Modernized Software for Calculation and Optimization of Absorbed Dose Distribution in a Homogeneous Medium during Radiation Therapy with Fast Neutrons

Purpose: To modernize software for calculation and optimization of isoeffective and absorbed dose distributions in a homogeneous media when planning fast neutron therapy for malignant tumours.

Material and Methods: The updated absorbed dose calculation system was applied to patients with two localisations, breast cancer (BC) and head and neck cancer (HNC). The study included data from 12 patients, of which 7 were patients with primary locally advanced breast cancer and 5 patients with head and neck cancer. In patients with BC, comprehensive treatment was performed. Patients with malignant tumours of the head and neck region underwent neutron and neutron-photon radiation therapy both in terms of combined treatment and as an independent type of treatment. Breast cancer was irradiated in fractionation mode with 4 fractions of 1.6 Gy each. Field docking was used. Patients diagnosed with head and neck cancer were irradiated in the mode of 3 fractions with a single dose of 2.4 Gy with the duration of the full course of treatment of 8 days. Irradiation took place on the therapeutic channel of the U-120 cyclotron located at Tomsk Polytechnic University.

Results: The planning results showed that the dose to the skin in the irradiation zone was 3.190 Gy and 3.143 Gy for beams 1 and 2, respectively. In the tumour centre, the dose was 3.253 Gy (isoeffective dose 7.980 isoGy). For critical sites (heart), the maximum doses ranged from 0.507 Gy to 1.943 Gy. ). The duration of exposure from each beam was 4 minutes and 26 seconds. For five patients with cancer in the head and neck region, planning was performed using 2 fields separated by an angle of 90 degrees (irradiation angles of 45 and 315 degrees). The fractionation regime included: 3 sessions with tumour dose 2.4 Gy, total dose 7.2 Gy per treatment course. The full course of neutron therapy was carried out in 8 days. TDF in the tumour zone was 55.4 units, with the maximum permissible value of 130 units. As a result, the dose to the skin was from 5.8 to 7.5 Gy. The dose to the tumour centre ranged from 7.1 to 7.23 Gy (taking into account RBE = 2.686 isoeffective dose ranged from 37.9 to 38.4 isoGy). Total treatment time per fraction was from 12.3 to 13.5 minutes.