Combined radiotherapy and concurrent tumor treating fields (TTFields) for glioblastoma: Dosimetric consequences on non-coplanar IMRT as initial results from a phase I trial

Theory and application of TTFields in newly diagnosed glioblastoma

BACKGROUND

Glioblastoma is the most common primary malignant brain tumor in adults. TTFields is a therapy that use intermediate-frequency and low-intensity alternating electric fields to treat tumors. For patients with ndGBM, the addition of TTFields after the concurrent chemoradiotherapy phase of the Stupp regimen can improve prognosis. However, TTFields still has the potential to further prolong the survival of ndGBM patients.

AIM

By summarizing the mechanism and application status of TTFields in the treatment of ndGBM, the application prospect of TTFields in ndbm treatment is prospected.

METHODS

We review the recent literature and included 76 articles to summarize the mechanism of TTfields in the treatment of ndGBM. The current clinical application status and potential health benefits of TTFields in the treatment of ndGBM are also discussed.

RESULTS

TTFields can interfere with tumor cell mitosis, lead to tumor cell apoptosis and increased autophagy, hinder DNA damage repair, induce ICD, activate tumor immune microenvironment, reduce cancer cell metastasis and invasion, and increase BBB permeability. TTFields combines with chemoradiotherapy has made progress, its optimal application time is being explored and the problems that need to be considered when retaining the electrode patches for radiotherapy are further discussed. TTFields shows potential in combination with immunotherapy, antimitotic agents, and PARP inhibitors, as well as in patients with subtentorial gliomas.

CONCLUSION

This review summarizes mechanisms of TTFields in the treatment of ndGBM, and describes the current clinical application of TTFields in ndGBM. Through the understanding of its principle and application status, we believe that TTFields still has the potential to further prolong the survival of ndGBM patients. Thus,research is still needed to explore new ways to combine TTFields with other therapies and optimize the use of TTFields to realize its full potential in ndGBM patients.

Phase 1 study of concomitant tumor treating fields and temozolomide chemoradiation for newly diagnosed glioblastoma

Background

Glioblastoma (GBM) is the most common and aggressive primary brain tumor and has limited effective therapies. Tumor treating fields (TTF; Optune Gio®) is an FDA-approved device with data supporting a significant survival benefit and minimal toxicity when added to maintenance chemotherapy. Uptake in clinical practice is not universal and might improve if a shorter duration of treatment is feasible. This phase 1 trial was designed to determine the safety and preliminary efficacy of TTF concomitant to chemoradiation.

Methods

Patients with newly diagnosed, histologically confirmed GBM were eligible. Following surgery, patients were treated with TTF concomitant to standard chemoradiation. The device continued through 2 monthly cycles of maintenance temozolomide with imaging and clinical assessments at regular intervals to assess toxicity and response. The primary endpoint was the safety and tolerability of combined modality treatment based upon the incidence and severity of adverse events. Secondary endpoints were overall survival (OS) and progression-free survival (PFS).

Results

Thirteen patients were enrolled. Dermatologic adverse events were frequent but limited to grade 1/2. There was only 1 serious adverse event possibly related to TTF and no patients were unable to complete the prescribed course of multimodality treatment due to TTF-associated toxicity. Twelve patients were evaluable for median and 6-month progression-free survival which were 8.5 months (mo) and 66.7%, respectively. Median and 12 mo overall survival were 16.0 mo and 83.3%, respectively.

Conclusions

TTF can be safely delivered in conjunction with chemoradiation. The potential for a finite TTF course merits further evaluation.

