Dosimetrists – who are they?

Medical dosimetry is a specialised field in radiation oncology that combines physics, radiobiology and knowledge of the human anatomy to design, calculate, and assess the radiation dose needed to target cancerous tumours while minimising damage to surrounding healthy tissues.

The team of dosimetrists in the Division of Radiation Oncology at the National Cancer Centre Singapore.

“When I joined as a junior dosimetrist in 2003, there were only three other dosimetrists in what was then the Department of Radiation Oncology” remarked Hu Jing, Head of Treatment Planning and Senior Principal Dosimetrist at the Division of Radiation Oncology, National Cancer Centre Singapore (NCCS). 

“Today, we have 22 dosimetrists on our team!” 

With such growth, it’s clear that the role of a medical dosimetrist has evolved and become more complex over the years. But what exactly does a dosimetrist do? 

The role of a dosimetrist in radiation therapy 

One of the mainstays of cancer treatment is radiation therapy, which uses high energy ionising radiation to shrink tumours and destroy cancer cells. However, while delivering radiation to tumours inside the body, there is risk of harming surrounding healthy tissues and organs. 

“To put it simply, we come up with a highly customised radiation treatment plan using advanced computer software to map the radiation that passes through the body to reach the tumour,” explained Hu Jing. 

The goal is to generate a plan to deliver an optimal dose to kill the cancer, while making sure that surrounding healthy tissues and critical organs receive As-Low-As-Reasonably-Achievable (a fundamental safety principle in radiation known as ALARA) dose goes to surrounding healthy tissues and critical organs. 

A customised radiation treatment plan of a head and neck patient demonstrating radiation dose distribution. 

Precision takes teamwork

“Creating a treatment plan requires specialised planning software and close collaboration amongst our multidisciplinary team of radiotherapy professionals,” said Hu Jing. 

First, patients undergo CT simulation performed by radiation therapists to map the patient’s anatomy. Dosimetrists import these images and diagnostic images from MRI, PET, or CT scans into a treatment planning system to generate fused 3D images of the patient’s body. Using this, organs at risk of being dosed with radiation will be outlined. A radiation oncologist will then outline the tumour and prescribe the optimal radiation dose. 

Dosimetrists design the treatment plans and determine the best radiation beam arrangement to target the cancer, incorporating dose and body position into the plan. The final dose is verified before the plan is approved by the radiation oncologist. Medical physicists ensure machine safety to deliver the radiation dose as planned while radiation therapists verify treatment parameters and administer prescribed radiation treatment. 

This multidisciplinary approach ensures accurate, safe and effective delivery of radiation therapy to the patient. 

Real life impact 

While the work of dosimetrists happens behind the scenes, their contribution has asignificant impact on patient’s lives. 

“We have planned treatment for patients with large, outwardly visible tumours. Comparing pictures of the tumour mass before treatment and after it has disappeared is incredibly encouraging. It gives us great satisfaction to know that we have contributed to our patients’ recovery,” shared Hu Jing. 

Sometimes, the role requires difficult decision-making. 

“In cases such as nasopharyngeal cancer, the tumour can be very close to the optic nerves. Our plan needs to ensure adequate radiation is delivered to the tumour so that the cancer is effectively treated while we also try to preserve the patient’s sight. It is a very delicate balance and requires multiple discussions with the radiation oncologists,” said Hu Jing. 

“In some cases, patients lose weight during their treatment, or their anatomy changes due to tumour shrinkage, requiring us to evaluate and adapt their treatment plans to ensure that they remain safe and effective.” 

How does one become a dosimetrist in Singapore?

To become a dosimetrist in Singapore, a formal education in radiation therapy or related field, often radiation therapy or medical physics, is required.  A bachelor’s degree in radiation therapy is the primary clinical qualification for radiation therapists in Singapore, while other relevant science or engineering degrees such as physics or medical physics can be useful, but most medical dosimetrists in Singapore have training in radiation therapy. 

The team of dedicated dosimetrists at NCCS care for the high volume of patients requiring External Beam Radiotherapy (EBRT), which is delivered using a linear accelerator, or Proton Beam Therapy (PBT) which is offered at the Goh Cheng Liang Proton Therapy Centre at NCCS. All undergo structured full-time on-the-job training. 

NCCS also offers the SingHealth Medical Dosimetry Residency Programme, a two-year structured clinical training path designed to build competencies in treatment planning and independent practice. It covers topics in radiation therapy, planning software, site-specific clinical mentorship, and research or quality improvement projects. 

From 2023 to 2025, six residents took the American Association of Medical Dosimetrist Certified Board (MDCB) exam, an international accreditation for Certified Medical Dosimetrist (CMD). 

Recent graduates of the Medical Dosimetrist Certified Board exam, (from left), Regine Ms. Ang Shi Ling, Mr. Ang Wei Jie, Ms. Ong Xue Jing, Ms. Nur Fadhilah Bte Mohd Ibrahim.

A team dedicated to your care

While patients may never meet them face-to-face, dosimetrists working behind the scenes are involved in every step of radiation treatment planning. Their expertise ensures that every treatment plan is carefully designed, reviewed, and tailored to individual patient’s needs – ensuring both safety and effectiveness. 

To learn more about radiation therapy at NCCS, visit Radiation Oncology.