Measurement of backscatter to the monitor chamber of medical accelerators using target charge

Lam, Kwok L.; Muthuswamy, Moorthy S.; Haken, Randall K. Ten

doi:10.1118/1.598203

Cited by 35 publications

(43 citation statements)

References 9 publications

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“…This also agrees very well with recently published results for Varian machines. 5,11 We have computed the relative backscatter for dynamic wedges. The results of S cb are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…the S cb (x,y) obtained from the Monte Carlo simulation was also compared to the measured data based on counting the electronic feedback pulses or accumulative charge from the electron target. 1,11 To evaluate the effect of the backscatter on treatment fields using jaw movement, S cp (x,y) was also calculated for treatment fields using dynamic wedges.…”

Section: Methodsmentioning

confidence: 99%

“…In the past, a number of methods were investigated, including those using ionization chambers and phantoms in telescopic settings, [3][4][5][6][7] as well as techniques based on measuring electron pulses, current, or charge from the electron target of linear accelerators. 5,[8][9][10][11] In general, these published data were limited to symmetrical field settings used for the measurements. Thus, it remains unknown how to extrapolate the available data and be able to predict the effect of the backscatter for any arbitrary field.…”

Section: Introductionmentioning

confidence: 99%

“…The change of the backscatter depends on the accelerator structure and the monitor chamber construction, as discussed by other research groups as well. [3][4][5][6][7][8][9][10][11] Although the effect of the backscatter is small compared to that of the head scatter and phantom scatter, to achieve more accurate dose calculation, it is important to include the correction for the backscatter in using the convolution algorithm or any other model-based methods. 12 However, how to determine the effect of the backscatter poses a challenging problem, because the change in photon output caused by the backscatter alone is often shadowed, and thus, difficult to assess experimentally.…”

Section: Introductionmentioning

confidence: 99%

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Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

2000

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Dose per monitor unit in photon fields generated by clinical linear accelerators can be affected by the backscattered radiation into the monitor chamber from collimator jaws. Thus, it is necessary to account for the backscattered radiation in computing monitor unit setting for a treatment field. In this work, we investigated effects of the backscatter from collimator jaws based on Monte Carlo simulations of a clinical linear accelerator. The backscattered radiation scored within the monitor chamber was identified as originating either from the upper jaws ͑Y jaws͒, or from the lower jaws ͑X jaws͒. From the results of Monte Carlo simulations, ratios of the monitor-chamber-scored dose caused by the backscatter to the dose caused by the forward radiation, R(x,y), were modeled as functions of the individual X and Y jaw positions. The amount of the backscattered radiation for any field setting was then computed as a compound contribution from both the X and Y jaws. The dose ratios of R(x,y) were then used to calculate the change in photon output caused by the backscatter, S cb (x,y). Results of these calculations were compared with available measured data based on counting the electron pulses or charge from the electron target of an accelerator. Data from this study showed that the backscattered radiation contributes approximately 3% to the monitorchamber-scored dose. A majority of the backscattered radiation comes from the upper jaws, which are located closer to the monitor chamber. The amount of the backscatter decreases approximately in a linear fashion with the jaw opening. This results in about a 2% increase of photon output from a 10 cmϫ10 cm field to a 40 cmϫ40 cm field. The off-axis location of the jaw opening does not have a significant effect on the magnitude of the backscatter. The backscatter effect is significant for monitor chambers using kapton windows, particularly for treatment fields using moving jaws. Applying the backscatter correction improves the accuracy of monitor-unit calculation using a model-based dose calculation algorithm such as the convolution method. © 2000 American Association of Physicists in Medicine. ͓S0094-2405͑00͒00904-4͔

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“…This also agrees very well with recently published results for Varian machines. 5,11 We have computed the relative backscatter for dynamic wedges. The results of S cb are shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

2000

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“…The charge measured by the monitor chamber is mainly due to the secondary electrons emerging from the beam flattening filter and from the entrance foil of the monitor chamber. Several studies [2,3,5,7,[9][10][11][12][13] have indicated that there is an additional charge measured by the beam monitor chamber due to photons and electrons backscattered from the upper and lower secondary collimator jaws.…”

Section: Introductionmentioning

confidence: 99%

Measurement of Backscattered Radiation from Secondary Collimator Jaws into the Beam Monitor Chamber from a Dual Energy Linear Accelerator

Ravikumar

Ravichandran

2001

Strahlenther Onkol

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From this study a maximum reduction of 4% and 4.3% in dose delivery was observed for 6 MV and 18 MV photon beams due to backscattered radiation originating mainly from upper collimator reaching the beam monitor chamber. For asymmetric fields it is felt that direct output measurement is more reliable in order to avoid errors in output factor due to radiation backscattered from the collimator jaws into beam monitor chamber.

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A Monte Carlo study of backscatter in the monitor ion chamber for clinical photon and electron beams

Verhaegen

Symonds‐Tayler

Mubata

et al. 2000

The Use of Computers in Radiation Therapy

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Measurement of backscatter to the monitor chamber of medical accelerators using target charge

Cited by 35 publications

References 9 publications

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

Modeling photon output caused by backscattered radiation into the monitor chamber from collimator jaws using a Monte Carlo technique

Measurement of Backscattered Radiation from Secondary Collimator Jaws into the Beam Monitor Chamber from a Dual Energy Linear Accelerator

A Monte Carlo study of backscatter in the monitor ion chamber for clinical photon and electron beams

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