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: introduction of a hydrogel spacer, VMAT (volumetric modulated arc therapy) and a single biological organ at risk objective for the rectum and bladder. Initial standard was a step-and-shoot IMRT (intensity modulated radiotherapy) without a spacer and conventional organ at risk objectives.&nbsp; Materials and Methods: Treatment plans were calculated using IMRT and VMAT techniques before and after spacer injection in 27 patients, respectively. Conventional organ at risk objectives have been used for the optimization of IMRT plans, only a single biological organ at risk objective for VMAT plans. VMAT vs. IMRT plans and plans before vs. after spacer injection were compared. Results: VMAT plans and independently the spacer demonstrated improved dose homogeneity, whereas VMAT additionally 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 &ge;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) &ndash; only 0.3% with VMAT and spacer gel. Conclusion: In addition to the decreased rectal dose following spacer injection, VMAT with single biological organ at risk optimization resulted in further dose reduction to the organs at risk and improved dose homogeneity and conformity in comparison to the step-and-shoot IMRT technique with conventional objectives. &nbsp;