Investigation of sponge medium for efficient concurrent tumor treating fields and radiotherapy for glioblastomas

Realizing precise therapy for glioblastomas (GBMs), a kind of high-frequency malignant brain tumor, is of great importance in improving the overall survival (OS) of patients. With relentless efforts made in the past few years, a sponge medium has been introduced into concurrent tumor treating fields (TTFields) and radiotherapy to enhance therapy efficacy for GBMs, and some progresses have been witnessed. However, the specific physical and chemical characteristics of the sponge that can be used for GBMs have not been reported as far as we know. Therefore, this study aims to develop a simple yet robust method to select a candidate sponge medium and verify its safety in advanced concurrent TTFields and radiotherapy for GBMs through interdisciplinary investigation among materials science, medical physics, and clinical radiation oncology. Significantly, latex-free polyurethane (PU) sponges with a Hounsfield unit (HU) value lower than -750, which exhibit almost no negative influence on planning computed tomography (CT) imaging and radiotherapy dosimetry, are demonstrated to be available for concurrent TTFields and radiotherapy for GBMs. Moreover, in clinical research, the achieved clear CT images, negligible scalp toxicity, lower residual positioning errors, and high compliant rate of 82% over the selected representative sponge sample corroborate the availability and safety of PU sponges in practical applications for GBM treatment.

Evaluation of Interfraction Setup Uncertainty of Patients With Glioblastoma Wearing TTFields (Tumor Treating Fields) During Radiation Therapy

PURPOSE

Tumor treating fields (TTFields) with concurrent radiation therapy (RT) might improve the outcome of patients with newly diagnosed glioblastoma. Several trials, including that conducted in our center, have allowed patients to wear TTFields during RT. We aimed to evaluate the setup uncertainty introduced by TTFields and calculate the planning target volume (PTV) margin for clinical reference.

METHODS AND MATERIALS

We collected and analyzed 201 cone beam computed tomography images of 22 patients in our center. Patients with or without TTFields were divided into the control and TTFields groups. We evaluated the setup errors in 6 degrees of freedom and 3 degrees of freedom and the magnitudes in the 3-dimensional vectors. An estimated PTV margin for patients requiring nonimaging-guided RT was recommended.

RESULTS

A significant difference was observed in the longitudinal axis between the TTFields and control groups (P < .05). These results were consistent with that of the intragroup comparison of the TTFields group. The position error of the longitudinal axis (from head to feet) was -0.51 ± 2.05 mm in the TTFields group.

CONCLUSIONS

Wearing TTFields during RT increased the uncertainty, especially in the longitudinal axis, with a system error of 1.40 mm and a random error of 1.28 mm. Daily image guided RT for TTFields patients seems necessary. However, the recommended expansion margin of the PTV is 5 mm for patients requiring nonimage-guided RT to enhance the safety and efficacy of treatment.

Enhancing glioblastoma treatment through the integration of tumor-treating fields

Glioblastoma (GBM) represents a significant therapeutic challenge due to its aggressive nature. Tumor Treating Fields (TTFields) present a promising approach to GBM therapy. The primary mechanism of TTFields, an antimitotic effect, alongside numerous indirect effects including increased cell membrane permeability, signifies their potential in combination with other treatment modalities. Current combinations often include chemotherapy, particularly with temozolomide (TMZ), however, emerging data suggests potential synergy with targeted therapies, radiotherapy, and immunotherapy as well. TTFields display minimal side effects, predominantly skin-related, posing no significant barrier to combined therapies. The effectiveness of TTFields in GBM treatment has been demonstrated through several post-registration studies, advocating for continued research to optimize overall survival (OS) and progression-free survival (PFS) in patients, as opposed to focusing solely on quality of life.

Effectiveness and safety of tumor-treating fields therapy for glioblastoma: A single-center study in a Chinese cohort

Objective

Tumor-treating fields (TTFields) are a new therapeutic modality for patients with glioblastoma (GBM). However, studies on survival outcomes of TTFields are rarely reported in China. This study aimed to examine the clinical efficacy and safety of TTFields therapy for GBM in China.

Methods

A total of 93 patients with newly diagnosed GBM (ndGBM) and recurrent GBM (rGBM) were included in our study retrospectively. They were divided into two groups based on whether they used TTFields. Progression-free survival (PFS), overall survival (OS), and toxicities were assessed.

