Technique, outcomes, and acute toxicities in adults treated with proton beam craniospinal irradiation

Results. Median doses to the thyroid gland, pituitary gland, hypothalamus, and cochleae were 0.003 Gy–relative biological effectiveness (RBE; range, 0.001–8.5), 36.1 Gy-RBE (22.5 –53.0), 37.1 Gy-RBE (22.3 –54.4), and 33.9 Gy-RBE (22.2 –52.4), respectively. Median percent weight loss during CSI was 1.6% (range, 10% weight loss to 14% weight gain). Mild nausea/vomiting was common (grade 1 ¼ 46%, grade 2 ¼ 20%); however, only 5 patients experienced grade ≥2 anorexia (weight loss .5% baseline weight). Median percent baseline white blood cells, hemoglobin, and platelets at nadir were 52% (range, 13% –100%), 97% (65%–112%), and 61% (10%–270%), respectively. Four patients developed grade ≥3 cytopenias. Overall and progression-free survival rates were 96% and 82%, respectively, at 2 years and 84% and 68% at 5 years. Conclusions. This large series of patients treated with p-CSI confirms low rates of acute toxicity, consistent with dosimetric models. Vertebral body-sparing p-CSI is feasible and should be considered as a way to reduce acute gastrointestinal and hematologic toxicity in adults requiring CSI.