G. Saint Martin

Submicroscopic kinetics of track formation in SSNTD

Abstract A theoretical description for submicroscopic kinetics of track formation in SSNTD is proposed. Kinetics of chemical attack in the primary damage region of the track is included. A good correlation between theory and experimental data obtained with Mazzeis replica method is achieved.

Induction time in Makrofol E

Abstract Induction time in Makrofol E is evaluated applying the nuclear track replica method and electron microscopy with 10 A resolution. The induction time is observed in foils with and without pre-etching. The track diameter vs etching time curves do not follow a linear relation for small track diameters.

The submicroscopic track kinetic theory and the variational principle

Abstract The variational principle was used to obtain the general equations for chemical etching track profiles inside and outside the physical damage region produced by energetic ions in Makrofol E. The track profiles developed at very short etching times were used to obtain the velocity profiles in order to perform computer determinations of track profiles for longer etching times. Track profiles obtained by means of the variational principle and the submicroscopic track kinetic theory are in good agreement, and compare favorably with experimental results.

Submicroscopic nuclear track kinetic theory applied to initial chemical etching of makrofol E

Abstract Chemical etching track profiles in the bulk region, as well as in the physical damage region, were described in a track kinetic theory by Mazzei et al. applying submicroscopic evaluations. In the present work this theory proves useful also to analyze the profiles of “new born” tracks. The equation describing height variations along each track profile is similar to that describing track velocity variation along the axis perpendicular to the ion incidence direction. The theory proves that for “new born” tracks, the chemical etching wave fronts generated in any point of the track are not exceeded by that wave front generated along the heavy ion incidence axis.

Applications of the submicroscopic nuclear track kinetic theory

Abstract The submicroscopic track kinetic theory (STKT) is able to deal with a broad range of cases. We derive here its behaviour for very short etching times (new born tracks) and also for long etching times, where the classical track kinetic theory is a particular case of the STKT. Experimental data obtained previously by Bean et al. using the electroconductivity method are then analyzed by the STKT method. We show that good agreement is obtained between Bean and STKT theoretical results for the track diameter evolution.

Toward a clinical application of ex situ boron neutron capture therapy for lung tumors at the RA-3 reactor in Argentina

PURPOSE Many types of lung tumors have a very poor prognosis due to their spread in the whole organ volume. The fact that boron neutron capture therapy (BNCT) would allow for selective targeting of all the nodules regardless of their position, prompted a preclinical feasibility study of ex situ BNCT at the thermal neutron facility of RA-3 reactor in the province of Buenos Aires, Argentina. (l)-4p-dihydroxy-borylphenylalanine fructose complex (BPA-F) biodistribution studies in an adult sheep model and computational dosimetry for a human explanted lung were performed to evaluate the feasibility and the therapeutic potential of ex situ BNCT. METHODS Two kinds of boron biodistribution studies were carried out in the healthy sheep: a set of pharmacokinetic studies without lung excision, and a set that consisted of evaluation of boron concentration in the explanted and perfused lung. In order to assess the feasibility of the clinical application of ex situ BNCT at RA-3, a case of multiple lung metastases was analyzed. A detailed computational representation of the geometry of the lung was built based on a real collapsed human lung. Dosimetric calculations and dose limiting considerations were based on the experimental results from the adult sheep, and on the most suitable information published in the literature. In addition, a workable treatment plan was considered to assess the clinical application in a realistic scenario. RESULTS Concentration-time profiles for the normal sheep showed that the boron kinetics in blood, lung, and skin would adequately represent the boron behavior and absolute uptake expected in human tissues. Results strongly suggest that the distribution of the boron compound is spatially homogeneous in the lung. A constant lung-to-blood ratio of 1.3 ± 0.1 was observed from 80 min after the end of BPA-F infusion. The fact that this ratio remains constant during time would allow the blood boron concentration to be used as a surrogate and indirect quantification of the estimated value in the explanted healthy lung. The proposed preclinical animal model allowed for the study of the explanted lung. As expected, the boron concentration values fell as a result of the application of the preservation protocol required to preserve the lung function. The distribution of the boron concentration retention factor was obtained for healthy lung, with a mean value of 0.46 ± 0.14 consistent with that reported for metastatic colon carcinoma model in rat perfused lung. Considering the human lung model and suitable tumor control probability for lung cancer, a promising average fraction of controlled lesions higher than 85% was obtained even for a low tumor-to-normal boron concentration ratio of 2. CONCLUSIONS This work reports for the first time data supporting the validity of the ovine model as an adequate human surrogate in terms of boron kinetics and uptake in clinically relevant tissues. Collectively, the results and analysis presented would strongly suggest that ex situ whole lung BNCT irradiation is a feasible and highly promising technique that could greatly contribute to the treatment of metastatic lung disease in those patients without extrapulmonary spread, increasing not only the expected overall survival but also the resulting quality of life.