Conformity of LINAC-based stereotactic radiosurgery using dynamic conformal arcs and micro-multileaf collimator.
OBJECTIVE
To assess the conformity of dynamic conformal arc linear accelerator-based stereotactic radiosurgery and to describe a standardized method of isodose surface (IDS) selection.


METHODS
In 174 targets, the conformity index (CI) at the prescription IDS used for treatment was calculated as CI = (PIV/PVTV)/(PVTV/TV), where TV is the target volume, PIV (prescription isodose volume) is the total volume encompassed by the prescription IDS, and PVTV is the TV encompassed by the IDS. In addition, a "standardized" prescription IDS (sIDS) was chosen according to the following criteria: 95% of the TV was encompassed by the PIV and 99% of TV was covered by 95% of the prescription dose. The CIs at the sIDS were also calculated.


RESULTS
The median CI at the prescription IDS and sIDS was 1.63 and 1.47, respectively (p < 0.001). In 132 of 174 cases, the volume of normal tissue in the PIV was reduced by the prescription to the sIDS compared with the prescription IDS, in 20 cases it remained unchanged, and in 22 cases it was increased.


CONCLUSIONS
The CIs obtained with linear accelerator-based stereotactic radiosurgery are comparable to those previously reported for gamma knife stereotactic radiosurgery. Using a uniform method to select the sIDS, adequate target coverage was usually achievable with prescription to an IDS greater than that chosen by the treating physician (prescription IDS), providing sparing of normal tissue. Thus, the sIDS might aid physicians in identifying a prescription IDS that balances coverage and conformity.
Hazard
Lisa J
LJ
Department of Radiation Oncology, Huntsman Cancer Hospital, University of Utah School of Medicine, Salt Lake City, UT, USA.
Wang
Brian
B
Skidmore
Thomas B
TB
Chern
Shyh-Shi
SS
Salter
Bill J
BJ
Jensen
Randy L
RL
Shrieve
Dennis C
DC
D000465:Algorithms; D001932:Brain Neoplasms / Q000473:pathology / Q000601:surgery*; D006801:Humans; D055656:Prescriptions / Q000592:standards*; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D012189:Retrospective Studies; D047368:Tumor Burden