Dose Delivery Concept and Instrumentation

Radiation therapy aims to deliver the prescribed amount of dose to a tumour at the same time as sparing the surrounding tissues as much as possible. In charged particle therapy, delivering the prescribed dose is equivalent to delivering the prescribed number of ions of a given energy at each position of the irradiation field. The accurate delivery is committed to a dose delivery (DD) system that shapes, guides and controls the beam before the patient entrance. Most of the early DD systems provided uniform lateral dose profiles by using different devices, mainly patient-specific, placed in the beam line to shape the three-dimensional final target dose. More recently, systems that provide highly conformal dose distributions using thousands of narrow beams at well-defined energy were developed which feature advanced scanning magnets and real-time beam monitors, without patient-specific hardware. This lecture will cover the general dose delivery concept as well as the different DD instrumentations depending mainly on the beam delivery technique and on the particle and accelerator types. Some characteristic worldwide DD and beam monitor systems will be mentioned.Comment: presented at the CAS- CERN Accelerator School on Accelerators for Medical Application, V\"osendorf, Austria, 26 May - 5 June, 201

Variation of the relative biological effectiveness with fractionation in proton therapy: analysis of prostate cancer response

Purpose: To present a methodology to analyze the variation of RBE with fractionation from clinical data of tumor control probability (TCP) and to apply it to study the response of prostate cancer to proton therapy. M&M: We analyzed the dependence of the RBE on the dose per fraction by using the LQ model and the Poisson TCP formalism. Clinical TCPs for prostate cancer treated with photon and proton therapy for conventional fractionation (2 Gy(RBE)x37 fractions), moderate hypofractionation (3 Gy(RBE)x20 fractions) and hypofractionation (7.25 Gy(RBE)x5 fractions) were obtained from the literature and analyzed. Results: The theoretical analysis showed three distinct regions with RBE monotonically decreasing, increasing or staying constant with the dose per fraction, depending on the change of ({\alpha}, \{beta}) values between photon and proton irradiation (the equilibrium point being at({\alpha}_p/\{beta}_p)=({\alpha}_X/\{beta}_X)({\alpha}_X/{\alpha}_p)). An analysis of the clinical data showed RBE values that decline with increasing dose per fraction: for low risk RBE=1.124, 1.119, and 1.102 for 1.82 Gy, 2.73 Gy and 6.59 Gy per fraction (physical proton doses), respectively; for intermediate risk RBE=1.119, and 1.102 for 1.82 Gy, and 6.59 Gy per fraction (physical proton doses), respectively. These values are nonetheless very close to the nominal 1.1 value. Conclusions: We presented a methodology to analyze the RBE for different fractionations, and we used it to study clinical data for prostate cancer. The analysis shows a monotonically decreasing RBE with increasing dose per fraction, which is expected from the LQ formalism and the changes in ({\alpha}, \{beta}) between photon and proton irradiation. However, the calculations in this study have to be considered with care as they may be biased by limitations in the modeling and/or by the clinical data set used for the analysis.Comment: Minor changes to match accepted manuscript; in press Medical Physic

Development of a front-end electronics for an innovative monitor chamber for high-intensity charged particle beams

A multi-gap ionization monitor chamber has been developed by INFN and Torino University, for monitoring of high intensity pulsed charged particle beams. The read-out of the chamber is based on a 64-channel ASIC, designed in CMOS 0.35μm technology which features for each channel an independent current-to-frequency converter followed by a synchronous counter. The chip was designed for connecting each channel to a different detector element. However, high beam intensities may lead to an input current above the saturation level of a single channel. A novel readout has been tested where all the input channels of the chip have been connected in parallel to the same detector element allowing to reach 64-times higher input current with only a modest deterioration of the resolution. Results will be presented in terms of linearity and noise, and will be compared to a simulation where the chip is modeled as a set of independent and uncorrelated channels

Fluence Beam Monitor for High-Intensity Particle Beams Based on a Multi-Gap Ionization Chamber and a Method for Ion Recombination Correction

This work presents the tests of a multi-gap detector (MGD), composed of three parallel-plate ionization chambers (ICs) with different gap widths, assembled to prove the capability of correcting for charge volume recombination which is expected to occur when high fluence rates are delivered. Such beam conditions occur with a compact accelerator for charged particle therapy developed to reduce the costs, to accomplish faster treatments and to exploit different beam delivery techniques and dose rates as needed, for example, for range modulation and FLASH irradiations, respectively. The MGD was tested with carbon ions at the Centro Nazionale di Adroterapia Oncologica (CNAO Pavia, Italy), and with protons in two different beam lines: at Bern University Hospital with continuous beams and at the Laboratori Nazionale del Sud (Catania, Italy) of the Italian National Center of Nuclear Physics (INFN) with pulsed beams. For each accelerator, we took measurements with different beam intensities (up to the maximum rate of ionization achievable) and changed the detector bias voltage (V) in order to study the charge collection efficiency. Charge recombination models were used to evaluate the expected collected charge and to measure the linearity of the rate of ionization with the beam fluence rate. A phenomenological approach was used to determine the collection efficiency (f1) of the chamber with thinnest gap from the relative efficiencies, f1/f2 and f1/f3, exploiting the condition that, for each measurement, the three chambers were exposed to the same rate of ionization. Results prove that two calibration curves can be determined and used to correct the online measurements for the charge losses in the ICs for recombination

Characterization of a front-end electronics for the monitoring and control of hadrontherapy beams

Abstract An integrated 64-channel device for the read-out of parallel plate pixel and strip ionization detectors has been developed by the INFN and University of Torino. The detectors will be used for the monitoring and control of hadrontherapy beams. The ASIC has been designed in CMOS 0.8 μm technology and it is based on a current-to-frequency converter followed by a synchronous counter. In this paper, we present a detailed characterization of the device done with 113 chips

'Ionizing radiation effects on a 64-channel charge measurement ASIC designed in CMOS 0.35 μm technology'

A 64-channel circuit Application Specific Integrated Circuit (ASIC) for charge measurement has been designed in CMOS 0.35mm technology and characterized with electrical tests. The ASIC has been conceived to be used as a front-end for dosimetry and beam monitoring detector read-out. For that application, the circuitry is housed at a few centimeters from the irradiated area of the detectors and therefore radiation damages can affect the chip performances. The ASIC has been tested on an X-ray beam. In this paper, the results of the test and an estimate of the expected lifetime of the ASIC in a standard radio-therapeutical treatment environment are presented. An increase of the background current of 2 fA/Gy has been observed at low doses, whilst the gain changes by less than 3% when irradiated up to 15 kGy. Furthermore it has been assessed that, when used as an on-line beam monitor and the annealing effect has been taken into account, the background current increase is � 440 fA/year