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- 1. PRELIMINARY STUDY OF A NEW GAMMA IMAGER FOR ON-‐LINE MONITORING PROMPT-‐GAMMA EMISSION DURING PROTON RADIOTHERAPY PAOLO BENNATI KTH -‐ SCHOOL OF TECHNOLOGY AND HEALTH STOCKHOLM, SWEDEN 14th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD16) 3 -‐ 6 October 2016 Siena, Italy
- 2. COLLABORATION • Royal Institute of Technology – KTH, Stockhom Sweden • Skandion Clinik, Uppsala Sweden • La Sapienza University, Roma Italy IPRD16 -‐ Siena, 3-‐6/October
- 3. PROTON THERAPY • Better dose delivery than X-‐ray could spares healthy tissue • An online imaging system is strongly requested to improve verification of range in tissue: Ø Prompt-‐gamma imager Ø IN-‐BEAM PET scanner (Beta+ emission) Ø Compton camera Images from “Proton-‐beam therapy” S.Yjanik, Springer (2013) • Requirements: • on-‐line with the treatment • 2 mm spatial resolution IPRD16 -‐ Siena, 3-‐6/October
- 4. SYSTEM CHARACTERISTICS • Compact gamma camera equipped with THIN scintillation crystal • Knife-‐edge collimator * I. 2 mm and 30° aperture. II. Magnification 2:1 * Perali I, et al. Phys Med Biol (2014) 59(19) Gamma camera developed at La Sapienza University, Rome Italy IPRD16 -‐ Siena, 3-‐6/October
- 5. DETECTOR SPECIFICATIONS Specifications pro cons Crystal Two new crystal: • Cry019 – 6 mm • LFS* – 2mm thickness • Fast and high-‐Z crystal • Free image digitization • Negligible Compton reabsorption Negligible efficiency at 2-‐6 MeV photons Phototodetector Hamamatsu H8500-‐100 multianodes-‐PMT • super bialkaly catode (QE -‐35%) • 50x50 mm2 area Metal channel dynodes and the new super-‐bialkaly photocatode offer high performances and reduced anode signal -‐ Electronics ($) • FPGA based • 64-‐independent channels read-‐out • 100KHz clock • About 20’000-‐30’000 max count rate • low noise • Single photon detection • Limited count-‐rate capability (for proton therapy!) • No trigger *Luthetium fine silicate ($) A.Fabbri et.al Nuclear Physics B-‐Proceedings Supplements 215 (1), 328-‐332, 2011 IPRD16 -‐ Siena, 3-‐6/October
- 6. GATE* MC SIMULATION -‐ 100, 150, 200 MeV Proton Energy -‐ PMMA Phantom – 16cm diam. x 24cm length -‐ Knife-‐edge collimator and a gamma camera with an ideal LYSO crystal -‐ Detector at 90° respect the proton beam -‐ NO magnification The simulation was divided in two phases: first, the interaction of protons in the phantom. Second, the imaging system was modeled and the first simulation was used as imput. *Gate 7.1 with QGSP-‐BIC-‐HP-‐EMZ reference physics list IPRD16 -‐ Siena, 3-‐6/October
- 7. GATE MC RESULTS • We verify a correlation between the inflection point and the position of the Bragg-‐ peak as for Janssen et al., which resulted about 9mm at 100, 150 and 200 MeV • MC shows that our detector could be able to identify the gamma profile. The gap with BP rise to 12mm. Inflection point Prompt gamma imaged by knife-‐edge gamma system Prompt gamma from 150MeV protons detected with no energy selection Gustaf Lönn, KTH Master Degree Thesis, ref:diva2:937846 IPRD16 -‐ Siena, 3-‐6/October
