Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck

Abstract

We report on the design of Marvin, a Model Anatomy for Radiotherapy Verification and audit In the head and Neck and present results demonstrating its use in the development of the Elekta volumetric modulated arc therapy (VMAT) technique at the Christie, and in the audit of TomoTherapy and Varian RapidArc at other institutions. The geometry of Marvin was generated from CT datasets of eight male and female patients lying in the treatment position, with removable inhomogeneities modelling the sinuses and mandible. A modular system allows the phantom to be used with a range of detectors, with the locations of the modules being based on an analysis of a range of typical treatment plans (27 in total) which were mapped onto the phantom geometry. Results demonstrate the use of Gafchromic EBT2/EBT3 film for measurement of relative dose in a plane through the target and organs-at-risk, and the use of a small-volume ionization chamber for measurement of absolute dose in the target and spinal cord. Measurements made during the development of the head and neck VMAT protocol at the Christie quantified the improvement in plan delivery resulting from the installation of the Elekta Integrity upgrade (which permits an effectively continuously variable dose rate), with plans delivered before and after the upgrade having 88.5 ± 9.4% and 98.0 ± 2.2% respectively of points passing a gamma analysis (at 4%, 4 mm, global). Audits of TomoTherapy and Varian RapidArc neck techniques at other institutions showed a similar quality of plan delivery as for post-Integrity Elekta VMAT: film measurements for both techniques had >99% of points passing a gamma analysis at the clinical criteria of 4%, 4 mm, global, and >95% of points passing at tighter criteria of 3%, 3 mm, global; and absolute dose measurements in the PTV and spinal cord were within 1.5% and 3.5% of the planned doses respectively for both techniques. The results demonstrate that Marvin is an efficient and effective means of assessing the quality of delivery of complex radiotherapy in the head and neck, and is a useful tool to assist development and audit of these techniques.

A preclinical radiotherapy dosimetry audit using a realistic 3D printed murine phantom

“…The calibration curve was parametrised using an equation of the form shown in Eq. ( 1 ), as described by Aitkenhead et al 31 . where A, B, C are the fit parameters and O.D.…”

“…Film measurements of the delivered dose were compared to that calculated by the TPS using gamma analysis 32 . Analysis was performed within an Octave environment 29 using in-house software which has previously been clinically commissioned for other applications 31 , 33 , 34 . For each centre, the film data formed the reference dataset while the planned dose grid formed the evaluation dataset, following the terminology used by Low et al 35 .…”

Feasibility study of using polyacrylamide gel dosimeter as brain equivalent material in therapeutic energy range of X-rays

“…Different materials such as glass, human bone, plastic, polystyrene, Perspex, acrylonitrile butadiene 2020 JINST 15 P03016 styrene, polycarbonate, polyurethane etc. have been used in construction of these phantoms [12][13][14][15][16][17]. Because the water can be considered to be a suitable substitute for brain [18], in head phantoms manufactured by different researchers, water is applied as the brain.…”

The incidence of the different sources of noise on the uncertainty in radiochromic film dosimetry using single channel and multichannel methods

“…These properties make the EBT3 film suitable for radiation dosimetry in quality assurance of treatment planning systems and linear accelerators. In particular, this film is a widely used verification tool for intensity modulated radiation therapy (Aitkenhead et al 2013, Marrazzo et al 2015. However, the response of RCFs has a poor spatial homogeneity, due to differences in the thickness of the active layer (Niroomand-Rad et al 1998), which constitutes a major drawback in dosimetric applications.…”