Limits...
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

Mean confidence limit as a function of commissioning set and depth. The abscissa is 4(i-1)+k, where i is the commissioning set index and k is the depth index (1 through 4). Thus, points 1 through 4 correspond to set 1, depths d1 through d4, while points 37 through 40 correspond to set 10, depths d1 through d4, for example. SSD = 100 cm (top), 110 cm (middle), 120 cm (bottom).
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Figure 4: Mean confidence limit as a function of commissioning set and depth. The abscissa is 4(i-1)+k, where i is the commissioning set index and k is the depth index (1 through 4). Thus, points 1 through 4 correspond to set 1, depths d1 through d4, while points 37 through 40 correspond to set 10, depths d1 through d4, for example. SSD = 100 cm (top), 110 cm (middle), 120 cm (bottom).

Mentions: We gain a fuller understanding of the simulation results by examining their depth dependence, which we have so far suppressed. Fig. 4 shows mean values of the depth dependent confidence limits as a function of depth index and commissioning set for SSD = 100 cm. (Graphs for SSD = 110 and 120 cm are similar, but show elevation of the confidence limits with increasing SSD.) The means in this case are only over beams. Especially noteworthy are two features. The first is the presence in some of the graphs of elevated values occurring at d4 = R50 and sometimes at d1 = 0.50 cm. Evidently, the confidence limits increase significantly at or near depths of R50 (though, curiously, Δ(RW50) decreases here), and this may suggest a trend of degraded performance with increasing depth. The other noteworthy feature concerns the two sets we have identified as stragglers, i.e. the minimal sets 1 and 6. Inspection shows that much of the increase in confidence limits associated with these sets is due to elevated values at d4, and that performance at lesser depths is comparable to performance of the remaining sets.


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

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

Mean confidence limit as a function of commissioning set and depth. The abscissa is 4(i-1)+k, where i is the commissioning set index and k is the depth index (1 through 4). Thus, points 1 through 4 correspond to set 1, depths d1 through d4, while points 37 through 40 correspond to set 10, depths d1 through d4, for example. SSD = 100 cm (top), 110 cm (middle), 120 cm (bottom).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC1074715&req=5

Figure 4: Mean confidence limit as a function of commissioning set and depth. The abscissa is 4(i-1)+k, where i is the commissioning set index and k is the depth index (1 through 4). Thus, points 1 through 4 correspond to set 1, depths d1 through d4, while points 37 through 40 correspond to set 10, depths d1 through d4, for example. SSD = 100 cm (top), 110 cm (middle), 120 cm (bottom).
Mentions: We gain a fuller understanding of the simulation results by examining their depth dependence, which we have so far suppressed. Fig. 4 shows mean values of the depth dependent confidence limits as a function of depth index and commissioning set for SSD = 100 cm. (Graphs for SSD = 110 and 120 cm are similar, but show elevation of the confidence limits with increasing SSD.) The means in this case are only over beams. Especially noteworthy are two features. The first is the presence in some of the graphs of elevated values occurring at d4 = R50 and sometimes at d1 = 0.50 cm. Evidently, the confidence limits increase significantly at or near depths of R50 (though, curiously, Δ(RW50) decreases here), and this may suggest a trend of degraded performance with increasing depth. The other noteworthy feature concerns the two sets we have identified as stragglers, i.e. the minimal sets 1 and 6. Inspection shows that much of the increase in confidence limits associated with these sets is due to elevated values at d4, and that performance at lesser depths is comparable to performance of the remaining sets.

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