A modified method of calculating the lateral build-up ratio for small electron fields

Tyner, Elaine; McCavana, Patrick; McClean, Brendan

doi:10.1088/0031-9155/51/12/n02

Cited by 4 publications

(9 citation statements)

References 9 publications

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“…where D is the dose, is the incidence fluence of the electron field at the phantom surface, R is radius of the cutout, R ∞ is the open field of the applicator, z is the depth of the measurement in the phantom relative to the surface, and E is energy of the electron beam. It is discussed by Khan et al 11 and Tyner et al 13 that the incident fluence of electrons is uniform in intensity and energy distribution inside the cutout regions at the surface of the phantom. Normalizing the depth dose curves at a depth between the surface and a depth of 2-3 mm removes the electron fluence dependence which simplifies Eq.…”

Section: Discussionmentioning

confidence: 99%

“…11,12 Khan et al 11 determined the LBR of an arbitrary circular cutout using its radius (R) and a lateral spread parameter [σ R (z)], which they assumed is independent of cutout size for a given energy and used the σ R (z) value of a 2.0 cm diameter circular cutout in their calculations. Tyner et al 13 determined the LBR values of an arbitrary cutout from interpolation of the measured PDD curves. Chow 14 employed Monte Carlo simulation to calculate the LBR and used the MC code to determine the PDD and dose per monitor unit of an irregular shaped cutout.…”

Section: Introductionmentioning

confidence: 99%

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Dose calculation for electron therapy using an improved LBR method

2013

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In this research, it is shown that the lateral spread parameter σR(z) increases with cutout size. For radii of circular cutout sizes up to the equilibrium range of the electron beam, the increase of σR(z) with the cutout size is linear. The percentage difference of the calculated PDD curve from the measured PDD data for irregularly shaped cutouts was under 1.0% in the region between the surface and therapeutic range of the electron beam. Similar results were obtained for four electron beam energies (6, 9, 12, and 15 MeV).

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Dose calculation for electron therapy using an improved LBR method

2013

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“…To calculate dose/MU at different depths for irregular fields using AF, CF and PDD data, the Fermi-Eyges theory 18 of small angle electron multiple Coulomb scattering ͑FE theory of MCS͒ was used to derive the nth root sector product method. The AFF, IFF, and LBR data were used in Tyner et al's method, 14 to calculate dose/MU for irregularly shaped fields.…”

Section: Methodsmentioning

confidence: 99%

“…where R 0 is the side of the reference square applicator, or is the radius of the reference circular applicator, and d 0 is the depth of normalization or fluence measurement in the phantom. Tyner et al 14 have defined the LBR, for a given electron beam of energy E, as the ratio of the depth dose for a circular field of radius R to the depth dose for a broad field of radius R ϱ , at depth z, which is given by…”

Section: Iia2 Definitions Of the Lbrmentioning

confidence: 99%

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The root percent depth dose method for calculating monitor units for irregularly shaped electron fields

Kehwar

Huq

2008

Medical Physics

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This study outlines an improved method for calculating dose per monitor unit values for irregularly shaped electron fields using the nth root percent depth dose method. This method calculates the percent depth dose and output factors for an irregularly shaped electron field directly from the measured electron beam percent depth dose curves and output factors for circular fields. The percent depth dose curves and output factors for circular fields are normalized and measured at a fixed depth of maximum dose for a reference field, respectively. When compared with the sector integral lateral buildup ratio method, the percent depth dose data calculated using the nth root method accounts more accurately for the change in lateral scatter with decreasing field size. Therefore, it provides more accurate values of dose per monitor unit at different depths for all type of field shapes and beam energies. For beam energies in the range of 6-21 MeV, the differences between measured and calculated dose per monitor unit values, at different depths, were found to be within +/- 1.0% when the nth root percent depth dose method was used for calculation and 12.6% when the sector integral lateral buildup ratio method was used. The nth root percent depth dose method was tested and compared with the sector integral lateral buildup ratio method for ten clinically used irregularly shaped inserts (cutouts). For small irregularly shaped fields, a maximum difference of 2% was found between calculated dose per monitor unit values and measurements when the nth root percent depth dose method was used; this difference changed to 7% when comparisons were made between measurements and calculations based on the sector integral lateral buildup ration method. For large irregular fields this difference was found to be within 1.5% and 3.5%, respectively.

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Planar dose calculation of electron therapy

Gebreamlak,

Alkhatib

2024

Biomed. Phys. Eng. Express

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Purpose:The purpose of this study is to compute the planar dose distribution of irregularly shaped electron beams at their maximum dose depth (zmax) using the modiﬁed lateral build-up-ratio (LBR) and curve-fitting methods.Methods:Circular and irregular cutouts were created using Cerrobend alloy for a 14×14 cm2 applicator. Percentage depth dose (PDD) at the standard source-surface-distance (SSD = 100 cm) and point dose at diﬀerent SSD were measured for each cutout. Orthogonal proﬁles of the cutouts were measured at zmax. The data were collected for 6, 9, 12, and 15 MeV electron beam energies on a VERSA HDTM LINAC using the iba Blue Phantom2 3D water phantom system. The planar dose distributions of the cutouts were also measured at zmax in solid water using EDR2 ﬁlms.Results:The measured PDD curves were normalized to a normalization depth (d0) of 1 mm. Each cutout's lateral-buildup-ratio (LBR), lateral spread parameter (σR(z)), and eﬀective SSD (SSDeff) were calculated using the PDD of the open applicator as the reference ﬁeld. The modified LBR method was then used to calculate the planar dose distribution of the irregular cutouts inside the field at least 5 mm from the edge. A simple curve-fitting model was developed based on the profile shapes of the circular cutouts around the field edge. This model was used to calculate the planar dose distribution of irregular cutouts in the region from 3 mm outside to 5 mm inside the field edge. Finally, the calculated dose distribution was compared with the film measurement. Conclusions:The planar dose distribution of electron therapy for irregular cutouts at zmax was calculated using the improved LBR method and a simple curve-fitting model. The calculated profiles were within 3% of the measured. The gamma passing rate with 3%/3mm was more than 96%.

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A modified method of calculating the lateral build-up ratio for small electron fields

Cited by 4 publications

References 9 publications

Dose calculation for electron therapy using an improved LBR method

Dose calculation for electron therapy using an improved LBR method

The root percent depth dose method for calculating monitor units for irregularly shaped electron fields

Planar dose calculation of electron therapy

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