It’s my second month in my specialist placement and so I’ve moved on from a dosimetry rotation into a brachytherapy rotation. Seeing a brachytherapy operation in my rotational placement was the first time I thought “maybe I want to be a radiotherapy physicist” and so this was a big deal for me!
Brachytherapy uses sealed radioactive sources to treat easily accessible tumours. This includes gynaecological tumours, prostate cancer and some skin tumours. Because of brachy’s unique ability to get up close and personal with tumours, there is a steep dose gradient associated with it. This means healthy tissue surrounding the tumour receives less dose. This reduces the risk of radiation induced side effects such as fibrosis, oedema and secondary cancers.
Low Dose Rate Prostate Brachytherapy is an operative procedure in which tiny I-125 seeds are placed in the prostate. The positioning of the seeds is determined by using an ultrasound probe to image the prostate and the organs at risk surrounding the prostate e.g. the urethra and rectum.
An oncologist uses these ultrasound images to draw 3-dimensional volumes of these organs on a computer program. Here is where the physicists come in! Using these volumes, we determine the best places to position the seeds such that the prostate receives a relatively homogeneous dose distribution of the correct prescription whilst minimising the dose to the healthy tissue in the nearby vicinity i.e. the urethra and rectum. The doctor and physicist collaborate together on the plan. The physicist uses their knowledge of treatment planning and dose distributions to help find the optimal solution whilst the doctor advises on which part of the prostate they would like to receive a higher dose and where healthy tissue sparing is more important.
All of this is done in the operating theatre with the patient on the bed so speed is of the essence! The plan is then continually adapted during the surgical insertion of the seeds themselves as the physicist tracks where the seeds are deposited and so an up to date treatment plan can be calculated and refined.
This is so cool!?!?! A physicist gets to be in the operating theatre, planning the patient treatment in real time, using all of their physics knowledge to help the doctor get the best treatment outcome! This is the job of a physicist usually but the direct connection between physics knowledge and treatment is so much more tangible in this scenario! I love LDR brachytherapy!!!
"You're obviously not a scientist" 