As simply defined by Prof. Lars Leksell, it is the 'delivery of a single, high dose of irradiation to a small and critically located intracranial volume through the intact skull.' When Linac-based machines and systems for immobilization and verification were developed, the terms ‘Frameless Radiosurgery’ and ‘Fractionated Radiosurgery’ originated.
In 2007, The International Commission on Radiation Units & Measurements Guidelines (ICRU), redefined the procedures as:
Stereotactic Radiosurgery: Typically performed in a single session, using a rigidly attached stereotactic guidance device, other immobilization technologies and/or a stereotactic image guidance system, but can be performed in a limited number of sessions, up to a maximum of five.
Fractionated Radiosurgery: When the target is identical and same (up to 5 sessions).
Staged Radiosurgery: Repeated sessions in different areas of the same target (volume staging).
On 24th March 2020, the DEGRO (The German Society for Radiation Oncology), a working group for Radiosurgery and Stereotactic Radiotherapy and the DGMP (The German Society for Medical Physics), a working group for Physics and Technology in Stereotactic Radiotherapy, came to a consensus and published their report.
This review covers:
Imaging for target volume definition,
Patient positioning and target volume localization,
Motion management,
Collimation of the irradiation and beam directions,
Dose calculation,
Treatment unit accuracy,
Dedicated quality assurance measures.
Stereotactic radiosurgery (SRS): Treatment of intracranial malignant or benign tumours and functional or vascular disorders with one single irradiation fraction.
Fractionated stereotactic radiotherapy (FSRT): Treatment of intracranial malignant or benign tumours and functional or vascular disorders.
Stereotactic body radiotherapy (SBRT): Treatment of extracranial malignant or benign tumours and functional or vascular disorders.
The purpose was to bring uniformity, and they also gave guidelines regarding SRS imaging, immobilization and planning.
They recommended:
Accuracy of Radiation Delivery
1 mm for SRS,
1.25 mm for FSRT and SBRT in non-moving phantoms.
1.5 mm for SBRT in moving phantoms.
Imaging Requirements
High Resolution 3D volume CT scan or enhanced CT scan, less than or 1.5 mm thickness.
3D volumetric enhance/plain MRI according to the disease on at least 1.5 Tesla machines.
For Arteriovenous malformation - CT Angio or Digital Subtraction angiography.
Radiation Delivery
For SRS, an invasive fixation using a stereotactic head frame can be used alternatively to image guidance.
For SRS and FSRT, non-invasive fixation of the patient’s head is combined with image-guidance.
Use of Multileaf Collimator
SRS with Multileaf Collimator (MLC) with leaf width 5 mm or cylindrical collimators of equivalent size, both at normal treatment distance, and used with systems allowing non-coplanar beam directions.
FSRT with MLC with leaf width 6.5 mm or cylindrical collimators of equivalent size, both at normal treatment distance.