AbstractID: 6981 Title: Dosimetric characteristics of Novalis Shaped Beam Surgery unit
Recently, a dedicated Novalis shaped beam surgery unit has become available to perform
high-precision radiosurgery for cranial and extracranial sites. The dedicated unit is
equipped with a built-in micro-multileaf collimator with a 6 MV single photon beam. It is
capable of delivering radiation through circle cone arcs, fixed shaped beams, fixed-shape
conformal arcs, dynamic shape conformal arcs, and static and dynamic intensitymodulation. High-precision and accurate radiotherapy is achieved through dedicated
patient positioning mechanisms and various image-guided target localization methods.
Accurate beam data characterization of small MLC fields (up to 6x6 mm) is critical for
conformal radiosurgery and is a very challenging task. We carried out systematic
measurements for percent depth dose, output factor, and beam profile with micro MLC
using a high resolution diode detector (Hi-pSi Field Detector for Stereotactic
Measurements), a mini ion-chamber (Wellhofer IC01), and conventional Kodak XV
films. With adequate arrangement of detectors, dosimetric data acquired from different
detectors were compared for field sizes up to 6x6 mm. The depth dose and output factors
measured using diode and mini-ion chamber were within 2% and the beam profiles were
found to be within 0.7 mm for both the field size and penumbra. Our data indicate that
the measured dosimetric data for the dedicated unit using either of these detectors are
reliable and the accurate measurement of small field size up to 6x6 mm is readily
achievable. Special attention is required when a mini ion-chamber is used to measure
small field sizes such as 6x6 mm and 12x12 mm.