480 likes | 913 Views
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.
E N D
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 • 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 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 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 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 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 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 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 .
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
Distribution of pelvic node metastases in patients with Ib-IIa cervical cancerGynecol Oncol 62:19-24, 1996 Tumor size <=4 cm Local advanced tumor
Pelvic irradiation portal in cervical cancer4-field box technique
Pelvic irradiation portal in cervical cancer4-field box technique
Combination of external beam pelvic irradiation and intracavitary brachytherapy (ICRT)
Brachytherapy in definitive radiotherapy of cervical cancer(Intracavity radiotherapy, ICRT)