Dose calculation for CBCT imaging in radiation therapy

• Forschungsstelle: BAG
• Projektnummer: 15.017754

Schlüsselwörter (Deutsch)

CBCT, Therapieplanung, Beschleuniger, IGRT, kV, Dosis, Bildgebung, Radioonkologie, Strahlentherapie

Kurzbeschreibung (Französisch)

Ce projet a pour but de développer un système de calcul qui donnerait une information globale de la distribution de dose lors d'une procédure d'IGRT. Pour réaliser ce système, nous devons modifier un système de planification afin d'y intégrer les noyaux de dispersion de la dose pour des énergies correspondant aux procédures d'IGRT. Le système permettra de calculer les doses délivrées par différants protocoles d'IGRT et ainsi de les optimiser.

Projektziele (Französisch)

• Amélioration de la protection du patient en radiothérapie
• Evaluation de l'expositon due à l'imagerie (IGRT) en radiothérapie
• Optimisation des protocoles d'imagerie en radiothérapie

Abstract (Englisch)

Dose calculation models for kV beams were implemented in Philips Pinnacle treatment planning system and validated in water and heterogeneous phantoms. We implemented a methodology h to determine the “effective” dose resulting from CBCT imaging protocols in radiotherapy and we tested it with five head and neck and five breast cases.
Globally, the effective dose resulting from one IGRT imaging is between 0.1 and 10 mSv depending on the protocol used. The corresponding risk is calculated with 30 fractions for H&N cases and 25 fractions for breast cases. The rough indicator of the risk for the whole treatment is therefore between 0.2 and 1.2%.
The method is clinically efficient and robust with an uncertainty on effective dose of about 8%.

Umsetzung und Anwendungen (Englisch)

Outcome of radiotherapy is strongly dependent not only on the planning dosimetry but also on the tumour localization at the time of beam delivery. Standard method of localization is based on image guidance by wall or gantry mounted X-ray tubes (Image Guided Radiation Therapy, IGRT) leading to extra dose delivered to the patient inside and outside the treated volume. Dose distributions of these acquisitions inside patients are complex depending not only on kV energy, gantry arc and filter, but also on patient anatomy especially in heterogeneous regions such as head and neck (H&N) and chest. Thus they cannot be characterized by only one quantity such as CTDI and should be fully calculated.
Calculation of kV dose distributions is not yet implemented in commercial software used for treatment planning systems (TPS), but several studies have demonstrated the feasibility of extending them to the kV domain. This project aims at calculating a set of dose distributions from IGRT of H&N and breast treatments, and extracting from them the effective dose as well as its variability.

Weiteres Vorgehen (Deutsch)

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