In air and in vivo measurement of the leaf open time in tomotherapy using the on-board detector pulse-by-pulse data.

Détails

ID Serval
serval:BIB_8381BE603F55
Type
Article: article d'un périodique ou d'un magazine.
Collection
Publications
Titre
In air and in vivo measurement of the leaf open time in tomotherapy using the on-board detector pulse-by-pulse data.
Périodique
Medical physics
Auteur(s)
Schopfer M., Bochud F.O., Bourhis J., Moeckli R.
ISSN
2473-4209 (Electronic)
ISSN-L
0094-2405
Statut éditorial
Publié
Date de publication
05/2019
Peer-reviewed
Oui
Volume
46
Numéro
5
Pages
1963-1971
Langue
anglais
Notes
Publication types: Journal Article
Publication Status: ppublish
Résumé
We developed an algorithm to measure the leaf open times (LOT) from the on-board detector (OBD) pulse-by-pulse data in tomotherapy. We assessed the feasibility of measuring the LOTs in dynamic jaw mode and validated the algorithm on machine QA and clinical data. Knowledge of the actual LOTs is a basis toward calculating the delivered dose and performing efficient phantom-less delivery quality assurance (DQA) controls of the multileaf collimator (MLC). In tomotherapy, the quality of the delivered dose depends on the correct performance of the MLC, hence on the accuracy of the LOTs.
In the detector signal, the period of time during which a leaf is open corresponds to a high intensity region. The algorithm described here locally normalizes the detector signal and measures the FWHM of the high intensity regions. The Daily QA module of the TomoTherapy Quality Assurance (TQA) tool measures LOT errors. The Daily QA detector data were collected during 9 days on two tomotherapy units. The errors yielded by the method were compared to these reported by the Daily QA module. In addition, clinical data were acquired on the two units (25 plans in total), in air without attenuation material in the beam path and in vivo during a treatment fraction. The study included plans with fields of all existing sizes (1.05, 2.51, 5.05 cm). The collimator jaws were in dynamic mode (TomoEDGE <sup>TM</sup> ). The feasibility of measuring the LOTs was assessed with respect to the jaw aperture.
The mean discrepancy between LOTs measured by the algorithm and those measured by TQA was of 0 ms, with a standard deviation of 0.3 ms. The LOT measured by the method had thus an uncertainty of 1 ms with a confidence level of 99%. In 5.05 cm dynamic jaw procedures, the detector is in the beam umbra at the beginning and at the end of the delivery. In such procedures, the algorithm could not measure the LOTs at jaw apertures between 7 and maximum 12.4 mm. Otherwise, no measurement error due to the jaw movement was observed. No LOT measurement difference between air and in vivo data was observed either.
The method we propose is reliable. It can equivalently measure the LOTs from data acquired in air or in vivo. It handles fully the static procedures and the 2.51 cm dynamic procedures. It handles partially the 5.05 cm dynamic procedures. The limitation was evaluated with respect to the jaw aperture.
Mots-clé
Algorithms, Humans, Neoplasms/radiotherapy, Quality Assurance, Health Care/standards, Radiometry/instrumentation, Radiometry/methods, Radiotherapy Dosage, Radiotherapy Planning, Computer-Assisted/methods, Radiotherapy, Intensity-Modulated/instrumentation, Radiotherapy, Intensity-Modulated/methods, leaf open time, machine QA, tomotherapy
Pubmed
Web of science
Création de la notice
31/03/2019 15:13
Dernière modification de la notice
24/09/2019 5:11
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