Malignant tumors are often treated with targeted x-ray radiation therapy. To gen

Question

Malignant tumors are often treated with targeted x-ray radiation therapy. To generate these medical x rays, a linear accelerator directs a high-energy beam of electrons toward a metal target (typically tungsten). As the electrons pass near the tungsten nuclei, they are deflected and accelerated, emitting high-energy photons in a process known as bremsstrahlung (from the German for “braking radiation”). The resulting x rays are collimated into a beam that is directed at the tumor. The photons can deposit energy in the tumor through Compton and photoelectric interactions. A typical tumor has 108 cells per cm3, and a full treatment may involve 4 MeV photons producing a dose of 70 Gy in 35 fractional exposures on different days. The gray (Gy) is a measure of the absorbed energy dose of radiation per unit mass of tissue: 1Gy=1J/kg.

Higher energy photons might be desired for the treatment of certain tumors. Which of the following would generate higher energy photons in the linear accelerator?

A. Increasing the number of electrons hitting the tungsten target B. Accelerating the electrons through a higher potential difference C. Both A and B D. None of the above

Explanation / Answer

In any accelerator, energy of photons is only increased by accelerating the electrons through high potential only. Increasing the number of electrons increases the intensity of radiation only, not the energy of photons. It is also a well known fact of photo electric emission. Hence option B is correct.

Related Questions

Navigate

• Browse (All)
• Browse M
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.