Accuracy of TomoEDGE dynamic jaw field widths

Abstract

Dynamic jaw delivery on the TomoTherapy H‐series platform, entitled TomoEDGE™, is an effective tool to decrease the patient dose along the superior and inferior edges of the treatment target. The aperture of the TomoTherapy jaws, that is, field width (FW), defines the longitudinal dose profile. A consistent FW dose profile is an important quantity for accurate and reproducible dose delivery in TomoTherapy. To date, no evaluation has been made of the accuracy and precision of the dose profiles produced by dynamic jaws. This study aims to provide a long‐term evaluation of the dynamic jaw FW dose profiles obtained on TomoTherapy utilizing the TomoTherapy Quality Assurance procedure (TQA). A total of 840 dose profiles were measured during 84 TQA procedures, performed over a 2‐yr period. The full width at half maximum (FWHM) and constancy of the FW dose profile measurements were analyzed and compared with the tolerances proposed by AAPM Task Group 148 (TG‐148) and those used by the manufacturer. The FWHM evaluation showed that the FWs > 2.0 cm respect the TG‐148 tolerance of 1%, while the asymmetric FWs ≤ 2.0 cm were outside the limit in 17.3% of measurements. Constancy results evaluated along the full profiles showed that 95.2% of measurements were within 3% of the baseline for symmetric FWs and 94.8% of measurements were within 4% of the baseline for asymmetric FWs. In conclusion, the analysis confirms the accuracy and precision of TomoEDGE™ technology in jaw positioning. This study has identified the potential to establish an appropriate QA tolerance for the asymmetric FWs used in dynamic jaw movement. Finally, the clinical significance of the observed discrepancies should be studied further to understand the dosimetric effect on patient treatments.

AAPM Task Group Report 306: Quality control and assurance for tomotherapy: An update to Task Group Report 148

“…A 2-year study of dynamic jaw performance showed that 1% FWHM tolerance may not be consistently met for small asymmetric field widths. 64 Since the commissioned asymmetric beam either shares an inferior or superior edge with the jaw setting of the 5.0 cm field width which is calibrated to within 1% of its FWHM, that is, 0.5 mm, a tolerance of 0.5 mm is more reasonable for the asymmetric field width accuracy. In addition, these asymmetric beams only apply to the inferior and superior target edges over a longitudinal region of one fixed beam width.…”

“…Longitudinal beam profile data is shown for an SSD = 85 cm at d max . Figures reprinted with permission from Urso et al 64 …”

“…Six of these additional beam profiles are asymmetric to the radiation isocentre along the longitudinal IEC Y direction. A 2‐year study of dynamic jaw performance showed that 1% FWHM tolerance may not be consistently met for small asymmetric field widths 64 . Since the commissioned asymmetric beam either shares an inferior or superior edge with the jaw setting of the 5.0 cm field width which is calibrated to within 1% of its FWHM, that is, 0.5 mm, a tolerance of 0.5 mm is more reasonable for the asymmetric field width accuracy.…”

Investigation on the accuracy of field widths and the quantitative relationship with energy variations for dynamic jaws helical tomotherapy

“…5 Urso et al attempted to evaluate the performance in terms of accuracy and precision of the dynamic jaws by measuring all 10 commissioned beam profiles of TomoEDGE technology for a 2-year duration. 6 Step-Wedge Helical) were the most susceptible to beam energy fluctuation. 9 Until now, no published studies on the evaluation concerning the relationship between TomoEDGE dynamic jaws field width and the energy variations.…”

“…Urso et al. attempted to evaluate the performance in terms of accuracy and precision of the dynamic jaws by measuring all 10 commissioned beam profiles of TomoEDGE technology for a 2‐year duration 6 . Binny et al.…”