Residency · Residency · Radiation Oncology

Whole Brain Radiation Therapy: Palliative Fractionation and Prognostic Scoring

Introduction

Brain metastases develop in 20-40% of cancer patients, most frequently arising from primary tumors of the lung, breast, melanoma, renal, and colorectal origins. Whole brain radiation therapy (WBRT) has long served as a cornerstone of palliative treatment for these patients. However, its role is evolving due to the increasing use of stereotactic radiosurgery (SRS) for treating larger numbers of metastases and growing awareness of the neurocognitive side effects associated with WBRT. This lecture explores the various WBRT fractionation regimens, prognostic scoring systems used to guide treatment, and strategies designed to reduce neurotoxicity.

Indications for WBRT

Currently, WBRT is indicated primarily for patients with multiple brain metastases, historically defined as more than 3 to 4 lesions, though some practices now consider WBRT appropriate for patients with more than 10 to 15 metastases. It is also used in cases of diffuse leptomeningeal carcinomatosis, in patients with poor performance status who are not candidates for SRS, and in the postoperative setting when SRS to the resection cavity is not feasible. Additionally, WBRT is employed as prophylactic cranial irradiation (PCI) in small cell lung cancer (SCLC).

The indications for WBRT are declining in certain contexts. For patients with limited brain metastases, typically 1 to 4 lesions, stereotactic radiosurgery is preferred according to ASTRO and ASCO guidelines. Emerging evidence supports the use of SRS even for patients with 5 to 15 or more metastases. Furthermore, the benefit of WBRT as an adjunct after SRS has been questioned by trials such as QUARTZ, which suggest limited survival or quality-of-life advantage in many patients.

Fractionation Regimens

The most commonly used WBRT fractionation regimen worldwide is 30 Gy delivered in 10 fractions of 3 Gy each. For patients with limited prognosis, a shorter course of 20 Gy in 5 fractions (4 Gy per fraction) is appropriate. Some protocols use a slightly higher total dose of 37.5 Gy in 15 fractions of 2.5 Gy each.

Short-course regimens, particularly 20 Gy in 5 fractions, have been shown to provide symptom palliation equivalent to the standard 30 Gy in 10 fractions for patients with poor prognosis. The Radiation Therapy Oncology Group (RTOG) recursive partitioning analysis has helped guide the selection of appropriate regimens based on patient characteristics. The QUARTZ trial specifically compared 20 Gy in 5 fractions plus dexamethasone versus dexamethasone alone in non-small cell lung cancer (NSCLC) patients with poor prognosis and brain metastases, demonstrating minimal benefit from WBRT in this population.

QUARTZ Trial

The QUARTZ trial enrolled NSCLC patients with brain metastases who were unsuitable for surgery or SRS. Participants were randomized to receive either WBRT at 20 Gy over 5 fractions combined with dexamethasone or dexamethasone alone. The trial found no significant difference in overall survival or quality-adjusted life years between the two groups. These findings suggest that WBRT may be safely omitted in poor-prognosis NSCLC patients who can be managed with supportive care alone.

Prognostic Scoring Systems

Several prognostic scoring systems assist clinicians in estimating survival and guiding treatment decisions for patients with brain metastases.

The Recursive Partitioning Analysis (RPA) developed by the RTOG in 1997 stratifies patients into three classes based on Karnofsky Performance Status (KPS), age, control of the primary tumor, and presence of extracranial metastases. Class I includes patients younger than 65 years with KPS greater than 70, controlled primary disease, and no extracranial metastases, with a median overall survival of 7.1 months. Class III comprises patients with KPS less than 70, who have a median survival of 2.3 months. Class II includes all other patients, with a median survival of 4.2 months.

The Graded Prognostic Assessment (GPA) is a more refined, disease-specific tool that incorporates variables tailored to the primary tumor type. For example, in NSCLC, the GPA considers age, KPS, extracranial metastases, number of brain metastases, and molecular markers such as EGFR and ALK mutations. In breast cancer, factors include age, KPS, and subtype (HER2-positive, hormone receptor-positive/HER2-negative, or triple-negative). Melanoma GPA accounts for KPS, number of brain metastases, and BRAF mutation status, while renal cell carcinoma GPA includes KPS, number of brain metastases, and hemoglobin levels. GPA scores range from 0 to 4.0, with higher scores indicating better prognosis. Median overall survival varies widely, from approximately 3 months for GPA scores of 0 to 1, up to more than 25 months for scores between 3.5 and 4.0, depending on tumor histology.

An updated molecular GPA incorporates molecular markers such as EGFR, ALK, HER2, and BRAF mutations. For instance, NSCLC patients positive for EGFR or ALK mutations have significantly better prognoses, and HER2-positive breast cancer patients fare better than those with triple-negative disease. These molecular subtypes can shift the GPA score by 0.5 to 1.0 points, refining prognostic accuracy.

