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

Abstract

BackgroundTumor-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.MethodsIn 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.ResultsMeasurements 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 < 0.5 Gy, which should be considered especially in cases next to the scull base.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.Electronic supplementary materialThe online version of this article (10.1186/s13014-018-0976-3) contains supplementary material, which is available to authorized users.

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

“…Back scatter experiments positioning the transducer arrays at the beam exit side of the body showed an enhancement of 23% of the depth dose at the beam exit side of the body. Li et al 2018 and Straube et al 2018 performed treatment planning and TTF dose measurement studies in an Anderson Rando phantom [30,31]. Either the Acuros XB v11 or the AAA13 algorithm, both implemented in the Eclipse planning system (Varian Medical Systems, Palo Alto, CA, US), were used by Li et al 2018 and Bender et al for dose calculation [29,30].…”

“…Li et al overwrote the density of the electrodes contoured on the CT of the Anderson RANDO phantom with the highest density allowed by the Acuros XB v11 algorithm, with the density of aluminium, that is lower than that of the TTFields [30]. Straube et al used the Hounsfield units from a keV-CT and MeV-CT to estimate the electron densities of the transducer arrays [31]. Straube's group noticed that the Hounsfield units from the keV-CT were at and above the upper limit of measurable values [31].…”

“…Straube et al used the Hounsfield units from a keV-CT and MeV-CT to estimate the electron densities of the transducer arrays [31]. Straube's group noticed that the Hounsfield units from the keV-CT were at and above the upper limit of measurable values [31]. The MeV-CT's tended to an underestimation of the HU by the electrodes.…”

Strahlentherapie spinaler Tumoren

“…B. bei der Verwendung von Metallen im Rahmen einer dorsalen Stabilisierung mit oder ohne Wirbelkörperersatz, können Artefakte die Genauigkeit der Dosisberechnung, der Zielvolumendefinition und der Segmentierung der Risikoorgane einschränken (▶ Abb. 1) [7]. Dies spielt insbesondere bei Re-Bestrahlungen oder bei hohen Bestrahlungsdosen, wie z.…”

“…Eine andere Option ist die Erstellung von Bestrahlungsplänen auf der Basis sog. MV-CTs [7]. Diese besonderen CTs werden mit spezialisierten medizinischen Linearbeschleunigern (z.…”