Radiation Therapy for Prostate Cancer: What You Need to Know

Andrew Siegel MD 9/7/2019      Prostate Cancer Awareness Month

Radiation oncology is the medical specialty devoted to the use of radiation for the treatment of patients with cancer. Radiation therapy, a.k.a. radiotherapy, utilizes high-energy x-rays that kill prostate cancer cells by damaging their DNA. Radiation can be delivered externally (from a source outside of the body) or internally (from a source within the body).  The former is known as external beam radiotherapy and the latter as brachytherapy. External radiotherapy (either alone or combined with brachytherapy) is intended as a curative therapy for prostate cancer and is the topic of today’s entry. Next week’s entry will cover brachytherapy.

 

Thank you Marijana1 at Pixabay for image above

 

Dr. Glen Gejerman, Medical Director of Radiation Oncology at New Jersey Urology

 

EXTERNAL RADIATION THERAPY

The goal of external radiation therapy is to cure prostate cancer by delivering a precise dose of radiation to a defined target while minimizing the dose to the adjacent tissues. A machine called a linear accelerator generates and directs beams of x-rays to the prostate target. The daily dose is delivered five days a week over the course of 8-9 weeks to achieve a cumulative dose sufficient to kill the cancer cells. Each daily treatment is painless and is delivered in 10 minutes or so.  An advantage of radiation therapy over surgery can be decreased side effects, with rare urinary incontinence and somewhat less erectile dysfunction.

External radiation therapy technology has undergone major refinements over the past few decades. Technology has evolved from conformal therapy that shaped the radiation beam to avoid adjacent structures, to intensity modulated radiotherapy (IMRT) that modulated the beam through various angles to further minimize the dose to adjacent organs, to the latest and most sophisticated technique—image guided radiation therapy (IGRT).

Image guided radiation therapy (IGRT) incorporates strategies to more accurately localize the prostate gland and optimize the radiation dose. Advances in radiotherapy imaging, planning and delivery systems have enabled unprecedented sophistication in the ability to target prostate cancer while sparing healthy tissue. Increasing the radiation dosage to the cancerous prostate gland has improved results and survival. Side effects are reduced because of less exposure to the bladder and rectum.

The prostate gland can move subtly in position from day to day, based upon the amount of urine in the bladder, gas and stool in the rectum and other factors. IGRT enables more precise localization of the exact position of the prostate, which reduces the radiation field. Without IGRT, the radiation field must be larger to account for the subtle changes in prostate size and movement, with the undesirable necessity for the radiation of healthy adjacent tissues. IGRT allows for fine adjustments in patient positioning to be made immediately before treatment, allowing reduced planning margins—the extra margin added to the clinical treatment volume because of uncertainties in prostate position due to prostate movement between radiotherapy treatments. Since the prostate location is precisely visualized using cone beam computerized tomography (CT) imaging, shifts in the treatment position can be made to correct for misalignment, reducing the planning margins and resulting in lower doses to adjacent tissues.

One such commonly used IGRT system is the Varian Rapid Arc system. After small gold markers (Visicoils) are implanted into the prostate gland, patients undergo CT simulation that creates 3-dimensional images of their anatomy, which allows conformal radiation planning. During the daily radiation treatment, a cone beam CT image of the prostate is obtained and by utilizing the Visicoils, fusion software allows accurate comparison of the daily prostate position to the planned position. Small shifts in the treatment position are made to correct for prostate movement, eliminating the need for wider radiotherapy margins that would expose more healthy tissues to the radiation dose.  RapidArc is a volumetric arc therapy that delivers a precisely sculpted 3-dimensional dose distribution with a single 360-degree rotation. Since RapidArc delivers treatments two to eight times faster than other systems, it is more precise and more convenient for the patient.