Neurocognitive Effects of WBRT

Cognitive decline is a significant adverse effect of WBRT, primarily due to damage to the hippocampus, which is critical for memory function. Between 50% and 90% of patients experience measurable cognitive decline within 4 to 6 months after treatment. The affected cognitive domains include verbal memory, learning, executive function, and processing speed. The Hopkins Verbal Learning Test-Revised (HVLT-R) is commonly used as a primary cognitive endpoint in clinical trials assessing these effects.

Several factors contribute to the risk of neurocognitive decline, including the total radiation dose and fraction size, patient age (with older patients being more vulnerable), pre-existing cognitive impairment, and concurrent or prior systemic therapies.

Strategies to Reduce Neurotoxicity

Hippocampal avoidance WBRT (HA-WBRT) is an intensity-modulated radiation therapy (IMRT) technique designed to spare the hippocampal neural stem cell niche. During treatment planning, the hippocampus is contoured as an organ at risk (OAR), with dose constraints set to keep the dose to 100% of the hippocampus below 9 Gy and the maximum dose below 16 Gy when delivering 30 Gy in 10 fractions. The NRG CC001 trial compared HA-WBRT plus memantine to standard WBRT plus memantine and found that HA-WBRT significantly preserved cognitive function, as measured by HVLT-R at 4 and 6 months, without compromising overall survival or intracranial tumor control. This trial established HA-WBRT combined with memantine as the new standard of care when WBRT is indicated.

Memantine, an NMDA receptor antagonist, may protect against radiation-induced excitotoxicity. The RTOG 0614 trial compared memantine to placebo during WBRT and observed a trend toward better cognitive preservation with memantine, particularly in executive function and processing speed at 24 weeks. The typical dosing starts at 5 mg daily, escalating to 10 mg twice daily, beginning at the start of WBRT and continuing for 24 weeks.

For patients with limited brain metastases, multiple randomized trials have demonstrated superior cognitive outcomes with SRS alone compared to SRS combined with WBRT. The NCCTG N0574 trial showed that adding WBRT to SRS caused significant cognitive decline at 3 months. Consequently, current recommendations favor SRS alone for patients with limited brain metastases, typically 1 to 4 lesions, with increasing acceptance for patients with 10 or more metastases.

Prophylactic Cranial Irradiation (PCI)

In limited-stage small cell lung cancer (SCLC), PCI is administered at 25 Gy in 10 fractions following a complete response to chemoradiation. This approach reduces the incidence of brain metastases from approximately 60% to 30% and improves overall survival. A meta-analysis by Auperin demonstrated an absolute overall survival benefit of 5.4% at 3 years.

For extensive-stage SCLC, the role of PCI is more controversial. The EORTC trial showed an overall survival benefit with PCI, whereas the Takahashi trial, which incorporated MRI surveillance, found no survival advantage. Current practice increasingly favors MRI surveillance as a viable alternative to PCI in extensive-stage disease, with shared decision-making recommended to balance the cognitive risks of PCI against its potential benefits.

In non-small cell lung cancer, PCI is not standard of care. The NVALT-11 trial showed that while PCI reduced the incidence of brain metastases, it did not improve overall survival. Therefore, PCI is not recommended outside of clinical trials in NSCLC.

Key Clinical Pearls

When WBRT is indicated, it should include hippocampal avoidance techniques combined with concurrent memantine administration, as established by the NRG CC001 trial, which represents the new standard of care. The QUARTZ trial demonstrated that WBRT may be omitted in poor-prognosis NSCLC patients, supporting best supportive care as a reasonable alternative in this group. Disease-specific GPA scoring, incorporating molecular markers, is essential for guiding prognosis and tailoring treatment intensity for patients with brain metastases. For limited brain metastases, stereotactic radiosurgery alone is preferred over WBRT to preserve neurocognitive function, with expanding indications from 1 to 4 lesions to 5 to 15 or more. Prophylactic cranial irradiation remains standard after complete response in limited-stage SCLC, while its role in extensive-stage SCLC continues to evolve with the advent of MRI surveillance.

References

1. Brown PD, Gondi V, Pugh S, et al. Hippocampal avoidance during whole-brain radiotherapy plus memantine for patients with brain metastases: phase III trial NRG Oncology CC001. J Clin Oncol. 2020;38(10):1019-1029.
2. Mulvenna P, Nankivell M, Barton R, et al. Dexamethasone and supportive care with or without whole brain radiotherapy in treating patients with non-small cell lung cancer with brain metastases unsuitable for resection or stereotactic radiotherapy (QUARTZ): results from a phase 3, non-inferiority, randomised trial. Lancet. 2016;388(10055):2004-2014.
3. Sperduto PW, Mesko S, Li J, et al. Survival in patients with brain metastases: summary report on the updated diagnosis-specific graded prognostic assessment and definition of the eligibility quotient. J Clin Oncol. 2020;38(32):3773-3784.
4. Brown PD, Jaeckle K, Ballman KV, et al. Effect of radiosurgery alone vs radiosurgery with whole brain radiation therapy on cognitive function in patients with 1 to 3 brain metastases: a randomized clinical trial. JAMA. 2016;316(4):401-409.

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