IV. Radiation Measurements with the Eldorado Cobalt 60 Teletherapy Unit

A 20 Curie Telecobalt Unit

“…One may expect that with our applicators the build-up ratio will be 1 very nearly unity and that the maxi-: mum will occur close to the surface, by , reason of both the short diaphragm-/ skin distance and the short source-skin neglected for the small irradiation fields used by us. This is in agreement with the measurements of backscatter given by DIXON, GARRETT and MORRISON (1952).…”

“…We have made an attempt to extend their investigations to smaller values of s.s.d. For this purpose we converted, using the "F" factor, the depth dose data obtained by JOHNS, Epp, CORMACK, FEDORUK (1952) and by DIXON, GARRETT, MORRISON (1952) for a source-skin distance of 60 em into data for the source-skin distances used by ourselves as well as by MEREWETHER, OSBORN, WYARD (1952) Table I, columns 4 and 6, and in Table II, columns 3 and 5. As may be seen, it seems that for small areas the "F" factor may be used for all depths and for all source-skin distances between about 15 em and 100 cm without introducing any appreciable error.…”

A 20 Curie Telecobalt Unit

“…One may expect that with our applicators the build-up ratio will be very nearly unity and that the maxi- uszd by us. This is in agreement with the measurements of backscatter given by DrxoN, GARRETT and MORRISON (1952).…”

The Effect of Source Size upon Integral Dose in Teletherapy Units

“…Use has been made of the Central Axis Depth Dose Data (2) assuming h. v. l's of 12, 10, and 8 mm Cu for the gamma rays of radium, 137CS and 192Ir respectively. Backscatter figures for these were obtained from the table given by MAYNEORD and LAMERTON (8), while the backscatter data of DIXON et al (3) was used for the 80 Co calculations. Comparison is made in the table with roentgen rays of h. v. 1.…”