Dataset Information

Dosimetric impact of tumor treating field (TTField) transducer arrays onto treatment plans for glioblastomas - a planning study.

ABSTRACT:

Background

Tumor-Treating Fields (TTFields) are a novel treatment strategy for glioblastoma (GBM) that is approved for the use concomitantly to adjuvant chemotherapy. Preclinical data suggest a synergistic interaction of TTFields and radiotherapy (RT). However, the dosimetric uncertainties caused by the highly dense arrays have led to caution of applying the TTF setup during RT.

Methods

In a RW3 slab phantom we compared the MV- and kV-CT based planned dose with the measured dose. VMAT-plans were optimized on MV-CTs of an Alderson head phantom without TTF arrays and then re-calculated on the same phantom equipped with TTF arrays. Dose at organs at risk (OAR) and target volumes (PTVs) were compared.

Results

Measurements at a depth of 2, 3 and 4 cm of a RW 3 slab phantom show an attenuation due to TTField arrays of 3.4, 3.7 and 2.7% respectively. This was in-line with calculated attenuations based on MV-CT (1.2, 2.5 and 2.5%) but not with the attenuation expected from kV-CT based calculations (7.1, 8.2 and 8.6%). Consecutive MV-CT based VMAT planning and re-calculation reveals, that the conformity and homogeneity are not affected by the presence of TTField arrays. The dose at organs at risk (OAR) can show increases or decreases by ConclusionMV-CT based dose calculation results in reliable dose distributions also in the presence of TTField arrays. There is a small but clinically not relevant interaction between the TTField arrays and VMAT dose application. Thus, daily replacement of TTField arrays is not necessary in regard to deeply located OARs. RT is feasible, when a VMAT treatment plan is optimized to an array free planning CT. As the biologic effect of a concomitant treatment especially on OARs is currently unknown, a concomitant treatment should be performed only within clinical trials.

SUBMITTER: Straube C

PROVIDER: S-EPMC5824562 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Publications

Dosimetric impact of tumor treating field (TTField) transducer arrays onto treatment plans for glioblastomas - a planning study.

Straube Christoph C Oechsner Markus M Kampfer Severin S Scharl Sophia S Schmidt-Graf Friederike F Wilkens Jan J JJ Combs Stephanie E SE

Radiation oncology (London, England) 20180223 1

<h4>Background</h4>Tumor-Treating Fields (TTFields) are a novel treatment strategy for glioblastoma (GBM) that is approved for the use concomitantly to adjuvant chemotherapy. Preclinical data suggest a synergistic interaction of TTFields and radiotherapy (RT). However, the dosimetric uncertainties caused by the highly dense arrays have led to caution of applying the TTF setup during RT.<h4>Methods</h4>In a RW3 slab phantom we compared the MV- and kV-CT based planned dose with the measured dose. ...[more]

PMID: 29471879

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Project description:PurposeThe 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 methodsLow-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 ( ? D0.05cm 2 , ? D25cm 2 ) size in the superficial skin layers were analyzed.ResultsNormal 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 (rs = 0.76; P < 0.0001).ConclusionSkin-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.

Project description:Abstract Background Tumor Treating Fields (TTFields) is an antimitotic cancer treatment that utilizes low intensity (1–3 V/cm) alternating electric fields in the intermediate frequency (100–300 kHz), approvedfor the treatment of Glioblastoma Multiforme (GBM) located in the supratentorial regions of the brain. A clinical trial testing the efficacy of TTFields for treating brain metastases is currently underway (METIS, NCT02831959). TTFields are delivered via two pairs of transducer arrays placed on the patient’s skin in proximity to the tumor. The standard array layouts used to deliver TTFields involve placement of the arrays on the supratentorial regions of the head. Using these layouts, therapeutic field intensities above 1 V/cm are achieved within the surpatentorial brain. However, field intensities in the infratenorium fall to sub-therapeutic levels. . Brain metastases commonly occur in the infratentorium. In addition, infratentorial tumors are common in the pediatric population. Hence, there is a need to for array layouts that can be used to deliver TTFields effectively to the infratentorial brain. Here we present a new array layout designed to deliver high field intensities to the infratentorial brain. Materials and methods To simulate delivery of TTFields to the brain, realistic computerized head models of an adult human female and an adult human male were used. Virtual transducer arrays were placed on the models, and boundary conditions were set to simulate delivery of TTFields at 200 kHz. Various array layouts were tested, and field distributions resulting from the layouts were evaluated. Results In both models, TTfields was delivered to the infratentorium most effectively with a layout, in which each array of one pair was laterally placed superficially to the lower region of the occipital lobe, and the two arrays of the second pair were placed on the calvarium and the superior aspect of the neck. In both models, the pair of arrays in which one array was placed on the calvarium and one array on the superior aspect of the neck delivered field intensities above 1.1 V/cm to over 95% of the volume of the infratentorial brain, and the pair of arrays placed on the lateral aspects of the occipital lobe delivered field intensities above 1 V/cm to over 95% of the infratentorial brain. Both pairs of arrays delivered field intensities above 1 V/cm to significant portions of the supratentorial brain. Conclusions This work suggests a practical approach for delivering TTFields to the cerebellum, brain-stem and surrounding regions which are located inferior to the tentorium.

Dataset Information

Dosimetric impact of tumor treating field (TTField) transducer arrays onto treatment plans for glioblastomas - a planning study.

Background

Methods

Results

Publications

Dosimetric impact of tumor treating field (TTField) transducer arrays onto treatment plans for glioblastomas - a planning study.

Similar Datasets

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