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 for treatment planning: introduc on of a hydrogel spacer, VMAT (volumetric modulated arc therapy) and a single biological organ at risk objec ve for the rectum and bladder. Ini al standard was a step-and-shoot IMRT (intensity modulated radiotherapy) without a spacer and conven onal organ at risk objec ves. Materials and Methods: Treatment plans were calculated using IMRT and VMAT techniques before and a(er spacer injec on in 27 pa ents, respec vely. Conven onal organ at risk objec ves have been used for the op miza on of IMRT plans, only a single biological organ at risk objec ve for VMAT plans. VMAT vs. IMRT plans and plans before vs. a(er spacer injec on were compared. Results: VMAT plans and independently the spacer demonstrated improved dose homogeneity, whereas VMAT addi onally displayed improved dose conformity. The dose to the bladder and rectum could be significantly decreased applying the VMAT technique (mean rectum volumes of 14%/10%/5% in VMAT vs. 36%/24%/12% in IMRT within the 50Gy/60Gy/70Gy isodoses; p<0.01). NTCP for ≥grade 3 rectum toxicity could be accordingly decreased 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 addi on to the decreased rectal dose following spacer injec on, VMAT with single biological organ at risk op miza on resulted in further dose reduc on to the organs at risk and improved dose homogeneity and conformity in comparison to the step-and-shoot IMRT technique with conven onal objec ves.