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Objective:To investigate the performance of optical surface imaging (OSI) in the postmastectomy radiotherapy setup and to assess the effects of 3D printed silicone bolus on OSI detection precision.Methods:A retrospective analysis was conducted for 16 patients treated with left-sided postmastectomy radiotherapy (PMRT) in West China Hopital, Sichuan University from January to April, 2021. The setup errors of 16 patients without bolus detected using OSI (OSI no-bolus, OSI n) were obtained before error correction was conducted using cone-beam CT (CBCT). The correlation between OSI n and CBCT was analyzed, and then the diagnostic efficacy of OSI was assessed using the receiver operating characteristic (ROC) curves. The setup errors of six patients with 3D printed silicone bolus detected using OSI (OSI bolus, OSI b) were obtained through off-line image registration, and then the detection precision of OSI n and OSI b in the translational directions was compared. Results:The setup errors in the case of OSI n were highly correlated with CBCT in the translational direction ( r ≥ 0.80), but were weakly correlated in the rotation direction ( r < 0.40). In the ROC analysis, the area under the curve (AUC) in the y direction was the lowest and was in the order of AUC 5 mm ≥AUC 3 mm > 0.75 for any translational direction. The difference in the detection precision between OSI n and OSI b was not statistically significant in the x and z directions ( P > 0.05), but was statistically significant in the y direction ( Z = -2.56, P = 0.01). In the y direction, the systematic error of detection precision in the case of OSI b was 3.11 mm higher than that in the case of OSI n, and the random error of detection precision in the case of OSI b was 1.9 mm higher than that in the case of OSI n. Conclusions:OSI cannot yet substitute CBCT in the postmastectomy radiotherapy setup, but its detection error is still within the clinically acceptable range. The performance of OSI-assisted setup is expected to be further improved by mitigating the interference of factors such as bolus in the imaging path through operational training.
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Objective To analyze set-up errors for irradiation of nasopharyngeal carcinoma by using kilo-voltage cone beam computed tomography (kV-KBCT) scanning, and to calculate the external margin from planning target volume (PTV) of nasopharyngeal carcinoma. Methods A total of 150 nasopharyngeal carcinoma patients in Meizhou People's Hospital from December 2014 to November 2016 were treated by image-guided radiation therapy (IGRT), kV-KBCT, CT image scanning matcthed by bone and grey alignment. PTV of nasopharyngeal carcinoma was also calculated. Results According to PTV formula, the external distance before radiotherapy guided by grey alignment was 0.5 mm in X-axis, 0.4 mm in Y-axis, 0.8 mm in Z-axis. While the distance was 0.1 mm in X-axis, 0.5 mm in Y-axis, 1.7 mm in Z-axis guided by bone alignment. After radiotherapy, the external distance guided by grey alignment was 0.4 mm in X-axis, 0.5 mm in Y-axis, 0.9 mm in Z-axis. While the distance was 0.1 mm in X-axis, 0.9 mm in Y-axis, 2.0 mm in Z-axis guided by bone alignment. There was no significant difference in set-up errors of 3 directions and 2 aligned ways before and after treatment.Conclusions The PTV within 3 mm is safe when IGRT is used for directing radiotherapy of nasopharyngeal carcinoma,and kV-KBCT is an effective image equipment.
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Objective To explore the set-up errors of position fixation with simple perforated foam pad in colorectal cancer radiotherapy and their causes as well as the improvement measures.Methods Sixty cases of color-ectal cancer patients undergoing radiotherapy were collected.Prone position was adopted with the position fixed by perforated foam pad and membrane.CBCT imaging was taken weekly before treatment,setup errors were corrected if necessary.Errors throughout the course of treatment for each patient were recorded and compared between patients, followed by analyzing the reasons of errors.Results Before calibration,the maximum errors on the direction of left and right (X-axis),front and back (Z),upside and downside (Y)in these 60 patients were 0.5cm,0.9cm and 0.7cm respectively with the average errors of (0.22 ±0.03)cm,(0.38 ±0.03)cm and (0.27 ±0.04)cm respec-tively.Conclusion The method of applying perforated foam pad and thermoplastic mask in colorectal cancer radio-therapy is currently the most commonly used in the clinical position fixation techniques,by which the small intestine, bladder and other pelvic tissues can be well protected.Due to poor comfort prone position,it is necessary to further improve perforated foam pad through improving the quality of the foam pad,thus improving patients comfort and posi-tioning repeatability and reducing position fixation errors.
