VMAT plans with ±45 degree collimator rotationsrequired on average 38% less monitor units comparedto plans with no collimator rotations and 20% lessmonitor units than plans with ±22.5 degree rotations.Plans with ±45 degree collimator rotations providedmore homogeneous dose distribution with an averageof 6% less maximal dose. VMAT plans with two arcsprovided improved conformity and homogeneity withan average of 3% lower maximal dose compared tosingle arc plans. However, increasing the number ofarcs to three did not provide any significantimprovement. Introduction of ±5 and ±10 degree tablerotations between arcs did not result in any significantdosimetric improvements. The selection of photonbeam energy between 6MV and 10MV did not provideany notable dosimetric differences either.

Introduction

Treatment planning, image guidance and treatmentdelivery protocol for hypo‐fractionated prostate SBRTwas developed with RapidArc VMAT using Novalis Tx,Exactrac stereoscopic imaging and Cone BeamComputed Tomography (CBCT). Three patients wereincluded in our initial investigation prior to the start ofthe protocol and seven additional patients have sincebeen added to the investigation and treated. Thedosimetric and other clinical consequences of numberof arcs, table rotations, collimator angle and photonbeam energy have been investigated.

Methods

Results

Nzhde Agazaryan, PhD, DABREmail: medphysics@gmail.com

Associate ProfessorBiomedical Physics and Radiation Oncology

The final selection of the protocol includes twocoplanar 10 MV Rapid Arcs with ±45 degree collimatorrotations. This prospective clinical trial is designed todeliver 5 fractions of 8 Gy with the prescription dosecovering the 95% of the planning target volume. Thebeam‐on time for each of the coplanar arcs isapproximately 2 minutes. For the purpose ofintrafraction motion management, two Rapid Arcs arefurther split to 4 half arcs with approximately oneminute treatment time for each segment (fFigure 1).The patient is stereoscopically imaged andrepositioned if necessary using ExacTrac prior to thedelivery of each arc. Additionally, CBCT is obtainedprior to each fraction for the purposes of confirmationof ExacTrac positioning and volumetric evaluation ofbladder and rectal filling.

Conclusions

Volumetric Modulated Arc Therapy Treatment Protocol for Hypo-fractionated Stereotactic Body Radiotherapyfor Localized Prostate Cancer

Nzhde Agazaryan, Steve Tenn, Phillip Chow, Chul Lee, Percy Lee, Michael Steinberg and Chris King

University of California Los Angeles, Los Angeles, CaliforniaASTRO 2010, Presentation Number: 3431, Poster Board Number: A-742, Poster Category: P-06 – Novel treatment delivery techniques

A single arm Phase IIa clinical trial has been initiated toobtain systematic quality of life data after a hypo‐fractionated course of stereotactic body radiotherapyfor the treatment of localized prostate cancer. Ourprincipal aims are: to quantify the quality of life basedupon validated QOL questionnaire tools that documentthree separate domains (urinary, bowel, and sexual)over the course of 2‐5 years after treatment; to quantifytumor response using the standard of care PSA‐basedpatterns after radiotherapy; to report any significantadverse events using standardized case report forms(CRF).

Objectives

Figure1: Thesequenceofimagingandtreatmentevents.ThepatientisstereoscopicallyimagedandrepositionedifnecessaryusingExacTrac priortothedeliveryofeacharc.

To establish treatment planning, image guidance andtreatment delivery protocol for a prospective singlearm Phase IIa clinical trial designed to obtainsystematic quality of life data after a hypo‐fractionatedcourse of Stereotactic Body Radiotherapy (SBRT) forthe treatment of localized prostate cancer.

Disclaimer:ResearchsponsoredbyVarianMedicalSystems.

Update

Since the submission of this abstract 6MV high doserate mode with 1000MU/min maximum dose rate hasbeen adapted for this study. The beam on time for eachof the half arcs is approximately 40‐50 secondsreducing potential large organ movements. At the timeof this poster preparation 21 patients have beentreated with the presented protocol.Figure 2: An example of a VMAT plan dose distribution. This prospective clinical trial is designed

to deliver 5 fractions of 8 Gy with the prescription dose covering 95% of the PTV.The protocol limits V50% to VPTV ratio less than 4 and Dmax less than 10% above prescription.

BladderRectum

CTV and PTV