open access

### Accuracy evaluation of distance inverse square law in determining virtual electron source location in Siemens Primus linac

open access

#### Abstract

**Aim**

The aim of this study is to evaluate the accuracy of the inverse square law (ISL) method for determining location of virtual electron source (S_{Vir}) in Siemens Primus linac.

**Background**

So far, different experimental methods have presented for determining virtual and effective electron source location such as Full Width at Half Maximum (FWHM), Multiple Coulomb Scattering (MCS), and Multi Pinhole Camera (MPC) and Inverse Square Law (ISL) methods. Among these methods, Inverse Square Law is the most common used method.

**Materials and methods**

Firstly, Siemens Primus linac was simulated using MCNPX Monte Carlo code. Then, by using dose profiles obtained from the Monte Carlo simulations, the location of S_{Vir} was calculated for 5, 7, 8, 10, 12 and 14[[ce:hsp sp="0.25"/]]MeV electron energies and 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm, 15[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]15[[ce:hsp sp="0.25"/]]cm, 20[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]20[[ce:hsp sp="0.25"/]]cm and 25[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]25[[ce:hsp sp="0.25"/]]cm field sizes. Additionally, the location of S_{Vir} was obtained by the ISL method for the mentioned electron energies and field sizes. Finally, the values obtained by the ISL method were compared to the values resulted from Monte Carlo simulation.

**Results**

The findings indicate that the calculated S_{Vir} values depend on beam energy and field size. For a specific energy, with increase of field size, the distance of S_{Vir} increases for most cases. Furthermore, for a special applicator, with increase of electron energy, the distance of S_{Vir} increases for most cases. The variation of S_{Vir} values versus change of field size in a certain energy is more than the variation of S_{Vir} values versus change of electron energy in a certain field size.

**Conclusion**

According to the results, it is concluded that the ISL method can be considered as a good method for calculation of S_{Vir} location in higher electron energies (14[[ce:hsp sp="0.25"/]]MeV).

#### Abstract

**Aim**

The aim of this study is to evaluate the accuracy of the inverse square law (ISL) method for determining location of virtual electron source (S_{Vir}) in Siemens Primus linac.

**Background**

So far, different experimental methods have presented for determining virtual and effective electron source location such as Full Width at Half Maximum (FWHM), Multiple Coulomb Scattering (MCS), and Multi Pinhole Camera (MPC) and Inverse Square Law (ISL) methods. Among these methods, Inverse Square Law is the most common used method.

**Materials and methods**

Firstly, Siemens Primus linac was simulated using MCNPX Monte Carlo code. Then, by using dose profiles obtained from the Monte Carlo simulations, the location of S_{Vir} was calculated for 5, 7, 8, 10, 12 and 14[[ce:hsp sp="0.25"/]]MeV electron energies and 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm, 15[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]15[[ce:hsp sp="0.25"/]]cm, 20[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]20[[ce:hsp sp="0.25"/]]cm and 25[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]25[[ce:hsp sp="0.25"/]]cm field sizes. Additionally, the location of S_{Vir} was obtained by the ISL method for the mentioned electron energies and field sizes. Finally, the values obtained by the ISL method were compared to the values resulted from Monte Carlo simulation.

**Results**

The findings indicate that the calculated S_{Vir} values depend on beam energy and field size. For a specific energy, with increase of field size, the distance of S_{Vir} increases for most cases. Furthermore, for a special applicator, with increase of electron energy, the distance of S_{Vir} increases for most cases. The variation of S_{Vir} values versus change of field size in a certain energy is more than the variation of S_{Vir} values versus change of electron energy in a certain field size.

**Conclusion**

According to the results, it is concluded that the ISL method can be considered as a good method for calculation of S_{Vir} location in higher electron energies (14[[ce:hsp sp="0.25"/]]MeV).

#### Keywords

Virtual electron source; Inverse square law; Electron energy; Field size; Monte Carlo simulation

###### Title

Accuracy evaluation of distance inverse square law in determining virtual electron source location in Siemens Primus linac

###### Journal

Reports of Practical Oncology and Radiotherapy

###### Issue

###### Pages

105-113

###### Published online

2018-03-01

###### DOI

10.1016/j.rpor.2018.01.002

###### Bibliographic record

Rep Pract Oncol Radiother 2018;23(2):105-113.

###### Keywords

Virtual electron source

Inverse square law

Electron energy

Field size

Monte Carlo simulation

###### Authors

Hamid Shafaei Douk

Mahmoud Reza Aghamiri

Mahdi Ghorbani

Bagher Farhood

Mohsen Bakhshandeh

Hamid Reza Hemmati