Protons 101: What is radiation therapy?

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The Three Primary Treatment Options for Cancer Patients

The 3 main oncology (cancer) physician specialties are:

  1. Surgical Oncology: removes the cancer or the majority of it with an operation

  2. Radiation Oncology: destroys the cancer cells with radiation damage

  3. Medical Oncology: chemotherapy or whole body treatments designed to treat / kill the cancer.

Surgery requires the least explanation as it is very well known and used for many reasons beyond cancer treatment. It is used for the primary treatment of many cancers. It is used at times to reduce the amount of cancer so that the other two therapies can be utilized more effectively.

Medical oncology focuses on more systemic or whole body approaches. The vast majority of their treatments affect the whole body. The traditional treatment delivered by a medical oncologist is chemotherapy which flows through the bloodstream and treats cancer throughout the body. More recently the field of medical oncology has used more targeted agents that are based on genetic findings of the tumor; but in simple terms they still are given to the whole body and attempt to treat disease irregardless of its site or location.

Radiation treatment is often in between these 2 treatment forms. It can often be more generous than surgery in providing local control coverage of cancers that are close to or immediately adjacent to critical structures. Cancer often has small microscopic fingers that extend out beyond the main visible mass on imaging and radiation is often used to address a little bit larger area than one can address with surgery. It’s also more localized than chemotherapy or systemic agents. The radiation only affects the area being treated. it does not cause side effects outside of the region treated with radiation.

Radiation and chemotherapy both damage cancer cells by causing damage in the DNA (genes) of the cells. If you can cause enough damage in the DNA of the cells, the cells cannot grow or die off quickly. The main goal of treatment is to use techniques or drugs that maximize the tumor damage and minimize normal tissue damage.

Radiation is a main part of treatment for a large number of cancer patients.

At least 1/2 of all cancer patients will receive radiation treatment.

On a national level about 1.7 million people will be diagnosed with cancer in the United States. Radiation therapy is used for at least 50% of cases and probably closer to 60% today. It is a central component of modern cancer treatment that has been proven, across a variety of cancers, to improve survival when included as part of the management for many cancers.

Within the field of radiation oncology (or radiation therapy or radiotherapy), there are various methods to deliver radiation treatment. The first method historically was to implant radioactive material directly into the tumor. This technique still remains effective and is called brachytherapy. For some tumors, you can deliver the very highest doses directly to the tumor using these techniques. They can achieve highly targeted dose but require high skill level and due to a number of issues logistical issues are becoming less and less common procedures. The most common form of current treatment today by far is external beam radiation delivered with a linear accelerator (or LINAC for short). This delivers high energy photon or x-ray radiation to the patient to treat the cancer. There are many specific techniques used to deliver high energy photon radiation. These include 3-D, IMRT, SRS and SBRT. These are all various techniques to deliver photon radiation – they are different in some ways on a detailed level, but in general, they all use x-rays to target the disease. Today in the United States there are well over 5000 LINAC based facilities. For superficial tumors, these machine also produce electrons which travel much less deep into tissue and are better for some skin cancers. In a regular treatment day, I’d guess 90% of treatments at most facilities will be photon treatments.

Proton Therapy vs Traditional External Radiation

Proton Therapy, in contrast, to traditional external radiation, uses protons – subatomic particles accelerated to speeds approaching the speed of light to deliver the treatment.

Proton therapy is a growing area of the field of radiation oncology. There are currently 31 facilities in the United States that deliver proton therapy. The basic concepts is that proton therapy allows the physician and team to shape the radiation dose in 3 dimensions rather than 2 dimensions – with traditional photon treatments, you have very little ability to adjust the depth of the radiation as it enters, travels through and then exits the body. With proton therapy one can adjust the depth of the high-energy deposition within the body to match the tumor location. This is a unique property of particle therapy (proton therapy) and is the rationale for the creation of this much less common form of radiation therapy. It is this property that makes proton therapy achieve a more targeted treatment plan for many complex cases.

Growing Use of Proton Therapy

Proton Therapy is growing in acceptance and use and represents a standard option at 9 of the top 10 US News and World report cancer treatment hospitals. Six facilities were constructed from 1990 – 2009. Twenty five have been constructed in the last decade. About 14 projects are currently in development today in the US.

Proton v Xray
Above is a comparison plan between a traditional x-ray plan (above) and a proton plan (below) for a lung cancer. Colors are dose levels. The depth control of proton therapy allows for the same tumor dose with less normal tissue doses.

On a basic level the goal of any radiotherapy planning is to deliver a maximum dose to the tumor and deliver minimum dose to the immediately adjacent critical structures. We have a number of tools available to help achieve this goal but that really is the common thread throughout the field of radiation treatment – more dose to tumor, less dose to normal tissues not at risk for cancer.

On a more global level, the goal of the cancer care is likewise very similar. Our goal is to obtain tumor control and cure while minimizing long-term toxicity from treatment by using the correct blend of the three primary oncologic specialties and even further, by using the correct options for each patient with in each of those specialties to create a customized plan that maximizes outcome and minimizes toxicity for long-term quality of life.

Dr. Mark Storey MD
Medical Director of Clinical Operations
The Oklahoma Proton Center