Special therapeutic procedures
Stereotactic extracranial radiosurgery is an external radiotherapy procedure that allows the administration of doses of high radiation with great accuracy protecting the healthy surrounding tissues, in order to control the illness in a non-invasive way and with the minimum secondary effects.
Nowadays, this treatment is prescribed for liver, lung and spinal metastases and some primary pancreatic tumors that cannot be operated according to clinical criteria. Due to their size or their closeness to critical structures, they require the most accurate immobilization and dose administration.
Radiosurgery is indicated for patients with liver or lung metastases, similarly to surgical procedures (the general condition of the patient must be acceptable, the primary tumor must be controlled, with at least four or five small metastatic injuries that must be easily identified in the CT or after the fusion with PET or MRI). Extracranial radiosurgery is also used as an excellent palliative treatment for spinal metastases, both as a primary treatment as well as re-radiations with great results in terms of pain and injury control. In primary tumors, it is specially indicated for lung tumors, which are inoperable due to the bad clinical situation of the patient. Radiosurgery is, in these cases, an excellent non-invasive option. This technique is also being used for primary liver and renal tumors.
The Radiotherapeutic oncology department at Centro Integral Oncológico Clara Campal (C.I.O.C.C.) works with a NOVALIS accelerator when performing extracranial radiosurgery. It includes a system for controlling the moves of the tumor while breathing (respiratory gating) as well as a real-time tracking system of the treatment (ExacTrac) which ensures the accuracy and the correct administration of the treatment (image-guided radiation therapy).
Extracranial radiosurgery treatments are hypofractionated, that is, they are administered in single doses or in several fractions depending on the pathology the location or the size of the injury.
This procedure involves the following stages:
- Treatment administration
- Tumor movement control: 4D radiotherapy
- Tracking of the treatment: image-guided radiation therapy
Once the treatment is prescribed, our Radiotherapeutic oncology department reproduces a simulating using a simulation CT (Somaton Sensation Open, fidutian Siemens) with body immobilization systems (vacuum matress), which enables repositioning the patient during the treatment and ensures the replication of the process.
When performing a gating on the thorax and abdomen, a few fiducial markers are placed according to a coordinate system in order to locate the tumor, orientate the planning and guide the treatment (the term “stereotatic” refers to the relation between the tumor location and these markers). As long as it is possible when treating liver and lung injuries, some markers are placed in the tumor guided by the CT but before the planning CT, in order to locate the tumor and check the treatment afterwards.
After that, the CT images are transferred to BrainLab's planning system, rebuilt in 3D and merged with MRI and PET images in order to establish an accurate definition of the radiation volumes. Thanks to BrainLab's radiosurgery planning system, the extracranial radiosurgery treatment is established using conformed dynamic arcs or inverse planning with IMRT (Intensity-Modulated Radiation Therapy). Thus, we can dynamically modulate the radiation beam in each position of the treatment, optimizing the dose received by the tumor and minimizing the radiation received by critical organs and surrounding healthy tissues.
BrainLab's Novalis accelerator includes a collimation of 3 mm multiple microlayers that adapts to the shape of the tumor in radiosurgical treatments.
BrainLab's Novalis accelerator Multiple microlayers system
Tumor moves control: 4D radiotherapy
Thanks to BrainLab’s Novalis accelerator, we can perform extracranial radiosurgery treatments with Gating, and therefore we can radiate the tumor taking into account the breathing moves of the patient. Thus, the radiation is only sent in a specific stage of the respiratory cycle (normally, when expiring) and the radiation beam is stopped for the rest of the cycle.
Tracking of the treatment: image-guided radiation therapy
Novalis accelerator includes ExacTrac, an image-guided system that takes images of the kilovolt in the radiation field and rebuilds them on real time in 3D, as well as merging them with the images obtained during the planning. This way, we can check the correct administration of the treatment.
In case of any conflict between the radiation field and the planning images, we can correct the position of the patient automatically thanks to the 6D table of Novalis accelerator, until both images match and we check the treatment is followed with the maximum accuracy.