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Objective To compare set?up error and the positioning and error correction time between the infrared markers automatic positioning+ ExacTrac ( A) and the manual positioning+ cone?beam computed tomography ( CBCT) image?guided radiotherapy ( IGRT) ( B) in intensity?modulated radiotherapy ( IMRT) for lung cancer. Methods A total of 20 patients with lung cancer were randomly divided into Group A and Group B. In Group A, after automatic positioning, a group of orthogonal X?rays images were taken using kV X?rays, which matched digitally reconstructed radiographs to obtain errors before correction. In group B, after manual positioning, images were taken using CBCT, which matched reference computed tomography images to obtain errors before correction. The positioning and error correction time was recorded in both groups. After error correction, errors after correction were obtained in each group using IGRT. Between?group comparison was made using the paired t test. Results The errors in lateral, longitudinal, vertical, and spinning vertical directions were significantly reduced after correction in both Group A and B (A:1.8±1?3 vs. 0.4±0?1, P=0?000;2.7±1?9 vs. 0.5±0?1, P=0?000;2.8±1?7 vs. 0.4±0?1, P=0?000;1.6±1?0 vs. 0.3±0?9, P=0?000;B:2.6±1?9 vs. 0.5±0?5, P=0?000;3.1±2?5 vs. 0.6±0?6, P=0?000;2.1±1?8 vs. 0.5±0?5, P=0?000;0.9±0?7 vs. 0.3±0?1, P=0?000). There were no significant differences in errors after correction between Group A and Group B (0.4±0?1 vs. 0.5±0?5, P=0?204;0.5±0?1 vs. 0.6± 0?6, P=0?257;0.4± 0?1 vs. 0.5± 0?5, P=0?518;0.3± 0?9 vs. 0.3± 0?1, P=0?755 ) . However, the positioning and error correction time in Group A was significantly shorter than that in Group B (199.1±16?2 vs. 315.2±13?7, P=0?000). Conclusions The application of ExacTrac or CBCT IGRT can substantially reduce set?up errors and improve set?up accuracy in IMRT. In addition, the application of the ExacTrac system can substantially shorten the positioning and error correction time.
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Objective:The purpose of this paper is to introduce a method of using compensate angles to eliminate rotation set-up errors without six-degree of freedom couch. Methods: To detect six-degree of freedom set-up errors, cone-beam computed tomography (CBCT) scans were acquired. These set-up errors were defined as a matrix to transform from accelerator coordinate system to patient coordinate system. Two independent vectors were defined to describe angles of gantry, collimator and couch in accelerator machine. Transformation of vectors were determined by transformation matrix and re-calculated back to the machine angles. Results:It was found that compensate angles can fully corrected the rotation angles in set-up with limited time consuming. It is feasible to implement compensate angles in routinely radiation procedure. Conclusion:With this method, it is possible to implement the complete corrections of set-up errors in radiotherapy without six-degree of freedom couch and it is convenient in operation as well.
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ObjectiveTo assess the impact of set-up correction on dosimetry using non-daily kilovolt cone-beam computed tomography (KVCBCT) for nasopharyngeal cancer patients treated with intensitymodulated radiotherapy (IMRT). MethodsThe mean shift values from 14 nasopharyngeal cancer patients received KVCBCT scans during the first 5 treatment fractions were calculated as prediction of systemic set-up errors and used for off-line correction at 1.5 mm threshold level. Presumed that the systemic errors can be corrected by moving couch without residual errors, the pre-correction set-up errors in the remaining fractions were the sum of actual set-up errors and predicted errors. The dosimetric effects of non-daily protocol were simulated in the planning system and analyzed with physical dose parameters in 14 IMRT plans. ResultsIn 10 patients with predicted systemic errors ＞ 1.5 mm, target dose was reduced significantly. The mean reduction of GTV-D98 ( dose received by 98％ of the volume of GTV ), CTVnx-D95 ( dose received by 95％ of the volume of CTVnx ), CTV1 -D98 ( dose received by 98％ of the volume CTV1 ) were 3. 8 Gy ( Z =- 2. 81,P =0. 005 ) ,4. 8 Gy ( Z =- 1.96, P =0. 050 ), 1.0 Gy ( Z =- 2. 82, P =0. 005 ), respectively. The effect on dose to CTV2 was much less. After correction, mean 3D vector positioning errors was reduced from 3. 6mm to 2. 3 mm (t =2.00,P =0. 000). After correction, the dose led to increase in GTV-D98, CTVns-D95,CTV1-D95 was 3.8 Gy (t=-2. 70,P=0.007),5.0 Gy (t =-2. 15,P=0.030),0.9 Gy (Z=-2.80,P=0. 005 ) respectively, and reduced the dose deviation greater than 3％ or 5％ for organs at risk.Conclusion Non-daily KVCBCT correction reduced dosimetric effect of set-up errors in IMRT for nasopharyngeal cancer patients.
