The most widely used type of radiation therapy is:

• A. Orthovoltage
• B. Brachytherapy
• C. Seed implantation
• D. External beam

Answer: (D)

The main idea here is how radiation therapy is delivered. External beam radiation therapy uses a machine outside the body to direct high-energy rays into the tumor. It’s the most widely used approach because it can treat a broad range of cancers at various depths and locations, and with modern techniques—such as 3D conformal planning, IMRT, VMAT, and image-guided delivery—it can precisely target the tumor while sparing surrounding normal tissue. This versatility makes it applicable to many patients and cancer types.

In contrast, ways like brachytherapy place radioactive sources inside or very close to the tumor, which delivers a high dose to a small area but is more site-specific and requires invasive placement. Orthovoltage therapy uses lower-energy X-rays and is mainly suited for superficial tumors, with limited depth penetration, so it’s far less common today. Therefore, external beam therapy remains the most widely used form of radiation therapy because of its broad applicability, noninvasiveness, and the advances that enhance precision and outcomes.