5
Oligometastatic Disease
➤ Some cancers are associated with only a small number of
macrometastases (termed oligometastatic cancer). In general, most
studies of oligometastatic cancer have included patients with one
to five distinct metastases. With a limited number of metastases,
it becomes theoretically possible to treat detectable tumors with
curative intention using surgery and/or locally ablative therapies,
realizing that occult metastatic disease may nevertheless exist.
Definition of Therapeutic Terms
Standard Radiation Prescription
➤ The unit dose of radiation is the Gray, abbreviated to Gy. Some
prescriptions are given in centiGray or cGy (1 Gy = 100 cGy). A
radiation prescription describes the total dose of radiation to be
delivered, the number of fractions (number of daily treatments), the
dose of each daily treatment, and the overall length of the treatment
course. The usual daily fraction size is 1.8 or 2 Gy. A standard
prescription in the setting of neck irradiation in ATC would be, for
instance: 66 Gy over 61/2 weeks, given as 33 daily fractions of 2 Gy
per day, 5 days a week for definitive treatment, but this is adjusted
depending on the clinical setting as discussed later in the document.
Altered Fractionation
➤ Altered fractionation implies a larger number of fractions
(hyperfractionated), or a smaller number of fractions
(hypofractionated), or a shorter overall treatment time (accelerated).
By using hyperfractionated treatment with more than one daily
fraction given, it enables the prescription to be given over a shorter
treatment time (accelerated hyperfractionated radiotherapy). In a
rapidly growing tumor such as ATC, accelerating the treatment has
the potential to minimize tumor growth that may occur over the
radiotherapy treatment course. By giving multiple small fractions,
the toxicity may also be reduced. An example of an accelerated
hyperfractionated prescription would be: 60 Gy over 4 weeks given as
40 twice-daily fractions of 1.5 Gy, 5 days a week.
