Dr. Tsubokura's Radiation Lecture Vol.71

January 12, 2020

Author: Masaharu Tsubokura

Editors: Akihiko Ozaki M.D., Yuki Senoo

 

141. Total body irradiation for bone marrow transplantation

The current standard "cancer" treatment consists of the following three types of therapies; surgery, chemotherapy, and radiation therapy. Several techniques for radiation therapy have been developed to reduce radiation exposure to normal surrounding tissues while concentrating radiation on cancer lesions. For example, the exposure of the lung and heart are avoided in the radiation therapy of breast cancer, and the exposure of the rectum and bladder are avoided in the radiation therapy of prostate cancer.

 

There is a type of radiation therapy that is given to the entire body. This type of radiation therapy is performed in bone marrow transplantation, a treatment for leukemia, one type of haematological cancer. Because blood is present all over the body, it is not effective enough to irradiate only a part of the patient’s body. In this radiation therapy, the entire body is exposed to a total of 12 sieverts of radiation (12 million microsieverts). divided into six sessions two times a day, in the morning and afternoon, for three days.

 

This level of radiation exposure is significantly higher compared with the level of radiation we receive in our everyday lives. Although such a high level of radiation exposure could eradicate cancer cells in patients, it could also temporally cause side effects, such as nausea, hair loss, diarrhea, and bleeding. Thus, health care professionals provide sufficient support to patients to overcome these side effects.

 

At this stage, a source of blood cells (bone marrow) obtained from other people is transplanted in patients to replace the patient’s blood with healthy blood, a procedure called bone transplantation. This treatment has enabled many people to overcome leukemia.

 

 

142. Measurement of air radiation dose rate using fluorescent substances

The extent of the exposure dose determines the impact of radiation on health. There are various measuring devices to detect the level of radiation and radioactivity.

 

Some of you may have alarm clocks with luminous dials that slightly illuminate after turning the room lights off. These dials are able to absorb and store energy from surrounding light sources, and they gradually emit light using the stored energy. Naturally, they will stop illumination when the stored energy runs out.

 

The substances that are able to absorb energy from light and emit different types of lights, are called "fluorescent substance." This explains the reason why fluorescence substances illuminate under a blacklight: when a fluorescent substance is exposed to a blacklight, it absorbs the ultraviolet light and emits the absorbed energy as visible light.

 

Actually, fluorescent substances are applied in various devices used to measure the air radiation dose rates. When the fluorescent substances placed in the detector, called a scintillator, are exposed to radiation, they absorb the energy of the radiation and emit faint light. The level of the radiation air dose rate is measured by examining the amount of light emitted. The measuring devices applying such a principle are called a scintillation detector.

 

 

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The Japanese version of the manuscript was originally published in Fukushima Minyu, a local newspaper in Fukushima prefecture, Japan, on 24th September and 1st October 2017 was reproduced for MRIC Global under the author's permission.

 

 

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