Brachytherapy and GYN malignancy

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Brachytherapy and GYN malignancy
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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.

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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

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Radioactive sources
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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 a particles and most
  of the ß 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

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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.

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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

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Radioactive sourcesIridium-192

• It has a complicated ? 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

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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.

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BrachytherapyPermanently Implanted
Source Energy T1/2 Dose Rate
222Rn 1.2MeV 3.83 0.75G/h
198Au 412keV 2.70 1.07G/h
125I 28keV 59.6 0.07G/h
13Pd 22keV 17 0.19G/h
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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 .

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Radioactive sources
Low Dose Rate (LDR) High Dose Rate (HDR)
Patient Long history of use. Ability to predict rate of late complications No long term confinement to bed. No indwelling bladder catheters. Not labeled radiation risk zone to relative, visitors, and staff. Avoid several anesthesias.
Clinical Improves chances of atching tumors in sensitive phase of cell cycle. Maintain position of the sources during the brief treatment. Patient preparation. No specialized nursing. Ability to treat great patient loads.
Physical Longer treatment times allow for leisurely review of and potential modifications to the treatment . Plan prior to the delivery of a significant portion of treatment. Favorable dose-rate effect on repair of normal tissues. Infrequent replacement and calibration of sources because of long isotope half-life. Short treatment times and minimal radiation protection problems. Possibility of optimizing dose distribution by altering the dwell times of the source at different
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Brachytherapy and GYN Malignancy
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Reference point from which lymph node position
were measured on lymphoangiograms and the range
of locationInt. J Radiat Oncol Biol Phys
34167-172, 1996
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Distribution of pelvic node metastases in
patients with Ib-IIa cervical cancer Gynecol
Oncol 6219-24, 1996
Tumor size lt4 cm
Local advanced tumor
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External beam radiotherapy for GYN Malignancy
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Pelvic irradiation portal in cervical
cancer4-field box technique
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Pelvic irradiation portal in cervical
cancer4-field box technique
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Combination of external beam pelvic irradiation
and intracavitary brachytherapy (ICRT)
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Brachytherapy in definitive radiotherapy of
cervical cancer(Intracavity radiotherapy, ICRT)
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Intracavitary Radiotherapy (ICRT)
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Applicator of ICRT
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Intracavitary insertion (ICRT)
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Postoperative brachytherapy(Intravaginal
radiotherapy)
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Intravaginal radiotherapy (IVRT)
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Female urethral cancer
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Endometrial cancer