Clinical factors determining curative tumor dose

The dominant factor determining treatment policy, when considering radiotherapy of a neoplastic disorder, is the biologic nature of the tumor process in relation to its spatial configuration. This is also the important factor determining curative tumor dose. With the exception of very small tumors and certain important radiosensitive conditions, it is the effect on normal tissues which defines the limits of irradiation and which effectively determines the prescription of dosage. The relationship between dose and volume is basic to this discussion and is considered with particular reference to the integrity of mesenchyme. When comparing the radiosensitivities of tumor and host tissues, it is important to compare like with like. The ultimate effect on a tumor is measured functionally, in terms of suppressing the only function by which the tumour is recognized—its capacity for indefinite proliferation—and reflected in 5‐ and 10‐year cure rates. The effects on normal tissues should therefore be similarly measured in dynamic terms of the final functional state rather than on any transient structural appearance. These features are considered in relation to three different clinical situations: certain radiosensitive tumors, accessible primary tumors of limited sensitivity, and large tumors situated deeply. It is emphasized that curative treatment requires careful clinical appraisal of all the relevant features in each individual patient. The state of both tumor and host reaction may change significantly during the period of treatment and there is no alternative to continuous clinical observation using all the ancillary aids available.