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Objective To explore a fast and precise registration algorithm for megavolt (MV) portal images(PIs) used for radiotherapy positioning verification, and find auto analysis method of set-up error using the computed image processing and mutual information comparison technology, which provide a basis for the development of automatic image guidance software. Methods MV PIs of patients undergoing radiotherapy were tested, pre-processed with noise reduction technique based on improved filtering algorithm and contrasted by gray-scale transforming using partial derivative threshold. The bone structures were then highlighted but soft tissues and the cavities were restrained simultaneously. Improved particle swarm optimization and powell hybrid algorithm were used to optimize and transform the mutual information based on wavelet multiresolution analysis when registering the Pls with digital reconstructed radiographs (DRRs) of treatment planning or X-ray simulation-film images(SIs). Application of the designed registration algorithm was verified and evaluated through simulated set-up shifts of head and neck phantom. Results The improved noise reduction algorithm satisfactorily met the requirements for contrast of bony structures in the MV PIs. The established mutual information registration method well behaved in both accuracy and speed of registration calculation. The processing of automatic registration took only 31.4 seconds averagely for the PIs and X-ray Sis of head-neck phantom. Mean errors of automatic registration of PIs and X-ray Sis in horizontal, vertical and rotational reduced by 62. 74% ,67. 32% and 66. 61% respectively compared with manual registration in the testing of 20-cases head and neck phantom. Conclusions A precise image registration algorithm and set-up error analysis method based on MV portal images is established, and it can meet the clinical application in registration accuracy and speed.
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Objective To analyze setup errors for irradiation of pelvic carcinoma by online conebeam CT (CBCT) scanning and to calculate the external margins from clinical target volume (CTV) to planning target volume (PTV) in treatment planning. Methods Twelve patients with rectal or prostate cancer were enrolled in this study. Translational errors (x,y,z) and rotational errors (u,v,w) were obtained by using CBCT in radiotherapy. Results The set-up errors were gathered from 229 sets of CBCT in 12patients. The systemic ± random errors on x,y,z, u,v and w axes were (0.49 ± 1.18) mm, (-0. 11 ±3.45) mm, (-2. 00 ± 1.59) mm, 1.14°±0. 67°, 0. 42°±O. 94°and -0. 32°±±0. 68°, respectively. Setup errors in the left-right, anterior-posterior, and superior-inferior directions were 4. 6 mm, 12. 5 mm, and 6. 2 mm, respectively. Conclusions Set-up errors were unavoidable in pelvic carcinoma irradiation. To minimize the influence of set-up errors, we suggest a PTV margin of 5 mm, 15 mm and 10 mm in the leftright, anterior-posterior and superior-inferior directions, respectively.
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Objective: To correct the set-up error of patients during radiotherapy is very important for increasing treatment effective. Methods: This paper proposes a registration method based on portal images and reference images. Canny Operator was used to extract edge features. The extracted edge features were set as datum mark to calculate the maximal mutual information between the portal images and reference images. Parameters were optimized with simplex-simulated annealing optimization strategy. Results: The portal images and reference images of 29 patients with the cervix cancer and prostatic carcinoma were registrated in this paper. The results showed that the registration was precise, and the registration speed was increased remarkably. Conclusion: So this registration method can be applied for online estimation for set-up errors in clinical radiation.
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Objective To evaluate the impact of breathing motion on target volume and the factors influencing the set-up errors during tangential whole breast irradiation.Methods From Jan 2003 to Dec 2003,patients with early-stage breast cancer after breast conserving surgery,were selected to be eligible for the study.All patients were immobilized in treatment position by breast beard of Med-Tec 250.The motion of the breast treatment volume was observed on a fluoroscope in different directions under free breathing in 16 patients.The set-up errors in different dimensions during irradiation were measured by weekly portal films (PF) in comparison with digital reconstructed radiographs (DRR) in 11 patients.Results The central lung distance (CLD) variation during free breathing was (2.1?1.2) mm which is greater than the motion to- wards the other directions.By comparing the PF and DRR,the systemic error,random error and overall er- ror in the outer,inner and cranio-caudal directions was 1.9,1.6,2.5 and 2.4,1.7,3.1 and 2.6,2.3, 3.5 mm,respectively.In addition,the discrepancy of the treatment position in cranio-caudal direction and breast volume was most obvious at the beginning 2 weeks with the peak of breast volume at the second week. It decreased gradually during the following 3 weeks.Conclusions This study suggests that the mean value of the motion of the breast target volume during one breathing cycle is less than 2 mm.The set-up errors dur- ing irradiation is the greatest in cranio-caudal direction,suggesting that the fixing precision of the breast board should be further improved.The set-up error during irradiation are most obvious at the beginning two weeks,with the peak of the breast volume in the second week.