In its Report 24 on ‘Determination of Absorbed Dose in a Patient Irradiated by
Beams of X or Gamma Rays in Radiotherapy Procedures’, the International
Commission on Radiation Units and Measurements (ICRU) [1] concluded
...
In its Report 24 on ‘Determination of Absorbed Dose in a Patient Irradiated by
Beams of X or Gamma Rays in Radiotherapy Procedures’, the International
Commission on Radiation Units and Measurements (ICRU) [1] concluded that
“although it is too early to generalize, the available evidence for certain types of
tumour points to the need for an accuracy of ±5% in the delivery of an absorbed dose
to a target volume if the eradication of the primary tumour is sought”. The ICRU
continues, “Some clinicians have requested even closer limits such as ±2%, but at
the present time (in 1976) it is virtually impossible to achieve such a standard”.
These statements were made in a context where uncertainties were estimated at the
95% confidence level, and have been interpreted as if they correspond to approximately two standard deviations. Thus the requirement for an accuracy of 5% in the
delivery of absorbed dose would correspond to a combined uncertainty of 2.5% at
the level of one standard deviation. Today it is considered that a goal in dose delivery
to the patient based on such an accuracy requirement is too strict and the figure
should be increased to about one standard deviation of 5%, but there are no definite
recommendations in this respect.1 The requirement for an accuracy of ±5% could,
on the other hand, also be interpreted as a tolerance of the deviation between the prescribed dose and the dose delivered to the target volume. Modern radiotherapy has
confirmed, in any case, the need for high accuracy in dose delivery if new techniques, including dose escalation in 3-D conformal radiotherapy, are to be applied.
Emerging technologies in radiotherapy, for example modern diagnostic tools for the
determination of the target volume, 3-D commercial treatment planning systems and
advanced accelerators for irradiation, can only be fully utilized if there is high
accuracy in dose determination and delivery.
The various steps between the calibration of ionization chambers in terms of
the quantity air kerma, Kair, at the standardizing dosimetry laboratories and the
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