An analytical method to calculate equivalent fields to irregular symmetric and asymmetric photon fields.
Equivalent field is frequently used for central axis depth-dose calculations of rectangular- and irregular-shaped photon beams. As most of the proposed models to calculate the equivalent square field are dosimetry based, a simple physical-based method to calculate the equivalent square field size was used as the basis of this study. The table of the sides of the equivalent square or rectangular fields was constructed and then compared with the well-known tables by BJR and Venselaar, et al. with the average relative error percentage of 2.5 ± 2.5% and 1.5 ± 1.5%, respectively. To evaluate the accuracy of this method, the percentage depth doses (PDDs) were measured for some special irregular symmetric and asymmetric treatment fields and their equivalent squares for Siemens Primus Plus linear accelerator for both energies, 6 and 18MV. The mean relative differences of PDDs measurement for these fields and their equivalent square was approximately 1% or less. As a result, this method can be employed to calculate equivalent field not only for rectangular fields but also for any irregular symmetric or asymmetric field.
['Tahmasebi Birgani|Mohamad J|MJ|', 'Chegeni|Nahid|N|', 'Zabihzadeh|Mansoor|M|', 'Hamzian|Nima|N|']
D003198:Computer Simulation D006801:Humans D008954:Models, Biological D009369:Neoplasms D017785:Photons D011879:Radiotherapy Dosage D011880:Radiotherapy Planning, Computer-Assisted D011881:Radiotherapy, Computer-Assisted D011882:Radiotherapy, High-Energy D015203:Reproducibility of Results D012680:Sensitivity and Specificity D016896:Treatment Outcome
Equivalent field Asymmetric field Irregular field Multileaf collimators