What is a Medical Dosimetrist?

A medical dosimetrist is an analytical member of the radiation oncology team who works closely in collaboration with the radiation therapists, medical physicists, and radiation oncologists within the department. A medical dosimetrist has an overall knowledge of math, physics, anatomy & physiology, radiobiology, and knows the characteristics and clinical relevance of radiation oncology treatment machines and equipment. With their expertise, medical dosimetrists design, generate, and measure radiation dose distributions and dose calculations while providing oversight to high level treatment procedures in both external beam radiation therapy and brachytherapy.

The Profession

Following consultation, the patient is simulated for tumor localization to ensure reproducibility and accuracy of treatment. The simulation consists of a CT scan of the specific area where the tumor or area of interest is located. During simulation, a medical dosimetrist may assist in creating molds and/or immobilization devices to establish the best body position for accurate daily treatment delivery. The radiation oncologist decides on the specific treatment modality and radiation dosage, based on the patient’s tumor type, stage, and location of cancer. CT scans, alone or in combination with MRI or PET scans, allow the physician to map out the exact location of the area to be treated. Medical dosimetrists use their knowledge and skills in conjunction with advanced computer technology to design a treatment plan specifically for each patient.

Clinical medical dosimetrists will typically specialize in one or more of the following types of radiation:

• External Beam Radiation Therapy- radiation delivered from outside the body to the tumor or treatment area.
  • Photon therapy- administered by a machine called a linear accelerator, which is a sophisticated device that produces high energy therapeutic x-rays that are used to treat tumors.
  • Proton therapy- treatment that uses high-energy proton beams to treat tumors. Proton beams are generated by an extremely large and complex particle accelerator—only a few dozen exist in the US.
• Brachytherapy- a radioactive source is placed directly inside or next to the area where the tumor is located. The radioactive source can be either temporary or permanent.

In external beam radiation therapy, the medical dosimetrist will carefully select the treatment technique, beam angles, and beam shapes to deliver a high dose of radiation to the tumor while sparing as many healthy cells and organs as possible. Once the medical dosimetrist has developed the best treatment plan given the anatomy, tumor location, and dose, the radiation oncologist will review and approve the plan.

Before the treatment plan can be executed, members of the radiation oncology team work together by performing rigorous quality assurance checks to ensure that the treatment plan is safe and effective. A medical dosimetrist will communicate the patient’s treatment plan to the radiation therapists by providing field arrangements, beam modification devices, and any concerns that may arise during treatment planning phase.  Medical dosimetrists may perform or assist a medical physicist with radiation measurements including ion chamber, thermoluminescent dosimeters (TLD), or film measurement. Another area a medical dosimetrist can contribute to quality assurance and safety is by providing technical and physics support.  This support could be in radiation protection, qualitative machine calibrations, and/or quality assurance of the radiation oncology equipment.

In conclusion, a medical dosimetrist is a vital member of the radiation oncology team who performs calculations for accurate delivery of the radiation oncologist's prescribed dose, documents pertinent information in the patient record, and verifies the mathematical accuracy of all calculations.

Images used with permission.

Content updated: November 2024