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Dose Calculation Algorithms

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Presentation on theme: "Dose Calculation Algorithms"— Presentation transcript:

1 Dose Calculation Algorithms
Kwangwoo 2017 Yonsei IMRT Workshop

2 Outline The past The present The future

3 The past

4 Hand Calculation Scatter Correction 𝑫 𝒑 = 𝑫 𝒑𝒓𝒊𝒎𝒂𝒓𝒚 + 𝑫 𝒔𝒄𝒂𝒕𝒕𝒆𝒓
PDD, TAR or TMR Lateral dose profile Collimator and Phantom scatter factor (Sc and Sp) Transmission factor (Wedge, Block, Tray, MLC) Beam calibrated output (MU/cGy) Clarkson’s Method 𝑇𝐴𝑅(𝑧,𝑟)= 𝑇𝐴𝑅 0 𝑧, 𝑟=0 +𝑆𝐴𝑅(𝑧,𝑟)

5 Correction-Based method
𝐷 𝑖𝑛ℎ𝑜𝑚 (𝑥,𝑦,𝑧)=𝐼𝐶𝐹 𝑥,𝑦,𝑧 × 𝐷 𝐻 2 𝑂 (𝑥,𝑦,𝑧) Using linear attenuation, ignoring patient specific densities and treatment beam parameters 𝐼𝐶𝐹 𝑥,𝑦,𝑧 = (% per 𝑐𝑚) × inhomogeneity thickness Using effective attenuation, including patient specific densities, excluding treatment beam parameters 𝐼𝐶𝐹 𝑥,𝑦,𝑧 = 𝑒 𝜇 ′ (𝑑− 𝑑 ′ )

6 Correction-Based method
𝐷 𝑖𝑛ℎ𝑜𝑚 (𝑥,𝑦,𝑧)=𝐼𝐶𝐹 𝑥,𝑦,𝑧 × 𝐷 𝐻 2 𝑂 (𝑥,𝑦,𝑧) Ratio of Tissue-Air Ratios (RTAR) 𝐼𝐶𝐹 𝑥,𝑦,𝑧 = 𝑇𝐴𝑅( 𝑑 ′ ,𝑊) 𝑇𝐴𝑅(𝑑,𝑊) Over-correction when 𝝆<𝟏 Under-correction when 𝝆>𝟏 Power law method (Batho) 𝐼𝐶𝐹 𝑥,𝑦,𝑧 = 𝑇𝐴𝑅( 𝑑 ′ ,𝑊) 𝜌 1 − 𝜌 2 𝑇𝐴𝑅(𝑑,𝑊) 1− 𝜌 2 Under-correction when 𝝆 𝟏 <𝟏 Over-correction when 𝝆 𝟏 >𝟏

7 The Present

8 Model-Based Method Terms: Kernel, Convolution & TERMA
“Kernel” is a function which define integral transform mathematically, Inversely, define propagator as in differential operator. 𝒇 and 𝒈 are convolute ! kernel ℎ 𝑥 = 𝑓 𝑥 𝑔 𝑥−𝑦 𝑑𝑦 = 𝑓 𝑥 ⨂𝑔 𝑥 Integral Transformation 𝑻 𝑬 𝑬, 𝒓 = 𝝁 𝑬, 𝒓 𝝆 𝒓 𝑬 𝜱 𝑬 𝑬, 𝒓 Energy fluence Mass attenuation “TERMA” is a total energy released per unit mass

9 𝑻( 𝒓 ′) 𝑲( 𝒓 − 𝒓 ′) 𝑫( 𝒓 )= 𝑻 𝒓 ′ 𝑲 𝒓 − 𝒓 ′ 𝒅𝑽′ 𝑫 𝒓 =𝑻 𝒓 ′ 𝑲 𝒓 − 𝒓 ′
Energy Fluence Photon TERMA 𝑻( 𝒓 ′) Propagate (scatter) dose 𝑲( 𝒓 − 𝒓 ′) 𝒓 ′ 𝒓 𝑫 𝒓 =𝑻 𝒓 ′ 𝑲 𝒓 − 𝒓 ′ 𝑫( 𝒓 )= 𝑻 𝒓 ′ 𝑲 𝒓 − 𝒓 ′ 𝒅𝑽′ =𝑻 𝒓 ′ ⨂𝑲 𝒓 − 𝒓 ′

10 Model-Based Method Collapsed Cone Convolution (CCC)
Fluence Pinnacle TERMA Dose Depth RayStation Collapse Cone Kernel TomoPlan

11 Model-Based Method Collapsed Cone Convolution (CCC)
𝑫( 𝒓 )= 𝑻 𝒓 ′ 𝑲 𝑪𝑪 𝒓 − 𝒓 ′ 𝝆( 𝒓 ′ )𝒅𝑽′ Energy transported and attenuated Heterogeneity correction by effective pathway through the position vector 𝒓 ′ Including kernel tilting effect Time consuming calculation Less accurate at large distances from cone vertex Errors are small due to point-spread functions Electron transport included

12 Model-Based Method Pencil Beam Convolution (PBC)
Fluence Dose Depth TERMA Monaco Pencil Kernel

13 Model-Based Method Pencil Beam Convolution (PBC)
Med. Phys. 13, 1 2D pencil beam kernel The dose distribution can be generated by integrating the pencil beam over the patient’s surface and by modifying the shape of the pencil beam with depth and tissue density Electron transport not modeled

14 Model-Based Method Anisotropic Analytical Algorithm (AAA) Acuros XB (AXB)
AAA is a pencil beam convolution/superposition algorithm For the fluence model used multi-source model (Eclipse, TomoPlan) Kernel can be determined using linear Boltzmann transport equation (LBTE)

15 Comparison… Phys. Med. Biol. 52, 1363

16 Comparison… Beam Quality (TPR20,10)
% difference w.r.t. MC 6MV MV AAA-ECL -0.30% 1.06% PBC-ECL -0.74% 1.60% CC-TMS 1.33% PB-TMS -0.44% 1.46% CCC-PIN -1.19% 0.93% FFTC-Xio 0.00% MGS-Xio -0.15%

17 Heterogeneity - Bone

18 Heterogeneity - Lung

19 Comparison… Phys. Med. Biol. 51, 5785 PBC CCC MC

20 PB vs MC Med. Dosim. 26, 157 Pencil Beam MC

21 PBC, CCC, and MC PBC CCC Calculation Speed MC Calculation Accuracy

22 The future Convolution/Superposition + MC MC with hardware development
Considering BED Developing algorithm for particle therapy Lanchun Lu, Internaltional Journal of Cancer Therapy and Oncology

23


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