Treatment planning

In radiotherapy, radiation treatment planning is the process in which a team consisting of radiation oncologists, radiation therapist, medical physicists and medical dosimetrists plan the appropriate external beam radiotherapy or internal brachytherapy treatment technique for a patient with cancer.

In the early days of radiotherapy planning was performed on 2D x-ray images, often by hand and with manual calculations. Computerised treatment planning systems began to be used in the 1970s to improve the accuracy and speed of dose calculations.

By the 1990s CT scans, more powerful computers, improved dose calculation algorithms and Multileaf collimators (MLCs) lead to 3D conformal planning (3DCRT), categorised as a Level 2 technique by the European Dynarad consortium. 3DCRT uses MLCs to shape the radiotherapy beam to closely match the shape of a target tumour, reducing the dose to healthy surrounding tissue.

Level 3 techniques such as IMRT and VMAT utilise inverse planning to provide further improved dose distributions (i.e. better coverage of target tumours and sparing of healthy tissue). These methods are growing in use, particularly for cancers in certain locations which have been shown to derive the greatest benefits.

Typically, medical imaging is used to form a virtual patient for a computer-aided design procedure. A CT scan is often the primary image set for treatment planning while magnetic resonance imaging provides excellent secondary image set for soft tissue contouring. Positron emission tomography is less commonly used and reserved for cases where specific uptake studies can enhance planning target volume delineation. Modern treatment planning systems provide tools for multimodality image matching, also known as image coregistration or fusion. Treatment simulations are used to plan the geometric, radiological, and dosimetric aspects of the therapy using radiation transport simulations and optimization. For intensity modulated radiation therapy (IMRT), this process involves selecting the appropriate beam type (which may include photons, electrons and protons), energy (e.g. 6, 18 megaelectronvolt (MeV) photons) and physical arrangements. In brachytherapy planning involves selecting the appropriate catheter positions and source dwell times (in HDR brachytherapy) or seed positions (in LDR brachytherapy).

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