Principles of radiation

1. Darren Fray

2. Outline
 Definition
 History
 Mechanisms of Action
 Methods of Delivery
 Complications

3. Definition
 Radiation therapy is the medical use of ionizing
radiation as part of cancer treatment to control
malignant cells.

4. History
 Has been used in medicine for over 100 years.
 Discovery of x-rays in in 1895 by Wilhelm Rontgen.
 Emil Grubbe was the first American physician to use x-
rays to treat cancer in 1896.

5.  The field of radiation therapy began to grow in the
early 1900s due to the groundbreaking work
of Curie (1867–1934), who discovered the radioactive
elements polonium and radium in 1898.

6.  Radium was used in various forms until the mid-1900s,
when cobalt therapy and caesium units came into use.
 Finally, Medical linear accelerators have been used as
radiation sources since the late 1940s.

7. Mechanism of Action
 Ionizing radiation is energy sufficiently strong to
remove an orbital electron from an atom.
 High-energy photons Photons that are released from
the nucleus of a radioactive atom are known as gamma
rays. High-energy radiations have a short wavelength
and a high frequency.

8. The interaction of a photon beam with matter results
in the attenuation of the beam. Five major types of
interactions typically occur:
 Coherent scattering
 Photoelectric effect
 Compton scattering
 Pair production
 Photodisintegration

9. Photo Electric Effect
 Incoming photon collides with a tightly bound
electron.
 The photon transfers all its energy to the electron and
disappears.
 The electron now has most of the energy from the
photon and starts to ionize surrounding molecules.

10. Compton Effect
 A photon collides with a free electron.
 Both the photon and electron are scattered.
 The photon continues to undergo other interactions.
 The electron ionizes surrounding molecules.

12. Pair Production
 Photon interacts with the nucleus of an atom not
electron.
 Photon gives up its energy to the nucleus.
 Creates a pair of positively and negatively charged
electrons.
 The positive electron ionizes until it combines with a
free electron
 This generates two photons that scatter in opposite
directions.

13. Biological Effect
 Double-stranded breaks of nuclear DNA is the most
important cellular effect of radiation.
 This breakage leads to irreversible loss of the
reproductive integrity of the cell and eventual cell
death.
 Affects the processes of the cell cycle necessary for cell
growth, cell senescence, and apoptosis.

14.  Radiation damage can be directly ionizing; however, in
clinical therapy, damage is most commonly indirectly
ionizing via free-radical intermediaries formed from
the radiolysis of cellular water.

15.  One of the major limitations of photon radiation
therapy is that the cells of solid tumors become
deficient in oxygen.
 Oxygen is a potent radio sensitizer, increasing the
effectiveness of a given dose of radiation by forming
DNA-damaging free radicals.

16.  Much research has been devoted to overcoming
hypoxia including the use of high pressure oxygen
tanks, hyperthermia therapy blood substitutes that
carry increased oxygen.

17. Dose
 The dose of radiation
absorbed is directly
proportional to the
energy of the beam.

18. Gray
 The basic unit of radiation
 Absorbed dose is the amount of energy
(joules)absorbed per unit mass (kg).
 This unit, known as the gray (Gy), has replaced the
unit of rad used in the past (100 rads = 1 Gy)

19.  For curative cases, the typical dose for a solid epithelial
tumor ranges from 60 to 80 Gy, while lymphomas are
treated with 20 to 40 Gy.
 Preventative doses are typically around 45–60 Gy in
1.8–2 Gy fractions (for breast, head, and neck
cancers.)

20. Fractionating
 The dose is spread over time.
 Allows normal cells time to recover, while tumor cells
are generally less efficient in repair between fractions.
 Allows tumor cells that were in a relatively radio-
resistant phase of the cell cycle during one treatment
to cycle into a sensitive phase before the next fraction
is given.
 Tumor cells that were hypoxic may reoxygenate
between fractions.

21. Planning Of Radiotherapy
 Once the decision is made to employ radiation,
consideration must be given to whether the radiation
will be prescribed as definitive, palliative, or adjuvant
therapy
 Whether it will be integrated with surgery and
chemotherapy.

22.  Contemporary treatment-planning computers allow
the incorporation of 3-dimensional anatomic data into
the planning of radiation fields.

23. Beam’s-eye-view technology

24. Types of Radiotherapy
 External beam radiation therapy (EBRT or XRT) or
teletherapy.
 Brachytherapy or sealed source radiation therapy.
 Systemic radioisotope therapy or unsealed source
radiotherapy.

25. Conventional External Beam
Radiation
 delivered via two-dimensional beams using linear
accelerator machines delivered to the patient from
several directions.
 Conventional refers to the way the treatment
is planned or simulated on a specially calibrated
diagnostic x-ray machine known as a simulator

26. Stereotactic Radiation
 It uses focused radiation beams targeting a well-
defined tumor using extremely detailed imaging scans.
 advantage to stereotactic treatments are they deliver
the right amount of radiation to the cancer in a shorter
amount of time than traditional treatments.
 One problem with stereotactic treatments is that they
are only suitable for certain small tumors.

28. Particle therapy
 Energetic ionizing particles (protons or carbon ions)
are directed at the target tumor.
 The dose increases while the particle penetrates the
tissue, up to a maximum (the Bragg peak) that occurs
near the end of the particle's range, and it then drops
to (almost) zero.

30. Brachytherapy
 Internal radiation therapy is delivered by placing
radiation source(s) inside or next to the area requiring
treatment.
 Radiation sources are precisely placed directly at the
site of the cancerous tumor. Tumor can be treated with
very high doses of localized radiation, whilst reducing
the probability of unnecessary damage to surrounding
healthy tissues.

32. Radioisotope Therapy (RIT)
 Systemic radioisotope therapy is a form of targeted
therapy.
 Targeting can be due to the chemical properties of the
isotope such as radioiodine which is specifically
absorbed by the thyroid gland a thousandfold better
than other bodily organs.
 Targeting can also be achieved by attaching the
radioisotope to another molecule or antibody to guide
it to the target tissue.

33. Acute Side Effects
 Nausea and vomiting.
 Damage to epithelial surfaces.
 Mouth throat and stomach sores.
 Intestinal discomfort.
 Swelling edema
 Infertility

34. Chronic Side Effects
 Fibrosis
 Epilation
 Dry mouth (xerostomia) and dry eyes (xerophthalmia)
 Lymphedema
 Heart disease
 Cognitive decline
 Radiation proctitis

35. The End

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