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Published in Harald Paganetti, Proton Therapy Physics, 2018
While all the earlier reported clinical experiences were limited to passively scattered proton beam delivery, monitoring of pencil beam scanning (PBS) delivery was first pursued at the Heidelberg Ion Beam Therapy Center in Germany, using a commercial latest generation PET/CT scanner (with TOF and point-spread-function reconstruction) installed outside of the treatment rooms. Compared to previous offline implementations, a dedicated shuttle solution was realized to share the same tabletop with immobilization devices between the robotic treatment couch and the PET/CT. Data reported for proton treatments indicated absolute range agreement between (planning) CT-based MC simulations and measurements of 4.2 ± 2.2 mm (mean ± std for ten patients with primary glioma [68]) and −2.7 ± 4.9 mm (from five patients with tumor in the head [52]). In all cases, reproducibility typically better than 1 mm between treatment sessions was observed, with only few reported higher deviations up to 2 mm. Recently, a study including MC calculations on properly calibrated CT images of the PET/CT scanner was reported for tumor indications in brain, head and neck, sarcoma, and spine [48]. The analysis showed feasibility of detecting range shifts up to ±3 mm from both PET measurements and simulations, found well correlated (typically within 1.8 mm) to anatomical changes derived from CT scans, in agreement with dose data. Although confirming the promising sensitivity of PET to detect interfractional range variations, this study acknowledged limitations of offline imaging due to insufficient accuracy of patient-specific biological washout modeling and low signal. Better results are expected from a dedicated dual-head scanner, based on state-of-the-art LFS scintillators coupled to multipixel photon counters, just entering clinical testing at the Centro Nazionale di Adroterapia Oncologica (CNAO) in Italy. It enables dynamic (with few seconds time resolution to accumulate sufficient statistics) reconstruction of applied treatment, as shown in the first clinical investigation with PBS proton irradiation [69]. Examples of installations and results for different implementations are shown in Figures 21.7 and 21.8, respectively.
Utilize empirical models of measured relative dose output factor (rDOF) and transverse penumbra (TP) to evaluate dosimetric uncertainties of in-air spot modelling for spot-scanning carbon-ion and proton radiotherapy
Published in Journal of Nuclear Science and Technology, 2023
Yongqiang Li, Wenchien Hsi, Wenbo Xie
The commercial treatment planning systems are available to perform treatment plans for different particle species over various delivery techniques. The particle species can be carbon-ion and proton. The delivery techniques include the passive scattering and the active spot-scattering methods. In this study, we focused on the spot scanning with the spot by spot and layer by layer method [1] for both carbon-ion and proton beams in our institute. This method of beam delivery in our institute is a pencil-beam-scanning (PBS) technique. These commercial TPS can provide a scaling factor to convert calculated dose to monitor units of delivery; referred as D/MU, for each spot in each field of a plan using PBS delivery technique. However, these TPS require an additional conversion tool outside the TPS for the scaling factor of D/MU to convert a dose at specific location to deliver correct MU for each field of a plan using the passive scattering technique.
Design and Optimization Based on Monte Carlo Method of a Range Shifter for Proton Therapy
Published in Nuclear Technology, 2021
Yecheng Yu, Ping Tan, Yinjie Lin, Yuying Hu, Huidong Guo, Hao Lei, Zhongqi Zhang, Jiadong Li, Delin Hu
Figure 1 shows the layout of the pencil-beam scanning nozzle. The distance from the front surface of the range shifter to the iso-center plane is 0.15 to 0.50 m and the position is adjustable. By changing the overlap thickness of the multiple wedges of the energy degrader in the upstream energy selection system, continuous adjustment of the energy at low-energy regions can be achieved while the thickness of the range shifter remains the same. Compared to passive-scattering schemes,7 devices such as collimators and compensators are not required in the beam path, so energy loss due to the inelastic interaction with the extra nuclear electrons is relatively small when the range shifter is not added. Table I shows the energy loss calculated by FLUKA in each device at 70 and 250 MeV without the range shifter.
Monte Carlo Simulation Using TOPAS for Gas Chamber Design of PBS Nozzle in Superconducting Proton Therapy Facility
Published in Nuclear Technology, 2020
Ming Wang, Jinxing Zheng, Yuntao Song, Xianhu Zeng, Ming Li, Wuquan Zhang, Pengyu Wang, Junsong Shen
In terms of the pencil beam scanning (PBS) nozzle, the transverse size of the proton beam affects the lateral distribution of the dose, especially for the cyclotron.8 In the path where the beams pass from the nozzle components to the isocenter, the high quantities of Z materials and a long length of air cause a large angular dispersion. To reduce the effect of the nozzle on a beam’s characteristics, an IBA nozzle uses two quadrupoles to focus the beam’s transverse size in the entrance of the nozzle, and a vacuum chamber is designed to reduce the air length.9 However, the quadrupoles in the nozzle lead to an increase in the radius of the gantry, resulting in increased costs. For the Varian and Hitachi proton therapy facility, the beam is designed to form a minimum size at the isocenter when creating the transport beamline. Varian and Hitachi also design a chamber filled with a vacuum or helium gas in the nozzle.10–13