Session Item

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.

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. 

All calculated radiotherapeutic plans, regardless of CTV delineation and margin expansion, met OAR DVH constraints, while at the same time achieving adequate target coverage, as suggested by the CHHiP trial protocol. TCP calculation was >99% for all plans and all cases. NTCP investigations revealed no statistically significant differences.

Data based on dosimetric and radiobiological comparisons demonstrate that our simpler institutional delineation protocol is at least as effective in regard to PTV coverage, and as safe in regard to OAR sparing, as the validated CHHiP trial PTV definition.