Monte Carlo study of ionization chamber magnetic field correction factors as a function of angle and beam quality
Notice bibliographique
Résumé
Purpose To use EGSnrc Monte Carlo simulations for magnetic field dosimetry to determine optimal measurement orientations, calculate beam quality conversion factors for 32 cylindrical and three parallel‐plate (PP) ion chambers, evaluate the beam quality and angular dependence of these factors, and examine the magnetic field effects on %dd(10) x and TPR . Methods Beam quality conversion factors, k , and magnetic field conversion factors, k B = k /k Q , are calculated as a function of chamber rotation for six cylindrical ionization chamber in either a 60 Co beam with a 0.35 T magnetic field or a 7 MV beam with a 1.5 T field, both magnetic fields are perpendicular to the photon beam. The chambers’ sensitive air volumes are varied by either using the entire geometric volume or excluding the air volume associated with the first 1 mm away from the stem. The k B and k factors are evaluated using four clinical photon spectra. The variation in %dd(10) x and TPR as a function of magnetic field for six photon spectra are studied using DOSXYZnrc. Results When the magnetic field is perpendicular to the photon beam, orienting the chamber parallel with the magnetic field reduces the magnetic field effect on chamber response (i.e., dose to air per water dose) and variations due to the unknown sensitive volume are essentially eliminated. Calculated k B factors are within 1% of unity for the majority of cylindrical chambers, although larger k B values are associated with chambers with high‐Z electrodes. PP chambers have k B corrections as large as 8.9% and have a larger angular sensitivity compared to cylindrical chambers. Values of k B for cylindrical ion chambers are independent of beam quality, except for chambers with high‐Z electrodes. For %dd(10) x values between 63.3% and 73.8%, k B varies by at most (0.26 ± 0.15)% when the magnetic field is perpendicular to the photon beam and parallel to the chamber. Differences in %dd(10) x , between no magnetic field and with a 1.5 T field perpendicular to the photon beam are (0.04 ± 0.10)%, (1.89 ± 0.10)%, and (6.20 ± 0.10)% for a 60 Co, 7, and 25 MV photon beam, respectively, while TPR shows less than (0.36 ± 0.10)% change. Applying the ICRU‐90 recommendations for stopping powers instead of ICRU‐37 is found to change k Q (and hence k B ) by less than 0.1%. Conclusions Orienting the chamber parallel to the magnetic field when the field is perpendicular to the photon beam will minimize the effect of the magnetic field on chamber response, and eliminate the problem of the unknown sensitive volume. Values of k B and k can bring ion chamber dosimetry in magnetic fields in‐line with the TG‐51 protocol. PP chamber are sensitive to the magnetic field and variation in chamber response due to small angular changes makes them unlikely candidates for clinical reference dosimetry in magnetic fields. The stability in TPR , as a function of magnetic fields and beam qualities, makes it the best beam quality specifier in magnetic fields.
Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.
Comment cette classification a été obtenuedéplier
Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,000 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule tête enseignante, pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».