What is treatment planning in radiation therapy

How does radiation treatment work?

Personal conversation

After the referral to the radiation therapist, the first contact takes place in the radiation therapy polyclinic. Here the doctor will ask about the patient's history in a personal conversation ...

examination

... as well as performing a physical exam. Indispensable sources of information are doctor's letters, examination results, operation reports, histological (body tissue-related) findings and the X-ray, CT (computed tomography) or MR (magnetic resonance tomography) images.

Create a treatment plan

Once the radiation therapist has gained a comprehensive picture of the patient and the course of the tumor to date, he can draw up an individual treatment plan.

enlightenment

An important part of the outpatient clinic appointment is also the clarification meeting, in which the indication, objective, procedure and possible side effects of the planned radiation treatment are explained in detail.

Set therapy

In many cases, determining the appropriate therapeutic approach requires consultation with the specialist disciplines involved in tumor treatment and, if necessary, the completion of the preliminary examinations. If the decision to irradiate is made together with the patient, further appointments are made to prepare and initiate the radiation treatment.

Treatment planning / simulation

During the simulation, the irradiation technique is determined and the irradiation fields are marked. For many patients, three-dimensional radiation planning is carried out, which requires additional planning steps including a computer tomography and / or magnetic resonance tomography specially created for this purpose. After completing all preparatory steps, which usually require several appointments on several consecutive days, the actual radiation treatment begins.

Outpatient / inpatient treatment

For the majority of patients, it is done on an outpatient basis, as far as the treatment concept, the general condition of the patient and the external circumstances allow. In certain situations, however, carrying out radiation therapy in an inpatient setting offers advantages, particularly when combined with chemotherapy, in order to ensure that the course of treatment is planned and with as few complications as possible.

Duration and time of treatment

As a rule, five irradiations are administered per week (Monday to Friday), with the same dose portion being irradiated every day. The respective irradiation time is short and generally lasts only a few minutes. For radiobiological reasons, longer irradiation pauses or interruptions are generally not planned or should be avoided in order not to endanger the effect of the irradiation.

Trusting relationship

The complex equipment of a modern radiation clinic serves to guarantee a safe, effective and at the same time gentle radiation treatment. The course of treatment, on the other hand, is determined by a trusting relationship between the patient on the one hand and doctors and medical-technical x-ray assistants (MTRA) on the other. This is of particular importance during the treatment, which usually lasts several weeks.

Aftercare

After completing the radiation treatment, the patient will be presented to the referring doctor. As soon as the overall treatment is finished, the radiotherapy follow-up follows, which takes place in close coordination with the other disciplines involved.

How does radiation therapy work?

Radiation acts as a "brake on growth" for living tissue. It inhibits cell division.

The smallest functional unit of every living organism - and every tumor too - is the cell. Most cells have a limited lifespan and must be constantly replaced. It does this by dividing the cells. Cell division is a basic function of life. Organs can only do their "work" when it is undisturbed. The growth of a tumor is also regulated by cell division. One of the main effects of radiation is to disrupt or even prevent cells from dividing.

Some biological principles

Inside each cell there is a nucleus as a "command center".

This is where it is decided whether and when a cell divides. The cell nucleus also contains the key substance for inheritance, the so-called deoxyribonucleic acid (DNA). This molecule is arranged helically in two strands and contains all of the genetic information.

Before cells divide, the DNA must make a "copy of itself". The DNA is divided into two equal portions, which are passed on to the two newly created "daughter cells" during cell division.

This is where radiation intervenes: It can change the structure of the "DNA screw" in such a way that the cell loses its ability to divide and dies over time.

However, if the DNA is damaged, cells have their own "repair system", which consists of special enzymes. These can - like scissors - cut out defective parts of the DNA and replace them. Repair processes do not only take place in the DNA, but also in the entire cell: Cells and tissues that have been damaged can develop the ability to accelerate growth and thus "compensate" for the damage.

The more pronounced the repair functions of a tissue, the lower its sensitivity to radiation. Or vice versa: a tissue is more sensitive to radiation, the less well this "repair system" works.

This ability to repair is much more pronounced in healthy tissue than in many tumors, so that the damaging effect of radiation on the tumor has far more influence than on the surrounding healthy organs.

It is precisely this difference in the ability to repair that is used for therapy: While healthy tissue usually recovers from the irradiation, tumors or even isolated tumor cells can be damaged or destroyed by the irradiation to the extent that renewed tumor growth and, under certain circumstances, also the Spread of tumor cells into other organs (metastasis) can be prevented. The repairs in normal tissue are made possible by biochemical processes, which, however, take a certain amount of time. This also makes it necessary to divide the total radiation dose into several individual sessions (fractions). After successful irradiation, tumor cells die and are broken down and cleared away by the body's own cells (including so-called scavenger cells = macrophages).

The dose administered

The dose unit in radiation therapy is called Gray (abbreviation Gy) after the physicist L. H. Gray. The dose required to destroy the tumor depends on the radiation sensitivity of the tumor in question and is usually between 40 and 70 Gy. The attending radiation oncologist usually determines the total dose aimed for for the individual patient and his illness before the start of treatment.

