(P024) Proton Radiotherapy for Midline CNS Lesions: A Class Solution

Neil C. Estabrook, MD, Kevin P. McMullen, MD, Mark W. McDonald, MD, Hoene A. Ted, MS, CMD, Peter A. Johnstone, MD, FACR, Jeffrey C. Buchsbaum, MD, PhD, AM; IU Health Proton Therapy Center, Indiana University School of Medicine

Objective: Midline and central lesions of the brain requiring conventional radiation therapy (RT) present complex difficulties in dose avoidance to organs at risk (OAR). In either the definitive or adjuvant setting, proper RT coverage of these lesions involves unnecessary treatment of large volumes of normal brain. We propose a class solution for these lesions using proton therapy (PrT).

Materials and Methods: The records of the IU Health Proton Therapy Center were reviewed for patients presenting between January 1, 2009 and March 1, 2013 with midline central nervous system (CNS) lesions. Nine patients were identified. After institutional review board (IRB) approval was granted, their dosimetry was reviewed for target volume doses and OAR dose avoidance.

Results: Most of these cases were craniopharyngiomas (five cases); the others were meningiomas (four cases). In all nine cases, fields that were formed by the vertex and anterior and/or posterior superior oblique PrT beams along the midsagittal plane were used to provide coverage with minimal dose to the brainstem deep or to the cerebral hemispheres. The median prescribed dose using only midsagittal fields to target planning target volume (PTV) was 52.2 Gy relative biological effectiveness (RBE) (range: 48.6–61.2 Gy RBE), with a mean dose of 53.2 Gy RBE. The average of the mean doses to the brainstems using these fields in the nine plans was 18.0 Gy RBE (range: 0.0–40.1 Gy RBE). Similarly, the average of the mean doses to the hippocampi was 17.1 Gy RBE (range: 0.0–45.9 Gy RBE).

Conclusions: We consider these patients to be optimally treated with PrT and preferentially refer patients whenever possible. The use of modified midsagittal PrT schemas allows for treatment of midline CNS lesions with sparing of most of the uninvolved brain.