Therapy treatment planning by radiation dose determination

A therapy planning method for radiation treatment of cancerous tissue by irradiation of the tissue with an optimum radiation dose comprising the steps of:

• estimating a radiation plan to produce said optimum dose, said estimated plan defining a radiation beam geometry;
• determining primary radiation dose to the patient based on the beam geometry;
• calculating scatter-air ratios based upon the beam geometry to produce a radial scatter-air ratio table;
• iteratively determining scatter dose to subregions within the patient by calculating radial distances from a subregion to irradiated points within the patient and attributing a scatter contribution from the radial scatter-air ratio table to each of said irradiated points for each subregion;
• combining scatter and primary dose to each subregion to produce a total dose mapping for the irradiated portion of the patient;
• comparing the dose mapping with the optimum dose for said tissue;
• and
• adjusting the radiation beam geometry to match the optimum with the calculated total radiation dose.

Apparatus for determining radiation dose for therapy treatment of a patient comprising:

• means for defining a radiation beam in terms of beam strength at locations within the beam;
• means for calculating a primary dose contribution from a radiation source to regions within said patient based upon beam strength data from the means for defining;
• means for calculating a scatter dose contribution to said region for radiation scattered from other regions within said patient by sequentially determining differential scatter-air ratios for incremental subregions within each plane of the patient by accessing data stored in a one dimensional radial scatter-air ratio matrix for radial distances within the plane by converting a two dimensional coordinate of the incremental subregion to a position within the one dimensional radial scatter-air ratio matrix;
• means for combining the primary and scatter contributions to provide a total patient dose to said regions;
• and
• means for displaying a mapping of radiation dose to said regions.

A method of determining beam strength for a region within a patient comprising the steps of:

• calculating a primary beam contribution from a source to a region of said patient;
• calculating a scatter beam contribution to said region for beam portions scattered from other regions within said patient by a differential scatter-air ratio method where the differential scatter-air ratios for subregions within a plane of the patient are stored in a one dimensional matrix and a differential scatter-air ratio for each subregion within the plane is accessed by converting a two dimensional coordinate within the plane to a position within the one dimensional matrix;
• combining the primary and scatter beam contributions to provide a total beam strength at the region;
• and
• mapping beam strength over a region of the patient.