- 8. THE PROTON FACILITY @ UPPSALA • The Skandion Clinic is the first clinical centre for proton therapy in Scandinavia joint investment of several university hospitals. • The clinic is planned to treat between 1000 and 2500 patients annually, each with an average of 15 fractions (individual treatments). • Two treatment room (a third one is planned) and a research room will use protons accelerated up to 260 MeV energy (at 60% of speed of light). Treatment room Aerial view of the clinic IPRD16 -‐ Siena, 3-‐6/October (from http://www.skandionkliniken.se)
- 9. EXPERIMENTAL SETUP: THE PROTON ROOM Proton noddle Patient bed gantry 10 cm FoV and centered at 12.5 cm 2.0 liters Water Phantomdetector Lead brick Proton beam Detector was installed on the patient bed. Lasers were used to align the phantom with the beam and the collimator IPRD16 -‐ Siena, 3-‐6/October
- 10. SUMMARY OF THE MEASUREMENTS Crystal used for the test Thickness Efficiency at 4 MeV* Phantom tested Proton energy range 1ST test CRY019 50mm diameter 6 mm 15% Water Phantom: 2liter bottle -‐ 12cm diameter) 110 > 145 MEV 2ND test LFS crystal 50 × 50 mm2 2 mm >5% PMMA Phantom 16 cm diameter X 24 cm length 100 > 160 MeV 3rd test LFS crystal +5mm step shifting of the phantom (fixed energy) 150 MeV *Value for LSO crystal >> photofraction = 2% IPRD16 -‐ Siena, 3-‐6/October
- 11. Calibration: Luthetium natural radioactivity Pulse height spectrum from Lu177 self-‐activityc Lu176 natural abundance (2.6% of Lu) is responsible of about 2800 cps detector count-‐rate. NB: In case of self-‐activity, the spectrum is the results of convolution of beta-‐ continuous spectrum (always) with 1, or plus, gamma-‐rays (modulated by the sensitivity of that energies) Correction for image non-‐uniformity Images shows less non-‐uniformity at the edges Light field image and image profile
- 12. CRY019 IMAGE CALIBRATION @511KEV Methods: 1 mm diameter Na22 free source was used to measure spatial resolution (SR) and position linearity -‐ Linearity = 1cm step scanning results in about (2.5-‐3) pixels -‐ Field of view: about 60 mm (far less that what expected!) 1 cm step scanning Results: Na22 source imaged as a line source ER% = 1/5.4 = 18% @ 511keV Na22 measured pulse height spectrum 511keV -‐ (15-‐20)% ERFWHM NB.Since the very low activity, PH spectrum and images were obtained by subtraction of an equivalent background. #1 #2 #3 #4 #5
- 13. CRY019 CRYSTAL: WATER PHANTOM EXPERIMENT Proton energy (MeV) WATER: BP depth (cm) PMMA: BP depth 130 12.6 10.7 135 13.5 11.4 145 15.3 12.9 Collimator aligned to “see” at “12.5 cm depth” Proton& beam expected&BP Detector& “plane” phantom IPRD16 -‐ Siena, 3-‐6/October
- 14. Results: Proton beam monitoring As function of proton Energy 12 Proton& beam expected&BP Detector& “plane” phantom Note: inverse projection
- 15. uFoV of the gamma camera Centered at 12.5 cm deep IMAGE PROFILE AT 135MEV Proton beam 60x60 image digit., Peak of gamma at pixel=29±1, that correspond to the center of the FoV that was set at 12.5 cm Polynomial fit to identify the maximum IPRD16 -‐ Siena, 3-‐6/October
- 16. NEW EXPERIMENT: 50X50 LFS CRYSTAL – PMMA PHANTOM Proton energy (MeV) WATER: BP depth PMMA: BP depth (cm) 130 12.6 10.7 135 13.5 11.4 140 14.4 12.2 145 15.3 12.9 150 16.2 13.7 155 17.2 14.5 160 18.1 15.4 Collimator centered To “see” at “13 cm depth” Proton& beam expected&BP Detector& “plane” phantom IPRD16 -‐ Siena, 3-‐6/October
