Prostate Cancer Therapies: External and Internal Radiation Therapy

You have experienced prostate cancer symptoms and the PSA test and have learned about prostate cancer stages and Gleason scores. Prostate cancer treatments come down to drugs, surgery, radiation, or active surveillance, also known as watchful waiting. Here we discuss radiation therapies.

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External beam radiation (EBT) precisely targets tumors within the prostate gland. While there can be side effects, EBT avoids the potential nerve involvement and resulting erectile dysfunction associated with radical prostatectomy.

Radiation treatment for prostate cancer involves using high-energy beams such as x-rays to kill cancer cells and prevent them from spreading. Treatment with radiation, called radiation therapy, may be used for two different purposes: to treat and hopefully cure the cancer or to reduce symptoms from what has been determined to be incurable cancer.

There are two main categories of radiation therapy (RT): external and internal. External RT is the most common form of RT used and involves directing energy beams towards the prostate from a machine outside the body. Internal RT involves the placement of radioactive materials inside the prostate itself.

External Radiation Therapy: What are the Options?

For much of the past, external radiation therapy was available in primarily one form:
External Beam Therapy (EBT). During EBT, a machine called a linear accelerator (linac) delivers high energy beams of radiation towards the targeted place on the body, called the treatment field. The treatment field is identified before EBT is started by using imaging such as magnetic resonance imaging (MRI) or computed tomography (CT) to identify the precise location of the prostate tumor. EBT is usually administered during brief sessions five days a week over the course of five to eight weeks.

More recently, newer methods of delivering external radiation have become available, allowing for better localization of radiation towards the prostate while sparing the surrounding normal or healthy tissue, including bladder and rectum.

  • Conformal EBT: Conformal EBT is a new type of radiation therapy in which the radiation beams are actually modified to “conform” to the shape of the tumor. Computerized three-dimensional images of the prostate are created in order to shape the beams which are then delivered from different directions towards the prostate. For this reason, conformal EBT is often called three-dimensional conformal radiation therapy or 3D-CRT. Another form of conformal EBT is called intensity modulated radiation therapy or IMRT. IMRT is delivered much like 3D-CRT with the exception that the dose delivered by the beams is changed or “modulated” to target certain parts of the prostate with higher or lower doses of radiation. Yet another form of conformal RT involves the same conforming of beams but utilizes protons instead of x-rays as the energy source. Proponents of proton beam therapy or conformal proton beam radiation therapy argue that protons are effective at killing targeted tissues at the end of their projected path while mostly sparing the tissues they pass through. Proton beam therapy is very expensive and not widely available. Its efficacy relative to other radiation therapies is currently being studied.
  • Intraoperative Radiation Therapy (IORT): IORT is, as the name suggests, radiation administered during prostate surgery. It is typically only performed if the tumor cannot be completely removed. It is a one-time high dose delivered to the prostate tumor while nearby healthy tissues are pushed aside and protected with special shields.
  • Image-Guided Radiation Therapy (IGRT): The position of the prostate can shift on a daily basis based on bladder and rectal filling. IGRT utilizes imaging modalities such as ultrasound, CT, or x-ray prior to each RT session to ensure that the radiation is directed as accurately as possible towards the prostate and not the surrounding tissues. In some instances, a urologist might place tiny gold markers called fiducials into the prostate in a procedure very similar to a prostate biopsy so that the markers can be used to better aim radiation towards the prostate tumor.

Internal Radiation: What are the Options?

Internal radiation, also called brachytherapy, involves placing radioactive material directly into the prostate through needles or catheters. There are two main types of brachytherapy:

  • Low-Dose-Rate (LDR) Brachytherapy: LDR brachytherapy is sometimes referred to as permanent brachytherapy because multiple (as many as 100) small radioactive seeds are permanently placed inside the prostate gland via hollow needles. Doctors use ultrasound or MRI to help guide placement of the seeds during the procedure, which is typically done from a transperineal (the area between the scrotum and anus) approach. The seeds emit a continuous low dose of radiation over weeks to months and then ultimately become inactive. This is usually an outpatient procedure that does not require general anesthesia.
  • High-Dose-Rate (HDR) Brachytherapy: HDR brachytherapy is sometimes referred to as temporary brachytherapy because the radiation is delivered directly into the prostate via tubes that are only temporarily inserted. Patients are placed under general anesthesia and doctors will transperineally insert hollow tubes or catheters into the prostate using ultrasound or x-ray guidance. Over the course of two days in the hospital, patients will receive three brief treatments in which radioactive isotopes are delivered into the prostate via the tubes. After the final treatment, the tubes are removed. HDR brachytherapy is typically only used in people with high-risk prostate cancer and usually follows a five week course of EBT.

What are the Potential Side Effects from Radiation Therapy?

Early side effects from external radiation therapy include skin irritation over the treatment field and generalized fatigue, both of which usually resolve. Internal radiation may result in temporary pain or tenderness over the needle or tube insertion sites. Internal and external RT can also cause many of the same side effects.

The degree to which the side effects are experienced may vary, depending on how precisely the radiation can be delivered to the tumor and how much of the radiation is absorbed by tissues surrounding the prostate. If you experience side effects that do not resolve, your doctor may be able to offer you treatment options to minimize your symptoms. The predominant side effects include:

  • Bladder Problems: Radiation damage to the bladder and nearby tissues can result in urinary frequency, dysuria (pain with urination), and urinary incontinence. Often these symptoms will improve with time.
  • Bowel Problems: Diarrhea, rectal leakage, rectal pain, and blood in the stool are all possible side effects of RT. As with urinary side effects, the majority of these problems will resolve with time.
  • Erectile Problems: Damage to the nerves or blood vessels involved in achieving an erection may occur as a consequence of RT resulting in erectile dysfunction. This often does not develop immediately but rather over the course of years.

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Helen Boehm Johnson, MD

Helen Boehm Johnson, MD, is a medical writer who brings the experience of a residency-trained physician to her writing. She has written Massachusetts General Hospital’s Combating Memory Loss report (2019, 2020, … Read More

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