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Endorectal Balloons in Post-Prostatectomy: Do Gains in Stability Lead to More Predictable Dosimetry?

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M Jameson

M Jameson1,2*, J De Leon1, A Windsor1,3, K Cloak1, L Holloway1,2,4, P Vial1,4, M Sidhom1,3, P Metcalfe2, (1) Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia (2)University of Wollongong, Wollongong, NSW, Australia (3) Collaboration for Cancer Outcomes Research and Evaluation, Liverpool, NSW, Australia (4) School of Physics, University of Sydney, Sydney, NSW, Australia

TH-C-BRA-4 Thursday 10:30:00 AM - 12:30:00 PM Room: Ballroom A

Purpose: To perform a comparative study assessing potential benefits of endorectal balloons (ERB) in post-prostatectomy patients

Methods: Ten retrospective post-prostatectomy patients without ERB and ten prospective patients with the ERB in situ were treated with IMRT using kilo voltage cone beam computed tomography (kVCBCT) image guidance (IGRT). A kVCBCT dataset from each treatment week was registered to the planning dataset, recontoured and the original plan recalculated on the kvCBCTs to recreate actual anatomical conditions during treatment. The imaging, structure and dose data were imported into Matlab. In house applications analysed geometric variation in the two groups and calculated cumulative equivalent uniform dose (EUD).

Results: Analysis of the kVCBCT datasets showed that the ERB improved target volume stabilization from millimetre to sub-millimetre reproducibility. The variation in bladder location in the non ERB cohort was 1.5 ± 0.9 cm compared to 0.6 ± 0.4 in the ERB group. While the superior rectum location variation was 1.1 ± 0.8 cm and 0.3 ± 0.3 cm for non ERB and ERB respectively. The mean difference in cumulative EUD and planned EUD for the clinical target volume (CTV) was 0.6 ± 0.04 Gy for non ERB and 0.4 ± 0.1 Gy for ERB. The largest normal tissue differences were seen for the bladder with an increase of 4.4 ± 0.1 Gy for non ERB and 1.2 ± 0.02 Gy for ERB in the cumulative compared with the planned EUD. Differences in delivered superior rectal EUD was improved in the ERB cohort with a difference of -0.2 ± 0.04 Gy verse 3.0 ± 0.3 Gy in the non ERB group.

Conclusions: The ERB cohort was found to have more stable and reproducible anatomy when compared to the non ERB cohort. Planned and cumulative EUD differences were greatest for the bladder and rectum.

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