Prostate Cancer
External Beam Radiotherapy: Three-dimensional Conformal Radiotherapy Intensity Modulated Radiotherapy
By Donald B. Fuller, M.D.
External Beam Radiotherapy for Prostate Cancer
Three-Dimensional Conformal Radiotherapy (3DCRT)
The initial breakthrough development that improved the radiation coverage of the prostate target volume was the advent of CT-based radiation planning (FIGURE 4). The CT scanner (FIGURE 5) allows visualization of the prostate target volume, the surrounding normal tissues, and the external body contour. The radiation oncologist is then able to map the prostate target volume and normal tissues on every relevant CT-slice, a process known as “contouring.” This allows the radiation-planning computer to identify and reconstruct these volumes three-dimensionally (FIGURE 6). This, in turn, allows the design of computer designed radiation beams that are custom tailored to cover the prostate target volume three-dimensionally (FIGURE 7) with accurately targeted radiation, while simultaneously sculpting the beam, to better shield adjacent normal tissues such as bladder and rectum from the high-dose region.
This process is known as “three-dimensional conformal radiotherapy” (3DCRT) and became the standard of care at most American radiotherapy centers during the 1990s. It resulted in both higher cure rates and lower complication rates compared with “two-dimensional radiotherapy,” because a higher radiation dose could be accurately delivered to the prostate target volume, even as the dose to surrounding tissues was reduced (2).
