Beam collimation and bolusing material optimizations for 10boron neutron capture enhancement of fast neutron (BNCEFN): definition of the optimum irradiation technique

Overview of hadron therapy: rationales, present status and future prospects

The rationales for hadron therapy are based on the physical selectivity and biological effects of the respective beams. Fastneutron therapy began as long ago as 1938 and subsequently proton, alpha particle, heavy ion, pion and neutron capture therapy have beenused. To date it is estimated that in excess of 50000 peoplehave undergone some form of hadron therapy. In the future it isexpected that fast neutron therapy will be used for selected tumourtypes for which neutrons are known to show improved cure rates. Thefuture trends in charged particle therapy will be driven by increasingcommercialization. The future of neutron capture therapy will dependon current clinical trials with epithermal neutron beams and thedevelopment of new tumour-seeking drugs.

Measured Microdosimetric Spectra and Therapeutic Potential of Boron Neutron Capture Enhancement of252Cf Brachytherapy

Californium-252 is a neutron-emitting radioisotope used as a brachytherapy source for radioresistant tumors. Presented here are microdosimetric spectra measured as a function of simulated site diameter and distance from applicator tube 252Cf sources. These spectra were measured using miniature tissue-equivalent proportional counters (TEPCs). An investigation of the clinical potential of boron neutron capture (BNC) enhancement of 252Cf brachytherapy is also provided. The absorbed dose from the BNC reaction was measured using a boron-loaded miniature TEPC. Measured neutron, photon and BNC absorbed dose components are provided as a function of distance from the source. In general, the absorbed dose results show good agreement with results from other measurement techniques. A concomitant boost to 252Cf brachytherapy may be provided through the use of the BNC reaction. The potential magnitude of this BNC enhancement increases with increasing distance from the source and is capable of providing a therapeutic gain greater than 30% at a distance of 5 cm from the source, assuming currently achievable boron concentrations.

Boron neutron capture enhancement of fast neutron radiotherapy utilizing a moderated fast neutron beam

An investigation of the therapeutic potential of boron neutron capture (BNC) enhancement of fast neutron therapy utilizing the Harper University Hospital superconducting cyclotron-produced d(48.5)+Be fast neutron therapy beam is presented. A technique for modification of the fast neutron beam to increase the BNC enhancement is presented along with an evaluation of the effects of beam moderation on the biological effectiveness of the absorbed dose. Characteristics of the photon, neutron, and boron neutron capture components of the absorbed dose are presented. Results demonstrate the possibility of therapeutic gains greater than 50% over conventional fast neutron therapy at depths required to treat brain lesions. This enhancement is estimated assuming currently achievable boron concentrations, and is more than adequate to provide a therapeutic window for the effective treatment of Glioblastoma Multiforme without prohibitive toxicity to the normal brain.

Filter, collimator and moderating material to achieve boron neutron capture enhanced fast neutron therapy

The combination of fast neutron therapy and boron neutron capture therapy is currently being studied as a possible treatment for some radio-resistant brain tumours. In an attempt to design a boron-enhanced fast neutron therapy beam for the Fermilab Fast Neutron Therapy Facility, the use of moderating material surrounding the patient's head has been investigated. Graphite, polyethylene, water and heavy water were studied as moderating materials, using MCNP. The use of tungsten, iron, lead and bismuth as materials for a small filter and collimator near the patient's head was investigated. Calculations showed that a filter and collimator made of tungsten with a graphite moderator was capable of producing a dose enhancement of 17.3 +/- 0.6% for a 100 microg g(-1) loading of 10B for a 5.6 cm diameter beam while delivering 1.5 Gy in 7 min.

Fast Neutron Beams for Boron Neutron Capture Therapy?

In view of Boron Neutron Capture Enhanced Fast Neutron Therapy (BNCEFNT) of brain tumours, the spatial distributions of thermal flux and fast neutron plus photon dose were measured in a hydrogenous cylinder phantom under conditions varying with respect to neutron energy, field size, and irradiation technique. The behaviour of the ratio thermal fluence per unit total dose leads to the conclusion that an appreciable dose contribution from the BNC reaction can be expected only with low energies and large fields. Beams from small apertures (< 6 x 6 cm2) produce only marginal BNC dose contributions, and might gain therapeutic relevance only in combination with a very effective tumour-seeking Boron-10 carrier.

Le traitement par neutrons : hadronthérapie partie II : bases physiques et expérience clinique

Neutrons have radiobiological characteristics, which differ from those of conventional radiotherapy beams (photons) and which offer a theoretical advantage over photons to fight radioresistance by the differential relative biological effect of them between normal and tumour tissues. Neutron therapy beneficed of great interest between 1975 and 1985. Many of phase III trials were conducted and indications have been definitively deducted of them. After briefly describing the properties of neutron beams, this review discusses the indication of neutron therapy on the basis of the clinical results. Salivary, prostate tumours and sarcomas are the main indications of neutron therapy. In concern to the prostate cancers, other alternative treatments reduce the neutron therapy field. For sarcomas, the lack of randomised trials limits the impact of the interest of neutrons. For other tumours, the ratio benefice/risk of neutron therapy is inferior to these obtained with photons and they could not be considered like classical indications.

Monte Carlo simulation of fast neutron spectra: mean lineal energy estimation with an effectiveness function and correlation to RBE

PURPOSE

Intercomparisons of radiotherapy trials conducted at different fast neutron facilities are complicated by the dependence of the relative biologic effectiveness (RBE) of the different beams on the fast neutrons spectra. To obtain a better understanding of the influence of neutron energy on radiation quality, Monte Carlo simulations were performed to calculate fast neutron (FN) spectra at different irradiation positions. To allow for comparisons with experimental data, the positions were chosen to be the same as that used by other investigators to obtain microdosimetry readings and radiobiological data.

METHODS AND MATERIALS

The primary neutron yield for beryllium targets bombarded with protons at the National Accelerator Center, Louvain, Nice, and Orleans facilities were calculated using the FLUKA code. Neutron transport simulations were performed with MCNP-4A, giving FN spectra for various phantom depths, hardening filter thickness, and field sizes. Using an effectiveness function, FN energy groups were correlated with mean lineal energies (y*-values) obtained experimentally by other workers.

RESULTS

Calculations confirm earlier measurements that a decrease in beam quality by a hardening filter is the result of a reduction in the low-energy neutron component, i.e., neutrons below 3 MeV. Variations in RBE due to changes in field size and different phantom depths could also be explained by variations of neutrons with energies between 3-15 MeV. The effectiveness function allows one to calculate changes in y* observed for the NAC beam with great accuracy (R(2) = 0.99, p < 0.0001). Also, when this function is applied to beams with different neutron energies, y* calculated values show a very significant correlation with measured RBE values (R(2) = 0.98, p < 0.0001).

CONCLUSION

The effectiveness function appears to be suitable to predict changes in y*-values and variations in RBE, using FN spectra simulated for various neutron therapy facilities.