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Brachytherapy and GYN malignancy. Brachytherapy. Brachytherapy ( brachy , from the Greek for “short distance”) consists of placing sealed radioactive sources close to or contact with the target tissue. Interstitial, intracavity, or transluminal approach. Temporary, or permanent implant.

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brachytherapy
Brachytherapy
  • Brachytherapy (brachy, from the Greek for “short distance”) consists of placing sealed radioactive sources close to or contact with the target tissue.
  • Interstitial, intracavity, or transluminal approach.
  • Temporary, or permanent implant.
  • Low or high dose rate.
introduction
Introduction
  • Discovery in 1898
  • Short distance (cm)
  • High radiation dose can be delivered locally to the tumor with rapid dose fall-off in the surrounding normal tissue
radioactive sources radium 226
Radioactive sourcesRadium-226
  • Average energy 0.83Mev (0.5mm of platinum)
  • A filtration of at least 0.5mm platinum is sufficient to absorb all the α particles and most of the β particles emitted by the radium and its daughter products.
  • Half life ~1600 years
  • It was loaded into cells about 1cm long and 1mm in diameter.
  • Radium sources are manufactured as needles or tubes in a variety of lengths and activities
radioactive sources cesium 137
Radioactive sourcesCesium-137
  • Substitute for radium in both interstitial and intracavitary brachytherapy
  • Energy 0.662Mev nearly the same penetrating power as radium
  • Half life 30 years (clinically used 7 years without replacement) It was doubly encapsulated in stainless-steel needles and tubes.
radioactive sources cobalt 60
Radioactive sourcesCobalt-60
  • High specific activity
  • Small sources required for some special applicators
  • More expensive than 137Cs and short half life (5.26 years)
  • The sources can be used to replace 226Ra in intracavitary application
radioactive sources iridium 192
Radioactive sourcesIridium-192
  • It has a complicated γ ray spectrum with an average energy of 0.38 MeV. → It required less shielding for personnel protection.
  • It has the disadvantage of a short half-life (73.8 days)
  • It is fabricated in the form of thin flexible wires which can be cut to desired lengths
radioactive sources iodine 125
Radioactive sourcesIodine-125
  • Widely used for permanent implants.
  • Longer half-life: 59.4 days (convenient for storage)
  • Low photon energy (0.028MeV) → less shielding.
  • Disadvantages: dosimetry of 125I is much more complex.
radioactive sources1
Radioactive sources
  • ICRU38

LDR sources: 0.4-2 Gy/hr (137Cs)

HDR sources: ≥ 12 Gy/hr (60Co, 192Ir)

  • 226Ra leakage Radon gas.
  • 137Cs better than 226Ra  less shielding and microsphere form with leakage gas.
  • 137Cs better than 60Co  less shielding and cheap.
  • 192Ir better than 137Cs  lower energy require less shielding for personnal protection and higher specific activity.
  • 103Pd better than 198Au and 125I  less shielding and biologic advantage .
slide18

Reference point from which lymph node position were measured on lymphoangiograms and the range of locationInt. J Radiat Oncol Biol Phys 34:167-172, 1996

slide19
Distribution of pelvic node metastases in patients with Ib-IIa cervical cancerGynecol Oncol 62:19-24, 1996

Tumor size <=4 cm

Local advanced tumor

combination of external beam pelvic irradiation and intracavitary brachytherapy icrt
Combination of external beam pelvic irradiation and intracavitary brachytherapy (ICRT)
slide25

Brachytherapy in definitive radiotherapy of cervical cancer(Intracavity radiotherapy, ICRT)