Photodynamic Therapy

Photodynamic is literally a treatment that uses nontoxic “light ray” that shoots out from lasers to terminate cancerous cells. It is not like burning the cancerous cells by laser beams, as many generally imagine. According to Dr. Usuda、“ with PDT, it is not like burning the cancer cells with high volume of lasers. What we are actually doing is we kill the cancer cells with low level of lasers together with using photosensitizers because with these, we create specific excited state of photosensitizers to kill the cancer cells. It is recognized as a treatment that is both minimally invasive and least toxic.

In other words, we inject photosensitizer intravenously. Four to 6 hours later, the photosensitizer accumulates at the cancer cells, and the tumor is irradiated by low power laser beam using bronchscpe. The photosensitizers are excited and singlet oxygen is induced. The singlet oxygen directly kills cancer cells by apoptosis and/or necrosis, and damages microvasculature around the tumors and induces thrombus formation. Moreover, PDT can activate and suppress the immune response.
This is the mechanism of the treatment PDT” .

Among the chemical substances, “ porphyrin” is a chemical compound that has a property that is easy to accumulate in a cancer cell. Also this chemical compound has a strong response to light and thus when exposed to light, it absorbs the light energy and becomes excited state. Thus, as a result of this, the activated oxygen is produced which degenerates cancer cells to become necrosis and apoptosis.

This PDT is not only recommended in Japan but also in the US, Canada and the Great Britain for treating early stage non-small cell lung cancer that is located around pulmonary hilar lesion. PDT was first approved for centrally located early lung cancers in 1994, and in 2010 PDT was approved for the improvement of the respiratory tract obstruction caused by advanced lung cancers, for the improvement of the quality of life (QOL), and for progressive lung cancer.

As PDT exercises minimal invasiveness, it can be performed with safety. Also its high effectiveness has been proven by its clinical tests. To be sure, the effectiveness of PDT against early lung cancer that was found in the central types of the lung that is less than 1cm in size, can terminate the cancer completely, the CR rate (Complete remission / complete response rate) was said to be as high as 95%.

In this way, when it comes to early lung cancer that is located in the central part of the lung which is the pulmonary hilar lesion, PDT is becoming to be the standard treatment; however, Dr. Usuda wants to make further progress so that PDT can be used for the treatment of other areas of the lung other than the entrance part, such as the peripheral lung.

A trial for using PDT for the treatment of peripheral area of small-sized lung cancer continues to increase

Excision of lobe of the lung would be the usual standard treatment for early-stage small-sized lung cancer that would not only treat cancer but also would remove a great part of lung together with the cancer. However, when the diameter of the cancer is less than 2cm, and the peripheral lung cancer’s image is like a CT image of “ground glass opacity”; we have been asking ourselves, tells Professor Usuda, “ from the past ten years accumulated knowledge and experiences, we need not to perform excision of a lobe of the lung. We could afford to treat it by removing just a little. We little by little began to understand more.”

In order to support this situation, Professor Usuda began to do extensive clinical research on PTD treatment towards patients who are impossible to receive operation on their peripheral lung cancer. Professor Usuda stated, “ we have high expectation of PDT treatment that in the near future, PDT would proved to be very safe and effective towards peripheral lung cancer as well and we would be able to contribute to many patients with PDT treatment.” He continues, “ especially because PDT can be used repeatedly unlike radiotherapy, and PDT does not have side effects like the ones you get by chemotherapy. Therefore, we have much hope in PDT treatment as it is minimally invasive as well.”

Also Professor Usuda took advantage of the “Virtual Brochoscopy” in treating peripheral lung cancer by PDT. Having led by the VB screen, he was able to develop a method to establish the course to the peripheral lesion. However, up until today, there had been no thin fiber that can actually reach the peripheral area even when the route to the peripheral lesion is detected.

Thus, Professor Usuda collaborated with an independent administrative agency called “Japan Atomic Energy Agency” and developed the compound model optical fiber of a diameter of 1mm . According to Professor Usuda, “ this fiber of a diameter of 1mm, has the system which transmits an image and a system to irradiate a laser beam simultaneously. In short, it can shoot laser beam at the same time as you see the image. It is a fantastic devise.”

Lastly, Professor Usuda stated, “ As Japan is going into the era of super aging society, both the country and the patients want minimal invasiveness as well as lower cost treatment. Also we aim to give treatment that can retain the respiratory function. We will continue to strive to do our utmost so that our research and clinical application will benefit our patients as much as possible.