A fiducial deployment system comprising: a needle including a generally tubular cannula body defining a needle lumen disposed through at least a lengthwise portion of the cannula body and a distal needle end region, the distal end region comprising a distal needle end opening at a distal end of the needle lumen; and at least one protrusion configured as a substantially inflexible detent; at least one fiducial comprising a generally columnar body slidably disposed in the needle lumen and including: a first lengthwise portion with a first outer diameter; a second lengthwise portion that is splayed with a second outer diameter greater than the first outer diameter; and a stylet extending through a portion of the needle lumen and configured to advance the at least one fiducial past the at least one protrusion and out of the distal needle end opening; characterised by: said protrusion extending radially into the needle lumen to form a restricted inner diameter that is less than an inner diameter of a major length of the needle lumen; where the first outer diameter of the fiducial is substantially the same as or less than the restricted inner needle diameter adjacent the at least one protrusion; and where the second outer diameter of the fiducial is substantially the same as or less than the inner diameter of the major length of the needle lumen. a needle including a generally tubular cannula body defining a needle lumen disposed through at least a lengthwise portion of the cannula body and a distal needle end region, the distal end region comprising a distal needle end opening at a distal end of the needle lumen; and at least one protrusion configured as a substantially inflexible detent; a generally tubular cannula body defining a needle lumen disposed through at least a lengthwise portion of the cannula body and a distal needle end region, the distal end region comprising a distal needle end opening at a distal end of the needle lumen; and at least one protrusion configured as a substantially inflexible detent; a distal needle end opening at a distal end of the needle lumen; and at least one protrusion configured as a substantially inflexible detent; at least one fiducial comprising a generally columnar body slidably disposed in the needle lumen and including: a first lengthwise portion with a first outer diameter; a second lengthwise portion that is splayed with a second outer diameter greater than the first outer diameter; and a stylet extending through a portion of the needle lumen and configured to advance the at least one fiducial past the at least one protrusion and out of the distal needle end opening; a generally columnar body slidably disposed in the needle lumen and including: a first lengthwise portion with a first outer diameter; a second lengthwise portion that is splayed with a a first lengthwise portion with a first outer diameter; a second lengthwise portion that is splayed with a second outer diameter greater than the first outer diameter; and a stylet extending through a portion of the needle lumen and configured to advance the at least one fiducial past the at least one protrusion and out of the distal needle end opening; characterised by: said protrusion extending radially into the needle lumen to form a restricted inner diameter that is less than an inner diameter of a major length of the needle lumen; where the first outer diameter of the fiducial is substantially the same as or less than the restricted inner needle diameter adjacent the at least one protrusion; and where the second outer diameter of the fiducial is substantially the same as or less than the inner diameter of the major length of the needle lumen. said protrusion extending radially into the needle lumen to form a restricted inner diameter that is less than an inner diameter of a major length of the needle lumen; where the first outer diameter of the fiducial is substantially the same as or less than the restricted inner needle diameter adjacent the at least one protrusion; and where the second outer diameter of the fiducial is substantially the same as or less than the inner diameter of the major length of the needle lumen.