Background & AimsA new real‐time tracking radiotherapy (RTRT) system, the SyncTraX FX4 (Shimadzu, Kyoto, Japan), consisting of four X‐ray tubes and four ceiling‐mounted flat panel detectors (FPDs) combined with a linear accelerator, was installed at Uonuma Kikan Hospital (Niigata, Japan) for the first time worldwide. In addition to RTRT, the SyncTraX FX4 system enables bony structure‐based patient verification. Here we provide the first report of this system's clinical commissioning for intracranial stereotactic radiotherapy (SRT).Materials & MethodsA total of five tests were performed for the commissioning: evaluations of (1) the system's image quality; (2) the imaging and treatment coordinate coincidence; and (3) the localization accuracy of cone‐beam computed tomography (CBCT) and SyncTraX FX4; (4) the measurement of air kerma; (5) an end‐to‐end test.Results & DiscussionThe tests revealed the following. (1) All image quality evaluation items satisfied each acceptable criterion in all FPDs. (2) The maximum offsets among the centers were ≤0.40 mm in all combinations of the FPD and X‐ray tubes (preset). (3) The isocenter localization discrepancies between CBCT and preset #3 in the SyncTraX FX4 system were 0.29 ± 0.084 mm for anterior‐posterior, −0.19 ± 0.13 mm for superior‐inferior, 0.076 ± 0.11 mm for left‐right, −0.11 ± 0.066° for rotation, −0.14 ± 0.064° for pitch, and 0.072±0.058° for roll direction. the Pearson's product‐moment correlation coefficient between the two systems was >0.98 in all directions. (4) The mean air kerma value for preset #3 was 0.11 ± 0.0002 mGy in predefined settings (80 kV, 200 mA, 50 msec). (5) For 16 combinations of gantry and couch angles, median offset value in all presets was 0.31 mm (range 0.14–0.57 mm).ConclusionOur results demonstrate a competent performance of the SyncTraX FX4 system in terms of the localization accuracy for intracranial SRT.
To calculate the individualized fraction regime (IFR) in stereotactic body radiotherapy (SBRT) for non-small cell lung cancer (NSCLC) patients using the uncomplicated tumor control probability (UTCP, P +) function. Materials/Methods: 33 patients with peripheral lung cancer or lung metastases who had undergone SBRT were analyzed. Treatment planning was performed using the dose regime of 48 Gy in 4 fractions. Dose volume histogram (DVH) data for the gross tumor volume (GTV), lung, chest wall (CW) and rib were exported and the dose was multiplied from 1% to 200% at a resolution of 1%. For each dose fraction, P + values were calculated by considering the tumor control probability (TCP), radiation-induced pneumonitis (RIP), chest wall pain (CWP) and radiation-induced rib fracture (RIRF). UTCP values as a function of physical dose were plotted and the maximum P + values corresponded to the optimal therapeutic gain. IFR in 3 fractions was also calculated with the same method by converted the dose using the linear quadratic (LQ) model. Results: 33 patients attained an IFR using the introduced methods. All the patients achieved TCP value higher than 92.0%. The IFR ranged from 3Â10.8 Gy to 3Â12.5 Gy for 3 fraction regimes and from 4Â9.2 Gy to 4Â10.7 Gy for 4 fraction regimes, respectively. Four patients with typical tumor characteristics demonstrated the IFR was patient-specific and could maximize the therapeutic gain. Patients with large tumor were associated with lower TCP, UTCP and smaller fractional dose than patients with small tumor. Patients with tumor adjacent to the organ at risk (OAR) or at high risk of RIP showed lower UTCP and smaller fractional dose compared with patients with tumor away from the OAR. Conclusion: The proposed method is capable of predicting the IFR for NSCLC patients undergoing SBRT. Further validation is required in clinical samples.
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