Because of the profound effects on the general health of the patient inevitably caused by radiation treatment for malignant conditions, the importance of the “total energy absorption” in radiation therapy has for many years past impressed the author as a factor which should be reckoned with in the planning and carrying out of such treatment. This is by no means a unique impression, but quantitative work on the subject has been impossible because of the difficulty of providing a suitable method of estimating the constitutional dose for clinical purposes. “Volume dose” is defined as the total amount of energy absorbed by the patient due to the treatment. In 1936 the author thought that the volume dose could probably be estimated by using depth dose curves of an X-ray beam. For instance, if a beam with a field of area 6 × 4 cm.2 was passing through 15 cm. of tissue it was thought that the area enclosed by the length of the depth dose curve corresponding to 15 cm. and the axes (of depth and percentage depth dose) would provide an estimate of the total energy absorbed by the tissues in giving 100 röntgens, if that area were multiplied by the area of the field—24 cm.2 The unit of this “volume dose” would thus be a “röntgen cubic centimetre.”