Recent proceedings in Brachytherapy Physics

Transcription

1 Recent proceedings in Brachytherapy Physics Frank-André Siebert UKSH, Campus Kiel, Germany Clinic of Radiotherapy Dept. Medical Physics

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3 Physical characteristics of brachytherapy (Courtesy Luc Beaulieu, published in Advances in Medical Physics 2016).

4 Physical characteristics of brachytherapy Brachytherapy is very conformal!! but, geometry is essential!!

5 Dose distributions for cervix carcinoma patients Georg et al. IJROBP 2008

6 Brachytherapy outcome: Cervix Image guided adaptive Brachytherapy 4D 2D 10% 15% Clinic of Radiotherapy Gill B et al. IJROBP 2014;90:1083 Sturdza et al. Improved local control and survival in LACC through Image guided adaptive brachytherapy, (2016)

7 Brachytherapy outcome: Prostate Low risk prostate cancer High risk prostate cancer Grimm et al (2012) BJUI, meta analysis of patients

8 Brachytherapy outcome: Breast Vol. 387, 2016

9 Brachytherapy clinically successful However, decrease of brachytherapy applications Complex logistics? Education? Reimbursement? Not sexy enough? Other techniques catched up?

10 Dose calculation

11 TG-43 formalism Standardized Completly described Consensus data available for most LDR and HDR sources Good results Fast computation

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14 Dose calculation algorithms Standard: TG-43 Formalism Dose calculation possible in all volume data (CT, MRI, US, ) TG-43 considers not: Tissue inhomogeneities Curved sources (wires) Lack of scattering from surfaces Inter-source absorption Shielding-effects in applicators Modern dose calculation algorithms Monte-Carlo Boltzmann transport equation Collapsed cone

15 Similar to External beam radiotherapy Lu et al. 2013

16 Real-time imaging for brachytherapy Ultrasound system Tracked stepper US probe and tracked stepper Treatment planning system

17 Real-time imaging for brachytherapy Enhanced patient follow-up data with LDR prostate real-time planning n=1176, mean FU 47 months I-125 prostate implants Matzin et al. Radiat Oncol 2013

18 Delineation in T2 data Ref.: light blue De Brabandere et al. Radiother Oncol 2012

19 CT T1+T2 CT+T2 Pat ient 1 Patient 2 Impact of interobserver variability on D90 Contouring large interobserver variability for D90 for all techniques Seeds CT: small interobserver spread for D90 slightly larger for technique (b), using T1 for seeds Fusion T1 + T2 : interobserver variability relatively small, but patient dependent CT + T2 : large interobserver variability CT T1+T2 CT+T2 Patient 3 BRAPHYQS WP: De Brabandere et al. Radiother Oncol 2012

20 More information on usage of image fusion in brachytherapy needed. New BRAPHYQS WP20 (chair Jamema Swamidas)

21 As we know, errors occur!! Risk management, treatment verification

22 Uncertainties vs. errors Brachytherapy treatment: Everything is prepared and planned well But how can we be sure that the dose is delivered correctly??

23 Possible errors in Brachytherapy Afterloader malfunction Swapped channels Wrong patient Incorrect single dose Incorrect indexer length Wrong air kerma strength Wrong step size Incorrect applicator position Movement of applicator

24 Risk management Increasing interest in risk managment in radiotherapy AAPM: TG100 report Europe: ACCIRAD report

25 Risk management European guidelines for Risk Management exist Room for individual implementation of risk management Not dedicated to brachytherapy Applicable to brachytherapy National guidelines are complementing European report German guidelines contain external beam radiotherapy, brachytherapy, nuclear medicine

26 Risk management Actual Target Problem Severity Likelihood Detectability Risk Severity Likelihood Detectability Risk Connecting applicators Swapping of channels Procedure to reduce risk: four eyes-principle, identification (coding) of catheters 0 S, L, D 10

27 Treatment verification in BT Is not a new approach The missing puzzle piece in brachytherapy TLDs MOSFET Diodes Alanine 23% of the clinics in Europe use in-vivo dosimetry in BT Guedea et al Challenges: High-gradient dose - > precise detector placement Large range of dose and dose rate

28 Treatment verification in BT Typical practise for prostate, gynae treatments: 5-fold rectum diode array Sagittal view K. Tanderup et al. 2013

