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Aim: The aim of the present study was to access the need of daily cone-beam computed tomography (CBCT) and the requirement of in-house protocols of image acquisition frequency to reduce unnecessary exposure to the patients undergoing radiotherapy treatment. Materials and Methods: The dose delivered during CBCT procedure (On-Board Imager, Trilogy, Varian medical system, Inc., Palo Alto, California) was assessed for pelvic and head and neck region. For dose estimation, cylindrical polymethyl methacrylate phantoms of 15 cm length, 16 cm, and 32 cm diameter were used to simulate the patient's head and neck and pelvic region thickness, respectively. More than 10 cm scatterer was added on either end of this phantom. Calibrated Ionization chamber DCT10 LEMO SN 1685 iba, dosimetry, Germany (10 cm active length) was used to measure the dose Index. The doses known as cone-beam dose index (CBDI100) were estimated for all the scanning protocols (kV and mAs setting) available on the machine. In this study, image acquisition frequency to correct the setup error was optimized. In-house protocol for image acquisition frequency during treatment has been suggested to reduce the dose. It was based on the principle of as low as reasonable achievable. Results: Optimized dose protocol observed was the “standard dose head” for which the CBDI100 was 2.43 mGy. Whereas for pelvic imaging, single protocol of 125 kV, 80 mA was available by which a dose of 7.61 mGy is likely to be received by the patient during scan. Maximum shift of 6 mm in lateral direction was observed to the patient of Pelvis region and 5 mm was observed in the longitudinal direction for the H and N patients. Angular shift measured in patient position was 3.8° and 3.1° for H and N and pelvic region, respectively. Conclusion: Three consecutive-day CBCT-imaging at the beginning of the treatment followed by once weekly CBCT and two-dimensional (2D) imaging in remaining days of treatment can be an optimized way of imaging for the patient having malignancy in the region of pelvic and abdomen. For H and N, once in a week, CBCT with standard dose head protocol, followed by 2D-imaging in remaining days can be an optimized way of imaging.
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Objective To explore the feasibility of reduction by using cone beam computed tomography (CBCT) before intensity modulated radiation therapy(IMRT) in the patients with nasopharyngeal carcinoma.Methods Twenty-three patients with nasopharyngeal carcinoma (NPC) undergoing IMRT were included in this study.The reverse IMRT plan with CBCT verification was prepared with location center coordinates origin as the planned central point.Before therapy,the CBCT reduction was adopted,the CBCT scanning was performed before the second and third radiotherapies.The registering data in 3 times were analyzed and summarized.Results In CBCT reduction,the absolute value at any direction≤3 mm accounted for 89.9％ (62/69),＜5 mm accounted for 98.6 ％ (68/69),and the deviation value at every direction was (0.6 ± 2.1)mm;in the second and third CBCT,the absolute value at any direction ≤3 mm accounted for 92.8％ (128 q38),＜5 mm accounted for 99.3％ (137/138),and the deviation value at every direction was (0.4 ± 2.0) mm:the difference between the two sets of data had no statistically significant difference (P＞ 0.05).Conclusion In formulating the nasopharyngeal carcinoma IMRT plan withthe location center coordinates origin as the planned central point,adopting the CBCT reduction is intuitional,convenient,practicable and feasible.
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Objective To explore the feasibility of reduction by using cone beam computed tomography (CBCT) before intensity modulated radiation therapy(IMRT) in the patients with nasopharyngeal carcinoma.Methods Twenty-three patients with nasopharyngeal carcinoma (NPC) undergoing IMRT were included in this study.The reverse IMRT plan with CBCT verification was prepared with location center coordinates origin as the planned central point.Before therapy,the CBCT reduction was adopted,the CBCT scanning was performed before the second and third radiotherapies.The registering data in 3 times were analyzed and summarized.Results In CBCT reduction,the absolute value at any direction≤3 mm accounted for 89.9％ (62/69),＜5 mm accounted for 98.6 ％ (68/69),and the deviation value at every direction was (0.6 ± 2.1)mm;in the second and third CBCT,the absolute value at any direction ≤3 mm accounted for 92.8％ (128 q38),＜5 mm accounted for 99.3％ (137/138),and the deviation value at every direction was (0.4 ± 2.0) mm:the difference between the two sets of data had no statistically significant difference (P＞ 0.05).Conclusion In formulating the nasopharyngeal carcinoma IMRT plan withthe location center coordinates origin as the planned central point,adopting the CBCT reduction is intuitional,convenient,practicable and feasible.
