Proton Radiotherapy for Midline Central Nervous System Lesions: A Class Solution

Abstract

Objective: Midline and central lesions of the brain requiring conventional radiotherapy (RT) present complex difficulties in dose avoidance to organs at risk (OAR). In either definitive or adjuvant settings, 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 radiotherapy (PrT). Materials and Methods: The records of the Indiana University Health Proton Therapy Center were reviewed for patients presenting between January 1, 2005 and October 1, 2013 with midline central nervous system (CNS) lesions. Twenty-four patients were identified. After Institutional Review Board approval was granted, their dosimetry was reviewed for target volume doses and OAR dose avoidance. Results: For these cases, meningiomas were the most common histology (8 cases), and next most prevalent were craniopharyngiomas (6 cases). The others were various different deep midline brain tumors (10 cases). In all cases, fields formed by vertex and/or anterior/posterior superior oblique PrT beams along the midsagittal plane were used to provide coverage with minimal dose to the brain stem or to the cerebral hemispheres. The median prescribed dose to the planning target volume for treating these patients was 54.0 Gy RBE (range 48.6-62.5) with a mean dose of 53.5 Gy RBE. The average of the mean doses to the brain stems using these fields in the 24 plans was 18.4 Gy RBE (range 0.0-44.7). Similarly, the average of the mean doses to the hippocampi was 15.8 Gy RBE (range 0.0-52.6). Conclusions: We consider these patients to be optimally treated with PrT. The use of modified midsagittal PrT schemas allows for the treatment of midline CNS lesions with sparing of most of the uninvolved brain.

Clinical Benefits of Proton Beam Therapy for Tumors of the Skull Base

“…The Bragg peak characteristic of protons allowed for the use of vertex and anterior and/or posterior superior oblique beams along the midsagittal plane to achieve a mean dose of 52.2 Gy (relative biological equivalent) to the target. 36 The decreased number of treatment beams and unique angles achieved with protons resulted in an improved plan distinct from what is currently possible with IMRT photons. 36 The reported midline central nervous system proton plans resulted in minimal doses to the normal tissue of the brain, as demonstrated by average mean doses of 18 Gy (relative biological equivalent) to the brainstem (range, 0.0-40.1) and 17.1 Gy (relative biological equivalent) to the hippocampi (range, 0.0-45.9).…”

“…36 The decreased number of treatment beams and unique angles achieved with protons resulted in an improved plan distinct from what is currently possible with IMRT photons. 36 The reported midline central nervous system proton plans resulted in minimal doses to the normal tissue of the brain, as demonstrated by average mean doses of 18 Gy (relative biological equivalent) to the brainstem (range, 0.0-40.1) and 17.1 Gy (relative biological equivalent) to the hippocampi (range, 0.0-45.9). 36 Fig 5 depicts a proton beam arrangement for parafalcine meningioma.…”

Proton beam therapy: clinical utility and current status in prostate cancer

“…We consider PrT to be critical in treating children, 4 as well as rare clinical situations such as craniospinal radiotherapy (RT), 5 recurrent chordomas, and midline central nervous system structures. 6 , 7 The enthusiastic adoption of PrT for treating prostate cancer (CaP) was based on the theoretical promise for superiority in sparing organs at risk such as bladder, rectum, and femoral head when compared with photons. However, much of the investment in proton centers was made with the expectation of significant return on investment by using PrT for CaP.…”

Quantifying Proton Fields for Midline Brain Tumors: A Benefit/Cost Analysis of Planning Objectives

“…Using proton therapy, each beam's maximal energy is deposited in the target, after which point energy deposition terminates, with essentially no exit dose radiation to normal tissue beyond the target [1]. We have previously described the application of proton therapy in midline central nervous system (CNS) tumors by using an array from 1 to 5 midline sagittal beams to target superficial or deep-seated brain tumors [2]. The midline sagittal beam arrangement facilitates avoidance of the temporal lobes and hippocampi, and when using proton therapy there is no exit dose through the body (Figure 1).…”