Proton Therapy for CNS and Skull Base Tumors is Gentle on Surrounding Brain Tissue

MedAustron study shows low incidence of radiation-induced contrast enhancement in healthy tissue. Clinical course is mostly unremarkable. Quality of life not affected.

The incidence of radiation-induced contrast enhancement in healthy tissue following proton beam therapy of tumors in the central nervous system (CNS) is low. This is the outstanding result of a study at MedAustron, Center for Ion Therapy and teaching and research site of the Karl Landsteiner University of Health Sciences, which examined the side effects of treating tumors in the CNS or near the base of the skull. The recently published results also show that the clinical course of this change is mostly unremarkable and does not affect patients’ quality of life. The study examined the occurrence and progression of an abnormality known as radiation-induced contrast enhancement in the vicinity of irradiated tumors. The study included 421 patients treated over a period of 4 years.

Particle therapy is the state of the art in cancer treatment. Charged particles such as protons (or carbon ions) are directed at tumors with high energy to destroy them. A major advantage of this form of therapy is that the particle beams can be stopped at a specific point in the tissue, thereby reducing the impact on healthy tissue. Among the known effects on surrounding tissue is an effect known as RICE (Radiation-Induced Contrast Enhancement), which shows up as a strong contrast in radiological images. How often, when, in what progression and with what effects on the quality of life these changes occur has now been investigated in a study at MedAustron. The focus was on the treatment of tumors of the CNS or near the skull base.

Rare & Asymptomatic

“In our study, we examined the course of 421 patients treated with proton beams between 2017 and 2021,” explains Dr. Carola Lütgendorf-Caucig, lead author of the study and Clinical Director Radiooncology and Director of Pediatric and CNS Particle Therapy at MedAustron. “In summary, the overall incidence of RICE was low at 15% and the majority of cases were asymptomatic. Further studies also showed that patients did not experience any reduction in quality of life as a result of RICE.” Another finding of the study was that the median duration of RICE was 9 months. This also confirms that these changes are reversible.

The large size of the study also allowed for complex statistical analyses that provided further insight into RICE. The study team was particularly interested in the influence of previous treatments or diseases on the occurrence and course of RICE – an issue that is important for the careful planning of proton beam treatment. “We were able to identify two important factors”, explains Prof. Petra Georg, Head of the Division of Radiotherapy – Radiation Oncology at the Krems University Hospital, a teaching and research site of the KL Krems, and last author of the study. In particular, the previous irradiation of the tumor had an effect. In fact, it was shown that this increased the risk of a symptomatic course of RICE. However, this was the only factor studied that showed this increased risk.” The research team also found that a history of diabetes increased the likelihood of RICE. However, factors such as gender and age (among others) did not play a significant role.

Reversible RICE

The study, which has now been published in the International Journal of Radiation Oncology, impressively demonstrates the safety of proton therapy in relation to the tissue surrounding the tumor. It also makes a significant contribution to better differentiating the radiological effects of radiotherapeutic tumor treatments. In fact, these types of cancer treatments have different effects on the surrounding (healthy) tissue, which can be seen in high-contrast imaging techniques. “Currently, in the official terminology for side effects, these are often summarized under the term “radiation necrosis”, explains Dr. Lütgendorf-Caucig. “However, necrosis is tissue damage that does not heal, whereas the tissue abnormalities known as RICE are reversible and – as we were able to show – often clinically asymptomatic.” This publication by the two partners in the Lower Austrian Oncology Research Network – MedAustron and KL Krems – summarizes the safety of proton beam therapy for surrounding healthy tissue. It also provides the basis for a better, clinically relevant classification of radiation-induced tissue changes.