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Objective To analyze the discrepancies between position adjustments obtained with the stereoscopic 2DKV XGS-10 system and the Varian OBI system for head-and-neck region IMRT treatments,and to compare for image acquisition and registration time.Methods CBCT images were obtained with OBI system and 2DKV images were acquired by XGS-10 system for 30 head-and-neck patients prior to Varian21EX IMRT treatment.The images were registered with planning image for localization,and position adjustments were given in LR,SI and AP directions,then the discrepancies between them were analyzed.On the comparison of the two different systems,the Pearson coefficient was used to analyzed the correlation and 95％ CI analysis to discern the consistence.Results Analysis of images acquired for the 30 patients yielded the following results:position adjustments with XGS-10 system were (-1.03 ± 2.15) mm,(0.86 ± 2.59) mm,(0.42 ± 1.66) mm in LR,SI and AP directions,whereas (0.00 ± 1.68) mm,(1.53 ± 2.12) mm,(0.10 ± 1.54) mm with CBCT in LR,SI and AP directions.The discrepancies were (-1.03 ± 1.24) mm,(-0.68 ± 1.78) mm and (0.32±1.61) mm in LR,SI and AP directions.The correlation coefficients between them were 0.817,0.731 and 0.495 in LR,SI and AP directions.95％ CI were (-1.47--0.59),(-1.32-0.04),(-0.26-0.90) mm.The average image acquisition and registration time were 10 s and ＜ 15 s in XGS-10 system,with 3 min and 8 min in OBI system.Conclusions Both of XGS-10 system and OBI system could be used to improve patient position accuracy,but XGS-10 system could cut down the total time.
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Objective Performing a daily quality assure (QA) program to get variation and error range of on board imager (OBI) system,so that the OBI system can meet the needs of clinical treatment.Methods The daily QA program including: mechanical accuracy,2D/2D Shift calculations accuracy,couch motion accuracy.Results The max deviation was-0.7 mm in lcft-right (LR) dircction and 0.8 mm in superior-inferior (S1) direction in Linac& OBI isocenter accuracy check.The max deviations in 4 blades (x1,x2,y2,y1) position accuracy check were:-2.1 mm,2.2 mm,± 1.7 mm,-2.1 mm.In OBI mechanical arms position accuracy check,31％ standard data was 85.2 cm with 0 mm deviation; 69％ standard data was 85.1 cm with 1 mm deviation.In LR,SI and anterior-posterior direction,2D/2D shift calculations accuracy was 0.46 mm,1.35 mm,-0.04 mm and couch motion accuracy was-0.1 mm,0.3 mm,0.2 mm,respectively.Conclusions By performing the daily QA program,it could be found whether OBI works properly and satisfies the clinical use.The physicist can pay more attention to the parameters which change frequently,and adjust the frequency of the parameters which are stable,so that working efficiently.
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Objective To study setup errors in precise radiotherapy by Varian ix accelerator OBI system and provide reference data for clinic.Methods 15 patients with pelvic cancer patients were studied in intensity modulated radiation therapy, measurement in patients with left and right (X), head and feet (Y),before and after the (Z) 3 directions respectivelY,the linear error and X,Y,Z axis to form the corresponding U, V, W rotation errors, online error correction anyway, and record the error values. The error data was analyzed before and after corrections using the two-parameter method to calculate the clinical target volume (CTV) to planning target volume (PTV) of putting boundaries (MPTV).Results 15 patients were preformed total 146 times of the first place after a and after treatment of conical CT scan,in the X,Y,Z direction system error ((x)) ± random error (s) were (1.23±0.134) mm,(2.02±7.96) mm and (1.87±3.13) mm,after treatment for respectively (0.49±1.14) mm,(0.98±2.28) mm and (1.87±3.13) mm.There was no significant difference on X direction of the tapered bed CT scan in the first place,before and after calibration,in Y and Z direction there were significant differences, corrected position error in Y and Z direction is lower compared with that of primary (P ＜ 0.05); the setup error were (0.72±1.23)°,(0.06±1.12)°,(0.12±0.97)° on U,V and W direction respectively. rotate error in general was not more than 3°. Since online correction only worked to the translation error correction, There was no difference in U,V and W before and after correction.The MPTV was 2.55,9.61 and 5.93 mm on X,Y,Z direction before correcting. Conclusions Online or offline using the OBI system to guide positioning error correction can improve the positioning accuracy and reduce the positioning uncertainty,while maintaining or increasing local control rate at the same time,reducing exposure to surrounding normal tissue,so as to improve treatment accuracy purposes.
