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Monte Carlo Commissioning of Low Energy Electron Radiotherapy Beams using NXEGS Software.

Both JA, Pawlicki T - Int J Med Sci (2004)

Bottom Line: Central axis depth-dose, primary axis and diagonal beam profiles, and output factors are the measurements necessary for commissioning of the code.We present a comparison of measured dose distributions with the distributions generated by NXEGS, using confidence limits on seven measures of error.We find that confidence limits are typically less than 3% or 3 mm, but increase with increasing source to surface distance (SSD) and depth at or beyond R(50).

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
This work is a report on the commissioning of low energy electron beams of a medical linear accelerator for Monte Carlo dose calculation using NXEGS software (NXEGS version 1.0.10.0, NX Medical Software, LLC). A unique feature of NXEGS is automated commissioning, a process whereby a combination of analytic and Monte Carlo methods generates beam models from dosimetric data collected in a water phantom. This study uses NXEGS to commission 6, 9, and 12 MeV electron beams of a Varian Clinac 2100C using three applicators with standard inserts. Central axis depth-dose, primary axis and diagonal beam profiles, and output factors are the measurements necessary for commissioning of the code. We present a comparison of measured dose distributions with the distributions generated by NXEGS, using confidence limits on seven measures of error. We find that confidence limits are typically less than 3% or 3 mm, but increase with increasing source to surface distance (SSD) and depth at or beyond R(50). We also investigate the dependence of NXEGS' performance on the size and composition of data used to commission the program, finding a weak dependence on number of dose profiles in the data set, but finding also that commissioning data need be measured at only two SSDs.

No MeSH data available.


Related in: MedlinePlus

Comparison of mean confidence limit as in Fig. 3, but for two independent commissionings of the 6 MeV 10×10 cm2 beam. Circle, δ1,pdd; × , δ 2,pdd; +, RW50; *, Fr; square, δ 2; diamond, δ 3; triangle, δ 4. SSD = 100 cm (left), 110 cm, 120 cm (right). The units of the ordinate are % or mm, as appropriate. Dotted and solid lines differentiate the cases 1 and 2.
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Figure 5: Comparison of mean confidence limit as in Fig. 3, but for two independent commissionings of the 6 MeV 10×10 cm2 beam. Circle, δ1,pdd; × , δ 2,pdd; +, RW50; *, Fr; square, δ 2; diamond, δ 3; triangle, δ 4. SSD = 100 cm (left), 110 cm, 120 cm (right). The units of the ordinate are % or mm, as appropriate. Dotted and solid lines differentiate the cases 1 and 2.

Mentions: Finally, it is important to note that any one simulation with NXEGS is in fact the result of two consecutive stochastic processes, namely the generation of the beam model from the commissioning set and the simulation of the beam with the model. It is of interest, therefore, to compare the results of two independent commissionings of NXEGS for the same beam, to see whether significant differences in beam simulation results arise. We arbitrarily choose the 6 MeV, 10×10 cm2 beam, and commission NXEGS twice, using different random number generator seeds, with data sets 1 through 10, as described in Table I. This results in 10 pairs of corresponding beam models. With each model, we perform five independent simulations of dose in a water phantom, and extract PDDs and profiles as described earlier. Then for each of the two sets of commissionings we calculate Δijkl =/ μijkl /+1.5 × σijkl and compute 〈Δijkl 〉 as given in Eqns. (1,2) (here the beam index m is suppressed). Fig. 5 superposes 〈Δijl 〉 for both commissioning trials. For the most part, these results track each other satisfactorily. We have found that the typical absolute percentage difference between 〈Δil 〉1 and 〈Δil 〉2 (defined by Eqn. (3); subscripts designate the commissioning trials) is on the order of 1-10%, which suggests reasonable insensitivity of NXEGS to random differences in beam models.


Monte Carlo Commissioning of Low Energy Electron Radiotherapy Beams using NXEGS Software.

Both JA, Pawlicki T - Int J Med Sci (2004)

Comparison of mean confidence limit as in Fig. 3, but for two independent commissionings of the 6 MeV 10×10 cm2 beam. Circle, δ1,pdd; × , δ 2,pdd; +, RW50; *, Fr; square, δ 2; diamond, δ 3; triangle, δ 4. SSD = 100 cm (left), 110 cm, 120 cm (right). The units of the ordinate are % or mm, as appropriate. Dotted and solid lines differentiate the cases 1 and 2.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC1074715&req=5

Figure 5: Comparison of mean confidence limit as in Fig. 3, but for two independent commissionings of the 6 MeV 10×10 cm2 beam. Circle, δ1,pdd; × , δ 2,pdd; +, RW50; *, Fr; square, δ 2; diamond, δ 3; triangle, δ 4. SSD = 100 cm (left), 110 cm, 120 cm (right). The units of the ordinate are % or mm, as appropriate. Dotted and solid lines differentiate the cases 1 and 2.
Mentions: Finally, it is important to note that any one simulation with NXEGS is in fact the result of two consecutive stochastic processes, namely the generation of the beam model from the commissioning set and the simulation of the beam with the model. It is of interest, therefore, to compare the results of two independent commissionings of NXEGS for the same beam, to see whether significant differences in beam simulation results arise. We arbitrarily choose the 6 MeV, 10×10 cm2 beam, and commission NXEGS twice, using different random number generator seeds, with data sets 1 through 10, as described in Table I. This results in 10 pairs of corresponding beam models. With each model, we perform five independent simulations of dose in a water phantom, and extract PDDs and profiles as described earlier. Then for each of the two sets of commissionings we calculate Δijkl =/ μijkl /+1.5 × σijkl and compute 〈Δijkl 〉 as given in Eqns. (1,2) (here the beam index m is suppressed). Fig. 5 superposes 〈Δijl 〉 for both commissioning trials. For the most part, these results track each other satisfactorily. We have found that the typical absolute percentage difference between 〈Δil 〉1 and 〈Δil 〉2 (defined by Eqn. (3); subscripts designate the commissioning trials) is on the order of 1-10%, which suggests reasonable insensitivity of NXEGS to random differences in beam models.

Bottom Line: Central axis depth-dose, primary axis and diagonal beam profiles, and output factors are the measurements necessary for commissioning of the code.We present a comparison of measured dose distributions with the distributions generated by NXEGS, using confidence limits on seven measures of error.We find that confidence limits are typically less than 3% or 3 mm, but increase with increasing source to surface distance (SSD) and depth at or beyond R(50).

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, CA 94305, USA.

ABSTRACT
This work is a report on the commissioning of low energy electron beams of a medical linear accelerator for Monte Carlo dose calculation using NXEGS software (NXEGS version 1.0.10.0, NX Medical Software, LLC). A unique feature of NXEGS is automated commissioning, a process whereby a combination of analytic and Monte Carlo methods generates beam models from dosimetric data collected in a water phantom. This study uses NXEGS to commission 6, 9, and 12 MeV electron beams of a Varian Clinac 2100C using three applicators with standard inserts. Central axis depth-dose, primary axis and diagonal beam profiles, and output factors are the measurements necessary for commissioning of the code. We present a comparison of measured dose distributions with the distributions generated by NXEGS, using confidence limits on seven measures of error. We find that confidence limits are typically less than 3% or 3 mm, but increase with increasing source to surface distance (SSD) and depth at or beyond R(50). We also investigate the dependence of NXEGS' performance on the size and composition of data used to commission the program, finding a weak dependence on number of dose profiles in the data set, but finding also that commissioning data need be measured at only two SSDs.

No MeSH data available.


Related in: MedlinePlus