Small‐field electron dosimetry for the Philips SL25 linear accelerator

Rashid, Harunor; Islam, Mohammad K.; Gaballa, H.; Rosenow, U.; Ting, Joseph

doi:10.1118/1.596471

Cited by 29 publications

(18 citation statements)

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“…Output factors for clinical electron beams are known to depend in a fairly unpredictable way on the electron energy and the geometry of the jaws, applicator, and the final fielddefining cutout. 6,7 This therefore makes analytical calcula-tion of output factors difficult, 8,9 especially for irregular and small fields. This was recently discussed by Kapur et al 10 Furthermore, measurement of output factors for the smallest fields used in clinical practice is beset with practical difficulties.…”

Section: Introductionmentioning

confidence: 99%

“…12 By comparing measured and calculated dose distributions in a water phantom, the MC simulation parameters were adjusted to give a reasonable match between measurements and calculation. For the [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] MeV energy range and a selection of square, rectangular, and circular fields, output factors were calculated and compared to measurements. A similar work, limited to square fields and three electron energies ͑6, 12, and 20 MeV͒ was recently presented by Kapur et al 10 It would be particularly useful if an MC model developed for a specific linac could also be used to model other similar linacs.…”

Section: Introductionmentioning

confidence: 99%

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Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6–20 MeV)

et al. 2001

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Monte Carlo (MC) techniques can be used to build a simulation model of an electron accelerator to calculate output factors for electron fields. This can be useful during commissioning of electron beams from a linac and in clinical practice where irregular fields are also encountered. The Monte Carlo code BEAM/EGS4 was used to model electron beams (6-20 MeV) from a Varian 2100C linear accelerator. After optimization of the Monte Carlo simulation model, agreement within 1% to 2% was obtained between calculated and measured (with a Si diode) lateral and depth dose distributions or within 1 mm in the penumbral regions. Output factors for square, rectangular, and circular fields were measured using two different plane-parallel ion chambers (Markus and NACP) and compared to MC simulations. The agreement was usually within 1% to 2%. This study was not primarily concerned with minimizing the simulation time required to obtain output factors but some considerations with respect to this are presented. It would be particularly useful if the MC model could also be used to calculate output factors for other, similar linacs. To see if this was possible, the primary electron energies in the MC model were retuned to model a recently commissioned similar linac. Good agreement between calculated and measured output factors was obtained for most field sizes for this second accelerator.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6–20 MeV)

et al. 2001

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“…10 In addition, outputs of rectangular fields have been predicted from square-field data, using the squareroot method and the one-dimensional method. 3,6,7,9,11,12 The use of polynomial equations to fit square and rectangular field outputs have also been described. 6,9,13 The equivalent-square and square-root methods do not accurately predict output factors for irregularly shaped fields.…”

Section: Introductionmentioning

confidence: 99%

A sector‐integration method for calculating the output factors of irregularly shaped electron fields

Jursinic¹,

Mueller²

1997

Medical Physics

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Articles you may be interested inFinal Aperture Superposition Technique applied to fast calculation of electron output factors and depth dose curves Med. A practical method for the calculation of multileaf collimator shaped fields output factors Med. Phys. 26, 2385 (1999); 10.1118/1.598754 Monte Carlo investigation of electron beam output factors versus size of square cutout Med. Phys. 26, 743 (1999); 10.1118/1.598582Calculating output factors for photon beam radiotherapy using a convolution/superposition method based on a dual source photon beam model Med.An empirical model is presented that uses a sector-integration method for calculating the output factors of irregularly shaped electron fields. The sector-integration method accounts for changes in electron fluence, lateral scatter equilibrium, and scatter from the edge of a cutout shield. This method is tested for elliptical and rectangular fields with a ratio of the long-to-short axis as great as 4 to 1. Differences between measured and calculated values for output factors were less than Ϯ1%.Comparisons were also carried out for a large number of cutout shields that were used in the clinic and similar levels of accuracy were obtained. © 1997 American Association of Physicists in Medicine. ͓S0094-2405͑97͒01211-X͔

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“…Results are not fully comparable due to the dissimilar geometries and materials of applicators, however it is worth to mention that a large component of collimator-scattered electrons in the useful beam has been reported for those collimators as well as results of Monte Carlo simulations. On the contrary, the phenomenon of OFs larger than unity generally does not take place for similar electron energies and analogous small-size fields obtained by blocking the open fields using lead or Cerrobend cut-outs placed at the end of standard applicators (blocked fields), minimizing the wall-scattered electron component (Rashid et al 1990, Björk et al 2004, Amin et al 2011. In such cases OFs monotonically decrease below unity for field size below 10 × 10 cm 2 .…”

Section: Discussionmentioning

confidence: 75%

Radiotherapy electron beams collimated by small tubular applicators: characterization by silicon and diamond diodes

Bagalà¹,

Venanzio²,

Falco³

et al. 2013

Phys. Med. Biol.

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High-energy electron beams generated by linear accelerators, typically in the range 6 to 20 MeV, are used in small field sizes for radiotherapy of localized superficial tumors. Unshielded silicon diodes (Si-D) are commonly considered suitable detectors for relative dose measurements in small electron fields due to their high spatial resolution. Recently, a novel synthetic single crystal diamond diode (SCDD) showed suitable properties for standard electron beams and small photon beams dosimetry. The aim of the present study is twofold: to characterize 6 to 15 MeV small electron beams shaped by using commercial tubular applicators with 2, 3, 4 and 5 cm diameter and to assess the dosimetric performance under such irradiation conditions of the novel SCDD dosimeter by comparison with commercially available dosimeters, namely a Si-D and a plane-parallel ionization chamber. Percentage depth dose curves, beam profiles and output factors (OFs) were measured. A good agreement among the dosimeters was observed in all of the performed measurements. As for the tubular applicators, two main effects were evidenced: (i) OFs larger than unity were measured for a number of field sizes and energies, with values up to about 1.3, that is an output 30% greater than that obtained at the 10 × 10 cm 2 reference field; (ii) for each diameter of the tubular applicator a noticeable increase of the OF values was observed with increasing beam energy, up to about 100% in the case of the smaller applicator. This OF behavior is remarkably different from what typically observed for small blocked fields having the same size and energy as those used in this study. OFs for tubular applicators depend considerably on the field size, so interpolation is unadvisable to predict the linear accelerator output for such applicators whereas reliable high-resolution detectors, as the

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Small‐field electron dosimetry for the Philips SL25 linear accelerator

Cited by 29 publications

References 0 publications

Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6–20 MeV)

Monte Carlo calculation of output factors for circular, rectangular, and square fields of electron accelerators (6–20 MeV)

A sector‐integration method for calculating the output factors of irregularly shaped electron fields

Radiotherapy electron beams collimated by small tubular applicators: characterization by silicon and diamond diodes

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