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Background: Patient’s conebeam computer tomography (CBCT) images have suggested a possibility for adaptive radiotherapy although the dose delivery is of structural complexity. It is of practical importance to verify and test the intensity-modulated radiation (IMRT) planning system for radiation therapy. Objective: Verify accuracy of dose calculations based on CBCT imaging. Materials and methods: Electron density calibration curve was generated for planning CT and CBCT data set using two CT phantoms (Gammex RMI® and Catphan® 600). Anthropomorphic head and neck phantom images were acquired from planning CT and CBCT. The routine IMRT technique was generated on the planning CT, which was applied to the CBCT. Dose distributions were computed. All LiF TLD-100 dosimeters were calibrated with gamma-ray. Forty-eight TLD measuring points were chosen in five different slices of the phantom. Measurements were repeated four times, and the average dose was compared to the reading doses on both CT and CBCT plans. Dose volume histograms (DVH) of various structures were generated, and dose statistics were analyzed. Results: Hounsfield unit obtained from Catphan phantom was similar between planning CT and CBCT. IMRT dose calculations based on the planning CT and CBCT agreed well with reading doses at 48 points. Statistical point doses by DVH calculation on CBCT were about 3% lower than those by the conventional CT. Dose ratios calculated over measured ones ranged from 0.82 to 1.09. Conclusion: Point doses and DVH calculations based on the planning CT and on-board CBCT were in acceptable agreement. CT phantom specifically designed for CBCT is recommended to improve accuracy of IMRT dose calculation on CBCT images.
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We evaluated the overall setup accuracy for the On-Board Imager (OBI, Varian Medical Systems Inc., Palo Alto, CA, USA), with attention to the laser, the gantry, and operator performance. We let experienced technicians place the marker block on the couch using a lock bar system, with alignment to the isocenter of the laser, every morning. A pair of radiographic images of the marker block was acquired at 0degrees and 270degrees angles to the kV arm to correct the position using a 2D/2D matching technique. Once the desired match was achieved, the couch was moved remotely to correct the setup error and the parameters were saved. The average for the vertical and the longitudinal displacements were 0.65 mm and 0.66 mm, and 0.01 mm for the lateral displacement. The average for the vertical and longitudinal displacements were statistically significant at the 0.05 level (p value=0.000 for both), while the p value for the lateral direction was 0.829. These results show that the tendencies to displacement in vertical and longitudinal directions occur through systematic error, while systematic error was not found in the lateral displacement. This daily overall evaluation is practical and easy to find the systematic and random errors in the setup system; however, a daily QA for laser and OBI alignment is still needed to minimize the systematic error in aligning patients.
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Humanos , Brazo , Desplazamiento Psicológico , Hipogonadismo , Transferencia Lineal de Energía , Enfermedades Mitocondriales , OftalmoplejíaRESUMEN
Purpose: To find the optimal slice thickness (Δτ) setting for patient registration with kilovoltage cone-beam CT (kVCBCT) on the Varian On Board Imager (OBI) system by investigating the relationship of slice thickness to automatic registration accuracy and contrast-to-noise ratio. Materials and method: Automatic registration was performed on kVCBCT studies of the head and pelvis of a RANDO anthropomorphic phantom. Images were reconstructed with 1.0 ≤ Δτ (mm) ≤ 5.0 at 1.0 mm increments. The phantoms were offset by a known amount, and the suggested shifts were compared to the known shifts by calculating the residual error. A uniform cylindrical phantom with cylindrical inserts of various known CT numbers was scanned with kVCBCT at 1.0 ≤ Δτ (mm) ≤ 5.0 at increments of 0.5 mm. The contrast-to-noise ratios for the inserts were measured at each Δτ. Results: For the planning CT slice thickness used in this study, there was no significant difference in residual error below a threshold equal to the planning CT slice thickness. For Δτ > 3.0 mm, residual error increased for both the head and pelvis phantom studies. The contrast-to-noise ratio is proportional to slice thickness until Δτ = 2.5 mm. Beyond this point, the contrast-to-noise ratio was not affected by Δτ. Conclusion: Automatic registration accuracy is greatest when 1.0 ≤ Δτ (mm) ≤ 3.0 is used. Contrast-to-noise ratio is optimal for the 2.5 ≤ Δτ (mm) ≤ 5.0 range. Therefore 2.5 ≤ Δτ (mm) ≤ 3.0 is recommended for kVCBCT patient registration where the planning CT is 3.0 mm
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To generate on-board digital tomosynthesis (DTS) for three-dimensionalimage-guided radiation therapy (IGRT) as an alternative to conventional portal imaging or on-board cone-beam computed tomography (CBCT), two clinical cases (liver and bladder) were selected to illustrate the capabilities of on-board DTS for IGRT. DTS images were generated from subsets of CBCT projection data (45, 162 projections) using half-fan mode scanning with a Feldkamp-type reconstruction algorithm. Digital tomosynthesis slices appeared similar to coincident CBCT planes and yielded substantially more anatomic information. Improved bony and soft-tissue visibility in DTS images is likely to improve target localization compared with radiographic verification techniques and might allow for daily localization of a soft-tissue target. Digital tomosynthesis might allow targeting of the treatment volume on the basis of daily localization.
