ESTRO 2022 - Abstract Book

S1180

Abstract book

ESTRO 2022

Conclusion SBRT monotherapy for low and intermediate risk prostate cancer patients is well-tolerated, has little impact on health related QOL and reveals excellent early bPFS which is in line with current body of literature. Post-SBRT interventions such as rectal biopsy may increase the risk of fistulas and should be avoided.

PO-1393 Hypofractionated prostate radiotherapy: alternate delineation approach vs validated trial protocol

I. Strouthos 1,2 , E. Karagiannis 1,3 , P. Doolan 4 , G. Antorkas 4 , M. Peraticou 1 , K. Ferentinos 1 , Y. Roussakis 4

1 German Oncology Center, Radiation Oncology, Limassol, Cyprus; 2 European university Cyprus, Medical School, Nicosia, Cyprus; 3 European University Cyprus, Medical School, Nicosia, Cyprus; 4 German Oncology Center, Medical Physics, Limassol, Cyprus Purpose or Objective Two sets of radiotherapeutic plans were calculated, for a series of patients treated for organ-confined prostate cancer with hypofractionated IGRT. Head-to-head dosimetric comparison of a validated trial delineation protocol against an alternative, simpler institutional approach was tested using dose-volume histogram for planning target volume (PTV), followed by radiobiological analysis of all cases plus “worst case” scenario. Materials and Methods Twenty-one patients with locally confined prostate adenocarcinoma treated initially with definitive, hypo-fractionated radiotherapy adhering to the CHHiP protocol were retrospectively selected. All patients were planned for volumetric modulated arc therapy (VMAT) on a conventional linear accelerator. In addition to the validated trial PTV definition, a set of “new” PTVs were defined for each case based on our institutional simplified delineation protocol for normo-fractionated prostate cancer. Adhering to ESTRO guidelines, two different, institutional CTVs were utilised. CTVa, which included the prostate and entire seminal vesicles and CTVb comprised of the prostate and proximal seminal vesicles 14 mm from prostatic base. The newly derived PTVs were created through an expansion of each of the delineated CTVs, 8 mm circumferentially plus a 6 mm expansion posteriorly. New plans were calculated for each of the derived PTVs, delivering a total physical dose of 60 Gy in 20 fractions, respecting and following the planning parameters and dosimetric constraints expressed by the CHHiP trial protocol. DVHs were used to evaluate the dose to the PTV and organs at risk (OAR). Radiobiological evaluation was performed for all plans, using the BioSuite software, calculating TCP for CTVb and NTCP for rectum and bladder, utilizing a range of parameters and endpoints from the literature.