Diodes and In Vivo Dosimetry

Diodes

Diodes are used during the first few occasions you attend for radiotherapy. They are basically small detectors attached to a long wire, and are used to measure the dose, you are receiving in 'real time', whilst having your radiotherapy treatment. They are normally attached to your body with tape at specific points, where the treatment beam enters your body. Many professionals feel they are important because they have the potential to detect any errors that may have slipped through the quality safety net. Every part of your radiotherapy treatment is checked and double checked and then checked again and even the treatment machine itself has a range of interlocks that activate should any parameter appear out of tolerance for even a moment. Therefore the chance of any error getting through this vigorous checking process, is incredibly unlikely. However, if the 'incredibly unlikely' did happen, then the diodes would detect the error so it could be rectified.

The argument against using diodes is that the quality process should pick up any error that may occur, which means the money needed to buy, calibrate and investigate the diode readings could be better used elsewhere.

Block diagram of in vivo dosimetry
 application

The dosimeter can be used as a tool for quantifying dose at depth, as well as to evaluate adherence between doses from the treatment planning and the delivered dose. Dependence of small filed sizes (less than 4 × 4 cm) would be of future interest, especially when small radiation segments are used during IMRT. The DVS dosimeter does not identify the specific cause of the difference in dose, but it can reliably alert the physician that a deviation between the planned and delivered dose has occurred. As such, the dosimeter can act as a fail-safe device with the potential to catch an over- or underdose situation before the mistake could be repeated.

There are important advantages to DVS dose verification. It can be reliably used for the verification of any possible change of the dose to the target or nearby organs. The system is capable of keeping a permanent patient dose record by monitoring the daily dose delivered. Based on the dosimeter readings and trends, the dose changes might be predicted. If the weekly average readings were outside the clinically implemented tolerance, the physician can investigate the patient position, clinical protocols, internal anatomy, and treatment plan, then apply corrections, if necessary. Furthermore, the DVS system provides medical physicists with an independent QA verification of machine performances. The extensive commissioning and implementation strategy detailed above can improve the usage of implantable dosimeters and may lead to improvements in patient treatment outcomes.

Mammography

mammography

Mammography is specialized medical imaging that uses a low-dose x-ray system to see inside the breasts. A mammography exam, called a mammogram, aids in the early detection and diagnosis of breast diseases in women.

An x-ray (radiograph) is a noninvasive medical test that helps physicians diagnose and treat medical conditions. Imaging with x-rays involves exposing a part of the body to a small dose of ionizing radiation to produce pictures of the inside of the body. X-rays are the oldest and most frequently used form of medical imaging.

Three recent advances in mammography include digital mammography, computer-aided detection and breast tomosynthesis.

Digital mammography
It also called full-field digital mammography (FFDM), is a mammography system in which the x-ray film is replaced by electronics that convert x-rays into mammographic pictures of the breast. These systems are similar to those found in digital cameras and their efficiency enables better pictures with a lower radiation dose. These images of the breast are transferred to a computer for review by the radiologist and for long term storage. The patient’s experience during a digital mammogram is similar to having a conventional film mammogram.

Computer-aided detection: (CAD) systems search digitized mammographic images for abnormal areas of density, mass, or calcification that may indicate the presence of cancer. The CAD system highlights these areas on the images, alerting the radiologist to carefully assess this area.

Breast tomosynthesis: It is also called three dimensional (3-D) mammography and digital breast tomosynthesis(DBT), is an advanced form of breast imaging where multiple images of the breast from different angles are captured and reconstructed ("synthesized") into a three-dimensional image set. In this way, 3-D breast imaging is similar to computed tomography (CT) imaging in which a series of thin "slices" are assembled together to create a 3-D reconstruction of the body.

What does the equipment look like?
A mammography unit is a rectangular box that houses the tube in which x-rays are produced. The unit is used exclusively for x-ray exams of the breast, with special accessories that allow only the breast to be exposed to the x-rays. Attached to the unit is a device that holds and compresses the breast and positions it so images can be obtained at different angles.

Breast tomosynthesis is performed using digital mammography units, but not all digital mammography machines are equipped to perform tomosynthesis imaging.

Benefits

🍄Imaging of the breast improves a physician's ability to detect small tumors. When cancers are small, the woman has more treatment options.
🍄The use of screening mammography increases the detection of small abnormal tissue growths confined to the milk ducts in the breast, called ductal carcinoma in situ (DCIS).
These early tumors cannot harm patients if they are removed at this stage and mammography is an excellent way to detect these tumors. It is also useful for detecting all types of breast cancer, including invasive ductal and invasive lobular cancer.
🍄No radiation remains in a patient's body after an x-ray examination.
🍄X-rays usually have no side effects in the typical diagnostic range for this exam.
Risks
📌There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
📌The effective radiation dose for this procedure varies. See the Safety page for more information about radiation dose.
📌False Positive Mammograms, Five percent to 15 percent of screening mammograms require more testing such as additional mammograms or ultrasound. Most of these tests turn out to be normal. If there is an abnormal finding, a follow-up or biopsy may have to be performed. Most of the biopsies confirm that no cancer was present. It is estimated that a woman who has yearly mammograms between ages 40 and 49 has about a 30 percent chance of having a false-positive mammogram at some point in that decade and about a 7 percent to 8 percent chance of having a breast biopsy within the 10-year period.
📌Women should always inform their physician or x-ray technologist if there is any possibility that they are pregnant. See the Safety page for more information about pregnancy and x-rays