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Radiobiological Evaluation of the Inter-Fractional Variations in Cervical Cancer Treatments with HDR Brachytherapy

B Tuazon¹*, C Esquivel², T Biggers³, P Mavroidis⁴, S Stathakis⁵, T Eng⁶, N Papanikolaou⁷, (1) ,,,(2) UT Health Sciences Center, San Antonio, TX, (3) University of Texas Health Science Center, UTHSCSA, San Antonio, TX, (4) Cancer Therapy and Research Center, San Antonio, TX, (5) University of Texas Health Sciences Center San Antonio, San Antonio, Texas, (6) University of Texas HSC SA, San Antonio, TX

SU-E-T-713 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The purpose of this study was to evaluate the treatment of cervical cancer using high dose rate iridium-192 tandem and ovoids using a deformable registration software and employing dosimetric and radiobiological measures.

Methods: High-dose-rate tandem and ovoid treatments using an iridium-192 source were planned in the Oncentra treatment planning system. Each of the 17 patients was given six fractions with total dose of about 35 Gy to point A. Using the VelocityAI software, the image sets from all the HDR procedures were registered to the first fraction CT image set using either rigid or deformable registration. The dose files were added together using the registration image sets. The contours of the organs at risk created in Oncentra were imported into the VelocityAI for the calculation of the DVHs. The biological effective doses (BED), biologically effective uniform doses (BEUD) and generalized equivalent uniform doses (gEUD) were additionally obtained.

Results: In one patient, the physical mean, BED, gEUD and BEUD doses to the target, rectum and bladder by the extrapolated first fraction of the HDR brachytherapy were 56.1, 189.3, 9.1 and 49.1 Gy for the target; 7.5, 7.4, 16.9 and 43.3 Gy for the rectum, 9.7, 9.7, 14.7 and 34.3 Gy for the bladder, respectively. For the combined deformed dose distribution, the average physical, BED, gEUD and BEUD doses were 42.9, 76.7, 4.1 and 65.3 Gy for the target, 4.2, 2.5, 5.9 and 26.3 Gy for the rectum and 4.6, 1.8, 5.3 and 0.0 Gy for the bladder, respectively.

Conclusion: It appears that the dose distributions in the organs between different HDR brachytherapy fractions can vary considerably. The individual fractional dose distributions tend to overestimate the doses that are received by the different organs.

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