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Vienna, Austria

ESTRO 2023

Session Item

Brachytherapy: Gynaecology
7014
Poster (Digital)
Brachytherapy
Analysis of time-dependent pretreatment OAR dose variation during Image-guided brachytherapy
Nadeem Pervez, Canada
PO-2154

Abstract

Analysis of time-dependent pretreatment OAR dose variation during Image-guided brachytherapy
Authors:

Agha Muhammad Hammad Khan1, Ana Paula Galerani Lopes2, Mahmoud Alfishawy3, Furhaan Altaf4, Tauseef Ali1, Mohammad Al Ghafri5, Sercan Yilmaz2, Nurgul Yilmaz5, Nirmal Babu6, Mohammed Ali5, Abid Ali Mirza Aman7, Abhishek Vidhwadharan8, Fatima Yousuf8, Mohsina Vellengara2, Iqbal Al Amri9, Salim Chaib Rassou1, Zahid Al Mandhari10, Nadeem Pervez2

1Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Oncology, Muscat , Oman; 2Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Oncology, Muscat, Oman; 3Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Physics , Muscat, Oman; 4Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Therapy , Muscat , Oman; 5Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Physics, Muscat , Oman; 6Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Physics, Muscat, Oman; 7Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Therapy, Muscat , Oman; 8Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Therapy, Muscat, Oman; 9Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Physics , Muscat , Oman; 10Sultan Qaboos Comprehensive Cancer Care and Research Centre, Radiation Oncology , Muscat , Oman

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Purpose or Objective

To assess the time-dependent variation in organs at risk (OAR) doses as a result of pretreatment motion during image-guided brachytherapy (IGBT).

Material and Methods

Retrospective data was collected in 13 consecutive patients with gynecological malignancies (Endometrial=5, Cervical=6 and Vaginal=2 cancers) from November, 2021 to September, 2022. These patients underwent planning CT and MRI scans for IGBT. We followed institutional bladder and rectal protocols. A Planning CT scan was performed after the implant followed by a planning MRI scan in all fractions. Images were registered using the applicator on both CT and MRI.  OARs were contoured on both CT and MRI images by two experienced radiation oncologists independently which was peer-reviewed as well. Patient’s demographic, applicator type and time between CT and MRI were recorded. Volumes, contour shifts and doses (D0.1cc and D2cc) of rectum, bladder and sigmoid were assessed. Statistical analysis was performed using SPSS version 21 to calculate the frequency and central tendencies of the recorded values.

Results

The median age was 64 years (range 33 to 74 years). The total number of implants was 31, of which 17 (54%) were multichannel cylinders and 14 (46%) implants were tandem and ovoids.
The recorded mean time between CT and MRI images was 28 minutes (range 18 to 50 minutes). The bladder volume increased by an average of 38% in 88% of patients between images. There was an average increase of 5.6% in sigmoid volume in 58% of the patients. The rectum volumes were reduced by an average of 14% in 91% of patients.
During analysis, we found that the center of the bladder and rectum contours were shifted on average by 0.4 and 0.1 cm away from the target respectively. However, sigmoid was shifted on average 0.1 cm toward the target.
These recorded volumes and shifts resulted in changes of D0.1cc and D2cc of OARs parameters. For bladder, there was an average increase of 2% for D0.1cc and 2.3% for D2cc. In the rectum, there was an average increase of 0.09% in D0.1cc and an average decrease of 1.3% in D2cc. For Sigmoid, there was an average increase of 4.9% D0.1cc and an average decrease of 2.8% in D2cc.  

Conclusion

Time-dependent analysis of pretreatment CT and MRI scans for IGBT in our institute identified that there is variation in OARs in between the acquired images. These changes resulted in deviations of OARs volumes and doses of D0.1cc and D2cc. These variation in OAR doses in IGBT during the interval between implant and treatment delivery is a cautionary alert that needs further investigation and correlation with the changes and their clinical impacts on OARs.