Biological Boron-10 compounds: the final frontier
Biochemists and biologists are racing to develop third-generation boron-10 delivery agents that will take full advantage of the optimised neutron beams produced by compact accelerator-based BNCT devices.
Researchers are taking pages out of the “handbook” for developing and evaluating modern substances for targeted biological therapy, for example, utilising low and high molecular-weight compounds as boron-10 carriers. As these compounds show greater specificity for cancerous cells, clinicians will be able to lower boron-10 treatment concentrations.
In parallel, work is continuing in improving the dosing and delivery of the well-established BPA and BSH agents.
Three hours in the life of a BNCT patient
So, how does a typical fraction with boron neutron capture therapy look to a patient?
In the preparation room of the outpatient BNCT clinic at a hospital, a nurse administers the boron-10 isotope delivery compound to the patient by intravenous infusion. The patient rests while the delivery agent accumulates in their cancerous cells.
At intervals, the nurse measures the patient’s blood-boron concentration, usually with a plasma optical-emission spectrometry device.
When the absorption values are sufficiently high, generally after a couple of hours, an oncology technician takes the patient to the treatment room and places them lying down on the robotic positioning couch in front of the BNCT’s beam shaping assembly.
To position the patient accurately before treatment delivery, the technician performs imaging with the in-room CT scanner for correlation with the planning images,
which increases treatment accuracy.
Irradiation with neutron beams follows. The epithermal neutrons react with the boron-10 substance accumulated in the patient’s cancer cells and selectively destroy them while leaving the healthy surrounding tissue intact.
Modern BNCT has a very slight impact on the patient’s quality of life – the smallest of all other radiation, chemotherapy or biological therapy modalities. And the fact that at most two fractions are enough means the patient does not have to be returning to the clinic for weeks and months. BNCT is therefore very suitable for recurring cancers where all other treatments are not permissible.
Boron neutron capture therapy will be in almost every hospital
Therapy directly in the oncology ward is possible because today’s BNCT devices can be very compact. For some models, the equipment of the specialised neutron source fits into a small shielded hospital room.
The BNCT device consists of a proton accelerator, a beam transport system, a solid lithium target for neutron generation and a neutron circular-beam shaping assembly. The device also has online monitoring systems for the proton and the neutron beam.
Usually, radiation oncologists perform simulations based on CT, PET and MRI images
to perform treatment planning for BNCT. The critical advantage of BNCT is that tumour marking is achieved biologically and not geometrically with a 3D model of the scanned image as in conventional radiation therapy.
Plan shortness is crucial from both the financial perspective (higher throughput of patients) and the comfort perspective of the patient being treated. There is a vast difference between lying still on a treatment couch for 20 minutes versus an hour.
On the other hand, the neutron beam in BNCT is stationary, so patient positioning may need to be more elaborate than in conventional radiation therapy. Sometimes positioning demands several couch settings to cover all treatment areas, but this is not inconvenient for the patient.