• Measuring the proton beam energy in different depths of Cancer Tumor
  • Ehsan Amiri,1,*
    1. Shahid Beheshti Sampad High School


  • Introduction: Radiation therapy (also called radiotherapy) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. Charged particles have a stable range in matter. They interact and produce ionization along their path in the material. When their velocity decreases, the ability to ionize and interact increases. Therefore, according to the particle energy, a peak is created in the depth of the target material. The highest depleted dose is called the Bragg peak. As we know, the accurate determination of Bragg curves can give us more precise results of proton energy in different depths of matter, so the study of Bragg curves is essential. There are three ways to determine Bragg curves in the target material: 1-Using the Monte Carlo simulation method: This method is achievable by using different nuclear codes. (such as MCNPX, GEANT4, etc.). 2-Using analytical calculation methods: Bragg curves are asymmetrical. One of the best presented analytical models for Bragg peaks, is the Bortfeld model. This model contains cylindrical parabolic functions and gamma rays. 3-Practical methods of dosimetry and detection: We use various types of detectors in this method.
  • Methods: The BL4S experiments take place in the T9 beam line of the CERN Proton Synchrotron (PS). The experimental area where the T9 beam line is located is one of the most intensively used. Thus, The CERN beam line is suitable for this measurement. Monte Carlo tool (GEANT4) is a simulation package for different geometries and transport of physical particles. In this research we used this tool to simulate a water phantom in the form of a cube. The energies of the proton beams are chosen so that the Bragg peaks cover the range between 8.2 and 12.9 cm. The energy range of the primary shots for 1 million protons is between 113-140 MeV. In order to ensure the accuracy of our simulation, we drew the Bragg peaks using Mathematica software in the same energy range. For a better review, we fitted the Bortfeld curve on the obtained curve from the GEANT4 simulation (for the energy of 119 MeV). Now we are looking for a practical Method to measure the deposited energy.
  • Results: we suggested a detector which is based on the operation of a type of transistor. This transistor is exposed to proton beams. Proton radiation to the negative n-type material of the detector increases the number of charge carriers which leads to generation of current. This sensor consists of a 300 µm silicon layer. The n-type Si-chip is implanted with boron and phosphorus on the front and backside, respectively. Aluminum electrodes are then sintered to provide electrical contacts. Now we provided an idea to place this sensor in a circuit. In this circuit, for a better recognition of proton interactions with the sensor, we can increase the generated current by using an amplifier (NPN transistor). We consider three ways for this detection: 1.The current through the galvanometer 2.Luminous intensity in LED (light emission diodes) 3.LEDs with different colors which are produced by different currents Protons with high energy can damage the detector. Consequently, we also put a one-millimeter aluminum sheets as protective layers. We have to put number of shields in the path of the beam line, based on the detector's depth in water phantom. The energy loss of protons in these sheets is precisely determined. In water phantom the closer we get to the Bragg peak, the more interaction The proton would have. As a result, we would have higher current along the track. The highest interaction would be at the Bragg peak’s location and afterwards the generated current highly decreases. The sensor can be designed in very small sizes due to the used technology. Thanks to this, the whole target screen can interact with protons in any depth. This function is used to calibrate the proton beams.
  • Conclusion: our scientific proposal underscores the vital importance of proton therapy in the treatment of cancer. Proton therapy offers a promising approach to deliver precise doses of radiation to cancer cells while minimizing damage to healthy tissues. The accurate determination of Bragg curves, as demonstrated in our research, plays a crucial role in optimizing proton therapy's effectiveness. By utilizing advanced methods such as Monte Carlo simulations and practical detectors, we have made significant strides in improving the precision and reliability of proton therapy. Our proposed detector, based on a type of transistor, offers a practical solution for measuring deposited energy during proton therapy, enabling better control and monitoring of the treatment process. Furthermore, the use of shields and the precise energy loss calculations for protons in various materials, as outlined in our proposal, enhance the safety and accuracy of proton therapy. This innovative approach allows for the calibration of proton beams and ensures that the highest interaction occurs precisely at the Bragg peak's location, leading to more effective cancer treatment. In conclusion, our research contributes to the ongoing advancement of proton therapy, highlighting its potential to revolutionize cancer treatment by delivering highly targeted radiation therapy and minimizing side effects on healthy tissues. Proton therapy holds great promise in improving the lives of cancer patients, and our work brings us one step closer to realizing that potential.
  • Keywords: Proton therapy, Bragg peak, Monte Carlo simulation, Detector technology, Radiation dosimetry