ring2 Short life s therefore range of damage small 2 3 nm from DNA

Ring2 short life s therefore range of damage small 2

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electrons on an open shell configuration. ring2 Short life-span ( 10 -10 s) therefore range of damage small 2-3 nm from DNA ring2 The unpaired electrons cause them to be highly chemically reactive
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Radiation Damage to DNA ring2 Amount/Type of damage depends on: 1) Type of radiation (photons, electrons, protons, heavy ions) 2) Cell cycle (late G2 + M most sensitive) 3) Oxygenation (H + O 2 barb2right HO 2 ) perhydroxyl molecule
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Kill Cancer Cells faster than Normal Cells For a given dose, what is that chance that we will control the cancer while minimizing injury to nearby critical (and healthy) tissues? ring2TCP → Tumour Control Probabilityring2NTCP → Normal Tissue Complication Probability
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Goal: Kill Cancer Cells faster than Normal Cells For a given dose, what is that probability that we will control the cancer while at the same time, minimizing injury to nearby healthy tissues? THERAPEUTIC RATIO = TCP(D) NTCP(D)
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Quantifying Properties of Ionizing Radiation ring2 Source strength → activity → Bequerel (Bq) or Curie (Ci) ring2 Radiation intensity → exposure → Roentgen (R) ring2 Absorbed energy by tissue → dose → Gray (Gy)
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Source Strength barb2right Activity ring2 Activity = # radioactive decays = s -1 second 1 decay / s = 1 Bequerel = 1 Bq ring2 37 GBq = 1 Curie = 1 Ci (roughly the activity in 1 gram of Ra 226 ) ring2 H. Bequerel = Nobel prize 1903 – discovered spontaneous radioactivity Marie & Pierre Curie = Nobel prize 1903 – discovered radium
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Radiation Intensity barb2right Exposure ring2 Exposure = # ionizations (at NTP) mass of air = Coulombs / kg ring2 1 Roentgen = 1 R = 2.58 x 10 -4 C / kg ring2 Roentgen – Nobel Prize 1901 – discovery of x-rays in 1985
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Absorbed Energy barb2right Dose ring2 Dose = Absorbed Energy = E ab Unit Mass medium kg = Joule / kg ring2 1 J / kg = 1 Gray = 1 Gy ring2 L.H. Gray = British physicist who studied the effects of radiation on biological systems
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Dose Deposition in Medium (i.e. humans) ring2 Dose = energy absorbed per unit mass of tissue (J/kg) ring2 2 Step Process for photons: 1) Photon interacts with atom Energy transferred to e- ( E tr ) barb2right energy transfer called KERMA ring2 barb2right KERMA = kinetic energy released per unit mass ring2 = dE tr /dm E tr
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Dose Deposition in Medium (i.e. humans) ring2 Dose = energy absorbed per unit mass of tissue (J/kg) ring2 2 Step Process for photons: 2) Medium absorbs energy from the e- ( E ab ) via a chain of excitations and ionizations DOSE = dE ab /dm E tr
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Typical Radiotherapy Doses ring2 Depends on how much tissue irradiated, type of cancer, near-by healthy organs ring2 Curative: 60-80Gy given in 30-40 fractions (~2 Gy / fraction) ring2 Curative/Ablative: 35 – 60 Gy in 5 – 8 fractions (~7 – 15 Gy / fraction) ring2 Palliative: ring2 ~10-30 Gy given in 5-10 fractions (~2-3 Gy fraction)
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Characteristics of Dose Deposition ring2 Different types of radiation have different dose deposition properties
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Choose your Radiation Type Carefully
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Which Radiation Beam?
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Which Radiation Beam?
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Which Radiation Beam?
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Radiation Delivery – External Beam ring2 Radiation beam directed at patient from external source ring2 Disease may be superficial (e.g. skin) or deep seated (e.g. prostate)
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