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Over 1,000 national and international experts spoke about clinically relevant topics, the latest study results, and their significance for everyday practice at the 95th annual meeting of the German Society for Otorhinolaryngology, Head and Neck Surgery last May in Essen. One expert gave exciting insights into proton beam therapy (PT) in base of skull (BoS) tumors, Sonja Buske reports. 

“The treatment of BoS tumors is challenging, as the tumors are often located in close proximity to critical organs such as the brain stem,” Prof. Beate Timmermann, Director of the Clinic for Particle Therapy at Essen University Hospital, said at the start of her presentation. “Furthermore, resection is often not a radical option, as the risk of complications is considerable.”

Radiotherapy is one way of improving local control, but it also carries risks, as some BoS tumors require very high doses. Proton therapy could be an opportunity, as protons can be used to precisely target the tissue at risk for tumor relapse and thus spare critical organs outside the target.

Most Challenging Tumor: Chordoma

In her talk, Timmermann focused on the treatment of chordoma, which is the typical and most challenging tumor in radiotherapy. “If you look into international consensus, adjuvant radiotherapy is considered for skull base and cervical spine chordomas, and for sacral and mobile spine chordoma if microscopic positive margins are noted in the final pathological examination or according to the surgeon’s opinion,” she said. 

However, the required doses for local disease control are high, Timmerman explained. “We have to approach a dose of at least 74 GyE, which exceeds the tolerance of normal structures, for example of the brain stem.”

Nevertheless, the German Society for Radiologic Oncology recommends proton therapy for chordomas due to the excellent clinical results obtained since the late 1950s.

IMPT radiation plan of a chondrosarcoma of the skull base in transverse view with consideration of the brain stem (light green line). Dark green and dark red line: target volumes. Red area: 95% isodose, light green area: 80% isodose, light blue area: 40% isodose.

Study to Investigate the Effectiveness of PT

In a prospective patient registry study of 142 patients with chordoma and chondrosarcoma, Timmermann’s team investigated the effectiveness of proton beam therapy. The patients included 115 adults and 27 children; the average age was 50.1 years. The patients were irradiated with a median dose of 73.5 GyE in a total of 35 sessions over an average period of 3.5 years. 18 patients experienced local failures or dissemination and 15 deceased after therapy. The three-year overall survival was 92 % and the progression-free survival was 91 %. “In these challenging tumors, we are delighted with the excellent results we have achieved,” Timmermann concluded.

However, she also pointed out that any local treatment of a BoS tumor remains a challenge. “Radiotherapy can improve local control in tumors that cannot be radically resected, and proton beam therapy is the treatment of choice after surgery for chordomas and chondrosarcomas, particularly in children,” said Timmermann, who also noted the increasing use of PT for other BoS tumors, such as nasopharyngeal cancer or head and neck tumors.

Interdisciplinary Cooperation is Crucial

She emphasized that interdisciplinary cooperation is particularly important for the success of therapy with such intensive and complex treatments. Surgeons, oncologists, radiologists, and radiation oncologists meet regularly to discuss the best approach for each patient. The data and experience gathered in prospective studies will allow important conclusions to be drawn about the chances of proton therapy and innovative techniques in the future. “Our experience shows high control rates and excellent feasibility in this challenging cohort of patients,” she concluded. 

Profile: Prof. Beate Timmermann is the Director of the Clinic for Particle Therapy at Essen University Hospital, and the Medical Director of the West German Proton Therapy Center (WPE). She studied medicine in Hamburg, obtained her doctorate in Tübingen, and habilitated in Münster. She has been involved in proton beam therapy since 2002. Her clinical specialties include sarcomas, chordomas, chondrosarcomas, and brain tumors in children and adults as well as late effects and quality of life. Timmermann is a member of the European Society for Radiotherapy and Oncology (ESTRO) and the German Society for Radiation Oncology (DEGRO), among others.