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. The obtained results are compared with TPS reference doses at different dose grid sizes and minimum dose cutoff thresholds for both 6X-FFF and 10X-FFF energies.

RESULTS

The percentages of measurable targets were 83.34% and 93.54% in standard and special set respectively.  In standard set, the average gamma passing rate was 97.63±1.26% and 97.78±1.09% for 6X-FFF and 10X-FFF respectively.  The mean gamma passing rates was 97.97±0.99% and 97.85±1.13% for 6X-FFF and 10X-FFF in special set respectively.  PSQA passing rate decreases with increasing TPS grid size in both the energies.  The mean gamma passing rate for 6X-FFF was 97.97±0.99% and 96.94±1.11% at 10% and 25% cutoff dose respectively. The mean gamma passing rate for 10X-FFF at 10% and 25% dose cutoff was 97.85±1.13% and 97.12±1.29% respectively. Low-dose masking effect was more in 6X-FFF than observed with 10X-FFF energy.

CONCLUSION

The performance of Octavius 1000 SRS for PSQA of VMAT based SRS were evaluated and found satisfactory at 6X-FFF and 10X-FFF energies in SIMT of brain metastases.