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PO155 Dosimetric impact of CT based target and organ at risk contouring in patients undergoing MR image based brachytherapy for cervical cancer

In Brachytherapy
By: Swamidas J.
Contributor(s): Mahantshetty U | Joshi K | Sharma P | Ranjan C | Deshpand DD | Shrivastava SK.
Material type: materialTypeLabelArticlePublisher: New York: Elsevier 2016Description: .Subject(s): Brachytherapy | Cervical cancer | GEC-ESTROOnline resources: PDF In: Brachytherapy Vol.15, Supplement no.1, p.S169-170Summary: Aim: To study the dosimetric impact on CT Image based target and OAR delineation in the absence of MR images for patients undergoing MR Image Based Adaptive Brachytherapy (IGABT) for Cervical Cancer. Materials and Methods: All patients (n521) underwent MR imaging (1.5T, GE, Signa), at diagnosis and brachytherapy as per GEC-ESTRO recommendations including contouring, planning and evaluation (Oncentra, Elekta v4.2). Subsequently, all patients underwent CT imaging with contrast, and a bladder filling protocol. High Risk CTV(HR-CTV) and OAR’s were delineated on CT imaging with the help of MR at diagnosis, clinical examination at diagnosis & BT and TRUS axial images acquired during BT procedure. The observer was blinded to the MR findings at BT. CT images with contours were registered with MR Images based on applicator points. After the registration, CT structures were transferred onto MR images (Eclipse, Aria 13.5) with clinical plan followed by evaluation and comparison. Wilcoxon rank sum test was used to evaluate the variation with a significance level less than 0.05. Results: The mean (sd) registration accuracy of applicator points was 1.7(0.8)mm. Comparison of D90, V100 for HR-CTV and 2cm3 doses to OAR for CT as compared to MR did not show any significance (Table 1), however D0.1cm3 was significantly higher on CT, which could be attributed to a large extent to contouring uncertainities for OAR on CT. To evaluate further, optimized plans for CT based contouring is ongoing. Conclusion: CT may replace MR in IGABT when CT contouring is based on MR at diagnosis, clinical findings at diagnosis and brachytherapy
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Articles Articles Tata Memorial Hospital
Available AR18285

Published in World Cogress of Brachytherapy June 27-29, 2016

Aim: To study the dosimetric impact on CT Image based target and OAR
delineation in the absence of MR images for patients undergoing MR
Image Based Adaptive Brachytherapy (IGABT) for Cervical Cancer.
Materials and Methods: All patients (n521) underwent MR imaging
(1.5T, GE, Signa), at diagnosis and brachytherapy as per GEC-ESTRO recommendations including contouring, planning and evaluation (Oncentra,
Elekta v4.2). Subsequently, all patients underwent CT imaging with
contrast, and a bladder filling protocol. High Risk CTV(HR-CTV) and
OAR’s were delineated on CT imaging with the help of MR at diagnosis,
clinical examination at diagnosis & BT and TRUS axial images acquired
during BT procedure. The observer was blinded to the MR findings at BT.
CT images with contours were registered with MR Images based on
applicator points. After the registration, CT structures were transferred
onto MR images (Eclipse, Aria 13.5) with clinical plan followed by
evaluation and comparison. Wilcoxon rank sum test was used to evaluate
the variation with a significance level less than 0.05.
Results: The mean (sd) registration accuracy of applicator points was
1.7(0.8)mm. Comparison of D90, V100 for HR-CTV and 2cm3 doses to
OAR for CT as compared to MR did not show any significance (Table 1),
however D0.1cm3 was significantly higher on CT, which could be
attributed to a large extent to contouring uncertainities for OAR on CT.
To evaluate further, optimized plans for CT based contouring is ongoing.
Conclusion: CT may replace MR in IGABT when CT contouring is based
on MR at diagnosis, clinical findings at diagnosis and brachytherapy

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