Conference proceeding
SU‐GG‐T‐220: Dosimetric Error From Inter‐Fraction Tumor Motion Variation in Phase Based Gating
Medical Physics, Vol.35(6), pp.2776-2776
06/2008
DOI: 10.1118/1.2961972
Abstract
Purpose: To characterize dosimetric errors from inter‐fraction tumor motion variation for phase‐based gated treatments that use strain gauge systems. Method and Materials: An ionization chamber in a Quasar Respiratory Motion Phantom was irradiated in a 6 MV 5×5 field, while moving with various amplitudes for both a sinusoidal waveform and a patient's respiratory trace. The resulting ionizations were compared to that for a stationary setup to determine the under‐dose. For each amplitude of the patient's respiratory trace, the Anzai gating system was operated at various gating phases to find the phase trigger that reduced the under‐dose below 1%. Results: The gating system gain and position settings affected the under‐doses, and for the worst case settings, a full motion range (FMR, 2x amplitude) of 12.5 mm for the patient trace, gated from 80% exhale to 80% inhale, had an under‐dose of 0.3%. FMRs of 18.8, 25 and 30 mm had under‐doses of 0.6, 3.7, and 7.2%, respectively. These FMRs correspond to gated motion ranges (GMR, motion during irradiation) of 10, 15, 20, and 24 mm. The under‐doses for sinusoidal waveforms were higher (6.4% for GMR = 20 mm), since the chamber spent less time at full exhale. The under‐doses for the patient trace are reduced to around 0.5% when the percentage phase trigger (80%) is multiplied by the ratio of the planned FMR (12.5 mm) to the observed FMR, so that an observed FMR of 25 mm requires a percentage phase trigger of 40%. Conclusion: Under‐doses are waveform dependent. A 20 mm lesion with a motion range of 10 mm can experience around a 5% under‐dose for an increase in motion of 10 mm. Errors can drop below 1% by reducing the gating phase trigger.
Details
- Title: Subtitle
- SU‐GG‐T‐220: Dosimetric Error From Inter‐Fraction Tumor Motion Variation in Phase Based Gating
- Creators
- R Siochi - University of IowaH Shukla - University of Iowa
- Resource Type
- Conference proceeding
- Publication Details
- Medical Physics, Vol.35(6), pp.2776-2776
- Publisher
- WILEY; HOBOKEN
- DOI
- 10.1118/1.2961972
- ISSN
- 0094-2405
- eISSN
- 2473-4209
- Number of pages
- 1
- Date published
- 06/2008
- Academic Unit
- Radiation Oncology
- Record Identifier
- 9984697739802771
Metrics
1 Record Views