Question

(ii) Briefly outline methods for BNCT beam production and their
advantages and disadvantages. Explain advantage of epithermal
neutron BNCT and the method of epithermal neutron beam production on a reactor .

Answer 1

Boron Neutron Capture Therapy (BNCT) :It arises from the propensity of the ¹⁰B nucleus to capture thermal neutrons; the resultant unstable ¹¹B nucleus produces a lithium ion and an a particle, as well as 0.48 MeV g-radiation:

¹⁰B + n ----> ⁷Li + ⁴He

¹⁰B is linked to an alanine (a-amino acid) to form the L-4-Boronophenyl- alanine, which is injected in the biological material subjected to thermal neutron irradiation. In the case of BNCT, the cancerous cells, having a more dynamic metabolism, accumulate the alanine – and implicitly the ¹⁰B – much faster than the normal ones.

The main features included in the neutron production and BNCT were related to:

• The use of the multipurpose Tandem accelerator
• The use of lithium compounds instead of metallic form in order to prevent the difficulties in handling a highly reactive element
• The long irradiation times necessary to induce decidable effects in biological cells prevented the use of living tissues; instead we used aqueous cells solutions which can be preserved for longer periods.

The same features, above described, brought the following experimental set-backs:

Small intensities for the incoming protons beam - the maximum proton beam current provided by the Tandem accelerator is about a few mA;

• As a corollary of the previous set-back: low production rate for neutrons;
• Insufficient biochemical data regarding the tissue and living organs behavior under neutron irradiation and alanine injection

Clearly, BNCT is a complex, multidisciplinary enterprise, encompassing the fields of neutron sources and neutronics, pharmaceuticals, medical imaging, radiobiology, and clinical planning and implementation. In spite of a long history of research first conceived in 1930s and of experimentation in early 1950s, progress of BNCT so far has fallen behind the photon- and ion-beam therapies in practical prevalence and treatment scope. For example, preclinical trials and treatments to date have taken place only at improvised neutron-delivery stations at fission-reactor sources that devote not entirely to medical purposes. Only two ¹⁰B-carrying drugs have been approved for treating head and neck cancers. The lack of proper neutron sources that can be integrable to the infrastructure of hospital or clinical facilities is a major problem.

Advantages:

1. The use of accelerator-driven neutron sources in lieu of nuclear reactors in principle offers several favorable characteristics such as the fissile-material-free operation
2. Easy on/off switch of neutron production
3. Neutron energies adjustable to treat cancers in different organs
4. Advances in accelerator and neutronics technologies have led to the realization of increasingly compact, relatively low cost
5. Reasonably intense neutron sources, readily to lend themselves to a variety of applications including BNCT

Challanges/disadvantages:

1. Naturally, networking the research communities and commercial enterprises toward a unified goal is a key challange due to the multidisciplinary nature of BNCT.
2. We note that the not yet sufficient neutron flux of CNGs (compact neutron generators) can be augmented by improvements of the neutron moderator design and beam optics as well as discoveries of novel, high ¹⁰B-content cancer-cell seeking drugs so that proofof-principle studies and preliminary testing of BNCT treatment of breast cancer can commence.