Physical Aspects of Cobalt 60 Teletherapy Using Wedge Filters: I. Physical Investigations

Physical Aspects of Cobalt 60 Teletherapy Using Wedge Filters: II. Dosimetric Considerations

“…The addition of 2 wedge fields for cobalt 60 γ rays is discussed in detail, using the analytical approach of COHEN (1959) and SEAR (1959). Examples of combined field isodose charts are given, and dosage tables permit a choice of 25 two-field arrangements for each wedge.…”

“…When the analytical framework just mentioned, which was originally developed for wedge therapy using 250 kV roentgen-rays, is applied to wedge fields used with cobalt y-rays, it is found that certain simplifica tions may be made. In the first place, as shown in part I (COHEN, BURNS & SEAR 1960) when the harder radiation is used the hot-spot doses for individual wedge fields are lower and the percentage depth doses higher. The resulting hot-spot factors in a 2-field arrangement are usually well within the stated clinical limit even without the addition of a non-wedge field.…”

“…PHYSICAL ASPECTS OF COBALT 60 TELETHERAPY USING WEDGE FILTERS 4 8 7 graphical analysis of the system has been described by COHEN (1959), from which practical dosage tables have been produced. When the analytical framework just mentioned, which was originally developed for wedge therapy using 250 kV roentgen-rays, is applied to wedge fields used with cobalt y-rays, it is found that certain simplifica tions may be made.…”

“…A slight extension of the definition of COHEN (1959) has been adopted whereby the plateau is said to include all points at which the dose-rate is 0.9 or more of the maximum occurring along the axis of symmetry. SEAR (1959) has shown that for each wedge a pair of angles θ χ and 0 2 may be defined such that, if 0 i > 0 > 0 2 , the plateau corresponds closely to the geometrical area of field overlap EFGG'.…”

Physical aspects of cobalt 60 teletherapy using wedge filters

“…I n the first place, as shown in part I (COHEN, BURNS & SEAR 1960) when the harder radiation is used the hot-spot doses for individual wedge fields are lower and the percentage depth doses higher. The resulting hot-spot factors in a %field arrangement are usually well within the stated clinical limit even without the addition of a non-wedge field.…”