Radiosurgery and stereotaxy

Stereotaxy is a radiotherapy technique in which a tumour is treated in a small volume and with high precision using very high daily radiation doses in just a few radiotherapy sessions. The aim of stereotaxy is to reduce the risk of side effects while maintaining the effectiveness of the treatment and to improve the patient's quality of life by significantly shortening the treatment time. By superimposing many different irradiation directions in the tumour, the surrounding, non-diseased tissue is exposed to significantly less radiation. The radiotherapy itself, including positioning, takes around half an hour. Patient positioning and radiation application are continuously monitored before and during treatment using a coordinated combination of control and safety systems.
At our clinic, stereotaxy is currently indicated for the following diseases:

Small metastases in the brain

Prostate cancer

Lung metastases

Inoperable stage I non-small cell lung cancer

Selected, mostly solitary bone metastases

At the Department of Radiotherapy and Radiation Oncology at Ulm University Hospital, patients with brain metastases have been receiving radiotherapy using a high-precision radiosurgical technique ("HyperArc") since April 2019. The advantages for patients: The treatment is considerably faster and can also be used for multiple tumour foci instead of individual metastases as was previously the case (duration of a radiotherapy session: approx. 15 minutes). The method is also just as effective and precise as previous procedures.

Whereas in the past, radiotherapy of the entire brain was usually required for two weeks, nowadays radiotherapy of the individual metastases is increasingly carried out with high doses on a few treatment days. Depending on the size and location of the metastasis, the number of radiotherapy sessions can be between 1 and 5.
In contrast to previous systems, where patients had to spend around an hour on the radiotherapy couch, the fully automated sequence of individual radiotherapy steps significantly reduces the treatment time.
This means that single or multiple brain metastases can be effectively treated with high doses within around 15 minutes. Compared to conventional systems, the very steep drop in dose means that the healthy tissue surrounding the metastases can be spared even better.
Patient positioning and radiation application are continuously monitored by a harmonised combination of control and safety systems. Until now, the patient's head usually had to be completely fixed in a mask before high-precision radiotherapy so that it could not be moved during treatment. The new system uses a thermoplastic mask material with a recess in the eye and nose area, making it much more comfortable. A surface scanning system helps to check the patient's position with millimetre precision. This method can be used for brain metastases, but also for benign tumours of the brain. Every year, 20-50 patients are irradiated with the new technology at Ulm University Hospital.

Since March 2021, selected patients with prostate cancer have been receiving stereotactic radiotherapy. This technique is being used at Ulm University Hospital as part of the SBRT/eHFX PCa registry study of the Prostate Cancer Working Group of the German Society for Radiooncology (DEGRO). With this technique, only 5 treatment sessions are required instead of 30-39. Treatment takes place every other day. For the duration of the treatment, a catheter with a non-ionising electromagnetic transmitter is placed in the urethra. This transmitter makes it possible to detect intrafractional movements of the prostate in real time. This information is used to optimise the dose application. This makes it possible to reduce the radiotherapy period from 7-8 weeks to 5 radiotherapy sessions with the same effectiveness.

The indications for precision radiotherapy include individual small lung metastases and early stages of non-small cell bronchial carcinomas. High doses enable the best possible tumour control, while the surrounding lung tissue is spared as much as possible thanks to a steep dose decrease. A 4D CT is used to plan the radiotherapy, which records the position of the tumour during each breathing phase. The radiotherapy session can therefore be carried out in comfortable free breathing and the duration can be reduced to around 15 minutes. Stereotactic radiotherapy is a sensible alternative, particularly for patients in whom radical surgery carries a high risk of complications due to secondary diseases and age. Depending on the location and size of the tumour, only 3-5 radiotherapy sessions are required.

Fig.3: Stereotactic radiotherapy of a lung tumour

In patients with few bone metastases (1-5 metastases), stereotactic radiotherapy can be useful. The aim is to completely destroy the tumour cells in the irradiated area. This is achieved by high single doses (7-8 Gy). The treatment usually comprises 5 radiotherapy sessions over 5 days.

Fig. 4: Target volume and dose distribution for stereotactic radiotherapy of bone metastases.