Sperling Prostate Center

How Does Radiation Kill Prostate Cancer?

Radiation as a prostate cancer treatment is an alternative to surgery, especially for patients whose age or other health conditions means they’re not good candidates for surgery. There are other reasons for choosing radiation, especially among men who don’t like what they learn about the potential urinary and sexual side effects of prostatectomy or a whole gland ablation.

Radiation is in a category all by itself

Radiation is unique among PCa treatments because it’s not an instant cancer-killer. Slow cancer death over time sets radiation apart from treatments that have immediate effect:

  • Radical prostatectomy – assuming PCa is confined to the gland, when the surgeon removes the prostate from the body, the cancer is immediately gone.
  • Ablation (tumor destruction inside the body) – assumes the tumor plus safety margin are encompassed within a zone of lethal heat or cold, at which point the cancer cells are immediately physically destroyed.

With radiation, cancer cells are NOT immediately destroyed. In fact, radiation does not directly cause cell destruction. Why do you think beam radiation is delivered daily over a period of weeks, or implanted radioactive seeds (brachytherapy) are permanently left in the gland? It’s because radiation exposure over time gradually stresses and damages the cell’s DNA so the cell can no longer reproduce itself. As the radiated cells die off, the tumor very gradually shrinks.

Furthermore, imaging cannot reveal how well the radiation is working, or even if the targeted tumor is the only area affected. Even with the excellence of today’s MRI, CT and CT-PET scans, the success of treatment can’t be seen while it’s happening. In effect, radiation takes blind faith, but when it’s appropriately matched to a patient’s risk level, radiation has comparable statistical success with prostatectomy. Thus, we know it works.

However, unlike ablation which can be monitored during treatment so the zone of destruction does not overextend into neighboring tissues, all radiation—even brachytherapy and proton beam—has some scatter that can cause collateral damage. While it’s true that healthy cells are more radiation-resistant than their more vulnerable cancerous cousins, no cell is 100% radiation-proof. This is why late onset rectal, urinary and sexual side effects can occur after radiation, including increased risk for secondary bladder and colorectal cancers years down the line. It also explains why salvage prostatectomy for radiation recurrence is a difficult surgery – radiation causes fused scar tissue in the radiation zone.

Roughly 30-35% of PCa patients can qualify for a focal therapy, meaning destruction of the tumor while sparing healthy prostate tissue. Neither focal surgery nor focal radiation is feasible, so focal treatment is done using ablation. The Sperling Prostate Center offers MRI-guided Focal Laser Ablation (FLA) of prostate tumors. We carefully qualify patient candidates starting with multiparametric MRI (mpMRI) to define the location, size, shape and aggressiveness of low-to-intermediate risk PCa tumors. We then perform an in-bore MRI-guided targeted biopsy, in order to diagnose the exact nature of a patient’s disease to confirm that the cell line is amenable to ablation—in this case, using lethal heat generated by the effect of laser light on tissue.

Finally, under real time MRI guidance, a laser optic fiber is inserted precisely into the core of the tumor. As the laser light is deployed, it immediately creates a lethal temperature to destroy cancer. As the zone of laser heat expands, we monitor the size, shape and region of destruction in real time using special MRI thermometry. Finally, within minutes of the ablation, mpMRI gives us visual confirmation that the tumor cells and their blood supply have been vanquished. This is not possible with radiation.

Here’s a summary of treatment features using a side-by-side chart:

Radiation Focal Laser Ablation
Cancer cells die off over time as their DNA is damaged – could take up to 18 months Cancer cells are immediately destroyed by heat. By the end of treatment, PCa is gone.
Not possible to track effect using imaging Zone of destruction tracked in real-time on MRI
Effectiveness not known for several months, and then only when PSA reaches its nadir (lowest point), possibly up to 18 months Effectiveness confirmed after ablation by MRI
Scatter effect may create collateral damage to neighboring structures (bladder, neurovascular bundles, colorectal tissues) Laser precision plus real-time monitoring means low risk of damage to urinary, sexual or rectal tissues
Hardy PCa cells that survive radiation may mutate into more aggressive disease Laser-generated heat kills cells within the zone of destruction. Cells encompassed by laser have very low likelihood of survival or mutation

Having said all that, there are PCa patients for whom beam radiation or brachytherapy is the best choice, given their disease and lifestyle wishes. The purpose of this blog is not to diminish the importance of treatment matching when all factors are taken into account. Rather, the purpose is to help patients understand that the unique mechanisms of radiation should not be confused with the nearly-instant mechanisms of ablation. Trying to compare slow cell death over many months (radiation) with immediate tumor/blood supply destruction (FLA) is like trying to compare a horse-drawn carriage to a racecar.

For more information, or to learn if you may be a candidate for Focal Laser Ablation for prostate cancer, contact Sperling Prostate Center.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.
 

About Dr. Dan Sperling

Dan Sperling, MD, DABR, is a board certified radiologist who is globally recognized as a leader in multiparametric MRI for the detection and diagnosis of a range of disease conditions. As Medical Director of the Sperling Prostate Center, Sperling Medical Group and Sperling Neurosurgery Associates, he and his team are on the leading edge of significant change in medical practice. He is the co-author of the new patient book Redefining Prostate Cancer, and is a contributing author on over 25 published studies. For more information, contact the Sperling Prostate Center.

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