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

Loss of carbonate ester bonds along Fe ion tracks in thin CR-39 films

In order to identify the chemical modification along nuclear tracks in CR-39 detectors, we have made a series of FT-IR measurements for thin CR-39 plastic films irradiated by Fe ions. The films were reduced in the thickness by long time chemical etchings down to 5 micrometer from as-received CR-39 sheets of 100 micrometer thick. It enabled us to obtain unsaturated IR spectra. The samples were exposed to 147 MeV Fe ions at HIMAC in air. Amount of loss of carbonated ester bonds due to the exposure was assessed from the changes in the absorbance of C=O and C-O-C bonds with Fe fluence. The assessed G-value for destroying carbonate ester bonds was found to be about 10 (scission/100 eV)

An evaluation of radial track etch rate in LR-115 detectors exposed to Fe ions by means of FT-IR spectrometry

Chemical modification of LR-115 induced by the irradiation of gamma-ray and 147 MeV Fe ions has been observed. Density of O-NO2 and C-O-C bonds in the sheets was decreased. We also confirmed the modification by chemical etching during early stage in LR-115 exposed to Fe ions. The absorption band around 1740 cm-1 was reduced rapidly, which can be attributable to C=O bonds of some additives containedin LR-115. We have derived the radial track etch rate from the reduction of the absorbance

Improved criterion of the mechanism for forming latent tracks in poly(allyl diglycol carbonate) based on the number of interactions induced by secondary electrons

In this study, we represent the track response data of poly (allyl diglycol carbonate) (PADC) using the number of interactions with the stopping medium induced by secondary electrons. The Number of Interactions induced by Secondary Electrons (NISE) is calculated using a Monte Carlo simulation code in Geant4-DNA. The description of the track response data given by NISE is improved compared with those proposed previously based on the stopping power and Radial Electron Fluence around Ion Tracks (REFIT). We also simulate the removal cross sections of the carbonate ester bond in PADC irradiated with protons and heavy ions (He, C, and Fe) based on the NISE. A radiation-oxidation kinetics model is combined with the estimation obtained in the present study. Discrepancies are found between the experimental results and our present simulation even after applying the radiation-oxidation kinetics model in the low stopping power region (<10 eV). Our results demonstrate that the interactions among electrons lying within the low-energy region (<7.4 eV) and the energy dependence of the yields due to bond breaks are crucial for obtaining more accurate estimation

Scintillation and chemical modifications induced by ions in a Polyvinyltoluene scintillator

23rd International Conference on Nuclear Tracks in Solid

Role of intermediate species in the formation of ion tracks in PADC: A review

This review paper intends at identifying the early processes arising during the formation of a latent ion track in Poly Allyl Diglycol Carbonate (PADC). We briefly summarize the physical and chemical processes specific to the description of the interaction of ionizing radiation with matter. Then we gather published information in relation to PADC response regarding energy absorption and further transient species formation. Emphasis is given to the chemistry of radicals. Due to a lack of available data in relation with clearly identified unpaired electron carriers in PADC, we use data stemming from surrogate molecules. Based on such data we suggest mechanisms for the decomposition of PADC during the early times of ion track formation. The a-sites of ether functional groups in PADC appear undoubtedly as critical targets which during further decomposition behave as the most probable origin of Carbon dioxide release. All suggested mechanisms are multi-step processes. Combining different concepts and data in relation with the dynamics of transient species formed in the ion track of a polymer material, we propose that the effective track radius may be described as the radial extension of reactive species formed rather than the maximum distance at which d-rays escape out of ion\u27s trajectory. Lastly, generalization of the different processes collected allows two major pathways to be proposed for describing the fate of damaged ether moieties in PADC. This way, evidence is given for a higher sensitivity of ether functional groups compared to ester carbonate ones. The latter generally being destroyed as a consequence of prior damaging of the ether group. Discussion presented here is of interest to the nuclear track community

On the tracks of proton and heavy ions in PC and PADC plastics detectors

In order to understand the latent track formation mechanics in polymeric nuclear track detectors, chemical modification along heavy ion tracks in bisphenol A polycarbonate, PC, and poly(allyldiglycol carbonate), PADC, has been examined using Fourier transform infrared, FT-IR, spectrometry. Track core radius for loss of carbonyl has different dependence on the stopping power between PC and PADC, indicating a quite different response to heavy ions from each others. This implies a possibility of controlling the track registration characteristics by changing the molecule structure between two carbonate ester bonds. In PC, the tracks have three different regions. The central region lost all three functional groups of carbonate ester bonds, phenyl rings and methyl groups, which surrounded by the second region in which the carbonate ester bonds and phenyl rings were damaged. In the outer region, the carbonate ester bonds were lost

Structural Modification along Heavy Ion Tracks in Poly(allyl diglycol carbonate) Films

To identify the chemical modifications along nuclear tracks in poly(allyl diglycol carbonate) (PADC), we have made a series of Fourier transform infrared (FT-IR) measurements for films with a thickness of about 3 mm that have been exposed to C, Ne, Ar, and Fe ions in air. The amount of carbonated ester bonds lost due to the exposure was estimated from the changes in the absorbance of C=O and C&#8211;O&#8211;C bonds with the heavy ion fluence. The G-value for the breaking of carbonate ester bonds and the corresponding track core radii were obtained as a function of stopping power. The calculated radial dose distribution indicated that the core was formed at regions where the local dose was higher than 106 Gy