Stereotactic radiotherapy

Stereotactic radiotherapy is one of the most modern radiotherapy techniques, in which high doses of radiation are delivered in a smaller number of sessions over a small area.

To ensure quality standards, this involves high-precision technology and an experienced team (radiotherapist, medical physicist, technician).

During stereotactic radiotherapy treatment we are able to deliver a single irradiation dose equivalent to approximately one week of external IMRT/VMAT radiotherapy.

Who is eligible for stereotactic radiotherapy?

The applicability of stereotactic irradiation is found in both early stage and metastatic cancers. In early bronchopulmonary cancers, stereotactic irradiation has been shown to be equivalent to surgery in local control. Eligible patients are those with small bronchopulmonary tumours (T1-T), who have no lymph node involvement (N0). Numerous studies have shown that ablative irradiation offers an elegant, non-invasive and much more tolerable solution to traditional invasive thoracic surgery.

In the palliative spectrum of breast, bronchopulmonary, prostate and other cancers, stereotactic surgery helps us to move the boundary of the definition of palliative towards the limit of curability. In this way, we can target brain metastases and succeed in destroying them using ablative doses. The SABR-COMET Phase II study (2019) proved that patients, despite having metastases, can benefit from prolonged survival with stereotaxy. It is estimated that they will have a survival of 41 months, compared to 28 months for standard treatment patients.

This irradiation also provides treatment for benign diseases, which although not having the characteristics of malignant diseases, through local growth cause destruction of surrounding tissue. Thus, stereotactic radiotherapy can be used in diseases: Vestibular schwannoma (acoustic neuroma), pituitary adenoma or meningeoma.

Patient selection is rigorous. Stereotaxy cannot be applied to all cancer patients. Each case has to be considered individually and requires a decision by a multidisciplinary committee. Amethyst clinics offer the possibility that through daily multidisciplinary committees, patients can receive a prompt response regarding eligibility for stereotactic treatment. In selected cases, stereotaxy can make it possible to irradiate already treated anatomical regions, which until recently was not feasible.

What can you expect during a treatment?

You will not feel any difference in the stages of stereotactic radiotherapy compared to IMRT/VMAT irradiation. The simulation processes with the fixation of the immobilisation means remain the same as in the irradiation you may have already performed. In the case of injuries to the chest or abdomen, it is possible to perform a special 4D CT simulation to target the lesions more precisely. In short, CT data is acquired in all respiratory phases.

The process for a stereotactic radiotherapy involves reinforcing each element in the IMRT external radiotherapy process chain. Patient immobilisation must be precise, as the high doses administered must hit the target and not healthy tissue. For this purpose it is possible to use a vacuum mattress to immobilise you. All patients undergoing irradiation at the Amethyst clinics undergo a CBCT (cone-beam CT) treatment position check prior to the RT session. In cases with stereotactic irradiation, this process is repeated both before and during treatment administration.

Advantages of the Versa HD system

With the Versa HD linear accelerators, Amethyst clinics offer the most modern radiotherapy solution in the Elekta product range. With this system you can benefit from fast stereotactic irradiation even shorter than 15 minutes, delivered with a high dose rate. By decreasing the time spent on the irradiation table, we ensure that your possible movements do not affect our radiotherapy plan.

The Versa HD system also offers the solution of anatomically guided stereotactic irradiation through 4D image-guided radiotherapy without the need to implant fiducial markers in the target tissue. This translates into sparing the patient from a prior marker placement intervention and the possibility of greater dose control in the target volume. Another strength of the system is the 6DOF (degree of freedom) table, which allows correction of the patient’s position even submillimetrically.

The state-of-the-art technology within Versa HD gives the physics department the ability to modulate the irradiation arc up to 6 times more, with an MLC (multileaf collimator) speed of 6.5cm/s. By integrating the Versa HD accelerator with the treatment plan system we have the possibility to deliver radiotherapy treatments with virtual MLC blades up to 1 mm and irradiation fields up to 40×40 cm. Furthermore, through a single isocentre, we have the ability to irradiate multiple small metastases.

The irradiation plan verification process, i.e. Quality Assurance (QA), is becoming more demanding, as stereotactic plans have to cope with a 2x2x0.5 mm3 resolution matrix verification, giving medical physicists at Amethyst clinics the ability to assess the dose delivered in a 0.003cm3 volume.

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