IORT_ in vivo dosimetry
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IORT_ in vivo dosimetry

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Radiochromic films and Monte Carlo simulations to analyze abnormal Mosfet readings in IOERT breast cancer treatments

Radiochromic films and Monte Carlo simulations to analyze abnormal Mosfet readings in IOERT breast cancer treatments

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IORT_ in vivo dosimetry IORT_ in vivo dosimetry Presentation Transcript

  • Radiochromic films and Monte Carlo simulations to analyze abnormal Mosfet readings in IOERT breast cancer treatments G.Taccini1, F. Cavagnetto1, L.Ferri1, R.Bampi1, M.Guenzi2, G.Iaccario3, A. Soriani3 1 AOU IRCCS San Martino IST, Medical Physics, Genoa, Italy 2 AOU IRCCS San Martino IST,Radiation Oncology, Genoa, Italy 3 Istituto Ragina Elena, IFO, Rome, Italy
  • IOeRT to treat early-stage breast cancer Dedicated mobile accelerator: LIAC Sordina, Italy  Electron beams: 4, 6 ,8, 10 MeV calibrated with Fricke dosimeters and two plane parallel ion chamber comparison*  PMMA cylindrical applicators : 4-10 cm ø for hard docking beam collimation  Steel-PTFE shielding disk (3mm+3mm) ; placed between the deep face of the residual breast and the pectoralis muscle to minimize thoracic wall irradiation  Every day dosimetry check to calculate optimized MU  In vivo dosimetry to check and properly correct MU Rosi A, Viti V. «Guidelines for quality assurance on ontra-operative radiation therapy» ISTISAN 2003 Report No. 03/1 EN Cavagnetto F. et al In vivo dosimetry in IORT cancer treatment. 2011; 99 Cavagnetto F. Et al A comparison between several dosimetric methods in IORT. ESTRO 31 PO-0835
  • Between September 2009 and April 2013: 512 patients. Eligibility criteria for IORT treatment evaluated at two different decisional steps: ―> first step decision after diagnosis ―> second step decision intrasurgery Full dose intraoperativly irradiation if: tumor diameter less than 2,5 cm, infiltrating ductal histology, no mammographic evidence of multifocality, negative resection margins, no more than 3 axillary nodes, no extensive intraductal component.  21 Gy alone for high local relapse risk (pT2-pT1c)  18 Gy alone for low local relapse risk (max ø 1cm, pT1a-pT1b)  10 Gy as boost to the tumor bed if not eligible to full dose irradiation  16 Gy to nipple area complex if nipple sparing mastectomy Guenzi M. et al A two step selection of breast cancer patients candidates for exclusive IORT with electrons: a mono-institutional experience. Anticancer Res. (2012) 32(4):1533-6
  • In vivo dosimetry to monitor exit dose : 293 patients  MicroMOSFET inside a steril and thin catheter is fastened to the PTFE face of the shielding disk –> dose at the deeper part of the target is checked.  Treatment splitted in two parts to correct MU according to detector half treatment reading.  Dose prescribed at the deeper part of the target and normalized at 90%: prescribed dose plus 10% is acceptable otherwise MU are properly correct. MicroMOSFET TN-502RDM (Best Medical Canadian):  Immediate readout  very small active volume 7” x 6.25” x 1.63”  Calibrated for each avaiable LIAC energy Ciocca M et al Real-time in vivo dosimetry using micro-MOSFET detectors during intraoperative electron beam radiation therapy in early-stage breast cancer. Radiother Oncol 2006; 78:213-6. Agostinelli et al. On line optimization of intraoperative electron beam radiotherapy of the breast. Radiother Oncol 2012; 103: 188-192.)
