Due to the promising physical dose distribution of carbon ion radiation therapy (CIRT), CIRT can be regarded as a novel tumor irradiation technique and is sometimes considered as a breakthrough therapy for various tumor types. However, it is unclear whether superiority or inferiority can be claimed when compared to standard irradiation. This study aimed to assess the scientific evidence regarding the effectiveness and safety of CIRT.

A systematic literature review was conducted using the European Network for Health Technology Assessment (EUnetHTA) Core Model® for rapid relative effectiveness assessment. The literature search for clinical outcome studies on CIRT was performed in four databases [Cochrane (Central), Centre for Research and Dissemination (CRD), Embase and OVID MEDLINE]. The risk of bias was assessed using the Cochrane Risk of Bias Tool (for randomized controlled trials) and the Institute of Health Economics (IHE) Checklist (for observational studies). The evidence synthesis was restricted to 12 tumor regions (and 54 indications) and studies with a low or moderate risk of bias, published between 2005 and 2017.

In total 27 studies were eligible for the qualitative synthesis of the evidence regarding the effectiveness and safety of CIRT; one randomized controlled trial that primarily focused on the feasibility of CIRT, three case-control studies, three before-after studies focusing on quality of life, and 20 further case series studies. Overall, insufficient scientific evidence was found for 13 (out of 54) indications in seven tumor regions and no scientific evidence was found for 41 (out of 54) indications.

Theoretically, CIRT is undoubtedly a promising cancer treatment. To date, however, 54 oncologic indications in 12 tumor regions under investigation lack randomized controlled trials assessing the long-term effectiveness and harms associated with its use. CIRT must be considered as an experimental treatment due to the lack of high-quality clinical research.