Design of a semiconductor sensor system for interceptive and real time beam monitoring in hadron therapy accelerators Luigi Gaioni FIRB Futuro in Ricerca 2013 March 28, 2013

General features of the project  Purpose: develop a semiconductor detection system which aims to measure the profile and the intensity of a proton and heavy ion beam used in hadron therapy for cancer treatment, along the HEBT lines  Duration: 3 years  Participating Units:  Università degli Studi di Bergamo (u1): Gaioni, Caldara, Manghisoni, Ratti, Re, Traversi  Università degli Studi di Bologna (u3): Giorgi, …  Università degli Studi di Trento (u2): Pancheri, Dalla Betta  ERC: PE7 + LS7  PE7_2 Electrical and electronic engineering: semiconductors, components, systems  LS7_2 Diagnostic tools (e.g. genetic, imaging) 1

Motivation  Hadrontherapy with protons and carbon ions is a fast developing methodology in radiation oncology, since it is an effective treatment against cancers located in areas which are inaccessible to the surgeon's instruments or which are hard to treat by radiotherapy  The facilities that treat patients with protons and ions are nowadays about 27 but several hospital based facilities will be operational in the next years (about 16).  Cyclotrons are employed, together with synchrotrons, for proton therapy while for carbon ion therapy synchrotrons have been till now the only option  Patient safety, accelerator operation, and optimum dose delivery would all benefit if the beam intensity and profile could be continuously monitored during treatment, rather than just during the set-up  This is not possible with existing interceptive monitors which interfere with the beam, causing a non-negligible beam blow up or a beam disruption for therapeutic kinetic energies (60 to 250 MeV for protons and 120 to 400 MeV/nucleon for carbon ions) 2

HEBT lines at the CNAO facility  3 treatment rooms  4 extraction lines  3 horizontal (T, U, Z)  1 vertical (V)  1 Qualification Monitor  Profile Monitor  Intensity Monitor  Scintillating Fibers Harp (SFH) monitors 3  The beam extracted into the HEBT lines is nominally a continuous beam, but it is subjected to strong modulations  Ions accelerated in the synchrotron are extracted during a period settable from 1 to 10 seconds, according to treatment planning requirements  Beam nominal intensities: 1x10 10 protons per spill and 4x10 8 Carbon ions per spill, corresponding to 1.6 nA and 0.38 nA, respectively (assuming 1 second long spill)

Qualification Monitor  As the beam enters the extraction line, after a quadrupoles triplet, it meets three dipoles and four Chopper magnets.  Chopper magnets are usually off and the not-bumped beam is stopped against a dump.  Only if the beam is allowed to go downstream, Chopper magnets are turned on and the beam is kicked so to avoid the dump and go to a treatment room  Just in front of the Dump, there is the so called “Beam Qualification Monitor” 4 Qualification Monitor The Beam Qualication Monitor is comprised of:  Profile Monitor (QPM): Orthogonal harps of scintillating fibers  Intensity Monitor (QIM): Scintillating plate coupled with a photomultiplier placed in air side

Final objectives of the project 5  This research project aims at the commissioning of a relatively large (in the square centimeter range), ultra-thin, pixellated silicon detector based on high density microelectronic processes (nanoscale) and on sparse (non sequential) readout architectures  The device to be developed is meant to be the elementary brick of a monitor for real-time measurement of profile and intensity of a proton or carbon ion beam  Typical applications for such an instrument are in the field of beam monitoring in HEBT lines of hadron therapy accelerators  Use of advanced processing (aggressive silicon wafer thinning and packaging) and design techniques for real-time, fast pixel detectors has the potential for signicantly improve the uniformity of the spill extracted for tumor scanning

Monitor Specifications  Properties  Real time  Interceptive  Beam profile  Beam intensity  Detector  Material: Semiconductor  Sensitive area: 64x64 mm 2  Pitch: 100 um  Thickness: < 50 um  System  Frame Rate: 10 kHz  Radiation hardness particle fluences of particles/cm 2 /year  Heat dissipation 6

