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How Deep Does Light Penetrate? It is sometimes asserted that light cannot penetrate the human body more than a few millimeters. Therefore, skeptics say, it is impossible to perform photodynamic therapy (PDT) for deep-seated tumors. Yet this statement contradicts common-sense experience. If you put an ordinary light, such as a laser pointer, up to your fingers, you can see the red light penetrate right through the bone and out the other side. Even with a light source as weak as a flashlight, if you shine it on your palm in a darkened room, some red light will emerge through the other side. The ability of light to penetrate tissues to depths much greater than a few millimeters has been confirmed scientifically. Dr. Harry T. Whelan of the Medical College of Wisconsin and NASA's Marshall Space Flight Center in Huntsville, Alabama, is an expert on the use of light-emitting diodes in medicine. He writes: "Spectra taken from the wrist flexor muscles in the human forearm and muscles in the calf of the leg demonstrate that most of the light photons at wavelengths between 630 and 800 nanometers (nm) travel 23 centimeters (cm) through the surface tissue and muscle between input and exit at the photon detector." Twenty-three centimeters is 9 inches. Logically, therefore, if you illuminate the whole body, front and back, light in the range of 630 to 800 nm can reach almost any part of the human body. This is roughly the range of wavelengths that photosensitizers absorb. Light is visible to the human eye as the colors of the rainbow, which have wavelengths ranging from 400 to 700 nm. Red light has the longest wavelength, ranging from 622 to 700 nm. Light at wavelengths greater than 700 nm is characterized as infrared. Most experimental and commercial photosensitizers absorb light in the range of 630 to 820 nm. For instance, Photofrin (which is approved by the Food and Drug Administration to treat several forms of cancer) absorbs light at 630 nm. ALA (Levulan) also absorbs at 630 nm. The experimental chlorin derivative Foscan absorbs at 652 nm. Visudyne, which is FDA approved for the treatment of macular degeneration, absorbs at 690 nm. Another chlorin derivative, SQN-400, absorbs in the infrared range at 740 nm. And certain bacteriopurpurins absorb light as high as 800 to 820 nm. PhotoFlora, the agent used in Cytoluminescent Therapy (CLT), is a chlorin derivative with an intensive absorption band at 663 nm. It also has an intense fluorescence reaction on tumors in the range of 658 to 688 nm. I believe that this agent is also metabolized in the body so that it absorbs at even higher wavelengths. Thus, the claim that photodynamic therapy is useful only for superficial tumors seems to me to be based on old thinking. It is based on the experience with first-generation photosensitizers such as Photofrin. Second-generation agents, particularly the green agents based on chlorin, have the potential to treat deeper tumors, even when the light is applied externally. ========= CLT Progress Report Patients who undergo successful cancer treatments often experience a period of intense malaise as the body struggles to rid itself of large amounts of dead tissue. This flu-like syndrome is particularly common with certain immune-based therapies such as interferon-alfa or interleukin-2. The same phenomenon is now being seen with Cytoluminescent Therapy (CLT). As Dr. William Porter, director of the CLT program at East Clinic, has said, "The inevitable breakdown of tumor presents a major challenge to the body. The extent of this challenge obviously is proportionate to the tumor load of each individual but for most patients it is present to greater or lesser degrees." Symptoms may include: --Tiredness --Chills and fever --Flu-like symptoms --Inflammation and/or irritation in areas of tumor breakdown --Discomfort in areas of tumor breakdown --Night sweats Patients with metastases in the lungs may experience productive coughing. Patients with liver or peritoneal spread of tumor may show signs of abdominal tenderness, discomfort or pain. These can be present for anywhere from two to six months depending on tumor load. Dr. Porter also says, "We find that it is sometimes difficult for people to be patient with this process but it is, after all, the essential desired effect and reason for doing the therapy in the first place." Having a truly sympathetic physician who is willing to assist the patient through this process is crucial to the success of this treatment. The steady support of a loving network of friends and family is also important. Above all, during this critical period, patients must not lose faith in the