Uncertainties of deformable image registration for dose accumulation of high-dose regions in bladder and rectum in locally advanced cervical cancer.
OBJECTIVE
To compare the dose accumulation for bladder and rectum by deformable image registration (DIR) and direct addition (DA) of dose volume histogram parameters in magnetic resonance image-guided adaptive brachytherapy (IGABT). Two DIR algorithms, contour- and intensity-based, also have been analyzed.


METHODS
Patients (n = 21) treated with IGABT for carcinoma cervix under the IntErnational study on MRI-guided BRachytherapy in locally Advanced CErvical cancer protocol were analyzed. Each patient underwent two HDR-BT applications, 1-week apart with two fractions of 7 Gy each delivered per application. For each application, magnetic resonance imaging, volume delineation, reconstruction, treatment planning (BT1 and BT2), and dose evaluation were carried out. BT1 and BT2 images were registered using an intensity-based DIR, followed by deformable dose accumulation (DDA), which was then compared with DA. To compare the intensity-based DIR to other DIR approaches, nine patients were further evaluated using an in-house contour-based DIR algorithm for bladder dose accumulation.


RESULTS
Mean (±standard deviation; range) percentage variation between DA and DDA was found to be 2.4% (±3.3;-1.8, 11.5) and 5.2% (±5.1;-1.7, 16.5) for the rectum and bladder, respectively. The differences between the DA and DDA were found to be statistically significant for both rectum (p = 0.008) and bladder (p = 0.0003). Intensity-based DIR algorithm resulted in a larger mean deviation between DDA and DA as compared with contour-based DIR, although statistically insignificant (p = 0.32). The difference between DDA and DA was 2.4 ± 2.0% and 1.3 ± 1.2%, for intensity- and contour-based DIR, respectively.


CONCLUSIONS
DA of dose volume histogram parameters provides a good estimate to the dose to the organs at risk; DIR based on image intensities may lead to systematic underestimation of dose due to implausible DIR.
Department of Medical Physics, Tata Memorial Hospital, Mumbai, India. Electronic address: svjamema@gmail.com.
Swamidas V
SV
Jamema
Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, India.
Umesh
U
Mahantshetty
Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
Else
E
Andersen
Computer Graphics Lab, The Alexandra Institute, Aarhus, Denmark.
Karsten Ø
KØ
Noe
Aarhus University, Aarhus, Denmark.
Thomas S
TS
Sørensen
Department of Oncology, Aarhus University Hospital, Aarhus, Denmark.
Jesper F
JF
Kallehauge
Department of Radiation Oncology, Tata Memorial Hospital, Mumbai, India.
Shyam K
SK
Shrivastava
Department of Medical Physics, Tata Memorial Hospital, Mumbai, India.
Deepak D
DD
Deshpande
Department of Oncology, Aarhus University Hospital, Aarhus, Denmark; Aarhus University, Aarhus, Denmark.
Kari
K
Tanderup
D000328:Adult; D000368:Aged; D000465:Algorithms; D001918:Brachytherapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D058958:Organs at Risk; D011829:Radiation Dosage; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided; D012007:Rectum; D035501:Uncertainty; D001743:Urinary Bladder; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*
Cervix brachytherapy; Deformable dose accumulation; Deformable image registration