Beam monitors: state of the art 7  Monitor based on gas detectors  pros: low material budget  cons: huge apparatus, low sensitivity  Secondary Emission Monitor (SEM) grids  pros: low material budget, real time, high rate  cons: huge apparatus, not interceptive  Scintillating materials with camera readout  pros: excellent sensitivity, simple readout  cons: low frame-rate, high material budget Typically the monitors installed at the existing hadron therapy facilities are based on:

FE chip technology options Monolithic CMOS MAPS will be chosen as the sensor technology for the development of the proposed monitor mainly due to the specification on the sensor thickness. Two options available:  DNW MAPS. The deep n-well process creates a large n-well which acts as the charge collecting diode and has an embedded p-well housing the nMOS transistors while the pMOS transistors are in an n-well which is geometrically smaller and less deep than the charge collecting deep n-well.Vertically integrated technologies  INMAPS quadruple well. This 180 nm process employs, beside a deep n-well, a deep p- well placed underneath the n-well containing the p-channel devices thus preventing it from acting as a charge drain. Process features providing a higher resistivity epitaxial layer for faster and more efficient charge collection are also available. The high resistivity substrate improves the radiation tolerance to bulk damage The first part of the monitor development activity will be devoted to the identication of a suitable CMOS technology compatible with MAPS fabrication to be used within the project 8

FE chip architecture options To be discussed… 9

Work-packages  WP1: test chip for small matrices and building blocks validation  1.1 sensor simulation and design (u3)  1.2 analog front-end design and simulation (u1)  1.3 digital front-end design and simulation (u2)  1.4 small matrices and building blocks characterization (u1, u2, u3)  WP2: design of the full matrix chip  2.1 sensor simulation, design and optimization (u3)  2.2 analog front-end simulation, design and optimization (u1)  2.3 digital front-end and readout architecture design and simulation (u2)  2.4 full matrix characterization (u1, u2, u3)  WP3: cm-scale multichip module integration  3.1 system integration (u2, u3)  3.2 module characterization and field tests (u1, u2, u3)  WP4: hardware tools for sensor assembly and test  4.1 investigation of available techniques for aggressive wafer thinning (u3)  4.2 development of a real time data acquisition system for sensor testing (u2)  4.3 flex hybrid and printed circuit board (PCB) design (u1, u2)  4.4 investigation of heat spreader and thermal conductivity aspects (u3) 10

Budget 11

Evaluation Procedure  Step 1: concise project proposal shall be evaluated (by April 19, 2013) according to the following criteria:  novelty and originality of proposed research and its methodology (5 points)  coordinator and research units scientific qualifications, with regard also to the proposed project with reference to the scientific evaluation of their activities and expertise in the area of proposal (5 points) Only projects that have obtained a score higher than 8/10 may be admitted to the second and third phases  Step 2: detailed project, evaluated according to the following criteria:  Project effectiveness (5 points)  research units qualifications, project feasibility (5 points)  impact of the proposed research (5 points)  Step 3: interviews 12

Backup slides 13

HEBT beam main parameters 14

Scintillating Fibers Harps (SFH) monitors layout 15

Detector Thickness Radiation Lengths X0 Silicon 9.4 cm Diamond12.3 cm Al2O cm d=1 m x<0.1 mm Monitor Treatment Room Beam <50 um in Si at 60 MeV 16 Multiple scattering angle

Monitor assembly 17 Support Foam Low mass Flex cable To service board

Work-packages 18  In each of the rst 3 WPs, an integrated detector prototype is expected to be delivered  Deliverable 1 (WP1): small scale (32x32 or 64x64 elements) 100 um pitch MAPS in CMOS technology  Deliverable 2 (WP2): centimeter scale 3-side buttable matrix (100 um pitch) featuring a selective digital readout architectures  Deliverable 3 (WP3): demonstrator composed of a 2x3 matrix of 3-side buttable chips