PDT Norfolk and the Norfolk and Waveney Prostate Cancer Support group hosted a talk by Stephen G Bown (Emeritus Professor University College London)
and in conversation with Dr Ian Gibson (Honary Senior Lecturer Norwich Medical School) on 4 September 2017 at Norfolk and Norwich University Hospital.
A Summary of the talk follows:
Photodynamic Therapy (PDT) for prostate cancer
Prostate cancer is a common disease, but there is considerable variation in its aggressiveness between patients. In some cases, no active treatment is required at the time of diagnosis and “active surveillance” (regular checks to see that the disease is not progressing) is a perfectly acceptable course of management. However, many patients are uncomfortable knowing that they have an untreated cancer on board.
There are two main ways of treating prostate cancer – radical surgery and radical radiotherapy (external and brachytherapy). Both have been in routine use for many years and control the disease effectively, but both are associated with a significant risk of incontinence and/or impotence. These risks have fallen as techniques have improved, but both surgery and radiotherapy involve ablating the whole gland and neither can be readily repeated for localised persistent or recurrent disease after treatment.
Recent developments have explored options for repeatable, focal treatment – mapping out the extent of disease within the gland and just treating the cancerous areas. Until recently, mapping cancer in the prostate could only be done by taking multiple biopsies, although this is now possible with MRI (magnetic resonance imaging), which is much simpler than taking biopsies and is non-invasive. Techniques for minimally invasive, focal treatment include HIFU (High Intensity Focused Ultrasound), cryotherapy (freezing the tissue) and PDT (Photodynamic Therapy), which has attracted much attention recently.
PDT involves the intravenous administration of a drug (a photosensitiser) that makes tissue sensitive to light. Light (usually from a laser) can be delivered to the prostate using thin optical fibres that are passed through needles inserted through the skin between the scrotum and the anus, under guidance from an ultrasound probe positioned in the rectum (which is immediately adjacent to the prostate). The photosensitiser has no effect in the absence of light of a colour appropriate to the absorption characteristics of the photosensitiser (red or near infra-red). The area of tissue destruction around a single fibre in the prostate is about 1.5cm in diameter, so in most cases, more than one fibre is required.
There are several specific advantages of PDT. The most important are:
It does not involve ionising radiation so can be repeated
It can be used in areas that have already received the maximum safe dose of radiotherapy.
The volume of tissue ablation is reasonably predictable, so the effect can be limited to cancerous areas of the prostate.
The risk of impotence or incontinence is much less than after surgery or radiotherapy.
It is minimally invasive (no open surgery, so potentially a day case treatment)
The first image guided PDT for prostate cancer was undertaken in University College Hospital, London, (UCH) in 1996. The first group of patients were those with localised recurrent disease after radical radiotherapy. The treatment proved safe with reduction in PSA (prostate specific antigen) in almost all. Many further studies since then culminated in a major trial involving more than 400 patients in 7 European countries (mainly France), led from University College London (UCL). This trial compared PDT with active surveillance in patients with newly diagnosed early cancer. After 2 years, disease progression was twice as common in the surveillance group as in the PDT group. As a result of this trial, PDT for prostate cancer is approved for routine use in Mexico in appropriate patients and European approval is anticipated in the next few months. If it is approved, its availability is likely to spread relatively slowly as more urologists get familiar with the technique.
PDT is not the answer for all prostate cancers, but may allow more men to consider it as a tissue preserving approach that could delay or avoid the need for later radical therapy.
Stephen G Bown MB, BChir, MD (Cantab), AM (Harvard), DSc (Hon. Lucknow), FRCP Emeritus Professor of Laser Medicine & Surgery University College London