What Are Tumor Treating Fields?
Tumor Treating Fields (TTFields) are a distinct class of cancer treatment — not chemotherapy, radiation, or immunotherapy. They use low-intensity alternating electric fields to disrupt how cancer cells divide. The device that delivers TTFields for glioblastoma (GBM) is currently marketed as Optune Gio.
The core idea is straightforward: rapidly dividing cells have physical properties that make them vulnerable to certain electric frequencies. TTFields therapy is a locoregional, anticancer treatment consisting of a noninvasive, portable device that delivers alternating electric fields to tumors through arrays placed on the skin. Because the fields are applied directly to the scalp rather than injected or swallowed, they stay local to the brain and avoid the systemic side effects common to intravenous therapies.
This makes TTFields a genuinely novel fourth modality in GBM care, sitting alongside surgery, radiation, and chemotherapy in evidence-based treatment guidelines.
How the Optune Gio Device Works: The Biology
To understand TTFields, it helps to know what happens when a cell divides. During mitosis, the cell must pull its chromosomes apart using rope-like protein structures called microtubules. It also has to physically pinch itself in two during a step called cytokinesis.
TTFields interfere with both steps. These alternating electrical fields physically interfere with cell division by causing misalignment of microtubule subunits in the mitotic spindle and by dielectrophoretic movement of intracellular macromolecules during cytokinesis. The result is failed cell division and eventual cancer cell death.
Frequency is critical. The frequency used for a particular treatment is specific to the cell type being treated — 200 kHz for glioblastoma multiforme. Normal adult brain cells divide very slowly or not at all, so they are thought to be largely unaffected by fields at this frequency.
More recent lab evidence suggests TTFields may also have an immunological effect. TTFields specifically kill cancer cells in several ways, including enhancement of the body's immune response against cancer cells. This is an active area of research and may help explain why some patients respond better than expected.
One practical consequence of this mechanism: there is no half-life associated with TTFields, meaning that once the device is powered off, therapy immediately halts. The fields only work while the device is running.
The Physical Device: What You Are Actually Wearing
The arrays look like adhesive patches. They attach directly to a shaved scalp and connect by wires to a small generator unit that can be carried in a bag or worn in a vest. The current second-generation system weighs roughly 2.7 pounds — about half the weight of the original model.
The array placement is determined based on individualized patient anatomy, with a corresponding layout defined by treatment planning software. Each patient's array map is calculated from MRI data to maximize field intensity at the specific tumor location.
The scalp must be shaved to maintain good contact. The electrodes must be replaced every 3–4 days and the scalp re-shaved in order to maintain optimal capacitative coupling between the electrodes and the patient's head. Most patients learn to do array changes at home.
The NCCN patient guidelines describe the overall look simply: the TTFields device looks something like a swim cap connected with wires to a carry-along battery pack. Patients can wear a wig, scarf, or hat over the arrays when going out.
FDA Approval Status and Clinical Guidelines
Based on efficacy and safety data from global pivotal randomized phase III clinical studies, TTFields therapy (Optune Gio) is FDA-approved for newly diagnosed and recurrent glioblastoma, and CE-marked for grade 4 glioma. The FDA first approved Optune for recurrent GBM in 2011, then for newly diagnosed GBM in 2015.
The NCCN — the body whose guidelines most U.S. oncologists follow — has assigned TTFields plus temozolomide a Category 1 preferred regimen for newly diagnosed supratentorial GBM in patients aged ≤70 with good performance status, following maximal safe resection and standard chemoradiation. Category 1 means: based upon high-level evidence, there is uniform NCCN consensus that the intervention is appropriate.
This places TTFields within the standard-of-care conversation for newly diagnosed GBM — a guideline-supported addition to the Stupp protocol. For patients interested in how molecular markers such as MGMT methylation interact with treatment planning, see our overview: Understanding Your GBM Molecular Profile: IDH, MGMT, EGFR & Why They Matter.
