Hall Book Ch 24 (Retreatment after Radiotherapy: The Possibilities and the Perils)

Question 1

Of patients presenting at major cancer centers in the Western world, ( )% present with a second cancer.

If the radiation tolerance of a given organ or tissue was exceeded by the initial treatment to the extent that function is lost, or is in process of being lost, then retreatment cannot be contemplated safely.

If the normal tissue tolerance was not exceeded by the initial treatment, some reirradiation at a later date is safe, varying very much with the tissue or organ involved and depending on other factors.

In general, ( ) tissues recover and tolerate retreatment better than ( ) tissues, but there are exceptions.

Answer 1

10, early-responding, late-responding

Question 2

Animal Studies

Radiation-induced ( ) damage recovers well, with restoration of almost ( ) radiation tolerance.

Recovery is slower after larger doses.

Poorer retreatment tolerance for ( ).

Answer 2

skin, full, fibrosis

Question 3

Retreatment with reduced doses is possible in both ( ) cord.

There are much data for spinal cord in both rodents and monkeys.

( ) are not capable of recovery from late functional damage.

Answer 3

lung and spinal

Kidney and bladder

Question 4

Clinical Studies
Most clinical studies involve small numbers of patients, variable doses, and
various time intervals between the initial treatment and reirradiation.
Reirradiation is possible in various sites with reduced doses and with a high
price in terms of morbidity.
Most data are for head and neck. Reirradiation with 50 to 60 Gy within a few
years of the initial treatment improves local control and possibly survival but
with severe toxicity and functional sequelae.
Studies using IMRT or, better still, protons to reduce the volume of normal
tissue exposed, as well as hyperfractionation to spare normal tissues, may be
called for in the future, but no data are available at the present time.