Aside from definitive treatment of prostate cancer, additional uses of external radiation are for adjuvant, salvage and palliative purposes:

Adjuvant radiation therapy

External radiation can be used as adjuvant therapy after prostatectomy when the pathology report demonstrates unfavorable features that incur a high risk of recurrence, including: invasion of the prostate capsule, cancer at the surgical margin, seminal vesicle invasion and/or lymph node involvement. Radiotherapy is delivered to the bed of the prostate to “sterilize” the remaining cancer cells to prevent progression and metastases.

Salvage radiation therapy

External radiation can be used as salvage therapy for those patients who develop biochemical recurrence, defined as a PSA elevation after surgery. In salvage radiation therapy, radiotherapy is delivered to the bed of the prostate to “sterilize” the remaining cancer cells to prevent progression and metastases.

Palliative radiation therapy

In addition to curative efforts, external radiation is used as palliative therapy to eliminate pain and improve skeletal integrity for those with metastatic disease to the bones. 75% or so of patients with painful bony metastases will have pain relief after palliative radiation is administered to the sites of concern.

Cyberknife is a technology originally conceived for treating brain and spinal tumors that has been adapted for prostate cancer.  Also known as stereotactic radiotherapy, it is a form of high intensity focused radiation that can be completed over a course of 5 sessions as opposed to 44 sessions of standard radiotherapy and is thus also known as hypo-fractionated radiotherapy. Its proponents claim that it is more “surgical” than standard radiotherapy, with reduced radiation dosing to adjacent organs.  A computer-controlled robotic arm swivels to shoot dozens of radiation beams from many angles, resulting in high doses that are “sculpted” to the cancer.  Although the concept of an accelerated and compressed course of radiation is convenient and inviting, data on the long-term effectiveness and urinary and bowel consequences of the Cyberknife are not yet available.

Proton beam therapy uses heavy particle beams (protons) generated by linear accelerators or cyclotrons as opposed to standard radiotherapy (that uses photons). These beams are difficult to produce and control, but possess a unique physical characteristic called the “Bragg peak” that allows for a sharp edge that can reduce the dose to tissue lying a few millimeters from the intended target. Proton therapy is excellent for tumors that are close to the surface and for tumors of the brain and spine but its long-term effectiveness for prostate cancer remains unknown. There is an increasing interest in this modality, but proton therapy remains a contentious issue in the field of radiation oncology.

Radiation therapy survival rates

Radiation therapy and RALP have similar 15-year survival rates with results being best for low risk disease and less effective for intermediate and high risk cancers. Serum PSA is widely accepted as the best marker for monitoring the effectiveness of treatment. Unlike surgery, patients successfully treated with radiation therapy still have a prostate gland and are not expected to achieve an undetectable PSA. An acceptable PSA following radiation is a low PSA (<1.0), which typically reaches its lowest point (nadir) 18-24 months after completion of therapy.

It is possible for prostate cancer cells to have spread beyond the prostate before radiation therapy, and at some point, these cells are capable of multiplying and producing a detectable PSA.  Biochemical failure is defined as 3 consecutive PSA rises over several months. In general, the shorter the PSA doubling time, the worse the prognosis.  Another definition of biochemical failure is a PSA rise of 2.0 above the lowest point. Serial PSA testing is particularly important after radiation therapy since it is possible for the PSA to “bounce” (a.k.a. “spike” or “bump”) up temporarily only to return to normal levels thereafter. This bounce phenomenon occurs most commonly with brachytherapy and usually within the first two years following the radiation.  Although the precise cause is unknown, it is theorized to be a delayed inflammatory reaction to the radiation therapy.

Radiation side effects

Radiation toxicity is divided into acute and chronic. Acute toxicity develops during the treatment period and may consist of fatigue and/or urinary frequency and irritation due to inflammation of the urethra (the channel that drains the bladder). Less commonly, patients develop frequent loose bowel movements due to irritation of the rectum. Chronic toxicity develops beyond 3 months or more after completing radiation therapy. Injury to the micro-vasculature (small blood vessels) of the organs adjacent to the prostate can cause proctitis, with intermittent rectal bleeding in 10% of patients and cystitis, with intermittent urinary tract bleeding in a small percentage of men. Erectile dysfunction occurs in 30-40% of men, which often responds to oral erectile dysfunction medications.

