Fighting cancer - VME system to destroy cancer cells and repair DNA

From the years 2000 to 2020, malignant tumors (cancer) will increase dramatically by 50 percent. A data acquisition and irradiation system based on VMEbus has been developed at the Friedrich-Alexander University Erlangen-Nuernberg, Uni Erlangen, where protons are used to detect the repair mechanism of Deoxyribonucleic Acid (DNA). The energy spectra have been measured with a beam going through different absorber foils to determine the energy-loss properties of the protons, and an experimental setup has been constructed to measure the energy loss of protons in air. With the irradiation of primary human fibroblasts (samples of human cells) at a small angle to the beam, the DNA damage along the tracks of single protons through the nucleus could be visualized. This allows further investigation of DNA repair mechanisms and the involved proteins.

Proton rays release most of their energy close to the end of their track (Bragg peak), concentrating on the target cells (tumor) deep inside the body without damaging cells along their route to the target. Experiments with a therapy using pi mesons (pions) at PSI, Switzerland, and TRIUMF, Canada, have been discontinued because of too much technical complexity. This is also true for experiments with anti-protons at CERN – the European Organization for Nuclear Research. Measurements on proton rays at Uni Erlangen were done using Medipix2 semiconductor detector chips developed at CERN, where detecting protons is routine work (Figure 1).

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Figure 1: Principle operation of Medipix chip (CMOS) where X-rays are replaced by proton rays, photo courtesy of CERN
(Click graphic to zoom)

 

Uni Erlangen is one of a dozen partners from several European countries that developed Medipix2. Medical applications involving radiation and human cells must be extremely reliable and precise. A custom-configured VMEbus system is used for this application. Some of the VME modules are briefly described:

·       The V775 from CAEN, Italy, is a VME module housing 32 Time-to-Digital Conversion (TDC) channels with a full-scale range from 140 ns to 1.2 microseconds. The outputs of the TDC sections are multiplexed and subsequently converted by two fast ADC modules. The ADCs use a sliding-scale technique to reduce the differential nonlinearity.

·       The V792 is a VME module featuring 32 Charge-to-Digital Conversion (QDC) channels. For each channel, the input charge is converted to a voltage level by a Charge-to-Amplitude Conversion (QAC) section. Input range is 0 ÷ 400 pC. The outputs of the QAC sections are multiplexed and subsequently converted by two fast 12-bit ADCs.

·       The V1290A is a VME module that houses 32 independent Multi Hit/Multi Event Time-to-Digital Conversion (TDC) channels. It uses four high-performance TDC chips, developed by CERN, with a Least Significant Bit (LSB) of 25 ps.

·       The V1718 is a VME master module and VME system controller with a USB connection to a standard PC. The I/O on the V1718 can be programmed via USB to implement functions such as timer, counter, pulse generator, I/O register, and so on. The V1718-to-PC interface is not slowed down by the transfer rate on the USB port.

·       The SIS3820 scaler from SIS GmbH, Germany, is a 6U VME card. It includes two 34-pin headers for the counters. The SIS3820 accepts inputs with a frequency up to 250 MHz.

European events

The electronica 24th international trade fair in Munich November 9-12 attracted 70,000 visitors (47 percent international) and 2,600 exhibitors. The SPS/IPC/DRIVES trade show for electrical/electronic automation in Nuernberg November 23-25 attracted more than 50,000 visitors and included products from 1,323 exhibitors. Both events are the largest of their kind worldwide.

For more information, e-mail Hermann at hstrass@opensystemsmedia.com.