The detector quality can be chosen quickly and easily from three preset values. Nominally, the number of measuring points in the detector range from 30 thousand on the coarse setting, to 2 million for the fine setting. You can expect low quality detectors to produce statistically significant results in less time at the expense of spatial resolution. This situation is usually acceptable when initially setting up your simulation, and before planning long simulation runs on the fine setting.
Detectors are the regions in which dose is accumulated. They are always boxes made of air, as this is the condition under which flucence to dose conversion is performed.