BSH
Meaning of BSH: A delivery vehicle rather than a drug: its entire job is to sit inside the tumor and wait for a neutron beam.
Definition of BSH
BSH is a boron-carrying compound injected into a vein before boron neutron capture therapy, a specialized form of radiation treatment. Its purpose is to load tumor tissue with boron-10, an isotope that splits apart when it captures a slow-moving neutron. The fragments released travel less than the width of a single cell, so the damage stays close to wherever the boron settled.
What happens when the neutron arrives?
A boron-10 nucleus that captures a low-energy neutron becomes unstable for an instant and breaks into two pieces: a helium nucleus, otherwise known as an alpha particle, and a lithium nucleus. Both are heavy and electrically charged, so they surrender all their energy within a few thousandths of a millimeter, roughly the width of one cell. That is the entire point of the design, because a cell holding boron is wrecked while its neighbor is untouched. Neither fragment is radioactive, and nothing is left behind emitting radiation afterward, which sets this apart from treatments using an implanted radioactive source.
Why is a carrier compound needed?
Boron is barely present in the body, and only the boron-10 form captures neutrons readily. That form makes up about a fifth of natural boron, so the compound is manufactured with the isotope enriched. Everything then depends on concentration: the treatment works to the extent that tumor tissue ends up holding more boron than the healthy tissue around it. That advantage is a matter of degree rather than an absolute separation, so surrounding tissue receives some dose, and the ratio achieved is a central limitation of the approach.
How does it compare with the other boron carrier?
| Carrier | How it distributes | Usual setting |
|---|---|---|
| BSH | Stays outside cells, entering where vessels leak | Brain tumors, where the barrier is broken |
| Boronophenylalanine | Carried inside cells by amino acid transporters | Melanoma and head and neck tumors |
| The two together | Reaches both compartments | Studied to raise total boron in tumor |
The treatment also needs a source of neutrons. That once meant a nuclear reactor, and compact accelerators have since taken over, but availability remains confined to a small number of centers, so boron neutron capture therapy has stayed a specialized option rather than a routine one. The compound is listed chemically as sodium borocaptate.
Also known as
Used in a sentence
BSH was infused several hours before the neutron beam was delivered.
Good to know
The neutron capture reaction releases charged particles that stop within about one cell width rather than leaving anything radioactive behind, and its selectivity depends entirely on how much more boron the tumor holds than the tissue around it.