Optimizing highly noncoplanar VMAT trajectories: the NoVo method

We introduce a new method called NoVo (Noncoplanar VMAT Optimization) to produce volumetric modulated arc therapy (VMAT) treatment plans with noncoplanar trajectories. While the use of noncoplanar beam arrangements for intensity modulated radiation therapy (IMRT), and in particular high fraction stereotactic radiosurgery (SRS), is common, noncoplanar beam trajectories for VMAT are less common as the availability of treatment machines handling these is limited. For both IMRT and VMAT, the beam angle selection problem is highly nonconvex in nature, which is why automated beam angle selection procedures have not entered mainstream clinical usage. NoVo determines a noncoplanar VMAT solution (i.e. the simultaneous trajectories of the gantry and the couch) by first computing a [Formula: see text] solution (beams from every possible direction, suitably discretized) and then eliminating beams by examing fluence contributions. Also all beam angles are scored via geometrical considerations only to find out the usefulness of the whole beam space in a very short time. A custom path finding algorithm is applied to find an optimized, continuous trajectory through the most promising beam angles using the calculated score of the beam space. Finally, using this trajectory a VMAT plan is optimized. For three clinical cases, a lung, brain, and liver case, we compare NoVo to the ideal [Formula: see text] solution, nine beam noncoplanar IMRT, coplanar VMAT, and a recently published noncoplanar VMAT algorithm. NoVo comes closest to the [Formula: see text] solution considering the lung case (brain and liver case: second), as well as improving the solution time by using geometrical considerations, followed by a time effective iterative process reducing the [Formula: see text] solution. Compared to a recently published noncoplanar VMAT algorithm, using NoVo the computation time is reduced by a factor of 2-3 (depending on the case). Compared to coplanar VMAT, NoVo reduces the objective function value by 24%, 49% and 6% for the lung, brain and liver cases, respectively

Laser-driven multi-MeV high-purity proton acceleration via anisotropic ambipolar expansion of micron-scale hydrogen clusters

強力なレーザーを使ってエネルギーがそろった純度100％の陽子ビーム発生に成功 --レーザー駆動陽子ビーム加速器の実現へ向けて大きく前進--. 京都大学プレスリリース. 2022-10-13.Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 ±0.3 × 10⁹/MeV/sr/shot with an energy of 2.8 ±1.9 MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications

Discriminative detection of laser-accelerated multi-MeV carbon ions utilizing solid state nuclear track detectors

A new diagnosis method for the discriminative detection of laser‐accelerated multi‐MeV carbon ions from background oxygen ions utilizing solid‐state nuclear track detectors (SSNTDs) is proposed. The idea is to combine two kinds of SSNTDs having different track registration sensitivities: Bisphenol A polycarbonate detects carbon and the heavier ions, and polyethylene terephthalate detects oxygen and the heavier ions. The method is calibrated with mono‐energetic carbon and oxygen ion beams from the heavy ion accelerator. Based on the calibration data, the method is applied to identify carbon ions accelerated from multilayered graphene targets irradiated by a high‐power laser, where the generation of high‐energy high‐purity carbon ions is expected. It is found that 93 ± 1% of the accelerated heavy ions with energies larger than 14 MeV are carbons. The results thus obtained support that carbon‐rich heavy ion acceleration is achieved

Methodological and Conceptual Progresses in Studies on the Latent Tracks in PADC

Modified structure along latent tracks and track formation process have been investigated in poly (allyl diglycol carbonate), PADC, which is well recognized as a sensitive etched track detector. This knowledge is essential to develop novel detectors with improved track registration property. The track structures of protons and heavy ions (He, C, Ne, Ar, Fe, Kr and Xe) have been examined by means of FT-IR spectrometry, covering the stopping power region between 1.2 to 12,000 eV/nm. Through a set of experiments on low-LET radiations—such as gamma ray-, multi-step damage process by electron hits was confirmed in the radiation-sensitive parts of the PADC repeat-unit. From this result, we unveiled for the first-time the layered structure in tracks, in relation with the number of secondary electrons. We also proved that the etch pit was formed when at least two repeat-units were destroyed along the track radial direction. To evaluate the number of secondary electrons around the tracks, a series of numerical simulations were performed with Geant4-DNA. Therefore, we are proposing new physical criterions to describe the detection thresholds. Furthermore, we propose a present issue of the definition of detection threshold for semi-relativistic C ions. Additionally, as a possible chemical criterion, formation density of hydroxyl group is suggested to express the response of PADC

