radiotherapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Ra ...

, radiation treatment planning (RTP) is the process in which a team consisting of

radiation oncologist A radiation oncologist is a specialist physician who uses ionizing radiation (such as megavoltage X-rays or radionuclides) in the treatment of cancer. Radiation oncology is one of the three primary specialties, the other two being surgical and ...

radiation therapist A radiation therapist, therapeutic radiographer or radiotherapist is an allied health professional who works in the field of radiation oncology. Radiation therapists plan and administer radiation treatments to cancer patients in most Western c ...

medical physicists Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care practices ...

and medical dosimetrists plan the appropriate external beam radiotherapy or internal

brachytherapy Brachytherapy is a form of radiation therapy where a sealed radiation source is placed inside or next to the area requiring treatment. ''Brachy'' is Greek for short. Brachytherapy is commonly used as an effective treatment for cervical, prost ...

treatment technique for a patient with

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal bl ...

History

In the early days of radiotherapy planning was performed on 2D

x-ray X-rays (or rarely, ''X-radiation'') are a form of high-energy electromagnetic radiation. In many languages, it is referred to as Röntgen radiation, after the German scientist Wilhelm Conrad Röntgen, who discovered it in 1895 and named it ' ...

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 scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

s, more powerful computers, improved dose calculation algorithms and

Multileaf collimator A multileaf collimator (MLC) is a Collimator or beam-limiting device that is made of individual "leaves" of a high atomic numbered material, usually tungsten, that can move independently in and out of the path of a radiotherapy beam in order to sh ...

s (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 Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...

and

VMAT The vesicular monoamine transporter (VMAT) is a transport protein integrated into the membranes of synaptic vesicles of presynaptic neurons. It transports monoamine neurotransmitters – such as dopamine, serotonin, norepinephrine, epinephrine ...

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.

Image guided planning

Typically, medical imaging is used to form a ''virtual patient'' for a computer-aided design procedure. A

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 Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, ...

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 Mathematical optimization (alternatively spelled ''optimisation'') or mathematical programming is the selection of a best element, with regard to some criterion, from some set of available alternatives. It is generally divided into two subfi ...

. For

intensity modulated radiation therapy Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radia ...

(

), this process involves selecting the appropriate beam type (which may include photons, electrons and protons), energy (e.g. 6, 18

megaelectronvolt In physics, an electronvolt (symbol eV, also written electron-volt and electron volt) is the measure of an amount of kinetic energy gained by a single electron accelerating from rest through an electric potential difference of one volt in vacuum ...

(MeV) photons) and physical arrangements. In

planning involves selecting the appropriate catheter positions and source dwell times (in HDR brachytherapy) or seed positions (in LDR brachytherapy). The more formal optimization process is typically referred to as ''forward planning'' and ''inverse planning''. Plans are often assessed with the aid of

dose-volume histogram A dose-volume histogram (DVH) is a histogram relating radiation dose to tissue volume in radiation therapy planning. DVHs are most commonly used as a plan evaluation tool and to compare doses from different plans or to structures. DVHs were introd ...

s, allowing the clinician to evaluate the uniformity of the dose to the diseased tissue (tumor) and sparing of healthy structures.

Forward planning

In forward planning, the planner places beams into a radiotherapy treatment planning system that can deliver sufficient radiation to a

tumour A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

while both sparing critical

organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...

s and minimising the dose to healthy tissue. The required decisions include how many radiation beams to use, which angles each will be delivered from, whether attenuating

wedges A wedge is a triangular shaped tool, and is a portable inclined plane, and one of the six simple machines. It can be used to separate two objects or portions of an object, lift up an object, or hold an object in place. It functions by conv ...

be used, and which MLC configuration will be used to shape the radiation from each beam. Once the treatment planner has made an initial plan, the treatment planning system calculates the required monitor units to deliver a prescribed dose to a specific area, and the distribution of dose in the body this will create. The dose distribution in the patient is dependent on the anatomy and beam modifiers such as wedges, specialized collimation, field sizes, tumor depth, etc. The information from a prior

of the patient allows more accurate modelling of the behaviour of the radiation as it travels through the patient's tissues. Different dose calculation models are available, including

pencil beam In optics, a pencil or pencil of rays is a geometric construct used to describe a beam or portion of a beam of electromagnetic radiation or charged particles, typically in the form of a narrow beam (conical or cylindrical). Antennas which stro ...

, convolution-superposition and

monte carlo simulation Monte Carlo methods, or Monte Carlo experiments, are a broad class of computational algorithms that rely on repeated random sampling to obtain numerical results. The underlying concept is to use randomness to solve problems that might be determ ...

, with precision versus computation time being the relevant trade-off. This type of planning is only sufficiently adept to handle relatively simple cases in which the tumour has a simple shape and is not near any critical organs.

Inverse planning

In inverse planning a radiation oncologist defines a patient's critical organs and tumour, after which a planner gives target doses and importance factors for each. Then, an optimisation program is run to find the treatment plan which best matches all the input criteria. In contrast to the manual trial-and-error process of forward planning, inverse planning uses the optimiser to solve the

Inverse Problem An inverse problem in science is the process of calculating from a set of observations the causal factors that produced them: for example, calculating an image in X-ray computed tomography, source reconstruction in acoustics, or calculating th ...

as set up by the planner.

References

{{DEFAULTSORT:Radiation Treatment Planning Radiation therapy Medical physics

History

Image guided planning

Forward planning

Inverse planning

See also

References