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Dosimetric Evaluation of Tandem-Based Cervical HDR Brachytherapy Treatment Planning Using ABS 2011 Recommendations


M Goyal

M Goyal1,2*, K Shide1, B Heintz1, D Rai2, T Kehwar3, J Barker1, (1) Texas Oncology, PA, Fort Worth, TX, (2) Shobhit University, Meerut, UP, (3) University of Pittsburgh Medical Center, Monroeville, PA,

SU-E-T-699 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
This study evaluated dosimetric parameters for cervical HDR brachytherapy treatment using varying dose prescription methods.

Methods:
We evaluated 20 unique tandem-based cervical HDR brachytherapy treatment plans. Radiotherapy dose was originally prescribed to a defined point (Point A, ICRU-report 38) for all plans. For this study, tumor volumes (HR-CTV) and organs at risk (OAR) were retrospectively delineated on the original 3D treatment planning CT datasets by the original treating physicians. We also carefully redefined the dose prescription point using ABS 2011 criteria. The coverage index (V100) for each HR-CTV was calculated using DVH parameters. A plot between HR-CTV volume (V) and V100 was generated using the best fit linear regression line (least-square fit analysis).

Results:
Mean prescribed dose to Point A (average of Rt and Lt point A doses) was 590.47 cGy ± 28.65cGy (range 499.10-612.45cGy; 95%CI 586.73-594.22cGy). Mean prescribed dose to ABS 2011 point A (average of Rt and Lt points) was 593.35 cGy ± 30.42cGyrange 501.00-625.50cGy; 95%CI 589.38-597.32cGy). There was no statistically significant difference between the original planned point A and new calculated ABS point A doses (p=0.23, paired t-student test). The plot between V and V100 was well defined and was described by the best fit linear regression line: V100= -0.0064V+1.0858, with correlation coefficient of 0.9519. Therefore, as V increases the coverage index decreases: when V<20cc, V100>95%; when V>20cc and <±29cc, V100 is between 90-95%; w⁻hen V>29cc, V100<90%.

Conclusion:
For cervical HDR brachytherapy, dose prescription to an arbitrarily defined point (e.g., point A) does not provide consistent coverage of HR-CTV. The difference in coverage between the two dose prescription approaches increases with increasing CTV volume. Our ongoing work evaluates the dosimetric consequences of volumetric dose prescription approaches for these patients.

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