Relative biological effectiveness (RBE) of thermal neutron capture therapy of cultured B-16 melanoma cells preincubated with 10B-paraboronophenylalanine

A comparative study of the biological effectiveness of 14-MeV neutron pulse and continuous radiation using mouse melanoma B-16 cells

The study was carried out using compact neutron generators with a sealed tube operating in pulsed (neutron generator ING-031) and continuous (NG-14) modes. Neutron radiation was formed due to reaction T(d,n)(4)He. The average flow of 14-MeV neutrons was 6.6×10(9) ns(-1) for ING-031 and 1.2-1.6×10(10) n s(-1) for NG-14. Duration of an impulse was ∼1 ms and pulse frequency of 50 Hz. The gamma rays of (60)Со source with an average energy of 1.25 MeV were standard radiation. Biological efficacy was estimated using the clonogenic activity of mice melanoma B-16 cells. Comparison of biological effects of neutron irradiation in pulse and continuous modes showed no significant difference between them. RBE values of pulse (ING-031) and continuous (NG-14) neutron radiation were equal-in the range of 2.4-2.6. According to the clonogenic activity of melanoma B-16 cells no dose rate effect was observed within the studied range of neutrons doses and dose rates.

Gadolinium neutron-capture therapy using novel gadopentetic acid-chitosan complex nanoparticles: in vivo growth suppression of experimental melanoma solid tumor

The potential of gadolinium neutron-capture therapy (Gd-NCT) for cancer was evaluated using chitosan nanoparticles as a novel gadolinium device. The nanoparticles, incorporating 1200 microg of natural gadolinium, were administered intratumorally twice in mice bearing subcutaneous B16F10 melanoma. The thermal neutron irradiation was performed for the tumor site, with the fluence of 6. 32x10(12) neutrons/cm(2), 8 h after the second gadolinium administration. After the irradiation, the tumor growth in the nanoparticle-administered group was significantly suppressed compared to that in the gadopentetate solution-administered group, despite radioresistance of melanoma and the smaller Gd dose than that administered in past Gd-NCT trials. This study demonstrated the potential usefulness of Gd-NCT using gadolinium-loaded nanoparticles.

New approaches to treating advanced melanoma: adjuvant treatment of high-risk primary melanoma and boron neutron capture therapy

Malignant melanoma is associated with an excellent long-term prognosis when detected and treated at an early stage. Surgery alone is sufficient for patients with thin melanomas. Patients with thicker tumors, who are at higher risk for metastasis, may benefit from additional therapy beyond surgical removal of the tumor. Adjuvant therapies are designed to reduce the risk of melanoma recurrence. In particular, the immunotherapies, which boost the host's immune response to the cancer, are proving to be valuable adjuncts to surgery. Once melanoma has metastasized to a visceral organ, the prognosis is poor. Metastatic melanoma has a poor response to most conventional treatments. Boron neutron capture therapy is a novel approach to cancer management. It is a binary therapy combining low energy, nonionizing neutron irradiation with a stable isotope of naturally occurring boron avidly absorbed by the tumor. The combined approach currently under investigation results in highly selective tumor destruction.

A comprehensive PC-based computer model for microdosimetry of BNCT

A computer model is described that performs microdosimetric calculations of the radiation dose delivered to tumour and normal tissue in boron neutron capture therapy (BNCT) by simulating capture reactions in a predefined three-dimensional space. The role of intracellular boron distributions and cellular dimensions on the radiation dose in clinical and experimental BNCT has been studied using a PC-based computer model. In order to calculate the radiation dose to low boron uptake cells, the extent of irradiation by boron containing adjacent cells (cross fire) is also dealt with. Radiation doses from boron and nitrogen neutron capture are converted to a biological effect by means of relative individual ion track segment efficacies, based on linear energy transfer along the particle track. A good correlation was found after comparing predicted values with previously published experimental data. A number of examples is given to illustrate the program's features.

Derivations of relative biological effectiveness for the high-let radiations produced during boron neutron capture irradiations of the 9L rat gliosarcoma in vitro and in vivo

PURPOSE

Relative biological effectiveness (RBE) values for the high linear-energy-transfer particles produced during boron neutron capture therapy have generally been based on theoretical considerations or in vitro experiments. The purpose of this study was to independently determine RBE values for all of the boron neutron capture therapy dose components.

METHODS AND MATERIALS

Clonogenic cell survival data were obtained for 9L rat gliosarcoma cells irradiated in the Brookhaven Medical Research Reactor thermal neutron beam both in vitro and as an intracerebral tumor. These data were analyzed using the linear quadratic model for cell survival to derive measured RBE values for all beam components and for a number of different boron compounds.

RESULTS

In the absence of boron, the combined effects of the protons from the nitrogen capture, 14N(n,p)14C, and the fast neutron scatter, 1H(n,n')p, reactions generated RBEs of 3.7 in vitro and 3.2 in an in vivo/in vitro excision assay, compared to 250 kVp X rays using an end point of 1% cell survival. Apparent RBEs for the 10B(n,alpha)7Li reaction products were calculated from cell survival data following reactor irradiations in the presence of the amino acid p-boronophenylalanine, the sulfhydryl dodecaborate monomer or dimer, or boric acid. Apparent RBEs for the 10B(n,alpha)7Li reaction ranged from 1.2 to 9.8 depending on which boron compound was used. RBEs from the in vitro studies were consistently higher than from the in vivo/in vitro studies. Under any conditions, the apparent RBE for the 10B(n,alpha)7Li reaction with p-boronophenylalanine was higher than that with any other boron compound tested.

CONCLUSIONS

Generally accepted RBE values for the fast neutron and 14N(n,p)14C reaction components of the total dose are too low. The apparent RBEs calculated for the 10B(n,alpha)7Li reaction were compound-dependent and consistent with differences in the distribution of 10B relative to glioma cell nuclei.