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  4. Pre-Treatment 3D Image Verification in Interstitial and Intracavitary High Dose-Rate Brachytherapy for Gynecological Cancer

Pre-Treatment 3D Image Verification in Interstitial and Intracavitary High Dose-Rate Brachytherapy for Gynecological Cancer

I Buzurovic*, M Bhagwat , D O'Farrell , T Harris , J Bredfeldt , R Cormack , P Devlin , D Buscariollo , M King , L Lee , Brigham and Women's Hospital, Harvard Medical School, Boston, MA

Presentations

(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: The current safety and QA protocols in interstitial and intracavitary HDR brachytherapy treatments of gynecological malignancies have not routinely required 3D imaging (CT scan or MRI) prior to each fraction in fractionated radiation therapy regiments. In this study, we have investigated the variation of the intra-fractional doses to both the clinical target volumes (CTV) and the organs at risk (OARs).

Methods: Two principal effects are responsible for dose variations in such cases: displacement of the interstitial needles and/or intracavitary applicators, and volumetric and positional uncertainties of the patient’s anatomy. We investigated 70 gynecological patients treated with interstitial (35), intracavitary (26) or combined (9) HDR brachytherapy during 2017. The patients included in this study received external beam radiation therapy followed by twice-daily treatment for a total of 3 to 8 fractions of HDR brachytherapy. Prior to delivery of each fraction, a CT scan was taken and registered to the CT/MR images (TPI) used for treatment planning.

Results: The total high-risk-CTV (HR-CTV) equivalent doses in 2 Gy fractions (EQD2) were in the range of 75–85Gy, depending on the clinical case specifics. Five patients (7.1%) required re-planning due to significant discrepancies in the needle/applicator position (up to 13.1mm). If the re-planning was not performed, the average decrease of the HR-CTV coverage per brachytherapy fraction would be 25.5% (SD=19.1%). Consequently, a potential total loss of the HR-CTV EQD2 would be 11.2% (SD=8.3%). The average increase (prior to re-planning) of the D2 cm3 for rectum, bladder and sigmoid per brachytherapy fractions was 15.3% (SD=8.2%), 10.5% (SD=17.6%), and 15.5% (SD=6.1%), respectively.

Conclusion: Pretreatment 3D imaging and registration with the TPI prior to each fraction reveal that the possible dose deviation could significantly impact treatment outcomes by under-dosing the HR-CTV. Therefore, implementing such procedures for all cases should be considered when feasible.

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