29 Treatment verification in BT New approaches needed EBRT Onboard imaging Real-time K. Tanderup, et al. 2013

30 Applicator misplacements 5 mm were detected Many channel connection errors were detected (17 out of 20)

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32 New techniques: unidirectional sources Pd-103 brachytherapy source with shielding Unidirectional sources Flexible LDR BT device (CivaSheet) Head&neck, colorectal cancer, soft tissue sorcoma, skin,

33 New techniques: 3D printing

34 GEC ESTRO BRAPHYQS Work Packages WP7 WP8 WP9 WP10 WP11 WP12 WP13 WP14 WP15 WP16 WP17 WP18 WP19 WP20 Phantom studies for physics part (completed) Evaluation of clinical part (completed) New recommendations (completed) DVH calculation evaluation (completed) Physics data on radiation protection (completed) QA for prostate implant dosimetry in LDR and HDR Uncertainties in Brachytherapy (completed) In-Vivo dosimetry Interobserver variability study (completed) Integral doses in BT (completed) DICOM standard in Brachytherapy Dosimetry of LDR sources at clinical level (new) Commissioning of BT treatment planning systems (new) Image Fusion in BT (new) BRAPHYQS/UroGEC meeting Benidorm 2016

35 WP7 Phantom studies Chair: M De Brabandere, FA Siebert Patient case Kiel-Phantom Impact on seed reconstruction tested: Seed type Slice thickness Field of view Axial or spiral Tube current Treatment planning system CT scanner BRAPHYQS work package results: (Multi centric mailed phantom investigations) Reconstruction independant on clinic and software CT slice thickness should be 3mm FA Siebert et al. Radiother Oncol 2007

36 WP11 Physics data on radiation protection Chaired: F Ballester, P Papagiannis, D Baltas No radioprotection data on design of brachytherapy vaults with maze exist Study of several Ir-192/Co-60 bunkers Geant4 used for computation against NCRP report no. 151 NCRP overestimates needed wall thickness

37 WP 13 Uncertainties in Brachytherapy Chair: C. Kirisits Brachytherapy: (only) treatment form in radiotherapy with systematic description of uncertainties, GEC ESTRO BRAPHYQS project, publ

38 WP16 Integral doses in BT Chair: A Henry This study shows both LDR and HDR brachytherapy monotherapy result in low estimated risks of radiation-induced rectal and bladder cancer. Compared to external beam techniques, second rectal and bladder cancer risks were lowest for brachytherapy. Murray et al. Radiother Oncol (2016)

39 WP18 Dosimetry of LDR sources at clinical level Chair: J Perez-Calatayud Aim: how to assay low energy photon sources at hospital level? -> GEC ESTRO recommendation Different regulations in Europe What equipment? How many sources to be checked (S k )? Batches? Level of uncertainty? Measurement vs. source certificate

40 WP19 Commissioning and QA of BT treatment planning systems Chair: M De Brabandere, A Rijnders 1. Geometry/Imaging: correct image import, image processing, contouring scaling/dimensions/orientation/zooming/ 2. Source and afterloaderspecification: source type, nuclide, decay factor, dose rate constant, TG43-parameters 3. Dose calculation accuracy and representation: TG43, point/line source, anisotropy, shielding, single source/multiple sources, possible correction for dose contribution during source movement, isodoses, DVH, point and line doses 4. Applicator specifications (library): types, dimensions, material?, specific parameters (no commissioning of the applicator) 5. Output/Data transfer: printouts/reports, export to the afterloader

41 WP19 Commissioning and QA of BT treatment planning systems Dose point dose test TPS Hand calculation 1 1 D = 0.635U 0.94cGyh U 2057h = Gy

42 WP19 Commissioning and QA of BT treatment planning systems DVH of great importance Reporting, dose contraints DVHs should be checked DVH calculations differ between TPSs

43 WP19 Commissioning and QA of BT treatment planning systems Imaging: CT, MRI, TRUS and stepper BT Data Flow Oncology Information System, PACS Brachytherapy TPS TG-43, MBDCAs Afterloading device Application of seeds, eye plaques, wires,

44 Close cooperation between GEC ESTRO and AAPM

45 Thank you for your attention!