✍ Scribed by J. van de Geijn
No coin nor oath required. For personal study only.
In radiation therapy, external beams of ionising radiation are used in empirical cross fire configurations to produce distributions of absorbed energy in living tissues. For a given configuration to be useful, certain conditions have to be satisfied. The present program applies to rectangular beams of high energy X-rays and 6°Co gamma radiation, interacting with unit density tissue. It is designed to simulate irradiation techniques generally employed in routine clinical practice. It is capable of producing relative distributions of absorbed energy (dose) in up to nine mutually parallel planes of a patient, thus enabling the radiotherapist to obtain quantitative information of the three dimensional dose distribution.
The central problem is the computation of the contribution of one beam to the absorbed dose at an arbitrary point in the irradiated volume, in dependence of beam dimensions, filtering and shape of the patient. A summary is given of a semi-empirical generating function for this purpose, which was described previously [ 1]. The distribution of absorbed dose, for any kind of cross fire technique, is obtained by accumulating the weighted contributions from all the beam positions at all points of a three dimensional grid. After suitable normalisation, a quadratic interpolation method is used to compute and display isodose surfaces by means of sets of isodose lines in muCaally parallel planes. Per plane of computation, a table of so-called zonal integral doses and zonal surface areas is produced as a potential means to compare the merits of different irradiation techniques. Finally, for 6°Co radiation machines, basic treatment times are calculated.
The program allows simulation of the following irradiation techniques, using beams limited by rectangular diaphragrns:
(a) stationary beam cross fire, with, per beam, options for one "wedge filter", and/or one of two "wedge type compensating filters", and/or one block type beam shaping filter;
(b) moving beam cross fire, to a maximum of five arcs per patient, with the same filter options per arc as mentioned in (a), either isocentric' (per arc), or tangential;
(c) moving beam cross fire, supplemented by stationary beams, with per arc, respectively stationary beam, the same filter options.
In all techniques, the central axes of the beams must be parallel to the planes of calculation. The beams may be rotated about their own axes.
Co 6° Beam model 3-D planning X-rays Generating function
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