Medical Radiation Physics - Medical Physics

Radiation therapy (Radiotherapy) is one of the main treatment modalities for cancer, along with surgery and chemotherapy. Radiotherapy is a cancer treatment that uses high doses of ionizing radiation to kill cancer cells and shrink tumors. The working principle of radiation here is to make small breaks in the DNA inside cells. These breaks prevent cancer cells from growing and dividing leading to their death.

About 50% of the newly diagnosed cancer patients are treated with radiotherapy. But, because each patient is anatomically unique, a personal treatment plan is essential and must be generated. A treatment plan contains information on how the dose, and consequently the probability of physical damage from irradiation is distributed inside the patient. The goal is to deliver a sufficient amount of dose to the tumor for its eradication, while minimizing the (unavoidable) dose to surrounding healthy tissues and organs at risk (OAR); each OAR has a different radio sensitivity.

Healthy tissue damaged by irradiation can cause severe short and long-term complications. For example, the functionality of salivary glands can be reduced after radiotherapy treatment of a head-and-neck tumor resulting in xerostomia (dry-mouth syndrome). Xerostomia urges the patient to drink some water every half-an-hour (day and night). Side-effects after radiotherapy of prostate cancer may be rectal bleeding, urinal and erection problems. It is worth mentioning that each complication has a significant impact on the quality-of-life of the patient, and it is thus of utmost importance to reduce the probability of developing treatment-induced complications. Improving the treatment plans is one of the ways to achieve this.

Improving implies reduced dose to the healthy tissue, or a better trade-off between doses to different organs, while still delivering a sufficient amount of dose to the tumor for its eradication. Radiotherapy treatment is performed by irradiating the tumor from several directions by ionizing radiation beams. The treatment device or linear accelerator (LINAC) has many degrees of freedom, and the result of the treatment planning are the machine parameter settings required to deliver the optimal treatment.

The effectiveness of patient care and treatment is dependent on the teamwork of individuals in the entire radiation therapy department, the patient, and related medical professionals. From the receptionist to the oncologist (physician), each individual has an important role in the goal of treating the person with cancer. The radiation oncologist has the overall responsibility for the patient’s care and treatment. Each member of the radiation therapy team, under the direction of the oncologist, is essential in providing the most effective patient care and treatment. Team members work together collaboratively to share their expertise and contribute their abilities to the treatment process.

Within the radiation oncology team, the medical radiation physicist is responsible for quality assurance of all radiation therapy equipment from acceptance testing and commissioning of new equipment to regularly scheduled calibration and testing of equipment already in the department. The medical physicist oversees all treatment planning and radiation safety programs and is involved with clinical physics procedures. Before treatment, the patient will undergo a simulation or a procedure designed to delineate the treatment fields and construct any necessary immobilization or treatment devices.

Usually several (rarely one) approaches are employed to diagnose cancer. These approaches include:

Physical examination by a physician.
Laboratory tests such as urine test and blood test can be used to identify abnormalities caused by cancer. For instance, in people with
- leukemia, a common blood test called complete blood count may reveal an unusual number or type of white blood cells,
- while others may provide information on some tumor markers such as Prostate-Specific Antigen (PSA) for prostate cancer or CA-125 for ovarian cancer.
Medical Imaging allow the examination of bones and internal organs in a noninvasive way. This may include
- a computerized tomography (CT) scan,
- X-rays,
- magnetic resonance imaging (MRI),
- positron emission tomography (PET) scan,
- ultrasound,
- etc.
Biopsy in which cells samples collected from the tumor (fine needle aspiration, solid tissues from surgery) are tested in both the
- Anatomic Pathology laboratory and
- Molecular Diagnostics laboratory.

Once cancer is diagnosed, its extent called stage is determined generally using Roman numerals - I through IV, with higher numerals indicating more advanced cancer. Other cancer staging however use letters or words.

After the cancer staging, a tumor board (a group composed of oncologists and other health care providers with different specialties such as medical radiation physicists} meets at the hospital to discuss the case and share knowledge. The board's goal is to determine the best possible cancer treatment and care plan for an individual patient. Many cancer treatments are available and each treatment options depend on several factors, such as the type and stage of cancer concerned, the patient general health condition and his/her preferences. Together, the patient and his/her oncologist usually weigh the benefits and risks of each cancer treatment in order to determine the best one.

Cancer treatments have different objectives, such as:

Cure. The goal of the treatment is to achieve a total cure of the cancer, allowing the patient to live a normal life span. Unfortunately, and depending on a patient’s specific situation, this is not always possible.
Primary treatment. The goal of a primary treatment is to completely remove the cancer from the patient’s body or to kill the cancer cells. Although the most common primary cancer treatment for the most common cancers is surgery, any cancer treatment can be used as a primary treatment, for example, when a cancer is particularly sensitive to radiation therapy or chemotherapy, the patient can receive one of those therapies as primary treatment.
Adjuvant treatment. Its goal is to kill any cancer cells that may remain after primary treatment (surgery) in order to reduce the chance of the cancer recurrence. Any cancer treatment can be used as an adjuvant therapy and the most common adjuvant therapies include chemotherapy, radiation therapy and hormone therapy.
Palliative treatment. These are treatments that may help relieve side effects of treatment or signs and symptoms caused by the cancer itself. Surgery, radiation, chemotherapy and hormone therapy can all be used to relieve signs and symptoms. Medications may relieve symptoms such as pain and shortness of breath. Palliative treatment can be used at the same time as other treatments intended to cure the patient’s cancer.

Radiotherapy

The role of a Medical Radiation Physicist

Cancer diagnosis

Cancer treatment

Types of cancer treatment

Some people with cancer will have only one treatment. But most people have a combination of treatments, such as surgery with chemotherapy and/or radiotherapy.. The different types of cancer treatment are presented below, but only Radiotherapy which is the focus of this website will be developed.

Surgery

Radiotherapy

Chemotherapy

Other treatments