ABSTRACT
Radiation oncologists use interstitial implant techniques for the treatment of many
different sites within the body. An interstitial implant administers a high dose of radiation to
the tumour, whilst effectively sparing surrounding normal tissue and nearby critical organs.
The dose homogeneity of such an implant will be different from that achievable with external-
beam radiotherapy, as there is a very high dose region immediately around the implanted
sources. This high dose region is within the target volume and is not clinically significant. In
order to ensure adequate tumour coverage and sparing of critical organs, dosimetry systems are
usually based on the minimum dose to a volume.
