Radiological Physics and Technology最新文献

This study evaluated the dose calculation accuracy of a Monte Carlo (MC)-based independent dose calculation system (IDCS) for CyberKnife brain stereotactic treatment plans and compared it with ray-tracing (RT) and MC algorithms within the MultiPlan treatment planning system (TPS). Beam modeling accuracy was validated for 11 circular fields using measured output factors (OPF), percentage depth dose (PDD), and off-center ratio (OCR). A total of 200 retrospective brain stereotactic treatment plans were analyzed (50 prescribed 23 Gy in 1 fraction, 50 prescribed 35 Gy in 3 fractions, and 100 prescribed 41.5 Gy in 5 fractions). Among these, 24 quality assurance (QA) plans were evaluated using homogeneous cylindrical phantoms and ionization chambers. Dose-volume histogram (DVH) was calculated, and gamma analysis (3%/1 mm, 10% threshold) was performed. IDCS aligned with measured data, with OPF and PDD/OCR errors within 3% and 4%, respectively, except for small-field underestimations in the build-up region. For QA plans, TPS overestimated the measured dose (RT: 0.5% ± 2.6%, p = 0.58, MC: 1.7% ± 3.1%, p = 0.07), while IDCS underestimated it (- 1.3% ± 2.3%, p = 0.07). Gamma passing rates were 98.9% ± 1.5% (TPS-RT vs. IDCS) and 99.9% ± 0.3% (TPS-MC vs. IDCS). DVH metrics (planning target volume [PTV]: D_98%, D_95%, and D_2%) showed clinically acceptable differences. IDCS showed greater dose calculation accuracy than the TPS-RT algorithm and could identify dose discrepancies in specific cases, thereby confirming its reliability for CyberKnife QA.

In internal target volume (ITV)-based treatment planning, respiratory-gated four-dimensional computed tomography (4D-CT) is used to visualize the respiratory motions of lung tumors. However, in cases of irregular breathing, conventional 4D-CT cannot be synchronized with patient-specific respiratory waveforms, which poses challenges to obtaining images that accurately represent the ITV of the tumor. To address this challenge, we propose "simulated respiratory-gated 4D-CT" synchronized with the simulated waveform. This study aimed to assess the precision of ITV delineation using simulated respiratory-gated 4D-CT in patients with irregular breathing. A respiratory motion phantom was employed by inserting a simulated tumor and assessing the method under sinusoidal and irregular breathing conditions. Irregular respiratory waveforms of 20 patients were used to simulate irregular breathing. The phantom was imaged using conventional 4D-CT, slow-scan CT, and our method. For conventional 4D-CT and our method, the average and maximum intensity projections (MIP) were obtained via postprocessing. ITVs corresponding to each respiratory motion were manually contoured. Furthermore, the Dice similarity coefficient (DSC) was computed based on the ITV of conventional 4D-CT. No significant disparity was found between the ITVs obtained using our method and those obtained using conventional 4D-CT under sinusoidal motion. The DSC values of the ITVs derived from our method using MIP were the highest. In the assessment of the irregular respiratory waveforms, the ITVs obtained via MIP using our method closely approximated the ideal ITV in 20 patients. These findings demonstrate that our method can enhance the accuracy of ITV delineation in lung tumors during irregular breathing episodes.