treatment and stop taking the oral medication, for this would interrupt the process of killing cancer cells. Who Should Not Attempt This Treatment Although the treatment itself is very easy on most patients, the aftereffects can be arduous. Therefore CLT is not for everyone. Certain individuals should definitely not attempt to undergo this treatment, including patients: --who are bedridden, non-ambulatory, or confined to wheelchairs --who are on supplemental oxygen most or all of the time and are too sick to travel --who are suffering from severe cachexia (the wasting syndrome) --who have had stents implanted for pancreatic or bile duct cancer --whose tumors compromise a major blood vessel (tumor breakdown could lead to hemorrhaging) --whose tumors involve the spinal column (removal of the tumor could lead to collapse of the vertebrae) --with the disease known as porphyria (a light-sensitizing condition) --who are clinically depressed (and are unlikely to follow through with treatment) --who are under the age of 18 --who are pregnant or contemplate getting pregnant within one year of undergoing treatment (as with most drugs, the effects of CLT on pregnancy are unknown) It is extremely important to understand that the final determination of who can, or cannot, be treated with CLT remains, legally and ethically, with4 the medical director of the clinic at the time the patient arrives. If the doctor determines that it is inadvisable to treat the patient, then the fee (minus administrative expenses) is immediately refunded. However, it is far better to avoid this possibility by strictly adhering to the inclusion criteria and informing the clinic of any significant change in one's health status. All patients are requested to come with a single companion to provide physical and moral support. Companions are not allowed in the treatment area (where potentially dangerous lasers are in use), although they are welcome to attend a variety of recreational, supportive and educational functions. [...] References Quote from Dr. Harry T. Whelan: http://www.mcw.edu/whelan/html/2 ------------------------------------------------------- Ralph W. Moss, Ph.D. Weekly CancerDecisions.com Newsletter #66 12/25/02 ------------------------------------------------------- PDT for Liver Metastases? A small study from Germany suggests the potential efficacy of photodynamic therapy (PDT) in the treatment of liver metastases. Results of this study were presented at the annual meeting of the Radiological Society of North America in December 2002. A research team led by Kerstin Engelmann, MD, of Johann Wolfgang Goethe University in Frankfurt-am-Main, treated five patients using a photosensitizing drug called SQN 400. This agent, manufactured by Scotia QuantaNova (SQN), is activated by infrared light at a wavelength of 740 nanometers. SQN 400 is the trade name of a chemical called meta-tetra(hydroxyphenyl) bacteriochlorin (mTHPBC), which is a chemically modified form of chlorophyll, or chlorin. All patients in the study had colorectal cancers that had spread to the liver, and all had been treated previously with chemotherapy. One had also received radiation therapy, and another had undergone the surgical removal of half his liver. Laser light was delivered through a catheter five days after the injection of the photosensitizer. Dr. Engelmann reported complete destruction of the cancer in three of five patients at follow-up examination three months after treatment. There were some serious side effects with SQN 400. Patients had to avoid bright electrical light for several days and direct sunlight for four weeks following treatment, due to the drug's photosensitizing effect and its slow elimination from the body. Three of the five patients reported local pain during injection. One reported that pain then spread to the shoulder. Several patients experienced minor burns. There are some significant differences between PDT using SQN 400 and Cytoluminescent Therapy (CLT) using PhotoFlora. PhotoFlora is absorbed and eliminated more quickly, and therefore has fewer side effects and less discomfort. Also, the source of light in CLT is whole-body red and infrared light that is administered externally, not through fiber optic catheters, making for a noninvasive procedure. Despite the differences, this study does show that the combination of light at high wavelengths and green chlorin-based photosensitizers is a promising cancer treatment. In the authors' words, "This pilot study establishes that the procedure…can eliminate metastatic liver tumors in some patients." But as they properly point out, more study is needed to see how useful the treatment is when compared with other ways of