Dose variations caused by setup errors in intracranial stereotactic radiotherapy: a PRESAGE study.

Area of Science:

• Medical Physics
• Radiotherapy
• Radiation Oncology

Background:

• Stereotactic radiotherapy (SRT) demands precise tumor targeting with narrow safety margins.
• Steep dose gradients in SRT make it highly sensitive to patient setup errors.
• No prior studies have quantified dosimetric variations from setup errors using a 3D dosimeter in intracranial SRT.

Purpose of the Study:

• To evaluate the impact of setup errors on dose distribution in intracranial SRT.
• To determine the threshold for clinically significant setup errors in this treatment modality.

Main Methods:

• Utilized a CIRS radiosurgery head phantom for computed tomography (CT) simulation.
• Generated an ideal treatment plan and performed treatments with and without simulated setup errors (translation and rotation).
• Employed a 3D dosimeter (PRESAGE) and optical CT scanning for dose analysis, validated by 3D gamma analysis.

Main Results:

• Setup errors exceeding 0.7mm translation and 0.5° rotation were found to be clinically significant.
• A 0.7mm translation and 0.5° rotation resulted in a 96.2% passing ratio in gamma analysis.
• Larger errors (e.g., 3mm translation, 2° rotation) led to significantly lower passing ratios (53.1%).

Conclusions:

• Preventing setup errors is crucial in intracranial SRT to maintain accurate dose delivery.
• Geometrical displacements greater than 0.7mm translation or 0.5° rotation significantly alter dose distribution to tumors and surrounding tissues.