Dosimetric plan evaluation of different size of tumour volumes in Stereotactic radio surgery
PO-1875
Abstract
Dosimetric plan evaluation of different size of tumour volumes in Stereotactic radio surgery
Authors: Aswathi Raj1,2, D Khanna3, Hridya VT1,4, Sathish P1, Abdul Malik1, P Mohandass5
1Aster Malabar Institute of Medical Sciences, Oncology, Calicut, India; 2Karunya Institute of Technology and SCiences, Physics, Coimbatore, India; 3Karunya Institute of Technology and Sciences, Physics, Coimabtore, India; 4Karunya Institute of Technology and Sciences, Physics, Coimbatore, India; 5Fortis Cancer Institute, Fortis Hospital, Radiation Oncology, Punjab, India
Show Affiliations
Hide Affiliations
Purpose or Objective
High levels
of conformity and steep dose gradient from the periphery of target to
surrounding tissues are the characteristics of Stereotactic
Radiosurgery (SRS) plans. Routinely the dose distribution and Dose
Volume Histograms (DVH) are used for the evaluation of plans. There
are various parameters used for evaluation of SRS plan to ensure its
quality. The objective of the present study focused on dosimetric
evaluation of different size of brain tumor volumes in Stereotactic
Radiosurgery.
Material and Methods
This is a
retrospective study of 15 brain metastasis patients treated using
TrueBeam™ STx linear
accelerator with RapidARC® Radiosurgery. A total
of 15 SRS patients of volume ranging from 2.9cc to 34.8cc planned
with High definition multileaf collimator (HDMLC) with 2.5mm at
isocenter. All the plans were approved by experienced radiation
oncologist. The quality of plans were compared using different
treatment coverage index such as Radiation
Therapy Oncology Group (RTOG) Conformity Index (CIRTOG),
RTOG Quality of Coverage (QRTOG),
Lomax Conformity Index (CILomax),
Paddick’s Conformity Index (CIPaddick)
and RTOG Homogeneity Index (HIRTOG)
for all the SRS plans. In addition, dose gradient parameters from
Paddick’s Gradient Index (GIPaddick),
Equivalent Fall-off Distance (EFOD), Quality of coverage (QOC),
Geometric overlap ratio (GOR) and R50% (ratio of
50% isodose line and tumour volume) were evaluated for the comparison
of different size of tumour volumes.
Results
The results
were analyzed and recorded for different CI respectively: CIRTOG
ranges from 0.92 to 1.6 with an average of
1.15±0.16;
The CIPaddick
ranges from 0.63 to 0.95 with an average of 0.85±0.08;
The CILomax
ranges from 0.92 to 1.0 with an average of 0.99±0.02.
Similarly, the HIRTOG
was observed as range of 1.09 to 1.33 with
an average of 1.18±0.08. The
GIPaddick was
found ranging from 2.9 to 4.0 with an average of 3.4±0.3.
The results of QOC, GOR and R50% were ranging
from 0.8 to 1.14; 0.85 to 1.0; 3.04 to 5.36 and with an average of
0.96±0.09, 0.98±0.04
and 3.99±0.72 respectively.
The EFOD were seen range of 0.15 to 0.46 and with an average of
0.28±0.09. In addition, an
increase of EFOD was observed linearly when tumor volume increased.
Conclusion
On
comparison of all dosimetric indices in SRS Rapid Arc®
plan, only EFOD was found to increase with tumor volume and rest all
parameters were found to be independent of tumor volume. The plan
quality matrix other than EFOD did not reveal any correlation from
their results.