NCS Report 12: Determination and use of scatter correction factors of megavoltage photon beams

Gasteren, J.J.M. van; Heukelom, S.; Jager, H.N.; Mijnheer, Ben J.; Laarse, R. van der; Kleffens, H.J. van; Venselaar, J.L.M.; Westermann, C.F.

doi:10.25030/ncs-012

Cited by 15 publications

(18 citation statements)

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“…The S C measured reflects the relative change of photon and electron fluence per monitor unit as a function of collimator opening. The recent ESTRO, literatures [5,18] recommend the use of build-up caps of square or cylindrical shapes with long axis parallel with beam central axis, and the ion chamber is placed at 5 or 10 cm depth. These build-up caps are generally called as columnar miniphantoms and the 5 or 10 cm depth completely avoids dose from contamination electrons depending on energy.…”

Section: Introduction Introduction Introductionmentioning

confidence: 99%

Measurement of Head Scatter Factor for Linear Accelerators using Indigenously Designed Columnar Mini Phantom

Appasamy¹,

Xavier

Thayalan

et al. 2011

Polish Journal of Medical Physics and Engineering

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A columnar mini phantom is designed as recommended by ESTRO to measure the Head Scatter Factor (S C ) for 6 MV beam of two linear accelerators. The measurement of S C at different orientations of the chamber, parallel and perpendicular at 1.5 cm depth predicts the deviation of 2.05% and 1.9% for Elekta and Siemens linear accelerators respectively. The measurement of S C at 1.5 cm is higher compared to 10 cm depth for both the linear accelerators suggesting the electron contamination at 1.5 cm depth. The effect of wedges on S C yields a significant contribution of 3.5% and 5% for Siemens and Elekta linear accelerators respectively. The collimator exchange effect reveals the opening of upper jaw increases the S C irrespective of the linear accelerator. The result emphasizes the need of S C measurement at 10 cm. The presence of wedge influences the S C value and the SSD has no influence on S C . The measured S C values are in good agreement with the published data.

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Section: Introduction Introduction Introductionmentioning

confidence: 99%

Measurement of Head Scatter Factor for Linear Accelerators using Indigenously Designed Columnar Mini Phantom

Appasamy¹,

Xavier

Thayalan

et al. 2011

Polish Journal of Medical Physics and Engineering

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“…It was observed in previous work 3 and in studies with wedges 15 that the change in phantom scatter contribution to the dose caused by the insertion of a tray in the beam can be ignored, as no noticeable beam hardening or softening occurs. Consequently, the ratio of phantom scatter correction factors in Eq.…”

Section: Methodsmentioning

confidence: 94%

“…Results of measurements with blocks have been described by several authors. 1,3,13,21 It was concluded that only in case the field of view of the flattening filter from the point of interest in the phantom is obscured by the blocks will the head-scatter component of the output factor vary. A systematic investigation of the influence of the blocks on the tray factor was performed by Jursinic in 6 and 18 MV beams.…”

Section: Discussionmentioning

confidence: 99%

“…This is consistent with the use of other quantities in a recommended dose calculation system, such as output factors and its constituents S c and S p , and wedge factors. 2,3,5 The influence of electron contamination on depth-dose characteristics due to the presence of a tray must be investigated separately and can be taken into account by using depth-dose data measured specifically for this purpose. As pointed out by Schaeken and Van Loon, a shift of d max can be found and the loss of skin sparing can be considerable.…”

Section: Discussionmentioning

confidence: 99%

“…However, from the equations given above it is clear that measurements performed in a miniphantom should in principle give similar results compared with those obtained at the same depth in a full-scatter water phantom if the same source-surface distance is applied. In addition to our previous work, 3 we have repeated a number of measurements in different beams to assess the limitations of this statement.…”

Section: Methodsmentioning

confidence: 99%

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Dependence of the tray transmission factor on collimator setting and source-surface distance

Kleffens¹,

Venselaar²,

Heukelom³

et al. 2000

Med. Phys.

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When blocks are placed on a tray in megavoltage x-ray beams, generally a single correction factor for the attenuation by the tray is applied for each photon beam quality. In this approach, the tray transmission factor is assumed to be independent of field size and source-surface distance (SSD). Analysis of a set of measurements performed in beams of 13 different linear accelerators demonstrates that there is, however, a slight variation of the tray transmission factor with field size and SSD. The tray factor changes about 1.5% for collimator settings varying between 4x4 cm and 40 x 40 cm for a 1 cm thick PMMA tray and approximately 3% for a 2 cm thick PMMA tray. The variation with field size is smaller if the source-surface distance is increased. The dependence on the collimator setting is not different, within the experimental uncertainty of about 0.5% (1 s.d.), for the nominal accelerating potentials and accelerator types applied in this study. It is shown that the variation of the tray transmission factor with field size and source-surface distance can easily be taken into account in the dose calculation by considering the volume of the irradiated tray material and the position of the tray in the beam. A relation is presented which can be used to calculate the numerical value of the tray transmission factor directly. These calculated values can be checked with only a few measurements using a cylindrical beam coaxial miniphantom.

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A comparison between direct TMR measurements and TMRs calculated from PDDs using BJR Supplement 25 data for flattened and unflattened photon beams

Sutherland¹,

Middlebrook²,

Kairn

et al. 2015

Australas Phys Eng Sci Med

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This study assessed the validity of the conversion from percentage depth dose (PDD) to tissue maximum ratio (TMR) using BJR Supplement 25 data for flattened and flattening filter free (FFF) beams. PDD and TMR scans for a variety of field sizes were measured in water using a Sun Nuclear Corporation 3D SCANNER™ on a Varian TrueBeam linear accelerator in 6 MV, 10 MV and 6 MV FFF beams. The BJR Supplement 25 data was used to convert the measured PDDs to TMRs and these were compared with the directly measured TMR data. The TMR plots calculated from PDD were within 1% for the 10 MV and 6 MV flattened beams, for field sizes 3 cm × 3 cm to 40 cm × 40 cm inclusive, at depths measured beyond the depth of maximum dose. The disagreement between the measured and calculated TMR plots for the 6 MV FFF beam increased with depth and field size to a maximum of 1.7% for a 40 cm × 40 cm field. The results found in this study indicate that the BJR Supplement 25 data should not be used for field sizes larger than 20 cm × 20 cm at depths greater than 15 cm for the 6 MV FFF beam. It is advised that PDD to TMR conversion for FFF beams should be done with phantom scatter ratios appropriate to FFF beams, or the TMR should be directly measured if required.

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NCS Report 12: Determination and use of scatter correction factors of megavoltage photon beams

Cited by 15 publications

References 0 publications

Measurement of Head Scatter Factor for Linear Accelerators using Indigenously Designed Columnar Mini Phantom

Measurement of Head Scatter Factor for Linear Accelerators using Indigenously Designed Columnar Mini Phantom

Dependence of the tray transmission factor on collimator setting and source-surface distance

A comparison between direct TMR measurements and TMRs calculated from PDDs using BJR Supplement 25 data for flattened and unflattened photon beams

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