Optimization of prostate cancer radiotherapy using of a spacer gel, volumetric modulated arc therapy and a single biological organ at risk objective

Background: the aim was to evaluate the benefit of technical advances fortreatment planning: introduction of a hydrogel spacer, vmat (volumetricmodulated arc therapy) and a single biological organ at risk objective for the rectumand bladder. initial standard was a step-and-shoot imrt (intensity modulatedradiotherapy) without a spacer and conventional organ at risk objectives.materials and methods: treatment plans were calculated using imrt and vmattechniques before and a(er spacer injection in 27 patients, respectively.conventional organ at risk objectives have been used for the optimization of imrtplans, only a single biological organ at risk objective for vmat plans. vmat vs. imrtplans and plans before vs. a(er spacer injection were compared. results: vmatplans and independently the spacer demonstrated improved dosehomogeneity, whereas vmat additionally displayed improved doseconformity. the dose to the bladder and rectum could be significantlydecreased applying the vmat technique (mean rectum volumes of14%/10%/5% in vmat vs. 36%/24%/12% in imrt within the 50gy/60gy/70gyisodoses; p<0.01). ntcp for ≥grade 3 rectum toxicity could be accordinglydecreased with the vmat technique (3.6 vs. 0.9% for imrt vs. vmat; p<0.01)and the spacer gel (3.3 vs. 1.2% for plans without vs. with spacer gel; p<0.01)– only 0.3% with vmat and spacer gel. conclusion: in addition to thedecreased rectal dose following spacer injection, vmat with single biological organat risk optimization resulted in further dose reduction to the organs at risk andimproved dose homogeneity and conformity in comparison to the step-and-shootimrt technique with conventional objectives.