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Dr. Tsubokura's Radiation Lecture Vol.131

Author: Masaharu Tsubokura PhD.

Editors: Akihiko Ozaki M.D.,PhD., Yuki Senoo

261. Using glucose to diagnose cancer

There are 2 types of radiation exposure: external and internal exposure. Previous articles have introduced 2 types of radiation therapy for malignant cells. The first type of radiotherapy is external radiation therapy, which uses an external device placed outside of the body that aims high-energy rays at cancer cells. The second type of radiotherapy is internal radiation therapy, also called brachytherapy, which directs radiation at cancer cells with the assistance of an encapsulated radioactive material that is ingested. Similarly, there are also 2 methods to deliver radiation in radiographic examinations. For instance, X-rays and CT scans are examples of radiation diagnostic techniques using an external radiation source. One example of radiographic techniques using an internal radiation source is a PET (positron emission tomography) scan. A PET scan is an imaging test that administers glucose labeled with a radioactive isotope. Once it is ingested into the body, the radioactive glucose emits a small amount of radiation, and then its concentration and location are detected using a PET scan. Generally, ingested glucose molecules spread throughout the body via the bloodstream and are absorbed by the organs. However, cancer cells consume glucose to produce energy at a much higher level than normal cells. Therefore, PET scans can detect the malignant cells’ size and location by taking advantage of their feature of absorbing glucose at a higher rate. The patient will receive internal exposure from the ingested radioactive materials. However, since the half-life of the radioactive materials used in this examination is approximately 2 hours, their radioactivity will become undetectable in a few days.

262. Combined method of internal and external radiation for radiographic inspection As with radiotherapy used t