Photodynamic Therapy Delivery System

Transcription

1 Photodynamic Therapy Delivery System Design Team Cobi Ben-David, Mike Bernatzky, Ryan Donovan, Simon Ioffe, Andrew Zamsky Design Advisor Prof. Beverly Jaeger Abstract Design Consultant Prof. Andrew Gouldstone Photodynamic therapy (PDT) is a non-invasive medical procedure that uses a combination of pharmaceuticals and light energy to eliminate targeted biological material. The Federal Drug Administration (FDA) has approved PDT for use in oncology, dermatology and other medical treatments. However, the current standards for PDT delivery systems and their administration procedures have some drawbacks and limitations, which have been identified through a series of clinician and subject matter expert consultations. The PDT devices on the market are only designed for specific body parts, target a limited number of potential applications, and tend to cause unnecessary patient discomfort. These shortcomings can be addressed by engineering a new PDT delivery system with a refined administration procedure. These design changes will result in a versatile device that will improve the quality of human life through addressing the aforementioned issues, as well as provide a valuable tool for researchers developing new applications of PDT. For future reference, Figure 1 below depicts the PDT process. Figure 1. Process depiction for photodynamic light therapy using a photosensitizing agent. For more information, please contact bkjaeger@coe.neu.edu. 95

2 The Need for Project A successful design will address the shortcomings of existing devices and allow for the modularity needed to improve the quality of life for the millions of people suffering from treatable dermatological ailments. Photodynamic therapy (PDT) is a dermatological treatment that has proven to be effective for skin conditions like acne and actinic keratosis that affect millions of people worldwide; PDT has even shown promise as a targeted oncological procedure. Today however, the administration of PDT requires expensive, single-purpose, difficult to use equipment. Patients have complained about discomfort, burning, and claustrophobia related to the existing devices. The current delivery methods have hindered the use of PDT in promising new fields and applications, disallowing an FDA-approved effective, cutting-edge procedure from reaching its potential. The goal of this project is to address the shortcomings of existing industry equipment, and to advance the versatility of these devices to meet the versatile and dynamic needs of clinicians, doctors, and researchers. A successful design will broaden accessibility of PDT through a low-cost design that decreases patient discomfort without sacrificing the effectiveness of the treatment. The design must feature adjustable optical qualities and versatility with respect to physiological treatment areas. This will allow one device to replace many and more importantly allow PDT to be administered to multiple parts of the body that previous devices couldn t treat. All of these objectives are aimed toward the ultimate goal of improving the quality of life for people suffering from treatable dermatological conditions and other medical pathologies. The Design Project Objectives and Requirements The objective is to design a PDT device that is flexible in application, comfortable for the patient and easy to use by clinicians. Design Objectives Before creating the design, several objectives were established that would allow the efficacy of a final design to be evaluated. An imperative design goal is to achieve a meaningful level of flexibility and modularity for the proposed device. The medical device will need to be able to treat all of the common body areas where PDT is needed and has been shown through research- to be clinically effective. Further, the design needs to minimize patient discomfort caused by the applied photosensitizing agent when activated by the light components. It also should consider possible claustrophobia experienced by some 96

3 patients. Another objective is to make the device easy to use for clinicians in terms of safety, set-up, and treatment settings. Design Requirements To meet the design objectives, the device will be designed modularly with standardized dimensions and materials for easy assembly, repair, and interchangeability of components. To maximize patient comfort and flexible applications, anthropometric data will be incorporated in the design metrics to conform to human dimensions for optimal comfortable applications. Incorporating feedback from clinicians and usability studies will ensure ease of use for clinicians. Design Concepts Considered The device will consist of a light source containing the clinically established and FDA-approved wavelength of 417nm ±5nm coupled to a delivery system. These three design concepts contributed to the group s final design synthesis, achieving design goals to improve patient comfort, ease of use, and modularity. Cast Design with End-Glow Fiber Optics This design consisted of a solid outer shell that conformed to a patient s extremity. The shell housed an array of end-glow fiber optic cables. Using end-glow cables would cause varying intensity in the light that shines on the patient s skin. It would not be possible to use this design on multiple parts of the body unless an entirely new cast was made. This would reduce the versatility of the device, an important design goal. This conceptualization contributed to further ideation. Flexible LED Array This design is a variation of what is most commonly used in PDT devices, panels of LED arrays. This would be a large flexible array of LEDs instead of the usual smaller flat panels. The problem with this design is the heat that is caused by the LEDs. To reduce the burning sensation associated with PDT the group decided to keep the heat production source further away from the patient. 97