Results

Among the patients with ndGBM, there were 13 cases with TTFields and 39 cases with no TTFields. The median PFS was 15.3 [95% confidence interval (CI): 6.5-24.1] months and 10.6 (95% CI: 5.4-15.8) months in the two groups, respectively, with P = 0.041. The median OS was 24.8 (95% CI: 6.8-42.8) months and 18.6 (95% CI: 11.4-25.8) months, respectively, with P = 0.368. Patients with subtotal resection (STR) who used TTFields had a better PFS than those who did not (P = 0.003). Among the patients with rGBM, there were 13 cases with TTFields and 28 cases with no TTFields. The median PFS in the two groups was 8.4 (95% CI: 1.7-15.2) months and 8.0 (95% CI: 5.8-10.2) months in the two groups, respectively, with P = 0.265. The median OS was 10.6 (95% CI: 4.8-16.4) months and 13.3 (95% CI: 11.0-15.6) months, respectively, with P = 0.655. A total of 21 patients (21/26, 80.8%) with TTFields developed dermatological adverse events (dAEs). All the dAEs could be resolved or controlled.

Conclusion

TTFields therapy is a safe and effective treatment for ndGBM, especially in patients with STR. However, it may not improve survival in patients with rGBM.

Evaluating the therapeutic effect of tumor treating fields (TTFields) by monitoring the impedance across TTFields electrode arrays

BACKGROUND

Tumor Treating Fields (TTFields), are a novel, non-invasive tissue ablation technology for treatment of cancer. Tissue ablation is achieved through the continuous delivery of a narrow range of electromagnetic fields across a tumor, for a period of months. TTFields are designed to affect only cells that divide and to interfere with the cell division process. The therapy is monitored with MRI imaging, performed every couple of months. Current technology is unable to assess the treatment effectiveness in real time.

METHODS

We propose that the effect of the treatment can be assessed, in real time, by continuously measuring the change in electrical impedance across the TTFields delivery electrode arrays. An in vitro anatomic skull experimental study, with brain and tumor mimics phantom tissues was conducted to confirm the potential value of the proposed monitoring system.

RESULTS

Experiments show that measuring the change in the impedance amplitude between opposite TTFields electrode arrays, at a typical TTFields treatment frequency of (200 kHz), can detect changes in the tumor radius with a sensitivity that increases with the radius of the tumor. The study shows that TTFields electrode arrays can be used to assess the effectiveness of TTFields treatment on changes in the tumor dimensions in real time, throughout the treatement. This monitoring system may become a valuable addition to the TTFields cancer treatment technology. It could provide the means to continuously assess the effectiveness of the treatment, and thereby optimize the design of the treatment protocol.

Progress and prospect in tumor treating fields treatment of glioblastoma

Glioblastoma (GBM) is a challenging cancer with poor prognosis. The classical standard for treatment is safe resection, followed by concurrent chemoradiotherapy with subsequent adjuvant temozolomide (TMZ). Despite several attempts at different treatments, the 5-year survival rate remains poor. In recent years, with the continuous progress of treatment technology, tumor treating fields (TTFields) were preferable. The device could generate an intermediate frequency alternating electric field and induce apoptosis of some specific types of cancer cells with few toxic and side effects. TTFields induced apoptosis through multiple activations of the pathway. TTFields have been Food and Drug Administration (FDA)-approved for diagnosis and recurrent GBM as additional clinical trial results are revealed. This study reviewed the current status, mechanisms, correlations with immune pathways, the prospects of applying TTFields for GBM, and the adverse events.

