Apparatus and method to monitor photodynamic therapy (PDT)

• US 6,128,525 A
• Filed: 07/29/1997
• Issued: 10/03/2000
• Est. Priority Date: 07/29/1997
• Status: Expired due to Fees

• Current Assignee: Derma Art Technologies, Inc.
• Original Assignee: Derma Art Technologies, Inc.
• Inventors: Zeng, Haishan, Lui, Harvey, McLean, David I., MacAulay, Calum, Palcic, Branko
• Primary Examiner(s): Lateef, Marvin M.
• Assistant Examiner(s): Imam, Ali M.
• Application Number:
  US08/901,999
• Time in Patent Office: 1,162 Days
• Field of Search: 372/21, 372/22, 372/23, 606/10, 606/16, 606/14, 382/133, 382/191, 600/476, 600/317
• US Class Current: 600/476
• CPC Class Codes: A61B 1/043 for fluorescence imaging
• CPC Class Codes: A61B 18/20 using laser
• CPC Class Codes: A61B 2018/00904 Automatic detection of target tissue
• CPC Class Codes: A61N 2005/0644 Handheld applicators
• CPC Class Codes: A61N 5/062 Photodynamic therapy, i.e. excitation of an agent
• CPC Class Codes: A61N 5/067 using laser light

Abstract

A method and apparatus for controlling the dosimetry of a photodynamic therapy that involves exposing a site to be treated to treatment light in order to generate toxic products at the site and other photoproducts. Often a photosensitizer drug is administered to the patient prior to treatment or the therapy relies on the presence of endogenous photosensitizers. The method comprises the steps of selecting a photoproduct having an identifying characteristic, which can be a fluorescence peak, and monitoring the photoproduct using the identifying characteristic (e.g. fluorescence) to determine the level of the photoproduct being generated. The photodynamic therapy is then terminated when the photoproduct being monitored reaches a predetermined level. The method allows for safe treatment of a site using photodynamic therapy and ensures that overexposure to treatment light leading to damage of normal tissue or underexposure leading to ineffective treatment of the lesion does not occur. Apparatus for automatically carrying out the method is also provided.

Claims

1. A method for controlling the dosimetry of photodynamic therapy (PDT) that involves exposing a site to be treated to treatment light in order to generate toxic products at the site and other photoproducts, comprising the steps of:

selecting at least one photoproduct such that the photoproduct has an identifying characteristic comprising a peak in a fluorescence spectrum of the at least one photoproduct and such that the level of the photoproduct being generated is proportional to the toxic effect of the PDT therapy;

monitoring the at least one photoproduct using the identifying characteristic to determine the level of the photoproduct being generated, the monitoring performed by a) exposing the treatment site to an excitation light;

b) capturing resulting fluorescence images by i) capturing a first fluorescence image over a narrow wavelength band around the peak in the fluorescence spectrum of the photoproduct;

ii) capturing a second fluorescence image over a wavelength band adjacent to the photoproduct peak and remote from any other PDT fluorescence peaks; and

, iii) dividing the fluorescence image captured in step i) by the fluorescence image captured in step b) to obtain a ratio image;

c) analysing the captured fluorescence images to determine the level of the at least one photoproduct by i) obtaining the ratio image of the site before exposing the site to treatment light; and

, ii) dividing each ratio image acquired during PDT treatment by the ratio image of step a) to determine the distribution at the site of the levels of the at least one photoproduct;

d) repeating steps a), b), and c) at set intervals;

terminating the photodynamic therapy when the at least one photoproduct being monitored reaches a predetermined level; and

,

modifying the distribution of the treatment light at the site based on the distribution at the site of the levels of the at least one photoproduct by controlling a light valve in the path of the treatment light to regulate how much treatment light will be received by different areas of the treatment site, wherein the light valve is a digital micromirror device.

2. Apparatus for controlling the dosimetry of photodynamic therapy that involves exposing a site to be treated to treatment light from a treatment light source in order to generate toxic products at the site and other photoproducts, at least one of the photoproducts being generated at levels proportional to the toxic effect of the PDT therapy and having an identifying characteristic comprising a peak in a fluorescence spectrum of the at least one photoproduct, comprising:

means for monitoring the identifying characteristic of the at least one photoproduct to determine the level of the photoproduct being generated, the means for monitoring comprising a light source for generating excitation light, means for delivering the excitation light to the site to be treated, means for capturing resulting fluorescence images comprising a CCD camera, and processing means for analysing the captured fluorescence images to determine the level of the at least one photoproduct wherein the processing means comprises a computer program to analyse the fluorescence images by generating a ratio image at predetermined intervals during PDT treatment according to the following steps;

a) measuring a first fluorescence image over a narrow wavelength band around the peak in the fluorescence spectrum of the photoproduct, b) measuring a second fluorescence image over a wavelength band adjacent to the photoproduct peak and remote form any other PDT fluorescence peaks, c) dividing the fluorescence image captured in step a) by the fluorescence image captured in step b) to obtain a ratio image of the treatment site, and d) dividing the ratio image of the site acquired at a predetermined interval by a ratio image of the site before exposure to treatment light to determine the distribution at the site of the levels of the at least one photoproduct;

means for terminating the photodynamic therapy when the at least one photoproduct being monitored reaches a predetermined level;

a computer to control the means for monitoring and the means for terminating the photodynamic therapy; and

a light valve positioned in the path of the treatment light to regulate the areas of the site that receive treatment light in response to control signals from the computer based on the distribution at the site of the levels of the at least one photoproduct, wherein the light valve is a digital micromirror device.