Adaptive Proton Therapy of Pediatric Head and Neck Cases Using MRI-Based Synthetic CTs: Initial Experience of the Prospective KiAPT Study

• Published in: Cancers Vol. 14; no. 11; p. 2616
• Main Authors: Bäumer, Christian, Frakulli, Rezarta, Kohl, Jessica, Nagaraja, Sindhu, Steinmeier, Theresa, Worawongsakul, Rasin, Timmermann, Beate
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 25.05.2022; MDPI
• Subjects: adaptive radiation therapy; Care and treatment; Children; Computed tomography; CT imaging; Diagnosis; Dosimetry; Head and neck; Head and neck cancer; head-and-neck tumors; Histology; Magnetic resonance imaging; MRI-guided radiation therapy; Neck; Patients; pediatric radiation oncology; Pediatric research; Pediatrics; Planning; Proton beam radiotherapy; proton therapy; Protons; Quality management; Quality of life; Radiation therapy; Registration; Rhabdomyosarcoma; Scanners; Skull; Spinal cord; synthetic CTs; Technology application; Tumors; Germany; United States > US; MRI-guided radiation therapy; adaptive radiation therapy; proton therapy; synthetic CTs; head-and-neck tumors; pediatric radiation oncology
• ISSN: 2072-6694; 2072-6694
• DOI: 10.3390/cancers14112616

Interfractional anatomical changes might affect the outcome of proton therapy (PT). We aimed to prospectively evaluate the role of Magnetic Resonance Imaging (MRI) based adaptive PT for children with tumors of the head and neck and base of skull. MRI verification images were acquired at half of the treatment course. A synthetic computed tomography (CT) image was created using this MRI and a deformable image registration (DIR) to the reference MRI. The methodology was verified with in-silico phantoms and validated using a clinical case with a shrinking cystic hygroma on the basis of dosimetric quantities of contoured structures. The dose distributions on the verification X-ray CT and on the synthetic CT were compared with a gamma-index test using global 2 mm/2% criteria. Regarding the clinical validation case, the gamma-index pass rate was 98.3%. Eleven patients were included in the clinical study. The most common diagnosis was rhabdomyosarcoma (73%). Craniofacial tumor site was predominant in 64% of patients, followed by base of skull (18%). For one individual case the synthetic CT showed an increase in the median D2 and Dmax dose on the spinal cord from 20.5 GyRBE to 24.8 GyRBE and 14.7 GyRBE to 25.1 GyRBE, respectively. Otherwise, doses received by OARs remained relatively stable. Similarly, the target volume coverage seen by D95% and V95% remained unchanged. The method of transferring anatomical changes from MRIs to a synthetic CTs was successfully implemented and validated with simple, commonly available tools. In the frame of our early results on a small cohort, no clinical relevant deterioration for neither PTV coverage nor an increased dose burden to OARs occurred. However, the study will be continued to identify a pediatric patient cohort, which benefits from adaptive treatment planning.