What is a backscatter factor?
Introduction. Backscatter factor (BSF) is defined as the ratio of the collision kerma of a phantom material; at the. surface of a full scatter phantom located at a point in the beam axis, to the collision kerma of the same. material; at the same point in the primary beam, with no phantom present [1][7].
What is backscatter factor in radiotherapy?
The backscatter factor can be defined as the quotient between the absorbed. dose in the surface layer of a phantom to the absorbed dose in the same.
What is small field dosimetry?
Small fields are usually defined between 4 cm × 4 cm and 0.3 cm × 0.3 cm. [1,2] Using such field sizes can cause uncertainty in dosimetry; therefore, special attention is required in both dose calculations and measurements.
How do you calculate backscatter?
The scattering coefficient can be calculated as b = c − a (McKee et al., 2003). The scattering coefficient can also be estimated from irradiance meter measurements of reflection and diffuse attenuation coefficients, using relationships given by Kirk (2011); a value for the backscattering ratio is needed to do this.
What is BSF in radiotherapy?
Accurate calculation and knowledge of backscatter factors (BSF) in superficial x-ray radiotherapy is required to perform accurate absorbed dose determination. These measurements have been performed historically with small thin parallel plate ionisation chambers and Thermoluminescent Dosimeters (TLD’s).
What is a small field?
1 At present a small field is generally defined as having dimensions smaller than the lateral range of the charged particles that contribute to the dose deposited at a point along the central axis. 2 According to these criteria, field sizes of less than 3 × 3 cm2 are considered to be small for a 6 MV photon beam.
What is backscatter coefficient in radar?
It is a measure of the reflective strength of a radar target. The normalised measure of the radar return from a distributed target is called the backscatter coefficient, or sigma nought , and is defined as per unit area on the ground. If the signal formed by backscatter is undesired, it is called clutter.
What factors affect backscatter intensity in radar systems?
The intensity of each pixel represents the proportion of microwave backscattered from that area on the ground which depends on a variety of factors: types, sizes, shapes and orientations of the scatterers in the target area; moisture content of the target area; frequency and polarisation of the radar pulses; as well as …
Does PDD increase with field size?
It was found that the values of PDD0 increase as field size increases. The percentage depth dose at surface (PDD0) for open beams, at 80 cm, 100 cm, and 120 cm FSDs were 13.89%, 11.71%, and 10.74%, respectively, for a 10 × 10 cm2 field.