4 Liquid Pouch Design One of the early design concepts considered was comprised of a flexible pouch filled with an inert transparent liquid that would convey required light wavelengths. This design allowed for flexibility as well as modularity over varying body parts. The key issue with this design was the delivery of the light. Using end-glow fiber optic cables would create patches of intensity in the light and side-glow fiber optic cables would not hold their form in a liquid. Through iteration this design was eventually modified to create the recommended design concept. Recommended Design Concept Photosensitizing light can be provided through a soft and flexible solid-state medium. Delivery apparatus unique design utilizes an array of fiber optic cables embedded in a mat of biocompatible silicon rubber Design Description The final design will consist of three primary components. The first of these is the light source, a 150-watt metal halide fiber optic illuminator, which can house an optical filter for wavelength selection. The second component is the 5-foot transmission cable, which is a bundle of seven 5mm fiber optic lines. The third component is the delivery apparatus, or the light pad. The light pad is comprised of a mat of molded translucent silicon rubber, and embedded within it a radial array of sidelight-emitting fiber optic cables as well as structural and reflective backing. The light mat is most innovative and important part of this design; it defies the convention of existing industry products. It will be layered such that the light emitted needs only to travel through a centimeter of silicon rubber, and a layer of reflective Mylar will only let light out of one side. A solute of titanium dioxide in the silicon rubber will act as a scattering agent, giving the silicon a uniformly backlit surface. Above the 98

5 Mylar, a layer of flexible wire will allow the mat to change shape and hold form as necessary. The ability for light in the nm spectrum to efficiently travel through the media utilized to control the directionality of light in this design, allows this delivery apparatus and methodology to address major shortcomings inherent in standard treatment mechanisms Analytical Investigations Materials selection was of the utmost importance. Since there are multiple media through which the light will pass, the optical qualities needed to be factored in to best understand what types of light may be absorbed and not delivered to the patient. Research demonstrates that fiber optic cables have very low line losses over distances this short, and the silicon rubber cures to a translucent material. Research was conducted on existing products and topical drugs and it was determined that.01 watts/cm 2 needs to be delivered to the patient s skin in order for the PSA drug to be activated. The success of the device s functionality will be measured by the transmission percent losses, of the activating spectrum through the delivery apparatus. Key Advantages of Recommended Concept The advantages of this concept when compared to existing industry products lay primarily within the light pad properties. The flexibility of the rubber will allow for one device to be used for treating many different parts of the body comfortably. The modular design keeps all the heat and electricity away from the patient, as to not exacerbate the chemical burning sensation often felt from the activation of the PSA drug. With this 99

6 modular design, the delivery apparatuses can be interchangeable, as to fit to the complex features of the face, or with more oblique angles or arcs to treat the chest or back. This would minimize the equipment required for the range of standard treatment procedures. Finally, being able to remove each modular medical-grade pad facilitates easy cleaning of the biocompatible contact surface. Financial Issues Existing PDT devices are being sold in the range of several thousand dollars to the tens of thousands. Currently the cost of the prototype development is approximately $1,000, using stock products not produced in mass quantities. Existing PDT devices are being sold anywhere from several thousand dollars to the tens of thousands. The cost of the prototype development is expected to be much lower, using stock products not purchased in mass quantities. Nominal manufacturing costs in the future will be valued at approximately $500-1,000 per unit depending on manufacturing capabilities and quantities. Plans are in place to utilize standard parts when possible. The total cost of the proof-of-concept prototype will be approximately $1,000. Recommended Improvements Conducting performance and usability testing on the prototype within a clinical environment will aid in advancing patient and clinician comfort as well as treatment room integration. Additional clinician controllable parameters should be implemented. These adjustable parameters will aid in exploring the full capability of PDT. Conducting further performance and usability evaluations on the prototype within a clinical environment will also be critical in advancing clinician satisfaction and patient comfort as well as treatment room integration. Such testing will allow for analysis of the device s ergonomics, validate the need for additional padding, and the incorporation of Zimmer air cooling. For eventual use on patients, the device may have to undergo clinical trials. For PDT research purposes additional clinician controllable parameters should be implemented. Adjustable parameters such as illumination intensity and duration, variable illumination patterns, and treatment programs will aid in exploring the full capability of PDT. 100