SU-GG-T-433: Study of the Dose Distributions in Serial and Helical Tomotherapy for CO-60, 6MV and 10MV Beams Using PENELOPE Monte Carlo

Abstract

Purpose: Study the dose distributions for 60Co, 6MV and 10MV beams in tomotherapy through PENELOPE Monte Carlo code. Methods and materials: PENELOPE was modified to simulate beam movement like used in serial and helical tomotherapy technique. The dose distributions in tomotherapy were simulated with a cylindrical phantom of 5 cm radius and 10 cm length. To simulate serial tomotherapy, the slice was obtained in 1 degree intervals until complete 360 degrees. A superposition software was developed in MatLab to obtain multi slices. To simulate the helical movement of the beam, relative to phantom length, for each rotation of 1 degree, the beam was displaced 0.00125 cm longitudinally. The SADs were 80 cm, 100 cm and 100 cm respectively to each beam, with a no modulate field of 1 × 1 cm2. To evaluate the simulated dose distributions the conformity index and Dose‐Volume Histograms (DVH) were used. A cylindrical Planned Target Volume of 0.2 cm radius and 2.2 cm length and an adjacent cylindrical ring organ‐at‐risk of 0.2 cm internal radius, 0.5 cm external radius and 4.4 cm length were defined inside the phantom. Results: The obtained conformity indexes were 0.78, 0.85 and 1 to serial tomotherapy and 0.67, 0.98 and 0.98 to helical tomotherapy to 60Co, 6MV and 10MV, respectively. Conclusions: In the serial tomotherapy 60Co and 6MV have shown similar behavior and have spared health tissues better than 10MV. To helical tomotherapy 6MV and 10MV have shown similar behavior but 60Co has shown a better sparing of health tissues while losing dose conformity. Helical tomotherapy conformed the dose in target volume better than serial tomotherapy, without hotspots.