A New Virtual Reality Simulation in Optimizing Non-coplanar Beam Orientations for Prostate Cancer IMRT

Charles Shang¹, Tim Williams¹, Andy W Beavis², James W Ward³, Roger Phillips³, L Page³,

¹ Lynn Regional Cancer Center/Boca Rotan Community Hospital, Florida, USA; ² Princess Royal Hospital, Hull, UK; ³ Department of Computer Science, University of Hull, Hull, UK

Purpose:

In prostate IMRT, the use of noncoplanar beam orientations has been limited, while the current simulation process is mainly suited for non-reciprocal, coplanar beam geometries. The objective of this study was, utilizing a new virtual reality simulation (VRS), to explore a dosimetrically more advanced noncoplanar beam settings for prostate cancer IMRT.

Methods and Materials:

A new VRS was employed in this study utilizing a presentation platform of an advanced 3D stereoscopic LCD screen. Investigators randomly selected 12 prostate IMRT cases as the control with initial treatment plans to 45 Gy. Of the seven evenly separated beams in each plan, four posteriorly positioned 18MV’s and three anteriorly positioned 6MV’s. In VRS optimized test group, all beams were rotated more anteriorly assisted with beam eye views; two anterior-oblique beams were tilted 30º inferiorly to clear the bladder without the risk of collisions. All plans were calculated with similar modulated intensity resolutions for comparisons.

Results: Improvement of PTV dose homogeneity in test group was indicated by >2% reduction in D₉₅ and maximal dose (p<0.01). The largest dose reduction (16%, p<0.01) was displayed in bladder mean dose. Enhanced rectal dose sparing was also suggested.

Conclusions: VRS enabled the process in selecting more optimal noncoplanar beam setups without risk of collision. Prostate IMRT plans using a non-coplanar beam arrangement developed in this study demonstrated superior dosimetric characteristics. Advantages of applying VRS to other anatomic sites are also suggested.