Open AccessEvaluation and verification of the QF ix Encompass TM couch insert for intracranial stereotactic radiosurgery
Author(s) -
Snyder Karen Chin,
Xhaferllari Ilma,
Huang Yimei,
Siddiqui M. Salim,
Chetty Indrin J.,
Wen Ning
Publication year - 2018
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.12387
Subject(s) - imaging phantom , attenuation , radiosurgery , insert (composites) , nuclear medicine , beam (structure) , materials science , optics , physics , medicine , radiation therapy , composite material , radiology
The QF ix Encompass TM stereotactic radiosurgery ( SRS ) immobilization system consists of a thermoplastic mask that attaches to the couch insert to immobilize patients treated with intracranial SRS . This study evaluates the dosimetric impact and verifies a vendor provided treatment planning system ( TPS ) model in the Eclipse TPS . A thermoplastic mask was constructed for a Lucy 3D phantom, and was scanned with and without the Encompass TM system. Attenuation measurements were performed in the Lucy phantom with and without the insert using a pinpoint ion chamber for energies of 6x FFF , 10x FFF and 6X, with three field sizes (2 × 2, 4 × 4, and 6 × 6 cm 2 ). The measurements were compared to two sets of calculations. The first set utilized the vendor provided Encompass TPS model (Encompass TPS ), which consists of two structures: the Encompass and Encompass base structure. Three HU values for the Encompass (200, 300, 400) and Encompass Base (−600, −500, −400) structures were evaluated. The second set of calculations consists of the Encompass insert included in the external body contour (Encompass EXT ) for dose calculation. The average measured percent attenuation in the posterior region of the insert ranged from 3.4%–3.8% for the 6x FFF beam, 2.9%–3.4% for the 10x FFF , and 3.3%–3.6% for the 6X beam. The maximum attenuation occurred at the region where the mask attaches to the insert, where attenuation up to 17% was measured for a 6x FFF beam. The difference between measured and calculated attenuation with either the Encompass EXT or Encompass TPS approach was within 0.5%. HU values in the Encompass TPS model that provided the best agreement with measurement was 400 for the Encompass structure and −400 for the Encompass base structure. Significant attenuation was observed at the area where the mask attaches to the insert. Larger differences can be observed when using few static beams compared to rotational treatment techniques.