Evaluation of Patient-Specific Quality Assurance in Single Isocenter Multitarget Stereotactic Radiosurgery of Brain Metastases Using Octavius 4D for Flattening Filter Free Beams.

Aim: To evaluate the patient-specific quality assurance (PSQA) in Single Isocenter Multitarget (SIMT) Stereotactic Radiosurgery (SRS) of brain metastases using Octavius 4D for flattening filter free (FFF) X-ray beams.

Materials And Methods: Octavius 4D with 1000 SRS detector array was used for doing PSQA in fifteen patients planned using volumetric modulated arc therapy (VMAT) based stereotactic radiosurgery (SRS) of SIMT technique for treating multiple brain metastases. Measurements were made both in standard setup as well as in special setup through which the region of measurement is increased.

Dosimetric Validation of Digital Megavolt Imager for Flattening Filter Free Beams in the Pre-Treatment Quality Assurance of Stereotactic Body Radiation Therapy for Liver Metastases.

Aim: The aim is to evaluate the use of digital megavolt imager (DMI) aS1200 in portal dosimetry with flattening filter free (FFF) beams.

Materials And Methods: Dosimetric properties of DMI is characterized at 6MV FFF beams for signal saturation, dose linearity, dependency on dose-rate and source-detector distance (SDD), signal lag (ghosting), and back scatter.  Portal dosimetry is done for twenty volumetric modulated arc therapy (VMAT) based stereotactic body radiotherapy (SBRT) plans for the treatment of liver metastases and the results are compared with repeated measurements of Octavius 4D.

Evaluation of beam matching accuracy among six linacs from the same vendor.

The purpose of this study was to evaluate the dosimetric variation among six non-beam-matched Varian linacs using different techniques for the same plans. Six non-beam-matched Varian machines, comprising two Clinac iX, two 600 C/D (Unique), and two True Beam Tx photon 6 MV X-ray devices were acquired. Sixty patients with of head and neck (H&N; 30) and pelvic (30) treatment sites were chosen.

Is the dose distribution distorted in IMRT and RapidArc treatment when patient plans are swapped across beam-matched machines?

The purpose of this study is to evaluate the degree of dose distribution distortion in advanced treatments like IMRT and RapidArc when patient plans are swapped across dosimetrically equivalent so-called "beam-matched" machines. For this purpose the entire work is divided into two stages. At forefront stage all basic beam properties of 6 MV X-rays like PDD, profiles, output factors, TPR20/10 and MLC transmission of two beam-matched machines - Varian Clinac iX and Varian 600 C/D Unique - are compared and evaluated for differences.