Dosimetry means the ‘measurement of dose’ and this is what the dosimetry team does in advance of your treatment as part of the process to ensure that when the radiotherapy treatment machine is switched on a suitable and safe treatment is given. Largely behind the scenes, dosimetrists (also known as treatment planners) typically work with computer software that allows them to simulate the intended treatment and so create a computerised plan, or set of instructions that treatment radiographers can use to operate the machine.
The process generally starts with the patient coming in for a CT planning scan, the Clinical Oncologist will then draw on these scans the area they wish to treat, stipulating a treatment dose to this target area and also any maximum dose limits to other regions that must not be exceeded. The aim of the treatment planner is to devise a pattern of beams that the treatment machine can deliver that will minimise dose to healthy tissues and organs but still allow a high enough dose to reach the target area. The dosimetrist will select the number of treatment beams needed, which directions they may come from and how long a beam is switched on for, in aiming to treat the drawd area as directed by the oncologist. The specialist computer program is able to model these different beam parameters, and calculate and display the dose absorbed by the tissues that the beams pass through for any particular beam configuration. The treatment planner will assess this dose and vary the treatment beams until the optimal balance between treating the target and avoiding healthy tissue is achieved. To achieve this optimal balance can take many attempts and further discussion with the patient’s oncologist and treatment radiographers before arriving at the best treatment plan for that patient.
On completion, each patient’s individualised treatment plan then goes through a series of independent checks before being approved by their Clinical Oncologist as suitable for treatment. The finished plan is a set of instructions in electronic format that guides the treatment machine. It is forwarded to the treatment radiographers who will input them into the treatment machines ready for your treatment.