This total dose is divided into individual portions (fractions). As a rule, these are 2 Gy, with deviations upwards and downwards possible. In principle, the following rule applies: the smaller the individual dose, the more tolerable the therapy and, in particular, the lower the risk of long-term complications.

What are the goals of radiation therapy?

There are basically two objectives:

Curative radiation treatment with the aim of curing the tumor disease

If this is possible, it is called curative radiation therapy. It can be used both in the case of a visible tumor and as a preventative measure if you do not see a tumor but fear that, for example, isolated tumor cells may still be left in the operating area. These should be destroyed by the radiation (adjuvant radiation therapy).
Some examples of the healing of visible tumors with radiation therapy alone: ​​lymph gland cancer, vocal cord cancer, skin cancer, and prostate cancer. Examples of adjuvant radiation: radiation therapy after organ-preserving surgery for breast cancer and follow-up radiation for colon cancer.

Symptomatic (palliative) radiation therapy with the aim of relieving symptoms

If the tumor cannot be cured, radiation therapy can alleviate tumor-related symptoms and often extend life. Pain in particular often responds particularly well to radiation. For example, about 80 percent of bone pain caused by tumor settlements (metastases) can be alleviated by radiation. In many cases the bone can then be rebuilt and fractures can often be prevented.

But also shortness of breath, swallowing difficulties, paralysis, urinary stasis, lymph stasis or bleeding can often be favorably influenced. Palliative radiation therapy is therefore a very effective measure for improving the quality of life for many tumor patients.

What types of radiation therapy are there?

The task of radiation therapy is the treatment of cancer with the help of high-energy rays that are applied to the tumor from the outside (percutaneous radiation, teletherapy) or from a short distance or inside (brachytherapy) in order to destroy the cancer cells as completely as possible.

Teletherapy (external radiation, external radiation therapy)

This makes up the largest part of radiation therapy. In a special therapy device, radiation is generated and radiated into the inside of the body from outside via fields of a specified size.

The radiation devices for teletherapy

There are different radiation devices; linear accelerators are used most frequently, and telecobalt devices in isolated cases. The main difference between linear accelerators and cobalt devices is that the radiation they produce penetrates the body to different depths. This penetration depth depends on the energy that the device "gives" to the radiation. Telekobalt devices produce gamma rays that are suitable for tumors that are more superficial ("half-deep"). The last telecobalt device in our clinic was shut down at the end of 2012. Linear accelerators have been used exclusively for percutaneous radiation since mid-2013.

Linear accelerators generate two types of radiation: firstly, ultra-hard X-rays (photons of higher energy), which are particularly suitable for treating deep-seated tumors, and secondly, negatively charged particles (electrons), which, on the other hand, only penetrate a few centimeters into the tissue and are therefore used for therapy near the surface local foci of disease are used.

However, the biological effect of the various rays of conventional therapy devices on the tumor is the same: If the same radiation dose is absorbed from a linear accelerator in a tissue structure, it achieves the same effect in the respective irradiated tissue. Modern irradiation devices are technically extremely complex. They are therefore checked daily before commissioning. In addition, the linear accelerator systems have a large number of "fuses". The device only releases the irradiation if all details (e.g. size of the field, angle, irradiation time) exactly match the planned data stored in the computer.

The device "refuses" the irradiation even with the smallest deviations. Thus, with modern devices it is almost impossible to "accidentally irradiate incorrectly". Every single irradiation is documented several times in all details, so that all details can be traced exactly even years later.

For the interested reader: the linear accelerator

Electron accelerators are most commonly used in the medical field. Electrons are tiny, negatively charged particles. The source in which they are generated and emitted is a filament. The electrons produced there are accelerated in a high vacuum tube so that they almost reach the speed of light. At the end of the tube, the electrons are deflected in their path in the desired direction with the help of strong magnets (so-called banding magnets).

These electrons can be used directly for therapy by distributing them over a defined area with a so-called scatter film and thus using them to irradiate superficial tumors. More often, however, photon irradiation is required for deep-seated tumors; it can be generated by letting the above-mentioned electrons hit a water-cooled metal (so-called target).

When they hit the tungsten target, the ultrafast electrons are braked abruptly, and energy conversion processes produce photons (also known as ultra-hard X-rays). Due to their physical properties, photons can - in contrast to electrons - penetrate deeper into the body. The more energetic the photon radiation, the greater its penetration depth.

Brachytherapy (radiation from the inside, afterloading)

Brachytherapy is used both alone and in addition to teletherapy for the treatment of gynecological tumors, tumors in the ENT area, the lungs, the esophagus and the soft tissues. In 3-D image-assisted brachytherapy with high dose rates (HDR - High Dose Rate), tubular catheters are temporarily placed in the treatment area (sometimes via an operation) and the tumor is then treated in a fractionated manner with a coated radioactive emitter inserted into this catheter. Alternatively, the radiator can be placed in a natural body cavity using an applicator.

The radiation devices for brachytherapy

The brachytherapy irradiation device is the so-called afterloader and consists of the enclosed radioactive emitter and the protective device, the so-called safe.