| [Purpose] To investigate the preliminary experience on the prostate positional variation using the daily B-mode Acquisition and Targeting System (BAT) ultrasound system, and assess the efficiency and feasibility of daily BAT in IMRT for prostate cancer. To define the planning target volume (PTV) margins in intensity-modulated radiotherapy (IMRT) for prostate cancer without imaging guidance using B-mode acquisition and targeting (BAT) ultrasound-based prostate localization. In order to investigate the method and feasibility of2D ionization chamber array MatriXX system in quality assurance of aperture of block made of lead.[Materials and Methods] Eight patients were treated with IMRT for prostate cancer who were carried out the BAT ultrasound alignment before each IMRT treatment, whereas before treatment machine calibration was also performed to ensure the accuracy of BAT system. The time required to complete the BAT alignment procedure w as calculated, and the couch shift in each direct ion and the PSA level variation during treatment w as analyzed. Ten patients with prostate cancer underwent BAT ultrasound alignment before each IMRT session. The set-up deviations, each consisting of isocenter displacements in3directions (anterior-posterior, right-left lateral, and superior-inferior), were recorded for a total of225times and analyzed with Kolmogorov-Smimov (K-S) method. The information of aperture was exported from TPS to thermal wire cutting machine of Hek Medical System as file format of dat. The block was made according to dat file and was put on the tray of the linear accelerator. The2D ionization chamber array MatriXX was set up to obtain the shape of the radiation field of the block when the beam was on. The shape and size of the radiation field at the isocenter plane was drawn out by dealing with the dat file exported from TPS. The50%isodose line of the radiation field measured by2D ionization chamber array MatriXX and the aperture drawn by matlab were made a comparison in the same workspace of the photoshop.[Results] The average BAT procedure included average daily BAT calibration (recorded for a total of206times)(8.32±5.53) min, BAT localization of the prostate (6.83±4.59) min, average beam-on time (12.44±5.30) min, which respectively accounted for30%,25%and46%of the average total time (27.59±6.61) min. The mean shift in each direction, averaged over all patients, was (2.90±3.88) mm,(3.81±3.82) mm, and (2.83±4.24) mm in the lateral (RL), anteroposterior (AP), and superior-inferior (SI) dimensions, which conformed to normal distribution. The percent of BAT procedures in which the shift was5mm was24.2%in RL,25.9%in SI, and27.2%in AP directions. The TPSA and CPSA obviously decreased with significant difference pre and post treatment (P were0.008and0.044) and there was a positive correlation between the TPSA level and radiotherapy (r=0.863, P=0.006). Ten patients with prostate cancer underwent BAT ultrasound alignment before each IMRT session. The set-up deviations, each consisting of isocenter displacements in3directions (anterior-posterior, right-left lateral, and superior-inferior), were recorded for a total of255times and analyzed with Kolmogorov-Smimov (K-S) method. Results The isocenter shift in each direction, which represented an average from all the patients, was2.77±4.08mm,3.50±4.03mm, and2.38±4.32mm in the lateral (RL), anteroposterior (AP), and superior-inferior (SI) dimensions, respectively, and the deviations in each direction conformed to a normal distribution (P=0.806, P=0.061, and P=0.106, respectively). In the absence of imaging guidance for IMRT for prostate cancer, the PTV margin should expand by5.4mm in the right,10.92mm in the left,11.56mm in the anterior,4.56mm in the posterior,5.94mm in the superior and10.7mm in the inferior to allow95%isodose curve to cover90%of the clinical target volume. After we make statistical analysis of20apertures we got the conclusion that the apertures measured by MatriXX and exported from TPS were able to match each other in general. There were some differences only in the field edge, especially the details of the edge changed continuously. The position deviation of the apertures was0.631mm, while the mean square error was0.776mm.[Conclusion] The ultrasound imagining guided localization, with simple operation, nonirradiation and small systemic error, can be real-time corrected. BAT guided prostate cancer radiotherapy, the error is close to the cone-beam CT compared with the traditional skin notation, and target conformal index and evenness index and the prescription dose covering the PTV percentage is better, reducing the rectum, bladder and femoral head dose, reducingrectal bleeding, expansion and late complications. The apertures measured by MatriXX and exported from TPS were able to match each other very well and basically met the requirement that the error of the aperture in radiation therapy was less than5mm. This error on the one hand caused by a mechanical error of the machine itself, on the other hand MatriXX detector matrix within the radiation field of data processing capabilities can only be accurate to lmm, the reasons is the beam blocklead in the production process errors. Overall, the application MatriXX ionization chamber matrix beam block lead for authentication is simple, fast and effective, able to meet the requirements of this part of the contents of radiotherapy quality control. To improve the accuracy of radiation therapy. |
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