Biomaterial Database

Dosimetric effects of matching electron fields with cobalt 60 fields in the management of head and neck cancer. 1995

N P Sidhu, and C J Smith

Tom Baker Cancer Centre, Calgary, Alberta, Canada.

The dose distributions in a blocked Co 60 beam with the area under the block irradiated with a 9-MeV electron beam at a nominal source to surface distance (SSD) of 100 cm and at an extended SSD of 115 cm were determined. The photon block was simulating the spinal cord shielding used when treating the posterior neck. A hot spot of 10% appeared close to the junction on the side of the photon field when electron treatment was given at a nominal SSD of 100 cm. At 115 cm SSD, the magnitude of the hot spot on the side of photon field increased to 20% and a cold spot on the order of 10% appeared in the distal area of the irradiated volume treated with electrons. A gap of 0.5 cm between the light field edges of the photon field and the electron field reduced the hot spot from 20% to 10% on the side of photon field. However, the magnitude of the cold spot on the side of electron field increased to 20%, and it appeared across the irradiated volume. Considering the limitation of the design of the electron applicators, which precludes the use of a nominal SSD of 100 cm for head and neck treatments, it is recommended that no gap should be allowed between the photon fields and the extended SSD electron fields. Clinically a limited hot spot of 20% is considered more acceptable than a cold spot of 20% extending from proximal to distal areas of the treatment volume.

UI	MeSH Term	Description	Entries
D008961	Models, Structural	A representation, generally small in scale, to show the structure, construction, or appearance of something. (From Random House Unabridged Dictionary, 2d ed)	Model, Structural,Structural Model,Structural Models
D011879	Radiotherapy Dosage	The total amount of radiation absorbed by tissues as a result of radiotherapy.	Dosage, Radiotherapy,Dosages, Radiotherapy,Radiotherapy Dosages
D003037	Cobalt Radioisotopes	Unstable isotopes of cobalt that decay or disintegrate emitting radiation. Co atoms with atomic weights of 54-64, except 59, are radioactive cobalt isotopes.	Radioisotopes, Cobalt
D004583	Electrons	Stable elementary particles having the smallest known negative charge, present in all elements; also called negatrons. Positively charged electrons are called positrons. The numbers, energies and arrangement of electrons around atomic nuclei determine the chemical identities of elements. Beams of electrons are called CATHODE RAYS.	Fast Electrons,Negatrons,Positrons,Electron,Electron, Fast,Electrons, Fast,Fast Electron,Negatron,Positron
D006258	Head and Neck Neoplasms	Soft tissue tumors or cancer arising from the mucosal surfaces of the LIP; oral cavity; PHARYNX; LARYNX; and cervical esophagus. Other sites included are the NOSE and PARANASAL SINUSES; SALIVARY GLANDS; THYROID GLAND and PARATHYROID GLANDS; and MELANOMA and non-melanoma skin cancers of the head and neck. (from Holland et al., Cancer Medicine, 4th ed, p1651)	Cancer of Head and Neck,Head Cancer,Head Neoplasm,Head and Neck Cancer,Head and Neck Neoplasm,Neck Cancer,Neck Neoplasm,Neck Neoplasms,Neoplasms, Upper Aerodigestive Tract,UADT Neoplasm,Upper Aerodigestive Tract Neoplasm,Upper Aerodigestive Tract Neoplasms,Cancer of Head,Cancer of Neck,Cancer of the Head,Cancer of the Head and Neck,Cancer of the Neck,Head Neoplasms,Head, Neck Neoplasms,Neoplasms, Head,Neoplasms, Head and Neck,Neoplasms, Neck,UADT Neoplasms,Cancer, Head,Cancer, Neck,Cancers, Head,Cancers, Neck,Head Cancers,Neck Cancers,Neoplasm, Head,Neoplasm, Neck,Neoplasm, UADT,Neoplasms, UADT
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man