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Humanos , Tomografía Computarizada de Haz Cónico , Posicionamiento del PacienteRESUMEN
PURPOSE: On-line image guided radiation therapy (on-line IGRT) and (kV X-ray images or cone beam CT images) were obtained by an on-board imager (OBI) and cone beam CT (CBCT), respectively. The images were then compared with simulated images to evaluate the patient's setup and correct for deviations. The setup deviations between the simulated images (kV or CBCT images), were computed from 2D/2D match or 3D/3D match programs, respectively. We then investigated the correctness of the calculated deviations. MATERIALS AND METHODS: After the simulation and treatment planning for the RANDO phantom, the phantom was positioned on the treatment table. The phantom setup process was performed with side wall lasers which standardized treatment setup of the phantom with the simulated images, after the establishment of tolerance limits for laser line thickness. After a known translation or rotation angle was applied to the phantom, the kV X-ray images and CBCT images were obtained. Next, 2D/2D match and 3D/3D match with simulation CT images were taken. Lastly, the results were analyzed for accuracy of positional correction. RESULTS: In the case of the 2D/2D match using kV X-ray and simulation images, a setup correction within 0.06degrees for rotation only, 1.8 mm for translation only, and 2.1 mm and 0.3degrees for both rotation and translation, respectively, was possible. As for the 3D/3D match using CBCT images, a correction within 0.03degrees for rotation only, 0.16 mm for translation only, and 1.5 mm for translation and 0.0degrees for rotation, respectively, was possible. CONCLUSION: The use of OBI or CBCT for the on-line IGRT provides the ability to exactly reproduce the simulated images in the setup of a patient in the treatment room. The fast detection and correction of a patient's positional error is possible in two dimensions via kV X-ray images from OBI and in three dimensions via CBCT with a higher accuracy. Consequently, the on-line IGRT represents a promising and reliable treatment procedure.
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Humanos , Tomografía Computarizada de Haz Cónico , Radioterapia Guiada por ImagenRESUMEN
In this study we estimated a geometric correlation among digitally reconstructed radiographic image (DRRI), kV x-ray image (kVXI) from the On-Board Imager (OBI) and electric portal image (EPI). To verify geometric correspondence of DRRI, kVXI and EPI, specially designed phantom with indexed 6 ball bearings (BBs) were employed. After accurate setup of the phantom on a treatment couch using orthogonal EPIs, we acquired set of orthogonal kVXIs and EPIs then compared the absolute positions of the center of the BBs calculated at each phantom plane for kVXI and EPI respectively. We also checked matching result for obliquely incident beam (gantry angle of 315 degrees) after 2D-2D matching provided by OBI application. A reference EPI obtained after initial setup of the phantom was compared with 10 series of EPIs acquired after each 2D-2D matching. Imaginary setup errors were generated from -5 mm to 5 mm at each couch motion direction. Calculated positions of all center positions of the BBs at three different images were agreed with the actual points within a millimeter and each other. Calculated center positions of the BBs from the reference and obtained EPIs after 2D-2D matching agreed within a millimeter. We could tentatively conclude that the OBI system was mechanically quite reliable for image guided radiation therapy (IGRT) purpose.
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Radioterapia Guiada por ImagenRESUMEN
PURPOSE: The purpose of this study is to develop a practical method for determining accurate marker positions for prostate cancer radiotherapy using CT images and kV x-ray images obtained from the use of the on-board imager (OBI). MATERIALS AND METHODS: Three gold seed markers were implanted into the reference position inside a prostate gland by a urologist. Multiple digital image processing techniques were used to determine seed marker position and the center-of-mass (COM) technique was employed to determine a representative reference seed marker position. A setup discrepancy can be estimated by comparing a computed COMOBI with the reference COMCT. A proposed algorithm was applied to a seed phantom and to four prostate cancer patients with seed implants treated in our clinic. RESULTS: In the phantom study, the calculated COMCT and COMOBI agreed with COMactual within a millimeter. The algorithm also could localize each seed marker correctly and calculated COMCT and COMOBI for all CT and kV x-ray image sets, respectively. Discrepancies of setup errors between 2D-2D matching results using the OBI application and results using the proposed algorithm were less than one millimeter for each axis. The setup error of each patient was in the range of 0.1+/-2.7~1.8+/-6.6 mm in the AP direction, 0.8+/-1.6~2.0+/-2.7 mm in the SI direction and -0.9+/-1.5~2.8+/-3.0 mm in the lateral direction, even though the setup error was quite patient dependent. CONCLUSION: As it took less than 10 seconds to evaluate a setup discrepancy, it can be helpful to reduce the setup correction time while minimizing subjective factors that may be user dependent. However, the on-line correction process should be integrated into the treatment machine control system for a more reliable procedure.