Temporal Muscle Thickness Does Not Predict Survival in Older Brain Cancer Patients

A thick temple may look like a trivial detail on a head scan, but in recent years radiologists have taken the temporalis muscle—the fan-shaped muscle of chewing that sits just beneath the scalp at the side of the skull—seriously as a window into the body’s overall muscle reserves. Because the temporalis thins along with the rest of the skeleton in wasting states such as sarcopenia and cachexia, its thickness on routine imaging has been proposed as a cheap, widely available marker of frailty and a possible predictor of how long cancer patients will live. A new study from Finland, however, delivers a cautionary message: in older patients with brain metastases undergoing radiation therapy, this seemingly promising biomarker does not hold up as an independent prognostic factor.

Researchers at Tampere University Hospital set out to answer a question that had not been addressed before: whether temporal muscle thickness, or TMT, measured on ordinary computed tomography scans, could predict survival in patients aged 70 or older who received brain radiotherapy for metastatic cancer. The question matters because prognostication in this population is exceptionally difficult and exceptionally important. Brain metastases affect an estimated 10 to 40 percent of patients with solid tumors, and population studies place the incidence between 8.3 and 14.3 per 100,000 people, a figure that almost certainly underestimates the true burden because not all cases are registered. Median survival across the field ranges from as little as two months to 21 months depending on the primary cancer, and for patients over 65, Surveillance, Epidemiology, and End Results data indicate a median survival of four months or less for nearly all common malignancies, including breast, colorectal, esophageal, renal, and lung cancer and melanoma.

Accurate prognostic tools would allow clinicians to tailor treatment intensity intelligently. Patients with a favorable outlook might benefit from more aggressive interventions, while those expected to survive only weeks could be spared the burdens of hospitalization, repeated radiotherapy sessions, or chemotherapy in the final weeks of life, interventions that may degrade quality of life without meaningfully extending it. Honest prognostic information also underpins shared decision-making, giving patients and families a realistic basis on which to weigh intensive treatment against palliative care. The Tampere team reasoned that if a simple measurement already embedded in the treatment-planning scan could sharpen these predictions, it would be a genuinely useful clinical instrument.

The study, published in Cancer Reports, took the form of a retrospective cohort analysis of consecutive patients aged 70 years or older who underwent brain radiotherapy, with or without prior surgical resection, for brain metastases between 2014 and 2022. From the hospital’s electronic radiotherapy database, 249 patients met the inclusion criteria: 136 men with a mean age of 76.0 years and 113 women with a mean age of 76.4 years. Lung cancer dominated the cohort, accounting for 113 patients or 45.4 percent, followed by breast cancer with 29 patients and melanoma with 27. Most participants, 226 in total, received radiotherapy alone, split between whole-brain radiotherapy, given to 151 patients, and stereotactic radiotherapy, delivered to 98, while 23 patients underwent surgical resection followed by postoperative radiation.

Measuring the temporalis muscle requires surprising methodological care. A single observer, blinded to patient outcomes, assessed TMT on each patient’s first radiotherapy planning head CT, or on a diagnostic CT performed within the preceding month. The measurement plane had to be oriented parallel to the falx cerebri, the membrane dividing the brain’s hemispheres, and tangential to the floor of the middle cranial fossa, with the image windowed to a narrow setting of 80 Hounsfield units width and 40 length to sharpen the muscle’s boundaries. On the first axial slice above the bony orbit, a tangent line was drawn from the muscle’s anterior attachment to the skull, and thickness was recorded at the muscle’s thickest point perpendicular to that line, deliberately excluding fat, fascia, and blood vessels. The average of left and right measurements was used in the analyses. To confirm the technique’s reliability, a second observer independently measured a random sub-cohort of 19 patients, and the agreement between readers was excellent, with an intraclass correlation coefficient of 0.942 for single measurements and 0.970 for averages—figures indicating that the measurement itself is robust and reproducible.

Because men naturally have thicker temporal muscles than women, the researchers derived sex-specific thresholds for low TMT by maximizing Youden’s index, a statistical measure balancing sensitivity and specificity, for three-month survival. The resulting cut-offs were 4.3 millimeters for men, with 46.7 percent sensitivity and 74.6 percent specificity, and 3.975 millimeters for women, with 64.6 percent sensitivity and 49.2 percent specificity. These thresholds are notably lower than those reported in earlier studies of younger patients, a difference the authors attribute to the advanced age of their cohort, in which temporal muscle wasting is already widespread. By these criteria, 35.3 percent of the men and 56.6 percent of the women had low temporal muscle thickness.

