18 May 2023
Check Up #14 - Internal and external radiotherapy
How are they different?
18 May 2023
How are they different?
Radiotherapy, or radiation therapy, is one of the pillars of cancer treatment. Radiotherapy preferentially uses X-rays to eliminate the solid manifestations of malignant tumours.
It is estimated that 60% of cancer patients are treated with radiotherapy at a given phase of their disease, either as part of radical therapeutics (ablative) protocols or of symptomatic and palliative protocols.
At therapeutic doses, radiotherapy damages cancer cells by causing irreversible changes in their DNA. Under the effect of radiation, the cells’ DNA eventually becomes irreparable and the cells are no longer able to maintain their metabolism nor divide or proliferate. Thus, they simply die (necrosis) or go into a process of programmed autophagy (apoptosis).
There are two types of therapeutic radiotherapy: internal (brachytherapy) and external. Brachytherapy, which can be interstitial or intracavitary, consists in inserting a radiation-emitting source into the patient’s body to treat cancer.
Each of these types of treatment can be performed with various techniques. For example, internal radiotherapy can be done with brachytherapy ou by administering radioactive microparticles or drugs (radiopharmaceuticals) to the patient. In the first case, the radioactive sources are sealed (solid body) and can be permanently or temporarily implanted. The permanent implant is inserted by the so-called interstitial method (inside the tissues), in which needles are inserted to guide the sealed radioactive sources, or “seeds”, thus creating a radiation exposure area very closely or even inside the tumours. Examples of cancers that are treated in this way are head and neck, breast and prostate neoplasias.
The temporary implant is essentially done with the intracavitary method, where the radioactive source is placed near the tumour with the help of applicators inserted into natural cavities (vagina, cervix). Other temporary implants are also used: for example, in interstitial brachytherapy for the treatment of breast cancer; in endoluminal brachytherapy, where the sealed radioactive source is temporarily placed through a catheter in a blood vessel or a hollow organ, such as the trachea or the bronchi; or in superficial brachytherapy to treat certain types of ocular and cutaneous tumours.
Brachytherapy is not performed at the Champalimaud Foundation. Nonetheless, the local or systemic administration of unsealed radioactive sources (in liquid form), such as radioactive microparticles or radiopharmaceuticals, which are other techniques of internal radiotherapy, also known as molecular radiotherapy, are performed at the Foundation and will be the subject of a future CheckUp.
All these techniques allow the application of high doses of radiation to the tumours, minimising adverse effects to tissues and surrounding organs.
External radiotherapy can also be performed at the Foundation with the help of various techniques. External or targeted radiotherapy is a treatment in which the radiation comes from a linear accelerator – that is, from outside the body.
Technological advances in the last two decades, such as modulated radiation intensity (IMRT, or intensity-modulated radiation therapy) and the new robotic platforms that dynamically irradiate the tumour volume by rotating the radiotherapy beam around the patient in an arc shape (VMAT, or volumetric modulated arc therapy) have radically changed the use of radiotherapy. Today, it is possible to “sculpt” the focally applied radiation dose, according to each patient’s individual anatomy, which effectively reduces the amount of unnecessary radiation delivered to adjacent tissues and organs, decreasing treatment toxicity to a minimum.
In the area of rectal cancer, for example, Champalimaud Foundation’s radiation oncologist Oriol Parés said in an interview, “nowadays, we are no longer irradiating the [whole] pelvis as if it were a box, but ‘sculpting’ the radiation dose in the shape of each patient’s mesorectum [the precise region within which the tumor is located]. This means that it is possible to modulate the intensity of [the radiation] beam, thus adapting it in a dynamic way to the shape of the tumour or of the organ that [we] want to irradiate.”
In general, several external radiotherapy sessions are required (daily for 5/6/7 weeks) to obtain the desired results. However, at the Champalimaud Foundation, where some of the most advanced radiotherapy techniques are being applied, and new variants are being developed, this conventional “fractionated” radiotherapy is replaced, when possible, by so-called precision stereotactic radiotherapy, which can be used on the brain and the body. This approach requires a very small number of irradiation sessions (one to five), and in some cases just one session (single-dose radiotherapy), to obtain the same effect – in some cases with considerable therapeutic gain (prostate, lung) – compared to conventional protocols.
To enable the application of the single-dose protocol, the Foundation’s radio-oncologists resort to image-guided radiotherapy (IGRT) either on the surface (breast tumours) or deeper (prostate tumours). Its use allows fo the visualisation of the patient’s 3D anatomy in real time, while the tumour is being irradiated. This minimises the irradiation of healthy adjacent tissues and organs. Consequently, the radiation dose administered in a single session can be increased, and the organs’ function preserved without significant clinical impact on quality of life.
We can say for a fact that external radiotherapy is increasingly becoming a type of radiosurgery – that is, a radiation surgery without the need for any surgically aggressive actions, as is the case for conventional surgery (open or robotic).
At the Champalimaud Foundation, radiosurgery is already being used, namely at treat metastatic lesions in patients with small numbers of metastases, in symptomatic lesions (pain, haemorrhaging, compression) and even to replace conventional surgery (prostate) in patients with well-localised primary tumours and in those who cannot or should not be submitted to surgical procedures (lung).