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. 2017 Jan 25;9(1):3523-3528.
doi: 10.19082/3523. eCollection 2017 Jan.

An Analytical Method to Calculate Phantom Scatter Factor for Photon Beam Accelerators

Mohammad Javad Tahmasebi Birgani  1 , Nahid Chegeni  2 , Mohammad Ali Behrooz  3 , Marziyeh Bagheri  4 , Amir Danyaei  2 , Azin Shamsi  5
Affiliations

An Analytical Method to Calculate Phantom Scatter Factor for Photon Beam Accelerators

Mohammad Javad Tahmasebi Birgani et al. Electron Physician. .

Abstract

Introduction: One of the important input factors in the commissioning of the radiotherapy treatment planning systems is the phantom scatter factor (Sp) which requires the same collimator opening for all radiation fields. In this study, we have proposed an analytical method to overcome this issue.

Methods: The measurements were performed using Siemens Primus Plus with photon energy 6 MV for field sizes from 5×5cm2 to 40×40cm2. Phantom scatter factor was measured through the division of total scatter output factors (Scp), and collimator scatter factor (Sc).

Results: The mean percent difference between the measured and calculated Sp was 1.00% and -3.11% for 5×5, 40×40 cm2 field size respectively.

Conclusion: This method is applicable especially for small fields used in IMRT which, measuring collimator scatter factor is not reliable due to the lateral electron disequilibrium.

Keywords: Phantom scatter factor; Radiotherapy; Total scatter factor.

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Conflict of interest statement

Conflict of Interest: There is no conflict of interest to be declared.

Figures

Figure 1
Figure 1
Formula in the study
Figure 2
Figure 2
(a) Diagram of under-radiation treatment volume in the standard mode of SSD=100 for reference field (VEFGH) and a small field (VABCD). In order to maintain collimator opening for smaller fields than the reference field, the phantom surface can be pulled up to the collimator location (A′B′). (b) DMCN, D″M″C″N″ are the projection the field size L at distance OS′, OJ′.
Figure 3
Figure 3
Polar system to calculate the scatter contribution to dosimeter location (S′) for a rectangular field with dimensions (2Y × 2X).
Figure 4
Figure 4
Phantom scatter factor (Sp) measured and calculated using various energy attenuation formula.
See this image and copyright information in PMC

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