Radiation kills cancer cells or slows their growth by damaging their DNA so the cells  stop dividing or die.  

The type of radiation used for Thymic cancers is called External Beam Radiation Therapy (EBRT). The radiation comes from a machine that beams radiation into your cancer. Unlike chemotherapy, which is systemic, radiation is localized, going directly to the tumor. 

Although the radiation beams can be directed directly to the cancer, radiation also affects affects normal cells as it travels inside the body, and out as they leave the body. There are devices, however, that limit this accidental radiation, as you will soon learn.

The other type of radiation is internal, where a radiative seed, ribbon, or capsule is inserted into the tumor. This is not used for Thymic cancer.

Radiation therapy can be used after surgery if the doctor thinks some cancer cells were left behind, or before surgery to shrink an inoperable tumor. Getting radiation does not hurt in itself, but it does cause side effects as your cells die.

Small dots tattooed on the skin for precise positioning

To prepare for radiation, the radiology team will take careful measurements to determine the correct angles for aiming the radiation beams and the proper dose of radiation. To help with precise aiming, small dots may be placed on your skin. They will also do special CT scans to help plan your treatments.

Types of Radiation

There are several types of EBRT machines used to treat Thymic cancer.

The key to any machine is it’s ability to provide precise targeting. This focuses all the machine’s radiation to the tumor while minimizing damage to healthy cells.

Two of the types are 3D CRT (conformal radiation treatment) and  IMRT (Intensity-modulated radiation therapy). Both of these create 3D images of the target area to target its beam. 4D scanning radiation machines add another element of preciseness by accounting for tumor motion during treatment. As the patient breaths, lungs and other organs move slightly. The 4D scanning creates computer models that allow the beam to adjust for those movements. IGRT (Image-guided radiation therapy) is similar in compensating for body movement. VMAT (Volumetric modulated arc therapy), uses a technique that delivers the radiation dose continuously as the treatment machine rotates. This technique accurately shapes the dose to the tumor while minimising the dose to the organs surrounding the tumor.

Proton Beam Radiation

Proton beam radiationy is a form of EBRT that uses protons rather than x-rays to treat cancer. A proton is a positively charged particle. Doctors may use proton therapy alone, or they may combine it with X-ray radiation therapy, surgery, chemotherapy, and/or immunotherapy.

A machine called a synchrotron or cyclotron speeds up protons which are then beamed into the cancer. This energy makes the protons travel to the desired depth in the body giving the targeted radiation dose in the tumor.

With proton therapy, there is less radiation dose outside of the tumor. In regular radiation therapy, x-rays continue to give radiation doses as they leave the person’s body. This means that radiation damages nearby healthy tissues, possibly causing side effects.

NCCN Guidelines for Radiation

The NCCN guidelines call for a minimum of 3D-CRT radiology for Thymic cancers. More advanced technologies are appropriate to deliver curative radiology safely. These include 4D-CT, IMRT/VMAT, IGRT, and Proton therapy. The guidelines state that IMRT is preferred over 3D-CRT. They also state that compared to IMRT, proton therapy has been shown to be better sparing the normal organs with favorable local control and toxicity, and is appropriate for certain patients.

Possible side effects of radiation

When you first start radiation therapy, you might not notice side effects right away. Thats because it can take days or weeks for the radiation to start affecting the cancer’s DNA. 

Common side effects of radiation therapy include:

  • Fatigue
  • Redness or blistering of the skin
  • Nausea and vomiting
  • Irritation of the esophagus, which could cause painful swallowing and eating problems
  • Poor appetite and weight loss

Once you stop radiation, you can expect the side effects to continue as the radiation continues to alter the DNA in the cancer cells. But most side effects are short-term and get better over time after radiation treatment is done.

Radiation can damage bone marrow leading to low blood counts. This can lead to anemia (low red blood cell counts) which can cause people to feel weak and tired. It can also lead to low white blood cell counts, which increases the risk of serious infections.

Chest radiation therapy can also damage lungs. This can lead to trouble breathing and shortness of breath. This usually gets better after radiation treatments stop, but sometimes the damage is long-term (or even permanent).

Most side effects are short-term and get better over time after radiation treatment is done.

Risks and benefits of proton therapy

Compared with x-ray radiation therapy, proton therapy has several benefits:

  • Usually, up to 60% less radiation can be delivered to the healthy tissues around the tumor. This lowers the risk of radiation damage to these tissues.
  • It may allow for a higher radiation dose to the tumor. This increases the chances that all of the tumor cells targeted by the proton therapy will be destroyed. 
  • It may cause fewer and less severe side effects such as low blood counts, fatigue, and nausea during and after treatment.

But there are also some drawbacks to proton therapy:

  • Because proton therapy requires highly specialized and costly equipment, it is available at just a few medical centers in the United States. 
  • It may cost more than x-ray radiation therapy. Insurance provider rules differ about which cancers are covered and how much a person needs to pay. Talk with your insurance provider to learn more.
  • Not all cancers can be treated with proton therapy.

Receiving treatment

Radiation treatments are relatively quick, just a few minutes. The most time is spent getting the patients situated and in position.  Because the radiation beam has to be exactly targeted, precise positioning and measuring is critical. You might even has an X-ray or CT scan performed prior to the treatment. Usually, the patient will be positioned exactly the same for every treatment. Most often, radiation treatments are given 5 days a week for several weeks.

Some proton treatment rooms have a machine called a gantry. It rotates around the person. This way, the treatment is delivered to the tumor from the best angles. During treatment, the gantry will also rotate around the person so that the machine’s nozzle is in its proper position. The nozzle is where the protons come out of the machine

Lifetime Dose Limits

There is a limit to the amount of radiation an area of your body can safely receive over the course of your lifetime. Depending on how much radiation an area has already been treated with, you may not be able to have radiation therapy to that area a second time. But, if one area of the body has already received the safe lifetime dose of radiation, another area might still be treated if the distance between the two areas is large enough.