Originally published 1/20/2015
It’s been seven years since we posted the blog below, and in today’s medical fields, lasers are used therapeutically to treat a broad spectrum of disease as well as cosmetic conditions. It’s worth a brief review of the different types of lasers, as well as their areas of application. As summarized by the Johns Hopkins website, lasers are now commonly used to debulk or destroy tumors, to seal blood vessels to diminish blood loss, in some eye surgeries and dental procedures, and to treat skin imperfections or lesions.
Clinical use of lasers takes advantage of tissues’ light absorption. Different types of lasers will create different types of changes in the tissues: physical, mechanical, chemical, temperature or a combination. There are two broad categories of medical lasers. The first, called wavelength-dependent, can be subdivided as follows:
- Photothermal reactions are based on heat, which diffuses into neighboring tissues at controllable depth. Depending on the laser device, heat can be used to vaporize, coagulate, or cut tissue. In the case of MRI-guided Focal Laser Ablation, technically called laser interstitial thermal therapy, a laser fiber inserted into the PCa tumor precisely destroys (ablates) the tumor while monitored by MRI thermometry, and the zone of ablation can be confirmed by MRI immediately afterward.
- Photochemical reactions do not create significant heating but cause molecular fragmentation by rupturing electronic bonds. These types of laser therapies include photodynamic therapy (for prostate tumors, the light-sensitized pharmaceutical TOOKAD is used), biostimulation or Low Level Laser Therapy (stimulate regeneration of soft tissues, promote pain relief), photoablation (destroy tissues without significant heat),
The second type, wavelength-independent, may be used for clean and precise surgery.
It’s safe to predict that the array of lasers and their uses will continue to increase, thanks to ongoing research and development. The ability to harness and convert light itself into a clinical tool is truly one of the wonders of medical science.
Today’s focal laser ablation (FLA) is accomplished by using MRI guidance to insert optical fibers directly into the tumor. Sometimes patients get confused about the difference between this type of therapy and something called Green Light Laser, a treatment to correct the constriction of the urethral passage caused by benign (noncancerous) prostate enlargement called benign prostatic hyperplasia (BPH).
To understand the difference, it’s important to know that different types of laser, at various wavelengths, have distinct effects in tissue. As a form of light, laser is absorbed by tissue where it is converted to heat. One effect is to vaporize it (Green Light Laser) with an aiming beam of laser; this method takes advantage of the high water content in prostatic tissue, and the tissue literally becomes vapor or tiny bubbles of gas. The other effect causes the tissue to coagulate spherically around the tip of a laser fiber; this leaves scar tissue in the body. (FLA).
BPH is a normal condition that occurs as men get older. Many men undergo urinary symptoms (frequent urge to urinate, difficulty passing urine) if the enlarged gland starts constricting the urethra that passes through it from the bladder to the penis. Green Light Laser (also called Photoselective Vaporization of the Prostate, or PVP) is an alternative to surgical cutting away of tissue (transurethral resection of the prostate, or TURP—what patients used to call “reaming out”). It relies on a non-contact beam laser called potassium-titanylphosphate (KTP) at high laser energy and density to create a very high temperature. The Green Light procedure is done under anesthesia, using direct visual guidance. The doctor inserts a scope that allows him to directly see the inside of the bladder and urethra. He then inserts the laser probe into the scope, and watches as he aims and “fires” the light at the tissue. He can see in real time as the tissue is literally obliterated, effectively carving out a larger urethral passage working backward from the bladder. Because the light doesn’t penetrate very far into the tissue, he has precise control over the size of the passage he’s creating. The advantage over surgery is the procedure is virtually bloodless, as the high temperature seals off blood vessels. This means quicker recovery time with few complications compared to TURP. Success is reflected by the patient’s ability to urinate normally.
FLA, on the other hand, uses a diode laser generator which requires much less energy, and creates temperatures high enough to destroy living tissue (range 70-85° Celsius) but not so high as to vaporize or char it. Ablation is accomplished by using MRI guidance to insert a very thin optical fiber directly into the core of a cancerous tumor, where it is in physical contact with the tissue. When the laser is activated it immediately creates a growing sphere of lethal heat that can be seen and tracked on a monitor; the thermal effect on tissue can also be seen on MRI during and after ablation. Unlike the Green Light laser beam, which is constantly being moved by the doctor as the urethra is enlarged, the FLA fiber remains in place for the few minutes it takes to accomplish the ablation. What happens to the tissue affected by the laser is a coagulation of the cell proteins into a sort of dry, small harmless mass, most of which is slowly reabsorbed by the body. In addition, the tumor’s blood supply is also destroyed. Once the laser is deactivated, the fiber is withdrawn from the patient’s body. The success of the ablation can be monitored over time using periodic MRI to make sure no cancer has come back in the zone that was treated.
Thus, two different technologies create two different types of prostate treatment.