- 17. LFS IMAGE CALIBRATION Methods: 1mm diameter Co57 collimated source 3mm scanning step scanning to measure spatial resolution (SR) and linearity LFS natural background (from Lu178 decay) 3 mm New image digit 60x60, 1.2mm =1px. When using the knife-‐edge collimator, this number become 1px=2.4mm (M=2:1) 50 > 200 FoV with #13 spot which corresponds to about 40mm linearity: Digit 250x250 >> 250um = 1px
- 18. GAMMA PROMPT IN PMMA PHANTOM Polynomial fit to identify the peak of the emission Centered at 12.5 cm deep Image profile of the central FoV IPRD16 -‐ Siena, 3-‐6/October
- 19. E (MeV) Expected BP “deep” (cm) “Estimated gamma peak” (cm)* Estimated BP position in cm (+12 mm of column #3) 140 12.2 cm 13-‐2.1 = 10.9± 0.3 12.1 ± 0.3 150 13.7 cm 13-0.7 = 12.3± 0.3 13.5 ± 0.3 160 15.4 cm 13+0.7 = 13.7± 0.3 14.9 ± 0.3 *From the polynomial fit Comparison at 150MeV: profile of gamma and Profile obtained by closing the collimator IPRD16 -‐ Siena, 3-‐6/October
- 20. 3RD EXPERIMENT: TRANSLATE THE PHANTOM AT FIXED PROTON ENERGY Metod: Ø 5 mm step translation of the phantom Ø Collimator aligned at 13 cm Ø Proton energy 150MeV –> exp. BP at 13.7 cm Result: The profile of gamma “moves” As function of the translation of the Phantom. Polinomial fit IPRD16 -‐ Siena, 3-‐6/October
- 21. # Energies (MeV) Collimator configuration Expected BP position (cm) Measured BP Count-‐ rate (cps) notes 2 110 Knife edge 9.1 Out of FoV ⋍21’000 0.3 nA 3 120 ‘’ 10.7 na ⋍25’000 4 135* ‘’ 13.1 13.0 cm ⋍33’000 Critical count-‐rate 5 145 ‘’ 14.9 na ⋍39’000 Critical count-‐rate 6 230 ‘’ >20 na ⋍47’000 (!) Excess of count/rate # Energies (MeV) Collimator config. Expected BP position (cm) Extimated BP (cm) Count-‐ rate (cps) notes 2 130 Knife edge 10.7 Out of FoV ⋍18’000 0.5 nA 3 135 ‘’ 11.4 na ⋍19’700 4 140* ‘’ 12.2 12.1 ⋍20’000 5 145 ‘’ 12.9 ⋍22’000 6 150* ‘’ 13.7 13.5 ⋍23’000 7 155 ‘’ 14.5 ⋍24’000 8 160* “ 15.4 14.9 ⋍25’000 LFS crystal & PMMA phantom Cry019 crystal & Water phantom * Measurement was also performed by closing the collimator IPRD16 -‐ Siena, 3-‐6/October
- 22. CONCLUSION • Results seems promising to realize an imaging device for online monitoring proton therapy, even though count-‐rate remain a critical point (max current is far from the clinical dose rate). • Cry019 shows higher image contrast than LFS, but is limited in FoV and sensitivity Future works (among others): • More and more simulation >> to assess the accuracy of the results • Design an improved imaging system (collimator, detector and geometry) • Image and spectral analysis >> remove double hit and improve positioning IPRD16 -‐ Siena, 3-‐6/October
- 23. ACKNOWLEDGEMENTS • Skandion Cliniken, Uppsala Sweden • Alexandru Dasu • KTH STH group, Stockholm • Massimiliano Colarieti Tosti • Gustaf Lönn • David Larsson • La Sapienza University, Rome Italy • Roberto Pani • Roma Tre University, Rome Italy • Andrea Fabbri • Francesco De Notaristefani Work supported by Stockholm Country Council (SLL) IPRD16 -‐ Siena, 3-‐6/October