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. 2015 May-Jun;20(3):170-80.
doi: 10.1016/j.rpor.2015.02.001. Epub 2015 Mar 1.

Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom

Sigamani Ashokkumar  1 , Arunai Nambiraj  2 , Sujit Nath Sinha  3 , Girigesh Yadav  3 , Kothanda Raman  3 , Manindra Bhushan  3 , Rajesh Thiyagarajan  1
Affiliations

Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom

Sigamani Ashokkumar et al. Rep Pract Oncol Radiother. 2015 May-Jun.

Abstract

Aim: To measure and compare the head scatter factor for 7 MV unflattened and 6 MV flattened photon beam using a home-made designed mini phantom.

Background: The head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators.

Materials and methods: A columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10 cm and d max dose water equivalent thickness.

Results: The Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6-2.2% (Primus), 0.2-1.4% (Artiste) and 0.6-3.7% (Clinac iX (2300CD))) for field sizes ranging from 10 cm × 10 cm to 40 cm × 40 cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF.

Conclusions: There were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10 cm × 10 cm to 40 cm × 04 cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms.

Keywords: 6MV-FB; 7MV-UFB; Linear accelerators; Mini phantom; Sc factor.

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Figures

Fig. 1
Fig. 1
Block diagram of PMMA columnar mini phantom.
Fig. 2
Fig. 2
Schematic diagram of columnar mini phantom experimental setup in linear accelerator.
Fig. 3
Fig. 3
Variation of Sc with field size for with the mini phantom and brass bulid-up cap at 10.0 cm and 1.5 cm equivalent depth respectively in Simens Priums and Artiste machines for 6MV-FB and 7MV-UFB beams.
Fig. 4
Fig. 4
Variation of Sc with various field sizes for 6MV-FB and 7MV-UFB measured in Siemens Artiste.
Fig. 5
Fig. 5
Variation of Sc with field size for different SSD for 6MV-FB and 7MV-UFB measured in Siemen (Artiste and Primus) and Varian (Clinac iX).
Fig. 6
Fig. 6
Variation of Sc with field size for wedge and open beams for 6MV-FB and 7MV-UFB measured in Siemens (Primus and Artiste).
Fig. 7
Fig. 7
Variation of Sc for different field size with 30° wedge filter for different SSD for 6MV-FB and 7MV-UFB measured in Siemens (Artiste and Primus) accelerator.
Fig. 8
Fig. 8
Sc values for three different linear accelerators with different field sizes for 6MV-FB and 7MV-UFB.
Fig. 9
Fig. 9
Variation of Sc for rectangular fields with X and Y jaws exchanged in Siemens (Artiste) and Varian (Clinac iX) linear accelerators.
Fig. 10
Fig. 10
The collimator exchange effect in 7MV-UFB for larger and smaller asymmetric fields. The measured Sc factors are plotted as a function of the one field side, keeping either the X-lower or the Y-(upper) jawas fixed at 5.0 cm.
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