Simultaneous integrated boost therapy of carcinoma of the hypopharynx/larynx with and without flattening filter - a treatment planning and dosimetry study

Barbara Dobler,Amine Khemissi,Tina Obermeier,Oliver Koelbl,Matthias G Hautmann

doi:10.1186/s13014-017-0850-8

Barbara Dobler, Amine Khemissi + Show 3 more

Open Access

https://doi.org/10.1186/s13014-017-0850-8

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Journal: Radiation Oncology	Publication Date: Jul 5, 2017
Citations: 10	License type: open-access

Affiliation: University Hospital Regensburg

Abstract

BackgroundThe aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx.MethodsFour treatment plans were created for each of 10 patients for an Elekta Synergy linac with Agility collimating device, a dual arc VMAT and a nine field step and shoot IMRT each with and without flattening filter. Plan quality was compared considering target coverage and dose to the organs at risk. All plans were verified by a 2D–ionization-chamber-array and delivery times were compared. Peripheral point doses were determined as a measure of second cancer risk. The Wilcoxon test was used for statistical analysis with a significance level of 0.05.ResultsPlan quality was similar for all four treatment plans without statistically significant differences of clinical relevance. The clinical goals were met in all plans for the PTV-SIB (V95% > 95%), the spinal cord (D1ccm < 45 Gy) and the brain stem (D1ccm < 48 Gy). For the parotids, the goal of D50% < 30 Gy was met in 70% and 60% of the plans for the left and right parotid respectively, and the V95% of the SIB reached an average of 94%. Delivery times were similar for FF and FFF and significantly decreased by around 70% for VMAT as compared to IMRT. Peripheral doses were significantly reduced by 18% in FFF mode as compared to FF and by 26% for VMAT as compared to IMRT. Lowest peripheral doses were found for VMAT FFF, followed by VMAT FF.ConclusionsThe FFF mode of a linear accelerator is advantageous for the treatment of hypopharynx/larynx carcinoma only with respect to reduction of second cancer induction in peripheral organs for the combination of Elekta Synergy linacs and Oncentra® External Beam v4.5 treatment planning system. This might be of interest in a therapy with curative intent.

Highlights

The aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx
The planning target volumes are derived from the clinical target volumes adding a margin for systematic and random setup errors and internal motion of 4 mm and are named Simultaneous Integrated Boost volume (SIB) and Planning Target Volume (PTV) respectively
Since the main subject of the study was the comparison of the two irradiation modes Flattening Filter (FF) and FFF, details about statistical significance are listed in the tables for this comparison

Summary

Introduction

The aim of this study was to investigate if the flattening filter free (FFF) irradiation mode of a linear accelerator (linac) is advantageous as compared to the flat beam (FF) irradiation mode in intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for carcinoma of the hypopharynx / larynx. Standard linear accelerators with large field sizes have been installed with an opportunity to irradiate patients without a flattening filter in the beam path to increase dose rate and reduce beam-on time [11]. A variety of planning studies has shown that the flattening filter free (FFF) mode of a linac allows reducing delivery times in stereotactic treatments with high fraction doses [13,14,15,16,17,18,19,20,21]. First planning studies for larger target types showed advantages for FFF for some combinations of target type, treatment technique, planning system and linac, whereas no advantage or even disadvantages could be observed in others [22,23,24,25,26,27,28], confirming the need of further investigations depending on target localization and equipment used, as already pointed out in [12, 29]

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