What the Evidence Shows: The EF-14 Trial
The main evidence for TTFields in newly diagnosed GBM comes from the phase III EF-14 trial. The EF-14 trial was a randomized, open-label trial that enrolled 695 newly diagnosed patients with GBM whose tumor was either resected or biopsied and who had completed concomitant radiation therapy with adjuvant temozolomide.
The median overall survival of the TTFields plus temozolomide group was 20.9 months, versus 16.0 months in the temozolomide-alone group. Progression-free survival also improved: the addition of TTFields to adjuvant temozolomide significantly increased progression-free survival (7.1 vs. 4.0 months) and overall survival (20.5 vs. 15.6 months) compared to temozolomide alone in a planned interim analysis.
The combination of TTFields and TMZ has resulted in the first report of 5-year GBM survival greater than 10% from a large clinical trial. That milestone is meaningful in a disease where long-term survival has historically been rare.
An important caveat: these are median values from a clinical trial population. Individual outcomes vary widely based on MGMT methylation status, performance status, age, extent of surgical resection, and how consistently the device is used. The trial does not predict what any individual patient will experience.
For recurrent GBM, TTFields is FDA-approved as a monotherapy option. In the pivotal EF-11 trial in recurrent GBM, overall survival of patients treated with the device was equivalent to those treated with standard chemotherapy alone, with a safety and toxicity profile that favored the Optune arm. This means TTFields may offer comparable efficacy at recurrence with potentially fewer systemic side effects than salvage chemotherapy. For more on recurrence options, see: Recurrent GBM: Why It Comes Back, What You Can Do, and How to Navigate What Comes Next.
Who Qualifies for TTFields?
TTFields is not appropriate for every GBM patient. The broad eligibility criteria, drawn from FDA labeling and clinical trial data, include:
- Age: Optune Gio is indicated for adult GBM patients aged 22 years or older.
- Tumor location: The tumor must be in the supratentorial region of the brain (above the brainstem). Infratentorial or brainstem tumors are not currently covered by this approval.
- Diagnosis: Histologically or radiologically confirmed GBM. For newly diagnosed patients, the device is added after completing the concurrent chemoradiation phase of the Stupp protocol. For recurrent patients, it is used after confirmed progression following prior chemotherapy.
- Performance status: Good functional status is generally required. NCCN guidelines specify a Karnofsky Performance Score (KPS) above 60 for newly diagnosed patients receiving the Category 1 recommendation.
- No active implanted electronic device: Use of Optune with implanted electronic devices has not been tested and may theoretically lead to malfunctioning of the implanted device. Patients with deep brain stimulators or certain pacemakers may not be candidates.
- No skull defects: Missing bone segments or metallic fragments in the skull may make the device unsafe or ineffective.
- No allergy to conductive hydrogel: The arrays use an adhesive hydrogel. A documented allergy is a contraindication.
- Not pregnant: Optune Gio should not be used if the patient is pregnant or is planning to become pregnant.
Your neuro-oncology team will assess all of these factors. Eligibility is determined case by case. If you are newly diagnosed and working through your first steps, our guide Newly Diagnosed Glioblastoma: What to Expect in the First 30 Days After Diagnosis covers how to organize your care team and which questions to prioritize early.
What to Expect: Daily Life With TTFields
Starting TTFields involves training. Patients and caregivers are taught by qualified personnel — typically a Novocure nurse specialist — how to change the arrays, shave the scalp, charge the battery, and troubleshoot the device. Most patients manage array changes at home after initial training.
The recommended daily use target is at least 18 hours per day. This is not arbitrary. Subset analyses from the phase 3 pivotal trials EF-14 and EF-11, as well as a commercial patient registry, consistently demonstrated that patient compliance of ≥75% — which equates to a monthly average of ≥18 hours per day — correlates with a statistically significant increase in overall survival compared to patients with less than 75% compliance.
