### Abstract

Wedged asymmetric fields are commonly encountered in radiation therapy. Most treatment planning systems (TPSs) calculate the off-axis wedge factors (WF_{oc}) by multiplying the central axis wedge factor (WF_{c}) by the ratio of transmissions along the off-axis ray to that along the central-axis. Therefore the wedge shape determines the off-axis wedge factors. However, during TPS commissioning, it is often necessary to modify the physical wedge shape in order to fit the measured wedged dose distributions. This can result an inaccurate calculation of WF_{oc}. To determine the accuracy of TPS calculations, WF_{oc} measurements for various asymmetric beams produced by dual energy VARIAN 2100C and 6/100R linear accelerators and a Theratronics-1000 Co-60 unit were done. For the 2100C linear accelerator, the FOCUS calculated WF_{oc}'s for all wedges were in good agreement with measured values (< 2% for 15°, 30°, and 45° wedges, and approximately 3% for 60° wedge). For 6/100R and Co-60 unit, the difference between calculated and measured WF_{oc} varied from 4 - 10% depending on the wedge angle and off-axis distance. To improve the accuracy of WF_{oc} calculations, wedges were represented in the TPS in two versions: planning and calculational. The planning wedge has a shape that produces accurate calculations of dose distributions and the calculational wedge shape assures an accurate (within ≈ 1%) calculation of WF_{oc}'s.

Original language | English (US) |
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Title of host publication | Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings |

Editors | J.D Enderle |

Pages | 1085-1087 |

Number of pages | 3 |

Volume | 2 |

State | Published - 2000 |

Externally published | Yes |

Event | 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society - Chicago, IL, United States Duration: Jul 23 2000 → Jul 28 2000 |

### Other

Other | 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society |
---|---|

Country | United States |

City | Chicago, IL |

Period | 7/23/00 → 7/28/00 |

### Fingerprint

### Keywords

- Asymmetric fields
- Off-axis wedge factors
- Treatment planning

### ASJC Scopus subject areas

- Bioengineering

### Cite this

*Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings*(Vol. 2, pp. 1085-1087)

**A method that significantly improves accuracy of MU/time calculations for wedged asymmetric fields.** / Leybovich, L.; Dogan, Nesrin; Sethi, A.

Research output: Chapter in Book/Report/Conference proceeding › Conference contribution

*Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings.*vol. 2, pp. 1085-1087, 22nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Chicago, IL, United States, 7/23/00.

}

TY - GEN

T1 - A method that significantly improves accuracy of MU/time calculations for wedged asymmetric fields

AU - Leybovich, L.

AU - Dogan, Nesrin

AU - Sethi, A.

PY - 2000

Y1 - 2000

N2 - Wedged asymmetric fields are commonly encountered in radiation therapy. Most treatment planning systems (TPSs) calculate the off-axis wedge factors (WFoc) by multiplying the central axis wedge factor (WFc) by the ratio of transmissions along the off-axis ray to that along the central-axis. Therefore the wedge shape determines the off-axis wedge factors. However, during TPS commissioning, it is often necessary to modify the physical wedge shape in order to fit the measured wedged dose distributions. This can result an inaccurate calculation of WFoc. To determine the accuracy of TPS calculations, WFoc measurements for various asymmetric beams produced by dual energy VARIAN 2100C and 6/100R linear accelerators and a Theratronics-1000 Co-60 unit were done. For the 2100C linear accelerator, the FOCUS calculated WFoc's for all wedges were in good agreement with measured values (< 2% for 15°, 30°, and 45° wedges, and approximately 3% for 60° wedge). For 6/100R and Co-60 unit, the difference between calculated and measured WFoc varied from 4 - 10% depending on the wedge angle and off-axis distance. To improve the accuracy of WFoc calculations, wedges were represented in the TPS in two versions: planning and calculational. The planning wedge has a shape that produces accurate calculations of dose distributions and the calculational wedge shape assures an accurate (within ≈ 1%) calculation of WFoc's.

AB - Wedged asymmetric fields are commonly encountered in radiation therapy. Most treatment planning systems (TPSs) calculate the off-axis wedge factors (WFoc) by multiplying the central axis wedge factor (WFc) by the ratio of transmissions along the off-axis ray to that along the central-axis. Therefore the wedge shape determines the off-axis wedge factors. However, during TPS commissioning, it is often necessary to modify the physical wedge shape in order to fit the measured wedged dose distributions. This can result an inaccurate calculation of WFoc. To determine the accuracy of TPS calculations, WFoc measurements for various asymmetric beams produced by dual energy VARIAN 2100C and 6/100R linear accelerators and a Theratronics-1000 Co-60 unit were done. For the 2100C linear accelerator, the FOCUS calculated WFoc's for all wedges were in good agreement with measured values (< 2% for 15°, 30°, and 45° wedges, and approximately 3% for 60° wedge). For 6/100R and Co-60 unit, the difference between calculated and measured WFoc varied from 4 - 10% depending on the wedge angle and off-axis distance. To improve the accuracy of WFoc calculations, wedges were represented in the TPS in two versions: planning and calculational. The planning wedge has a shape that produces accurate calculations of dose distributions and the calculational wedge shape assures an accurate (within ≈ 1%) calculation of WFoc's.

KW - Asymmetric fields

KW - Off-axis wedge factors

KW - Treatment planning

UR - http://www.scopus.com/inward/record.url?scp=0034445048&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0034445048&partnerID=8YFLogxK

M3 - Conference contribution

VL - 2

SP - 1085

EP - 1087

BT - Annual International Conference of the IEEE Engineering in Medicine and Biology - Proceedings

A2 - Enderle, J.D

ER -