The MC commissioning of CyberKnife with MLC (Tips and Tricks)

Transcription

1 The MC commissioning of CyberKnife with MLC (Tips and Tricks) Alain Guemnie Tafo, PhD UPMC Pinnacle, Harrisburg, PA Institute Gustave Roussy, Villejuif, France

2 Disclaimer & Disclosure The views expressed in this presentation are those of the presenters and do not necessarily reflect the views or policies of Accuray Incorporated or its subsidiaries. No official endorsement by Accuray Incorporated or any of its subsidiaries of any vendor, products or services contained in this presentation is intended or should be inferred. An honorarium is provided by Accuray for this presentation

3 Guidelines MC Data/Commissioning MC source model MC Validation MC clinical implementation

4 MC Data/Commissioning In air Output Factor: same as for Ray Tracing Open field dose profile: Profile acquired with no collimator fixed to the Linac head 25mm depth) Central PDD for the 60mm collimator Material: Diode PTW Accuray s excel spread sheet is useful to compare with composite data OF correction factor in literature (Francescon et al 2017 Phys. Med. Biol )

5 MC source model Adjustment of the Energy factor: allow to adjust the photon energy spectrum to match the PDDs (choice of the photon mean energy and w/o beam hardening). Adjustment of the Gaussian spread: Allow to adjust the source size to match the penumbras (choice of the sigma of a Gaussian) Adjustment of Leaves related parameters

6 TPR Model (ECF factor) TPR 6MeV, 1mm, 7.6mm TPR 6.4MeV, 1.8mm, 7.6mm TPR 7MeV, 4mm, 7.6mm TPR 6MeV, 1mm, 84.6mm TPR 6.4MeV, 1.8mm, 84.6mm TPR 7MeV, 4mm, 84.6mm

7 OCR Model (Source size) TPR 6MeV, 1mm, 7.6mm, d=100mm TPR 6.4MeV, 1.8mm, 7.6mm, d=100mm TPR 7MeV, 4mm, 7.6mm, d=100mm TPR 6MeV, 1mm, 84.6mm, d=100mm TPR 6.4MeV, 1.8mm, 84.6mm, d=100mm TPR 7MeV, 4mm, 84.6mm, d=100mm

8 OCR Model (Source size) TPR 6.4MeV, 1.8mm, 7.6mm, d=300mm TPR 6.4MeV, 1.8mm, 7.6mm, d=300mm TPR 6.4MeV, 1.8mm, 7.6mm, d=300mm Proposed Source size and E spectrum are a good starting point No multiple scatter source in the model so the shoulder is not well-matched for large field size and deep depth Using a Diamond detector is recommended for tails measurement accuracy Underestimation of the shoulder for large field size and depth Overestimation of the tail using a Diode detector (correction possible using correction factors, Francescon 2017)

9 MC Validation Beam Configuration Single Beam in a homogeneous phantom Single Beam in a heterogeneous phantom Multiple Beam in a homogeneous phantom Multiple beam in a heterogeneous phantom Multiple Beam in an anthropomorphic phantom

10 Single Beam in a Homogeneous Phantom Field size ranging from 23.1x23.1cm to 100x100.1 cm 800mm SAD PTW (0.125cc) Chamber positioned in the central axis of the beam at 1.5, 55, 10 and 20 cm depth.

11 Single Beam in a Heterogeneous Phantom Water-Lung-Water Configuration (EPE) WATER 8 cm Water-Lung-Water-Lung- Water Configuration -Low (WLWLW-Low) WATER LUNG WATER LUNG 5 cm 8.5 cm 4 cm 5 cm LUNG WATER 2 cm Ionization Chamber Water-Lung-Water-Lung- Water Configuration - High (WLWLW-High) WATER LUNG WATER LUNG 2 cm Ionization Chamber 13.5 cm 8 cm 5 cm 8.5 cm 4 cm 5 cm Field size ranging from 23.1x23.1cm to 100x100.1 cm 800 mm SAD 2 setups slab phantom: Water Lung Water and Water-Lung-Water-Lung-Water PTW (0.125cc) Chamber positioned in the central axis of the beam at 23.5cm depth in the WLW configuration and 15.5cm and 24.5cm for the WLWLW-High and WLWLW-Low configurations WATER 2 cm 8 cm WATER 5 cm Ionization Chamber

12 Results Monte Carlo calculation is in good agreement with measurement for all configurations (<2%) FSPBLS calculation showed a good agreement?

13 Multiple Beam in a Homogeneous Phantom PTW Ionization chamber 5cm depth Field sizes from 23x23.1cm to 100x100.1cm Sequential optimization with PTV size matching the field size Monte Carlo results show a larger discrepancy as compared to FSPB or FSPB- LS but stays within 2%.

14 Multiple beam in a Heterogeneous Phantom Setup 1: Ionization Chamber in a water equivalent plug located in the Mediastinum region Setup 2: Ionization Chamber in a water equivalent plug located in the Lung region Phantom CIRS 002LFC Ionization chamber PTW (0.007cc) 2 setups: Mediastinum and Lung (with tissue like material chamber plug) for Isocentric and Sequential beam optimization Measurement/Calculation agreed within <2% FSPBLS was in good agreement with measurement

15 Multiple Beam in an Anthropomorphic Phantom Anthropomorphic phantom ATOM 701 (CIRS) TLD measurement from EQUAL ESTRO (European Accredited Laboratory) 2 different plans with 30mm and 50mm cone Uniform dose distribution

16 TLD Results MC calculation are in a good agreement with the measurement (within 4% in the non gradient region) FSPBLS dose calculation is in better agreement with measurement as compared to FSPB

17 MLC Clinical gain 7 Lung cases Plans were calculated on fix MC and have been recalculated using the MLC collimator Time reduction is observed (20%) but also highest conformality for the studied cases (5%)

18 MC Clinical gain 4 Liver cases Plans were calculated on fix MC and have been recalculated using the MLC collimator Treatment time reduction observed (25%) but also highest conformality

19 Summary MLC allows to quicken the treatment time for the patient MLC allow to treat larger target MC for MLC is a great addition for extracranial treatments Commissioning and modeling are pretty straight forward Modeling showed a lack of scatter visible on the profile shoulders for large fields and large depth Validation showed good agreements for 1D measurement in homogeneous, heterogeneous and anthropomorphic configurations FSPB-LS seems to be a more accurate starting point for optimization prior to MC calculation Lung and Liver treatment with MLC showed a more conformal and faster treatment time

20 THANK YOU!