Unit 2 Medical Physics

Paul Kane

School of Health Sciences

UUJ

Topics for this session

• Fibre Optics and Lasers in medicine

• Light in therapy

• Ultrasound in therapy

• Radioisotopes in therapy

• Choosing modalities

Fibre Optics

Fibre Optics Explained

• Glass fibres around 120 micrometres dia

• Can carry light up to 50km without need for repeaters or boosting

• Commonly known applications are in data and voice communications

Why the light “Stays in”

• When light meets an interface between 2 materials it will be transmitted or reflected

• Fibre optics manipulate this phenomenon

Refractive Index and TIR

Low to High High to Low

ZigZag – NOT STRAIGHT!

Lower Refractive Index

Medical Application

Medical Application

• Fibre optic tube• Light source• Lens• Can be used to

explore natural body cavities

• OR small artificial ones

Advantages

• Can examine a variety of structures without requiring surgery

• Minor apertures can expand role further

• Can carry out surgical procedures via specialised variants of endoscope

Light in Therapy

• Fibre optics can convey special light such as LASERs

• Light Amplified by Stimulation of Emitted Radiation

• LASER useful as surgical tool

Laser Applications

• Eye Surgery

• Hair Removal

• Procedures on skin

• General Surgery

• Neurosurgery

• Urology

Other Light Applications

• SAD (Seasonal Affective Disorder)

• Skin Disorders

• Delayed Sleep Phase Syndrome

Ultrasound in Therapy

• Useful with injuries to soft tissue and joints

• Can aid the bodies own repair mechanisms

• Relieve pain and increase mobility

• Sports medicine makes great use of it

Specialised Technique

• Lithotripsy

• Derived from the greek for “Breaking Stones”

• Break down of areas of calcification in areas like kidneys and gall bladder

Why use Ultrasound?

• Readily available

• Proven technology

• Painless

• No need for surgery

• Safe and relatively cheap

• Not always effective

• Some procedures may require repetition

Radioisotopes in Therapy

• Nuclear medicine utilises unsealed radioactive sources often attaching to a pharmaceutical to encourage uptake by specific tissue

• Therapeutic applications also use sealed sources

Example Applications

• I131 – thyroid cancer or thyrotoxicosis

• Ir192 – breast cancer

• Cs137 – endometrial tumours

• Co60 – teletherapy units

Afterloading

• Catheters introduced to treatment area

• Therapist controls insertion of sources from behind shielding

Teletherapy

• Useful for a wide variety of radiotherapy applications

Attributes of Therapeutic Isotopes

• In a form which can be manipulated

• Tend to be beta emitters

• Co60 is a gamma emitter

Problems

• Radiation protection issues

• Dosimetry

• Finite life span of isotopes

Which Modality?

• What is available

• What does the clinician recommend

• What can the patient tolerate

• Is there a safer/cheaper alternative?

• Can potential risks be justified?

QUESTIONS?