Application of CR-39 Solid State Nuclear Track Detectors to Laser-Driven Ion Acceleration Experiments

The solid state nuclear track detector CR-39 is the most reliable ion detec- tor used in laser-driven ion acceleration experiments. This is because CR-39 detectors can measure from one ion without X-ray and electron noise generated by the inter- action between the intense laser pulse and the target matter. In addition, the incident energy and the spatial distributions of the laser-accelerated ions are also revealed by the careful analysis of the etch pits in CR-39 detectors. The present paper comments on CR-39 detectors based on previous studies with a focus on an analysis technique of the etch pits to obtain the incident energy of the laser-accelerated ions

Distinct step-like changes in G values for the losses of typical functional groups in poly(ethylene terephthalate) along boron ion tracks around the detection threshold

G values of the losses of typical functional groups in PET films along boron ion tracks have been determined using FT-IR spectrometry. G value for the loss of aromatic-ring clearly increases above 270 eV/nm. Those of ester and ethylene increase around the slightly lower stopping power of 250 eV/nm. The detection thresholds are defined by determining the original points from which the evolution of etch pit starts along the latent track, when the chemical etching was progressing starting from the front surface of each incident ion trajectory. The thresholds for B, C, N, O, Ar and Kr ions have been determined for other kind of PET sheets. Values of the sensitivity at the thresholds are fairly higher at heavy ions with smaller atomic number

Design of the energy spectrometer for laser-accelerated protons using stacked CR-39 detector

In the laser-driven ion acceleration experiment, CR-39 track detectors have been used for the measurement of laser-accelerated ions. This is because CR-39 detectors are insensitive for X-rays and energetic electrons, which are simultaneously generated with ions by the interaction between intense laser pulse and the target material. To evaluate the energy spectrum of laser-accelerated protons, which has the broad energy spectrum, the stacked CR-39 detectors are required because the energetic protons penetrate through the single layer of CR-39. For example, in the case of HARZLAS (TD-1) type CR-39 detector, which can detect up to 20 MeV protons, with the thickness of 0.9 mm, more than 9.63 MeV protons penetrate through the single layer. In other words, the protons with the energies more than 9.63 MeV create the etch pits not only on first layer but also on second layer. In such case, the accurate energy spectrum is not able to obtain by the numbers of etch pits on each layer of CR-39. In the present study, to measure the precise energy spectrum of laser-accelerated protons, we have designed the stacked detector using HARZLAS (TD-1) and energy moderators. Particle and Heavy Ion Transport Code System (PHITS) has been used for the optimization of the thickness of energy moderator and proof-of-principal calculation of the designed detector. We have applied polytetrafluoroethylene (PTFE) as the energy moderators because PTFE has the largest stopping power in the plastics. The thickness of PTFE has been determined as 1.8 mm to avoid a 20 MeV proton entering into the second layer of HARZLAS (TD-1). Therefore, the repetition of 0.9 mm thick HARZLAS (TD-1) and 1.8 mm thick PTFE can obtain the accurate energy spectrum of broad energy spread proton beams. In order to confirm the capability of the designed stacked detector, we have tried to reconstruct the model energy spectrum using the PHITS code simulation. Figure 1 shows the comparison between the model spectrum and the calculated spectrum. From the results of this simulation, the obtained energy spectrum almost reconstructed the model energy spectrum. Thus, the designed stacked detector can be applied to laser-driven ion acceleration experiments as the energy spectrometer for laser-accelerated protons.The 12th International Workshop on Ionizing Radiation Monitorin