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An international survey of imaging practices in radiotherapy

Martin CJ, Kron T, Vassileva J, Wood TJ, Joyce C, Ung NM, et al.

Phys Med, 2021 Oct;90:53-65.
PMID: 34562809 DOI: 10.1016/j.ejmp.2021.09.004

Improvements in delivery of radiation dose to target tissues in radiotherapy have increased the need for better image quality and led to a higher frequency of imaging patients. Imaging for treatment planning extends to function and motion assessment and devices are incorporated into medical linear accelerators (linacs) so that regions of tissue can be imaged at time of treatment delivery to ensure dose distributions are delivered as accurately as possible. A survey of imaging in 97 radiotherapy centres in nine countries on six continents has been undertaken with an on-line questionnaire administered through the International Commission on Radiological Protection mentorship programme to provide a snapshot of imaging practices. Responses show that all centres use CT for planning treatments and many utilise additional information from magnetic resonance imaging and positron emission tomography scans. Most centres have kV cone beam CT attached to at least some linacs and use this for the majority of treatment fractions. The imaging options available declined with the human development index (HDI) of the country, and the frequency of imaging during treatment depended more on country than treatment site with countries having lower HDIs imaging less frequently. The country with the lowest HDI had few kV imaging facilities and relied on MV planar imaging intermittently during treatment. Imaging protocols supplied by vendors are used in most centres and under half adapt exposure conditions to individual patients. Recording of patient doses, a knowledge of which is important in optimisation of imaging protocols, was limited primarily to European countries.
Cone beam CT (CBCT) in radiotherapy: Assessment of doses using a pragmatic setup in an international setting

Djukelic M, Martin CJ, Abuhaimed A, Kron T, Gros S, Wood T, et al.

Phys Med, 2025 Feb 21;131:104937.
PMID: 39985958 DOI: 10.1016/j.ejmp.2025.104937

INTRODUCTION: The imaging modality kV CBCT on linear accelerators (linacs) is utilised to verify positioning and anatomy in cancer patients undergoing radiotherapy treatment. There is a need for optimisation of radiological protection in kV CBCT imaging protocols to avoid unnecessarily high exposures to normal tissues surrounding the target.
METHODS: A network of ICRP mentees from 23 countries were surveyed for available dosimetry equipment. Standardised measurements on CBCT linac imaging systems were conducted using a cone beam dose index (CBDI) devised as a straightforward measurement for wide beam doses. Measurements were made with (a) 100 mm ionisation chambers or (b) 0.6 cc Farmer ionisation chambers and cylindrical CT PMMA phantoms, and (c) an alternative setup of Farmer chambers and cubical phantoms comprised of slabs of water equivalent material readily available in radiotherapy centres. The measurements were compared with Monte Carlo (MC) simulations.
RESULTS: The survey showed limited availability for the reference setup using 100 mm chambers and CT phantoms. Correction factors were derived to convert normalised CBDI from alternative setups to the reference setup and are on average within 2% of MC simulations.
CONCLUSION: The slab phantom in combination with a Farmer chamber provides an alternative to quantify CBCT radiation dose indices from linac-based image-guided radiotherapy using materials accessible in most centres worldwide. A method is presented to use correction factors for Varian Truebeam linacs if traditional 100 mm chambers and cylindrical CT phantoms are not available. This will enable most radiotherapy centres across the world to engage in meaningful imaging dose measurement and optimisation.

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