ESTRO 2024 - Abstract Book

S3521

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

Keywords: dose painting, focal planning, heterogeneity

References:

1. Zhao, Y., et al., Patient ‐ specific voxel ‐ level dose prescription for prostate cancer radiotherapy considering tumour cell density and grade distribution. Medical Physics, 2023.

2. Reynolds, H.M., et al. Cell density in prostate histopathology images as a measure of tumor distribution. in Medical Imaging 2014: Digital Pathology. 2014. International Society for Optics and Photonics.

3. Finnegan, R.N., et al., A statistical, voxelised model of prostate cancer for biologically optimised radiotherapy. Physics and imaging in radiation oncology, 2022. 21: p. 136-145.

941

Digital Poster

Should Varian HyperArc make us re-think how we use conventional linacs for SRS?

Christopher Dean 1 , Sweta Bowles 1 , Niall MacDougall 1 , Hamoun Rozati 2 , Jo Cook 1 , Rachel Lewis 2

1 Barts Health NHS Trust, Radiotherapy Physics, London, United Kingdom. 2 Barts Health NHS Trust, Clinical Oncology, London, United Kingdom

Purpose/Objective:

The use of stereotactic radiosurgery (SRS) as a treatment method for patients with intracranial disease is increasing, especially for smaller more numerous metastases (1). In the UK, a range of SRS treatment platforms are benchmarked by the Radiotherapy Trials Quality Assurance (RTTQA) group and commissioned by NHS England (2). One example is Varian HyperArc, a multiple non-coplanar arc (4-pi) VMAT solution offering specific SRS normal tissue and collimator angle optimisation. Because this approach can be applied on widely available conventional linear accelerators, it is an attractive option for institutions in terms of cost-effectiveness and delivery speed when compared with competing specialised stereotactic platforms such as Elekta GammaKnife and Accuray CyberKnife. Despite this, the treatment of small targets (namely 0.01cc to 0.50cc (~3mm to ~10mm PTV diameter)) or those with highly complex shapes, largely remains dominated by specialised platforms with fixed collimation (3). One of the key reasons stated for this reluctance to use VMAT for such lesions is concern over delivered dosimetric certainty using dynamic secondary collimation, with many departments opting for high definition (2.5mm width) MLCs at additional cost and reduced versatility. The purpose of this work is to assess the achievable dosimetric accuracy for such lesions using Varian HyperArc with a 120 Millennium MLC (5mm width in the central region). This work, if positive, could change perceptions of dosimetric limitations of HyperArc on a standard Truebeam and improve access to high-quality SRS using a wide network of readily available linear accelerators, truly bridging a gap in SRS service provision.

Material/Methods: