Behind the beam: Who are medical physicists?

When a patient undergoes radiation therapy as part of their cancer treatment, they commonly interact with their oncologist, nurses and radiation therapists. But there is another healthcare expert working quietly behind the scenes whose work is critical to delivering the treatment. Patients may never meet medical physicists, but they ensure that radiation is delivered precisely to tumours while minimising damage to surrounding healthy tissue. 

As Mr Andrew Wibawa, Principal Medical Physicist, Proton, National Cancer Centre Singapore (NCCS) put it, “Medical physicists make sure that the radiation coming out of the machine to treat the patient reaches the right place, at the right time, every single time.”

Keeping radiation therapy on target  

The medical physics team at NCCS has 25 medical physicists – eight who specialise in proton therapy and 17 in conventional radiotherapy. While day-to-day duties vary, core responsibilities include regularly checking and calibrating radiation therapy equipment, reviewing treatment plans to ensure they are safe and deliverable, and overseeing the smooth running of operations in the treatment suites.

Radiation therapy is planned using treatment planning software and computed tomography (CT) images of a patient’s body. Though the software and scans aim to ensure that radiation is delivered to a precise site within the body, they do not always capture the variations and heterogeneity of a patient’s body well enough. Medical physicists scrutinise each treatment plan to anticipate these real-world variables, so that the right dose is delivered to precisely the right spot during treatment. 

The radiation therapy machine’s output can also change over time due to mechanical wear or changes in temperature. To ensure treatment accuracy, medical physicists perform rigorous quality assurance checks on a daily, monthly and annual basis. 

"We interact a lot with technology, gadgets, and machines, and we make sure they are well incorporated into our daily operations and workflows," said Mr Wibawa. This includes using specialised equipment to verify the accuracy of radiation therapy beams, as well as ensuring that data transfers seamlessly between the various software systems involved in treatment planning.

Making waves as a late entrant

NCCS started offering proton therapy in 2023, but the team of medical physicists has already made a lasting impact in the field.

While NCCS only began treating patients with proton therapy in June 2023, the team has already made a lasting impact in the field.

The team identified and investigated dose fluctuations produced by the proton therapy machine, tracing them to the way the beam moves through the machine. Their findings, along with practical solutions to address these inconsistencies, were published in the Medical Physics and Physics in Medicine and Biology journals.

“After we published our findings, other cancer centres from around the world got in touch to share that they had observed similar fluctuations but could not figure out the root cause and how to address it,” shared Dr Tan Hong Qi, Deputy Head of Medical Physics, Proton, NCCS.

“We were pleased that our work made a difference and helps to improve the way proton therapy is delivered globally.”

Moments that make the work matter

Although medical physicists rarely interact with patients, there are moments that bring them face-to-face with the impact of their work. One example is when medical physicists are required to be present during treatment for complex cases, in case adjustments need to be made to the plan during the session.

Dr Tan recalls observing proton therapy sessions involving young patients, "Whenever I see paediatric patients come in for radiation therapy, they are afraid and anxious."

"As children are still growing and developing, radiation exposure carries the risk of late-onset side effects that can affect their health and quality of life in as they get older. For certain paediatric patients, proton therapy is recommended because it reduces overall radiation exposure to healthy tissues, lowering the risk of long-term effects."

“During these treatment sessions, I know that we did the right thing in making proton therapy available for these young patients, so that there is a smaller chance of radiation affecting them later in life.”

Mr Melvin Chew, Deputy Head of Medical Physics, Photon, NCCS, also meets patients when giving safety briefings for brachytherapy. This is when a small radioactive implant is placed in or very close to the tumour. Before the procedure, medical physicists brief patients on how to insert the implant and what precautions to take to protect the people around them from radiation exposure.

“I always find these interactions with patients very meaningful, and feel satisfied knowing we can help to keep them and their families safe,” said Mr Chew. 

Training tomorrow’s medical physicists

Medical physicists come from a range of undergraduate backgrounds, with most holding a bachelor’s degree in physics, bioengineering, or a related field. Many have also undergone post-graduate training in medical physics, and NCCS offers residency positions for physics graduates to build their capabilities.

Currently, medical physics is not offered as a post-graduate programme in Singapore, but the team hopes to contribute to creating more options for those interested in joining the vocation. 

Dr Tan is one of the few medical physicists in NCCS who holds a teaching position in medical physics at Nanyang Technological University, where he also helps design medical physics modules. He shared, “My goal is to groom the next generation of medical physicists in Singapore who can contribute to serving our growing local healthcare needs and also make a global impact in the field.”

As president of the Society of Medical Physicists Singapore, Mr Chew plays an important role nationally – raising awareness for the profession, promoting medical physics research and education, and representing Singapore at international medical physics conferences. 

“It is not just about shaping the career paths of medical physicists, but also about shaping the care that cancer patients in Singapore will receive in the future,” Mr Chew said.