C;respectively.The 3D direction externally extended boundaries for cervical cancer bone matching were respectively 5mm,10 mm and 5mm,the ultrasonic 3D direction externally extended boundary values were respectively 8mm,11 mm and9mm,and the gray matching 3D direction externally extended boundary values were respectively 5mm,9mm and 5mm.Conclusions:In the intensity modulated radiation therapy(IMRT)for cervical cancer,the ultrasonic image guidance of the Clarity system can break through the technical limitation of CBCT,which directly takes clear uterus and cervix morphologies to match the soft tissues.It also could observe the variance and the withdrawal process of the target volumes,and reflect the mobility degree of the gross target volumes of tumor more directly and more preciselycompared with the CBCT image guidance.Moreover,as the ultrasonic guidance is safe and has no extra radiation or invasiveness,to use ultrasonic image guidance to verify the positioning errors in cervical cancer can bring forth a relatively good efficacy. |
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