  • 18% of MOSFET readings at half treatment > 10% Shielding disk backscattering radiation MOSFET directional radiation dependance Air gaps and non homogeneous tissue could create high dose hot spot in the irradiated glandular tissue due to electrons nature. Monte Carlo simulation -> no evidence of backscattering rad BOLUS AIR MOSFET TEFLON STEEL 0% 20% 40% 60% 80% 100% 120% 0,0 10,0 20,0 30,0 40,0 50,0 60,0 70,0 D% mm experimental set-up water Our hipothesis Monte Carlo simulations supplied by A Soriani, G.Iaccario
  • 18% of MOSFET readings at half treatment > 10% Shielding disk backscattering MOSFET directional radiation dependance Air gaps and non homogeneous tissue tissue could create high dose hot spot in the irradiated glandular tissue due to electrons nature.  Micro-MOSFETs in slab water phantom under full build up conditions irradiated using electron beams supplied by LIAC.  Directional dependences of microMOSFET were found to be within ±2% between 0 and 45 degree LIAC angles. Chung J.,Suh T. et al Dosimetric Characteristics of Standard and Micro MOSFET Dosimeters as In-vivo Dosimeter for Clinical Electron Beam J. Korean Phys.Soc. 55,2566 Ciocca M. et al Real-time in vivo dosimetry using micro-MOSFET detectors during intraoperative electron beam radiation therapy in early-stage breast cancer. Radiother Oncol. 2006 Feb;78(2):213-6. Epub 2005 Dec 15 Our hipothesis
  • 18% of MOSFET readings at half treatment > 10% Shielding disk backscattering MOSFET directional radiation dependance Air gaps and non homogeneous tissue tissue could create high dose hot spot in the irradiated glandular tissue due to electrons nature. Air gaps and non homogeneous tissue simulated with a filled water glove ; GAFCHROMIC EBT2 radiochromic film irradiation Our hipothesis
  • Air gap between two “fingers” overdosages EBT2 C. Fiandra et al. “Absolute and relative dose measurements with Gafchromic™ EBT film for high energy electron beams with different doses per pulse” Med Phys, 35, 2008  Energy 10 MeV  Applicator 60 mm straight- end  500 cGy to R90 according to daily dosimetry check  Expected dose ≤ 556 cGy Epson Expression 10000XL to scan films  Picodose Pro® to extract red channel PTW VeriSoft® to determine isodoses and profiles.
  • 7% 9% 11% 13% 15% 17% 19% 21% -10 -8 -6 -4 -2 0 2 4 6 8 10 DoseDifference% profile(mm) % Difference between measured and expected dose
  • % Difference between measured and expected dose 7% 8% 9% 10% 11% 12% 13% 14% 15% 16% 17% -10 -8 -6 -4 -2 0 2 4 6 8 10 DoseDifference% Profile(mm) Key: gap size Our purpose: confirm overdosages with Monte Carlo simulations
  • to see overdosages the key is : gap size Reproducible set up  Various heights: 0.5-1 cm  Various widths: 0.2-0.5 cm Results normilized to the expected dose at the appropriate depth.
  • Monte Carlo simulation confirms our experimental results Peak Height: +13%EGS ncr/BEAMnrcode, 1mm simulation step, voxel dimension 1x 5mmx 29mm (GAF thickness) Monte Carlo simulations supplied by A Soriani, G.Iaccario
  • Summary  September 2009 / april 2013: 512 patients affected by early-stage breast unifocal cancer treated with IOeRT .  In vivo dosimetry using micro-MOSFET performed on 293 patients.  Micro-MOSFET placed in the deeper part of the target to check the dose delivered during the first half of the treatment and eventually correct the second half.  Half treatment MOSFET readings, normalized to prescribed dose are higher than 10%in the 18% of cases .  Gafchromic EBT2 films under non homogeneous tissue simulated with a glove filled with water show overdoses at air-water interfaces.  Experimental set up with air gap of various size and EBT2 led us to evaluate the gap size effect.  Monte Carlo simulation confirm overdosages at air/water interfaces.  In vivo investigation with both micro MOSFET and GafCHROMIC F. Cavagnetto et al. In vivo dosimetry using MOSFET and radiochromic films in intraoperative radiotherapy for breast cancer treatments, OC-0487 2nd ESTRO Forum 2013