Fact: In the early phase, radiation induces inflammation and edema (tissue swelling) of the prostate whereas in the late phase it induces microvascular damage (damage to the smallest blood vessels), tissue hypoxemia (low concentrations of oxygen) and fibrosis (scarring).

An absorbable hydrogel spacer is a new means of providing protection to the rectum in men who opt to undergo radiation therapy for prostate cancer. The anatomic proximity of the rectum and the prostate puts the rectum at risk for radiation exposure and toxicity. This absorbable material is implanted via an injection in the perineum (area between the scrotum and the anus) into the space between the prostate and rectum. The creation of increased space between the rectum and prostate results in a reduced radiation dose to the rectum, which diminishes rectal pain and decreases long-term rectal, urinary and sexual complications. The absorbable hydrogel spacer lasts over the course of the radiation therapy and thereafter is gradually resorbed by the body. The only prostate cancer spacing device that is approved by the FDA for use in the USA is SpaceOAR, which uses polyethylene glycol as the spacing material.

Advantages of external radiotherapy:

• Excellent cancer control without major invasive surgery and anesthesia
• Can treat locally-advanced cancer that extends beyond the prostate
• Outpatient
• Less urinary control side effects than surgery
• Can be used for men who have had prior prostate surgery and a local recurrence

Disadvantages of external radiotherapy:

• Need for multiple treatment visits to the radiation center
• Technically-challenging procedure requiring sophisticated equipment and multidisciplinary interactions among radiation oncologists, radiologists, medical physicists and computer planners
• Leaves prostate intact (as opposed to completely removing the diseased organ)
• Short-term side effects: fatigue, urinary frequency and frequent bowel movements
• Long-term side effects: possible bladder bleeding and irritative lower urinary tract symptoms (radiation cystitis), rectal bleeding and irritative bowel symptoms (radiation proctitis) and erectile dysfunction
• If radiation fails, “salvage” prostatectomy is possible but is a more challenging surgery with more significant side effects because of scarring around the prostate gland; other options for radiation failure are androgen deprivation therapy, cryosurgery and high intensity focused ultrasound
• Small increase in secondary cancers including those of the bladder and rectum

Wishing you the best of health,

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Dr. Andrew Siegel is a physician and urological surgeon who is board-certified in urology as well as in female pelvic medicine and reconstructive surgery.  He is an Assistant Clinical Professor of Surgery at the Rutgers-New Jersey Medical School and is a Castle Connolly Top Doctor New York Metro Area, Inside Jersey Top Doctor and Inside Jersey Top Doctor for Women’s Health. His mission is to “bridge the gap” between the public and the medical community. He is a urologist at New Jersey Urology, the largest urology practice in the United States.

The content of this entry is excerpted from his new book, PROSTATE CANCER 20/20: A Practical Guide to Understanding Management Options for Patients and Their Families

Video trailer for Prostate Cancer 20/20

Preview of Prostate Cancer 20/20

Andrew Siegel MD Amazon author page

Prostate Cancer 20/20 on Apple iBooks

Dr. Siegel’s other books:

FINDING YOUR OWN FOUNTAIN OF YOUTH: The Essential Guide to Maximizing Health, Wellness, Fitness and Longevity

PROMISCUOUS EATING— Understanding and Ending Our Self-Destructive Relationship with Food

MALE PELVIC FITNESS: Optimizing Sexual and Urinary Health

THE KEGEL FIX: Recharging Female Pelvic, Sexual, and Urinary Health

 

 

 

 

 

 

 

 

Tags: adjuvant radiation, Andrew Siegel MD, palliative radiation, prostate cancer, Prostate Cancer 20/20, prostate radiation therapy, salvage radiation