The cancer treatment machine is scheduled to be installed in a radiation-proof room in the middle of next year.
As the new machine was larger than the one it was replacing, the radiation bunker needed to be expanded and radiation shielding upgraded to accommodate it, Southern District Health Board specialist services executive director Patrick Ng said.
"The new machine provides advanced technology and allows us to deliver more precise radiation doses to smaller areas," Mr Ng said.
"Rather than providing additional capacity per se, it will allow us to provide enhanced treatment capabilities whilst reducing adverse effects for the patients whom we treat."
The board hoped the upgrade would take three months to complete.
"We will be working with two machines from when construction starts until the new machine is able to be installed," Mr Ng said.
The two machines would run for extended hours and possibly in the weekends.
The upgrade of the bunker seemingly scuttles the hopes of some senior clinicians in the oncology department that it will be shifted into the new Dunedin Hospital.
Mr Ng said the board still planned radiation oncology would remain in its current location.
The board expected the new machine would allow it to meet its targets under the national cancer care strategy.
