Plenary Oral Presentations - Macquarie University Hospital

More documents

Recommendations

Info

16 th International Meeting of the Leksell Gamma Knife ® SocietyMarch 2012, Sydney, AustraliaPH-242Initial performance characterization and clinicalimplementation of a novel image-guided system for Perfexion1,2Mark Ruschin, 1 Paul De Jean, 1 Steve Ansell, 1 Greg Bootsma, 1,2 Caroline Chung, 1,2 Cynthia Menard,1,2Young-Bin Cho, 1,2 David Jaffray1Radiation Medicine Program, Princess Margaret <strong>Hospital</strong>, Toronto, ON, Canada2Department of Radiation Oncology, <strong>University</strong> of Toronto, Toronto, ON, CanadaObjective: A novel cone-beam CT (CBCT) image-guidance system has been installed on a Perfexionunit at our institution and has been used for patient imaging. The purpose of this study is to describethe initial performance and clinical experience with this image-guided Perfexion (IGP) system.Methods: The initial CBCT prototype could achieve a 188-degree scan. Adjustable imaging parametersincluded: beam quality (tube potential and filter), patient dose, scan speed, reconstructionresolution, and number of projections. The optimal beam quality was determined by measuring thecontrast-to-noise ratio in known objects at different tube potentials and filter combinations. Withthe optimized beam quality, the minimum required patient dose for sufficient image quality was thendetermined by reviewing images of anthropomorphic phantoms. Target localization accuracy wasdetermined by simulating the treatment planning process in end-to-end testing in phantoms usingCBCT images defined in Gammaplan. Our initial clinical protocol was designed to allow CBCTimages of patients with brain metastases to be acquired immediately prior to and after treatment andretrospectively analyzed for setup accuracy and intra-fraction motion.Results: The optimal beam quality – taking into account contrast and patient dose – was determinedto be 90 kV with a bowtie filter plus 0.1mm copper. Using 0.5mAs per projection and 188 projections(1 per degree) resulted in a CBCT dose of approximately 1cGy to the centre of a 16cm head phantom.Low-contrast details such as polyethylene inserts (CT number=-100) in water could be detected. Highcontrast resolution of 7-8lp/cm and 3-4lp/cm was attained using 0.5mm and 1.0mm reconstructedcubic voxels respectively. The scan time was set to 1min, after which the reconstructed volume isavailable in
16 th International Meeting of the Leksell Gamma Knife ® SocietyMarch 2012, Sydney, AustraliaPH-256A treatment planning algorithm optimizing TCP based on adose-rate dependent LQ-modelHåkan Nordström, Karl Danielsson, Pär LidbergElekta Instrument AB Box 7593, SE-10393 StockholmObjective: Planning objectives in the Gamma Knife ® Radio Surgery are in general to have a highcoverage and selectivity of the planning iso-dose to the target as well as low dose to surroundingtissue and organs at risk (OARs). The basic assumption is that there is a strong correlation betweenthe clinical outcome and the physical prescribed dose. As has been pointed out by several authors theradiobiological effect may also be dependent on overall treatment time, a function of both the doseratein tissue and the number of iso-centers used, for which models that have been developed that takethese variables into account. The purpose of this study is to discuss planning based on radiobiologicalmodels rather than physical dosimetric based objectives.Methods: A prototype version of the inverse planning software in Leksell Gamma Plan ® has beendeveloped that optimizes the tumor control probability (TCP) calculated with a modified LQ-modelsuggested by J. Hopewell, B. Millar et al. This model depends explicitly on the dose rate as a functionof time during the treatment delivery. Penalty functions for OARs are also incorporated in the optimization.For several clinical indications TCP-optimized plans have been derived and compared to plansbased on dose metrics (coverage, selectivity and dose gradients). Plans with similar dose metrics butwith different number of iso-centers have been generated to see the influence of dose-rate on TCP.To the test the sensitivity on the outcome the parameter α and β as well as the half-times repair ofsublethal radiation damage have been varied.Results: The suggested method makes it possible to create plans optimized with regards to TCPdetermined by models incorporating dose-rate.TCP optimized plans will in general be different to plans based on optimized dose metrics.Conclusion: A framework has been created that makes it possible to include radiobiological objectivesinto dose plan optimization.65
Page 2 and 3:
16 th International Meeting of the
Page 4 and 5:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14: 16 th International Meeting of the
Page 63: 16 th International Meeting of the
Page 83 and 84: Author IndexAAhluwalia Manmeet 49,
Page 85: RRadatz Matthias 12, 16Radatz Matth
show all

Plenary Oral Presentations - Macquarie University Hospital

Create successful ePaper yourself

Delete template?

Save as template?