PHOTO DYNAMIC THERAPY

-LALITHA KAVYA

INTRODUCTION It form of phototherapy using nontoxic light-sensitive

compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells.

PDT has proven ability to kill microbial cells including bacteria, fungi and viruses.

In PDT, the usage of the right wavelength of the light,the correct light-sensitive compounds which are at the same time highly effective to treat the targetted tissue is an important step that needs to be followed.

INTRODUCTION-WHY PDT?• It is the best alternative for extensive surgery.

• It does not take long time.

• It is minimally invasive therefore it saves recovery time .(minimal recovery period).

• It is minimally toxic.

• Less scarring (when compared to the extensive surgery)

• Patient suffering due to pain post PDT is very minimal.

• Preparation time is also minimal.

KEY COMPONENTS• PDT has three essential components:-

1. LIGHT SOURCE

2. PHOTO SENSITIZER

3. MOLECULAR OXYGEN

• The obvious requirement for the action of PDT is a TARGET TISSUE.

KEY COMPONENTS• PHOTO SENSITISER is a substance which absorbs the

wave length of the light focussed on it and inhibits photo reaction to other normal cells surrounding the tissue.

• Use of visible and near infra red light with a photo sensitiser to treat the diseased tissue.

• The wavelength of the light source needs to be appropriate for exciting the photosensitizer to produce REACTIVE OXYGEN SPECIES. combination of these three components leads to the chemical destruction of any tissues that have been exposed to this light.

PRINCIPLEA photo sensitiser is administered to the

Targetted tissue (for example a tumor).Light is

then allowed to concentrate on this targetted

tissue which is absorbed by the photo sensitiser

and this causes the generation of reactive

oxygen species.

• Example of photo sensitisers:-

• PORFIMER SODIUM,AMINOLEVULINIC ACID

PDT-LASER

MECHANISM OF ACTION • The photosensitizer is excited from a ground singlet state

to an excited singlet state. It then undergoes intersystem crossing to a longer-lived excited triplet state.

• One of the few chemical species present with a ground triplet state is “MOLECULAR OXYGEN”. When the photosensitizer and an oxygen molecule are in proximity, an energy transfer can take place that allows the photosensitizer to relax to its ground singlet state, and create an excited singlet state oxygen molecule.

• Singlet oxygen is a very aggressive chemical species and will very rapidly react with any nearby biomolecules.

MECHANISM• Ultimately, these destructive reactions will kill

cells through apoptosis or necrosis.

• PDT can be considered a form of targeted ’singlet oxygen chemotherapy’wherethe targeting is achieved with the combination of the photosensitizer and intense light.

MECHANISM• Photosensitizer(p.s) Oxygen

Ground triplet state

Ground singlet state EXCITED SINGLET STATE

Excited singlet state

Excited triplet state

GROUND SINGLET STATE

INCIDENT LIGHT

Oxygen (excited singlet state)

P.S ( ground singlet

state)

TREATMENT-PORFIMER SODIUM• First, the porfimer sodium(photo sensitiser) is

administered intravenously into the cancer patient.

• It travels through the bloodstream and is absorbed by every cell in the body (both the normal and the cancerous cells).

• The normal cells get rid of porfimer sodium in a couple of days.But a lot of the drug stays in the cancer and normal skin cells.

• Porfimer sodium is activated or turned on by light (visible/infra red) after 2-3 days of administering it into the body.

• This gives normal cells to get rid of the drug.

TREATMENT-PORFIMER SODIUM• The doctor directs a laser light at the area of cancer

cells through a thin fiber optic glass strand.

• LASER used is a low power light so it does not burn.Itgives minimal or no pain.

• Depending on the size of the tumor,the light is given from 5-40 minutes.

• Any dead tissue left in the treated are is removed after 4-5 days.

• The treatment can be repeated.

TREATMENT-AMINOLEVULINIC ACID• Aminolevulinic acid is a topical drug applied directly

on skin to treat actinic keratosis (a pre malignant condition).

• It is a solution that is applied directly on face or scalp (unlike porfimer sodium,this does not reach other body parts).

• After 14-15 hours of application of the drug,doctorpasses BLUE LIGHT onto the area for 15 minutes.

• The area may become red,scaly and crusty for almost 4 weeks before healing.

• If the lesion does not go away completely,it can be treated again after 8 weeks.

ACTINIC KERATOSIS

PDT-ADVANTAGES AND LIMITATIONS• PDT is considered to be both minimally invasive and

minimally toxic, these advantages alone make PDT an attractive alternative.

• Compared to radiotherapy, chemotherapy and surgical operation for the treatment of cancers, PDT is in almost all cases a much cheaper alternative.

• Furthermore, post-operative recovery after PDT is typically hours or days rather than weeks.

PDT-ADVANTAGES AND LIMITATIONS

• It cannot be used to treat all types of cancers.

• The photosensitisers in some cases,might be harmful as the normal cells feed up on it and

the patient’s eyes and skin might become very photo sensitive for about 30 days.

• The skin might burn or blister or swell if exposed to direct sunlight.

• The availability of PDT is scanty as research is still going on about its applications and suitability in various geographical areas.

PDT-ITS RESULTS

PDT-ITS RESULTS

CONCLUSION• Photodynamic therapy is one of the best

techniques to cure many ailments which normal clinical techniques are inefficient in solving .

• In a few years its popularity and also availability to the common man is foreseen.

• It comes across as a very safe and potential way to solve cases of cancer, skin ailments etc.

• The awareness of photodynamic therapy is increasing rapidly and soon it will attain a position where it will be considered a “BOON” to the medical and scientific fields…

THANK YOU FOR YOUR TIME AND PATIENCE…