Role of Tertiary Collimation for Linac-Based Radiosurgery

Validation of MLC-based linac radiosurgery for trigeminal neuralgia

This study details a validation process for linear accelerator‐based treatment of trigeminal neuralgia using HD‐MLC field collimation. Nine trigeminal neuralgia treatment plans utilizing HD‐MLC were selected for absolute dose measurement at isocenter using a commercial scintillating detector in an anthropomorphic phantom. Four plans were chosen for film dosimetry measurements in each of the three principal planes to assess spatial dose distribution agreement with the treatment planning system. Additionally, trajectory log analysis for each treatment field in the nine cases was performed to assess mechanical positioning accuracy of the MLC system during delivery. Scintillator and film measurements both revealed mean dose agreement at isocenter of better than 3% while FWHM of the 2D dose distribution in each plane showed agreement between plan and measurement within 0.2 mm. Analysis of log files revealed a maximum MLC leaf positioning error of 0.04 mm across 178 treatment fields. In conjunction with a quality‐controlled treatment delivery methodology, an appropriately commissioned treatment planning system can be used for accurate and clinically appropriate design of trigeminal neuralgia treatment plans utilizing HD‐MLC.

Single-Fraction Stereotactic Radiosurgery for Intracranial Targets

Stereotactic radiosurgery (SRS) is a technique for treating intracranial lesions with a high dose of ionizing radiation, usually in a single session, using a stereotactic apparatus for accurate localization and patient immobilization. This article describes several modalities of SRS and some of its applications, particularly for intracranial lesions.

[Technical evolution of irradiation in stereotactic conditions: dose fractionation]

The development of non-invasive head fixation systems, allowing 3D determination of the target coordinates, has lead to the increased use of fractionated stereotactic irradiation. These systems have been checked for accuracy and the mean precision of repositioning has been evaluated to +/- 1 mm. With the mean geometrical accuracy set at +/- 1 mm, a 2 mm safety margin is usually added to the clinical target volume in order to define the planning target volume. Quality assurance procedures must conform to the required precision of the technique while remaining realistic in day-to-day use relative to planned conventional treatments. Biologically different from single dose irradiation, the fractionated stereotactic irradiation completes the range of techniques used in the treatment of intra-cerebral lesions.