Mechanisms of temozolomide resistance in glioblastoma - a comprehensive review

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and has an exceedingly low median overall survival of only 15 months. Current standard-of-care for GBM consists of gross total surgical resection followed by radiation with concurrent and adjuvant chemotherapy. Temozolomide (TMZ) is the first-choice chemotherapeutic agent in GBM; however, the development of resistance to TMZ often becomes the limiting factor in effective treatment. While O6-methylguanine-DNA methyltransferase repair activity and uniquely resistant populations of glioma stem cells are the most well-known contributors to TMZ resistance, many other molecular mechanisms have come to light in recent years. Key emerging mechanisms include the involvement of other DNA repair systems, aberrant signaling pathways, autophagy, epigenetic modifications, microRNAs, and extracellular vesicle production. This review aims to provide a comprehensive overview of the clinically relevant molecular mechanisms and their extensive interconnections to better inform efforts to combat TMZ resistance.

Observations on the anti-glioma potential of electrical fields: is there a role for surgical neuromodulation?

Alternating electrical field therapy represents a recent addition to the armamentarium against high grade glioma. Randomised trial evidence suggests a survival benefit from adjunctive scalp delivered Tumour Treating Fields (TTFields) in glioblastoma. Any underlying anti-glioma effect is not fully understood, but interference with cell division and microtubule assembly has been averred. The survival benefit claimed for TTFields is modest and is associated with mild reductions in health-related quality of life indices amid costs that presently preclude routine use. I review possible mechanisms by which alternating electrical fields may confer an anti-glioma effect. As scalp and skull are poor conductors of an electrical field, a case is made here for implantable electrodes, perhaps placed at the time of tumour debulking. Such a system may deliver an electrical field directly to the tumour resection cavity and with greater precision.

Dosimetric impact of the positioning variation of tumor treating field electrodes in the PriCoTTF-phase I/II trial

Purpose

The aim of the present study based on the PriCoTTF‐phase I/II trial is the quantification of skin‐normal tissue complication probabilities of patients with newly diagnosed glioblastoma multiforme treated with Tumor Treating Field (TTField) electrodes, concurrent radiotherapy, and temozolomide. Furthermore, the skin‐sparing effect by the clinically applied strategy of repetitive transducer array fixation around their center position shall be examined.

Material and Methods

Low‐dose cone‐beam computed tomography (CBCT) scans of all fractions of the first seven patients of the PriCoTTF‐phase I/II trial, used for image guidance, were applied for the dosimetric analysis, for precise TTField transducer array positioning and contour delineation. Within this trial, array positioning was varied from fixation‐to‐fixation period with a standard deviation of 1.1 cm in the direction of the largest variation of positioning and 0.7 cm in the perpendicular direction. Physical TTField electrode composition was examined and a respective Hounsfield Unit attributed to the TTField electrodes. Dose distributions in the planning CT with TTField electrodes in place, as derived from prefraction CBCTs, were calculated and accumulated with the algorithm Acuros XB. Dose‐volume histograms were obtained for the first and second 2 mm scalp layer with and without migrating electrodes and compared with those with fixed electrodes in an average position. Skin toxicity was quantified according to Lyman's model. Minimum doses in hot‐spots of 0.05 cm² and 25 cm² (ΔD_0.05cm², ΔD_25cm²) size in the superficial skin layers were analyzed.

Results

Normal tissue complication probabilities (NTCPs) for skin necrosis ranged from 0.005% to 1.474% (median 0.111%) for the different patients without electrodes. NTCP logarithms were significantly dependent on patient (P < 0.0001) and scenario (P < 0.0001) as classification variables. Fixed positioning of TTField arrays increased skin‐NTCP by a factor of 5.50 (95%, CI: 3.66–8.27). The variation of array positioning increased skin‐NTCP by a factor of only 3.54 (95%, CI: 2.36–5.32) (P < 0.0001, comparison to irradiation without electrodes; P = 0.036, comparison to irradiation with fixed electrodes). NTCP showed a significant rank correlation with D25cm² over all patients and scenarios (r_s = 0.76; P < 0.0001).

Conclusion

Skin‐NTCP calculation uncovers significant interpatient heterogeneity and may be used to stratify patients into high‐ and low‐risk groups of skin toxicity. Array position variation may mitigate about one‐third of the increase in surface dose and skin‐NTCP by the TTField electrodes.