Elsevier

The Lancet Oncology

Volume 6, Issue 2, February 2005, Pages 112-117
The Lancet Oncology

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Theragnostic imaging for radiation oncology: dose-painting by numbers

https://doi.org/10.1016/S1470-2045(05)01737-7Get rights and content

Summary

Theragnostic imaging for radiation oncology is the use of molecular and functional imaging to prescribe the distribution of radiation in four dimensions—the three dimensions of space plus time—of radiotherapy alone or combined with other treatment modalities in an individual patient. Several new imaging targets for positron-emission tomography, single-photon-emission CT, and magnetic resonance spectroscopy allow variations in microenvironmental or cellular phenotypes that modulate the effect of radiation to be mapped in three dimensions. Dose-painting by numbers is a strategy by which the dose distribution delivered by inverse planned intensity-modulated radiotherapy is prescribed in four dimensions. This approach will revolutionise the way that radiotherapy is prescribed and planned and, at least in theory, will improve the therapeutic outcome in terms of local tumour control and side-effects to unaffected tissue

Section snippets

Intensity-modulated radiotherapy (IMRT)

One of the key features underpinning this research is the theoretical and technological development of IMRT and inverse treatment planning (figure 1).3 IMRT is the administration of non-uniform intensities of radiation (or photon fluence profiles) to patients as a way to create a specified, non-uniform absorbed dose distribution. This approach has become feasible as a result of the increased computer control of linear accelerators used for radiotherapy during the past few decades, in

Theragnostic imaging for radiation oncology

Theragnostic imaging for radiation oncology aims to map in three dimensions the distribution of a tumour, tissue, or functional feature, and to provide information about the clinical response of tumours or healthy tissues to radiotherapy. In solid tumours, the aim is to provide images of phenotypic or microenvironmental characteristics known to affect the clinical response. Most research has been based on imaging techniques that use radionuclide-labelled compounds: single-photon-emission CT

From dose-painting to dose-painting by numbers

Dose-painting was the term coined by Ling and colleagues29 in their review of image-guided radiotherapy. The idea was to visualise tumour subvolumes with a potential resistance problem and to paint some additional dose onto that volume. This notion was applied in a study by Chao and co-workers,30 who identified regions with pronounced retention of 62Cu(II)-diacetyl-bis(N(4)-methylthiosemicarba-zone) on a PET scan of a patient with a squamous-cell carcinoma of the head and neck. In a planning

Dosimetric features of IMRT delivery

Although a review of the advantages and drawbacks of IMRT compared with conventional radiotherapy is beyond the scope of this report, a brief summary of some of these from the viewpoint of dose-painting by numbers is relevant. Three-dimensional conformal radiotherapy (3D-CRT) is a broad class of radiotherapy techniques that aim to improve the match between the clinical target volume and the volume irradiated to a high radiation dose. This aim is achieved without intensity modulation by use of a

Are we ready for dose-painting by numbers?

Validation of the imaging target is the first objective in building the case for a new theragnostic imaging procedure. This aim generally involves two steps. The first is to show that the imaging variable correlates with a local biological property, such as a local microelectrode measurement of oxygen tension for hypoxic imaging or a mitotic index or a Ki-67 labelling index for imaging of cell proliferation. The second step is to show the clinical importance of the validation marker for the

Search strategy and selection criteria

Data were identified by searches of PubMed using the search terms “radiotherapy or radiation oncology”, “functional imaging”, “molecular imaging”, “positron emission tomography”, “magnetic resonance imaging”, and “magnetic resonance spectroscopy”.

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