Borges C 1, Zarza- Moreno M 2, Teixeira N 2, Vaz P 3 1 Medicalconsult SA, Lisboa, Portugal; 2 Escola Superior de Tecnologias da Saúde, Lisboa, Portugal; 3 InsEtuto Tecnológico e Nuclear, InsEtuto Superior Técnico, Universidade Técnica de Lisboa, Sacavém, Portugal
Breast cancer is the most common malignancy among U.S. women, with more than 200,000 new cases diagnosed annually (Jemal et al, CA Cancer J Clin 2004; 54: 8-29) (Siegel R, et al. CA Cancer J Clin 2012; 62: 10 29) 2
RT is indicated after BCS to improve local tumor control As current practice, at least 50 Gy are administered to the whole breast 3
Investigation of the breast doses using different breast external beam irradiation techniques New techniques are being employed for breast treatment Compromise between breast irradiation and undesired irradiation of the healthy tissues surrounding Radiological Protection Issue Patient Related 4
1. 2. 3. Different left breast irradiation techniques iplan BrainLab TPS: f-imrt, IMRT2 and IMRT5 Two calculation algorithms: PBC and imc RT linear accelerator Simulations of the clinac + HD120 MLC Validations in solid water phantoms MC Simulations of breast cancer treatments Comparison of the 3 irradiation techniques Comparison of the 3 calculation algorithms 5
Typical prescribed dose: 50 Gy to the PTV after BCS Avoid the OAR: contralateral breast, heart, lungs and normal tissue exposure 6
f-imrt IMRT2 IMRT5 7
Model-based algorithms Pencil-beam algorithm Superposition and Convolution algorithms Application of dose kernels and TERMA Monte Carlo algorithms 8
7 patients iplan BrainLab TPS: Pencil Beam Convolution (PBC) For Optimization Monte Carlo (imc) Applying the same beam configuration 9
I f-imrt II IMRT2 III IMRT5 Results published: Borges C et al. Phys Med 2013 10
V xxgy percentage volume of specific tissue that receives xx Gy D yy% - percentage dose received by yy% of the specific tissue V5% HI homogeneity index V 95% CI conformity index V RI TV CN Conformation Number TV RI TV TV V RI RI Statistical analysis SPSS IBM v20: Wilcoxon test p-value 0.05 11
1. Monte Carlo simulations BEAMnrc/EGSnrc DOSXYZnrc homogeneous water phantom + patient dose calculations 2. Clinac Trilogy ix (2300 C/D) Varian Medical Systems Validation of the 6 MV beam, up to the jaws, on a water phantom with ionization chambers 3. High Definition Multileaf Collimator (HD120 MLC) Validation on a water phantom with ionization chambers + film dosimetry 4. CERR for dose analysis and SPSS for statistical analysis 12
Incident electron energy: 6.2 MeV Gaussian intensity profile with a FWHM of 1.2 mm Target: 2 layers: tungsten and copper Primary collimator: tungsten fixed mandibles Flattening Filter: Modeled with18 layers Jaws & MLC: Patient specific beam modifiers 13
Lateral Profiles Depth Dose Profiles (PDD) Profiles: <2% (2SD) Discrepancies PDD: < 2 % after build up < 4 % in the build up σ<2% (2SD) 14
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Half Target 7x 16x Quarter Target 7x Half Target Leaf material Half Isocenter Quarter Isocenter Half Isocenter Screw Hole Air 16
A. Ray tracing B. AbuZng gap: 0.03 cm C. HDMLC density: 18.7 g/cc A. B. C. 17
A. B. A. Depth Dose Profiles B. Lateral Profiles C. Alternated paaern D. Dynamic MLC paaern C. D. Results published: Borges C et al. Med Phys 2012; 39 (1) 415-24 18
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f-imrt IMRT2 IMRT5 2D-gamma % passing points 98.54% 99.47% 93.63% Analysis performed using CERR software, a MATLAB toolbox 1 patient PBC vs BEAMnrc MC Major differences observed in the lung region (not considering the couch which was not included in iplan calculations but was in the CT image for the BEAMnrc simulations) 21
PBC vs BEAMnrc MC imc vs BEAMnrc MC f-imrt 96,18% 98,71% IMRT2 97,32% 98,98% IMRT5 98,02% 98,45% Better agreement between imc and BEAMnrc 22
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HDMLC successfully modeled to simulate RT treatments in fixed gantry mode for static and dynamic MLC Comparing the techniques: It is not straightforward that more complex techniques are better for the breast irradiation (e.g IMRT5 more low doses in the OAR) Comparing the algorithms: PBC seems to overestimate doses in the PTV (doses >45Gy) compared to imc and BEAMnrc MC, with differences up to 5Gy imc results with ~2% differences BEAMnrc MC Major differences between MC and PBC in higher doses in lung tissue The choice of the calculation algorithm used in clinical practice is of utmost importance for the accuracy of dose calculation in patients, especially if heterogeneities are present. 24
Centro Oncológico Dra Natália Chaves Quadrantes Varian Medical Systems Centro Física Nuclear da Universidade de Lisboa CFN-UL Instituto Tecnológico Nuclear Dr Emily Heath Ryerson University 25