Key Background
6
Radiotherapy Dose
➤ There are many different potential radiation prescription doses.
For the purpose of this report they have been grouped as definitive-
intention or palliative-intention.
Definitive-intention radiotherapy is high-dose radiation given with or
without concurrent chemotherapy with the intent of maximizing the
chance of long-term local control. Examples range from 50 Gy in 20
fractions, 2.5 Gy per fraction over 4 weeks at the low end, to 70 Gy in
35 fractions, 2 Gy per fraction over 7 weeks at the high end.
Palliative-intention Radiotherapy is lower dose radiotherapy given over a
shorter time period with the primary aim of improving local symptoms
and achieving initial disease control while minimizing hospital/clinic
visits. This may be directed to the primary tumor or to metastases.
Typical examples could be 20 Gy in 5 fractions, 4 Gy per fraction over
1 week and 30 Gy in 10 fractions, 3 Gy per fraction over 2 weeks.
Conformal Radiation
➤ In conformal radiotherapy, the volume treated is tailored to and
"conforms" to the shape of the tumor. The toxicity of radiation to the
surrounding normal tissues is thereby reduced.
Intensity Modulated Radiotherapy (IMRT)
➤ By modulating the intensity of the radiation fields as well as shape
of the fields, the radiation can be made more conformal (tailored),
thereby reducing toxicity to the adjacent normal structures and
potentially enabling a higher radiation dose to be given to the tumor
areas.
Radiosurgery and Stereotactic Body Radiotherapy
(Stereotactic Radio-surgeries)
➤ Radiosurgery and stereotactic body radiotherapy (SBRT) are highly
conformal/focused radiation that allows a single large fraction of
radiation to be given. Stereotactic radiosurgery usually refers to
radiosurgery to the brain (e.g., Gamma Knife
®
). Stereotactic body
radiosurgery usually refers to radiosurgery to parts of the body other
than to the brain (e.g., CyberKnife®, X-Knife
®
) and SBRT usually
refers to highly conformal radiotherapy given in 3–10 fractions.