The survival picture in the cohort was stark. Median overall survival was just 90 days, or roughly three months, and by the one-year mark 86.7 percent of the patients had died. Patients with normal TMT did live somewhat longer on average than those with low TMT, with a median of 103 days versus 75 days, and in univariate analyses low TMT was significantly associated with worse survival at three months, with a hazard ratio of 1.54, and at six months, with a hazard ratio of 1.41. At one month and twelve months, no association reached statistical significance. But the crucial test came when the researchers adjusted their models for other clinical variables: age, body mass index, surgical treatment, and type of radiotherapy. Once these factors were accounted for, the relationship between TMT and survival evaporated entirely at every time horizon, with the adjusted three-month hazard ratio falling to 1.40 and losing significance.

What did predict survival, independently, were other clinical variables. Receiving whole-brain radiotherapy rather than stereotactic radiotherapy carried a substantially higher risk of death at every time point, with an adjusted hazard ratio of 5.98 for one-month survival and approximately 2.3 at the longer horizons. This likely reflects treatment selection rather than harm: whole-brain radiotherapy is generally reserved for patients with multiple metastases and poorer prognosis, while stereotactic techniques are favored for those with limited, more favorable disease. Similarly, patients who did not undergo surgical resection had markedly higher mortality across all time frames, since surgery is typically offered only to younger patients with solitary lesions and better expected outcomes. Higher body mass index was protective for one-month survival, with a hazard ratio of 0.31, and advancing age independently worsened six- and twelve-month survival. The authors are candid that these patterns largely mirror the realities of clinical decision-making.

The contrast with previous research is instructive. Of six earlier studies evaluating TMT in patients with brain metastases, three found that low thickness predicted shorter survival, while others found no association once confounders were considered. Crucially, those studies examined patients on average more than a decade younger, with median survival extending from three to eleven months, and several included only surgically treated patients. The Tampere cohort, by contrast, was older, sicker, and predominantly managed with radiotherapy alone. The researchers also tested whether TMT predicted survival within their largest tumor subgroup, the 113 lung cancer patients, and found no significant association at any time point, which discouraged further subgroup analyses. Additional limitations deserve mention: performance status, number of brain lesions, intracranial tumor volume, extracranial disease status, and systemic therapy were not incorporated into the models, and the derived sex-specific cut-offs may risk overfitting, making external replication essential.

The study’s conclusion is refreshingly direct: temporal muscle thickness should not be regarded as a prognostic factor in patients aged 70 or older with brain metastases treated with radiotherapy. The finding is a valuable corrective to a growing enthusiasm for imaging-derived body-composition markers, reminding clinicians and researchers that a measurement can be technically reliable, easily obtained, and biologically plausible yet still fail to add independent predictive value in the population that matters. In very old, profoundly ill patients whose median survival is measured in weeks, disease aggressiveness and treatment selection appear to overwhelm any signal carried by skeletal muscle reserves. For this vulnerable group, prognostic conversations must continue to rest on established clinical variables, while the search for better tools goes on.

Subject of Research: Temporal muscle thickness as a prognostic marker for survival in older patients with brain metastases treated with radiotherapy

Article Title: Association Between Temporal Muscle Thickness and Survival in Older Patients With Brain Metastases Undergoing Radiation Therapy

Article References: Pikkarainen, L., Korhonen, T. K., Tolonen, A., Pesonen, E. K., Hernandez, N., Skyttä, T., & Arponen, O. (2026). Association Between Temporal Muscle Thickness and Survival in Older Patients With Brain Metastases Undergoing Radiation Therapy. Cancer Reports, 9(9), Article e70671. https://doi.org/10.1002/cnr2.70671

Image Credits: AI Generated

DOI: 10.1002/cnr2.70671

Keywords: temporal muscle thickness, brain metastases, radiotherapy, survival, sarcopenia, cachexia, prognostication, computed tomography, whole-brain radiotherapy, stereotactic radiotherapy, older patients, Cancer Reports