Brain Tumor Res Treat.  2024 Apr;12(2):141-147. 10.14791/btrt.2024.0017.

Excessively Delayed Radiation Changes After Proton Beam Therapy for Brain Tumors: Report of Two Cases

• Han J
• Lee SW
• Han NY
• Gwak HS

• KMID: 2555874
• DOI: http://doi.org/10.14791/btrt.2024.0017

Abstract

Delayed cerebral necrosis is a well-known complication of radiation therapy (RT). Because of its irreversible nature, it should be avoided if possible, but avoidance occurs at the expense of potentially compromised tumor control, despite the use of the modern advanced technique of conformal RT that minimizes radiation to normal brain tissue. Risk factors for radiation-induced cerebral necrosis include a higher dose per fraction, larger treatment volume, higher cumulative dose, and shorter time interval (for re-irradiation). The same principle can be applied to proton beam therapy (PBT) to avoid delayed cerebral necrosis. However, conversion of PBT radiation energy into conventional RT is still short of clinical support, compared to conventional RT. Herein, we describe two patients with excessively delayed cerebral necrosis after PBT, in whom follow-up MRI showed no RT-induced changes prior to 3 years after treatment. One patient developed radiation necrosis at 4 years after PBT to the resection cavity of an astroblastoma, and the other developed brainstem necrosis that became symptomatic 6 months after its first appearance on the 3-year follow-up brain MRI. We also discuss possible differences between radiation changes after PBT versus conventional RT.

Keyword

Brain neoplasms; Case reports; Cerebrum; Necrosis; Proton therapy; Radiotherapy

Figure

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  Fig. 1 T1 (A), T2 (B and D), and T1 gadolinium-enhanced (C and E) MRI images preoperatively (upper row) and postoperatively, at 3 months before radiation therapy (lower row). (F) Proton beam therapy planning image (isodose line 100% represents 5,500 cGy delivered in 25 fractions).

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  Fig. 2 Photomicrographs of surgical specimens (hematoxylin & eosin, ×100) showing a low-grade glial neoplasm composed of radially arranged tumor cells with centrally located stromal blood vessels. Typical perivascular and pericellular hyalinization is observed.

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  Fig. 3 T1 (A and D), T2 (B and E), and T1 gadolinium-enhanced (C, F, and H) MRI at 3 years post-radiation (upper row), 4 years post-radiation (middle row), and at 4 years and 3 months post-radiation (lower row). (G) MR perfusion shows decreased cerebral perfusion of the lesion, and (I) MRI shows slight decrease of enhancement of the lesion at 4 years and 9 months after PBT.

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  Fig. 4 Pretreatment brain CT (A) and MRI (B and C) images showing widening of the jugular foramen and a partially enhancing ovoid 4.5-cm extra-axial mass eroding the petrous bone. (D) Proton beam therapy planning image showing two ports were used for beam direction: posterior anterior (PA) and right anterior oblique (RAO) (isodose line 100% represents 6,000 cGy delivered in 25 fractions).

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  Fig. 5 MRI images after proton beam therapy (PBT). A and B: MRI images at 2 years after PBT showing neither tumor growth nor radiation changes in adjacent brain tissue. C and D: MRI at 3 years post-PBT revealing T2 high-intensity signal changes in the adjacent cerebellum with central enhancement, suggestive of radiation-induced changes. E–H: MRI at 3 years and 6 months after PBT showing additional enhancing lesions with perilesional edema in the medulla and trigeminal entry zone, correlating with the patient’s developing symptoms.

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