Patients with monthly compliance greater than 90% had maximal survival benefit, with a median survival of 24.9 months and a 5-year survival rate of 29.3%. This link between wear time and outcome is one of the most consistent findings across TTFields studies, and it shapes how clinicians discuss compliance with patients from the start.
In practice, most patients sleep with the device, wear it during most daytime activities, and remove it only for bathing or brief breaks. The portability of the device allows for its use at home and during routine activities, incorporating it into the daily life of patients. Patients can work, travel, exercise lightly, and socialize while wearing it.
Side Effects and How to Manage Them
Because TTFields are delivered locally and do not enter the bloodstream, they do not cause the systemic side effects associated with chemotherapy — no additional nausea, hair loss beyond shaving, bone marrow suppression, or immune compromise from the device itself.
The main side effects are skin-related. TTFields-associated skin reactions include contact dermatitis (irritant or allergic), hyperhidrosis, xerosis or pruritus, and more rarely, skin erosions, ulcers, and infections.
When used with temozolomide, additional effects from the chemotherapy — such as low platelet count, nausea, constipation, fatigue, and headache — are also possible. These come from TMZ, not from the device.
There is also an adjustment period. Some patients report headaches from wearing the arrays, and mild anxiety or disrupted sleep as they adapt to the device in their daily routine. Strategies that increase the safe use and integration of Optune into the activities of daily living of GBM patients will maximize the chance for patients to respond to therapy.
Caregivers play an important logistical role in TTFields treatment — from helping with array changes to monitoring skin health and device compliance. If you are managing the caregiver role alongside this treatment, see: Caregiver Burnout During Glioblastoma Treatment: How to Recognize It and Ask for Help.
Active Research: What Comes Next for TTFields
Research on TTFields is ongoing. Several areas are under active investigation:
- Earlier integration: The TRIDENT trial (EF-32) tested TTFields delivered alongside radiation and temozolomide during the concurrent chemoradiation phase — earlier than the current standard approval. This randomized controlled study enrolled 981 patients and has completed enrollment. Results are awaited.
- Higher-intensity delivery: New high-density transducer array designs aim to deliver stronger fields to the tumor while keeping the safety profile unchanged, potentially improving outcomes beyond current levels.
- Combination with immunotherapy: Multiple trials are combining TTFields with checkpoint inhibitors and other immune agents, based on evidence that TTFields may stimulate the immune system against tumor cells.
- Pediatric and other CNS tumors: Ongoing studies are exploring TTFields beyond adult GBM.
Patients interested in combining TTFields with broader integrative or metabolic strategies may find relevant context in our article on Integrative Treatments for Glioblastoma: Evidence-Based Complementary Therapies That May Help.
Insurance, Access, and Practical Logistics
In the United States, Optune Gio is covered by many insurance plans, including Medicare, for approved indications. Coverage depends on diagnosis, prior treatment, and individual plan rules. Novocure has patient support programs that help with insurance and supply logistics.
The device requires ongoing supply management: arrays must be replaced every few days, batteries charged regularly, and the generator maintained. Most patients receive supplies by direct shipment. Device logs are monitored by care teams and by Novocure support nurses who can troubleshoot issues remotely.
Discuss access and logistics with your neuro-oncology team and the device manufacturer's support line before starting treatment, so practical barriers do not delay or interrupt therapy.
When to Talk to Your Doctor
Talk to your neuro-oncologist or care team about TTFields if:
- You have been newly diagnosed with GBM and are approaching the end of your concurrent chemoradiation phase.
- Your GBM has recurred and you are evaluating next steps.
- You have questions about whether your performance status, tumor location, or implanted devices affect eligibility.
- You are experiencing skin reactions under the arrays that are disrupting your ability to maintain adequate wear time.
- You want to understand how TTFields fits alongside other parts of your treatment plan, including clinical trials.
This article is for general information and is not a substitute for medical advice. Always consult your oncologist or care team about your specific situation.