3-D Treatment Planning

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The purpose of any radiation therapy program is to deliver a lethal amount of radiation to the cancer – and at the same time to avoid delivering equally high doses to the normal tissues next to or in a direct line from the tumor. As we treat a deep-seated tumor from outside the body, the radiation beams will pass through normal structures on the way. It is usual to treat the tumor from two or more entry points with radiation beams that meet and "crossfire" the target volume deep within the patient’s body; this limits the radiation dose to the organs and tissues to a safe level.

Treatment Planning

Your Mission Viejo team will utilize the advanced 3-D Conformal Treatment Planning to ensure the highest dose to the tumor and the lowest dose to normal tissue. Employing computerized tomography (CT), our radiation oncologists electronically reconstruct the tumor and its surroundings in three dimensions. These sophisticated images can then be used to develop treatment plans that deliver precisely focused radiation to the tumor while sparing as much as possible of the normal tissue and nearby organs.

It is common to periodically reduce the total treatment area during the course of therapy, and to move the entry points of the radiation beams, so that by the end of the whole program the highest radiation dose has been delivered to the smallest volume with the greatest concentration of cancer cells. Using this shrinking-fields methodology and sometimes changing the treatment plan to bring the treatment beams through different areas of normal tissue on their way to the target, allows more of the nearby normal tissue to be excluded from radiation. The treatment as planned should be precise, repeatable, comprehensive, and effective.

Simulating the Treatment

Treatment Planning

After the planning is completed to the Radiation Oncologist's satisfaction, we proceed to the simulation. This is a "dry run" of the proposed treatment using a diagnostic x-ray unit that exactly parallels the functions of the radiation treatment machine. In the process, the planned treatment portals – i.e. points of entry for the radiation beams - are drawn on the patient. The X-rays taken verify that the plan does in fact treat the necessary regions of the body, and that the portals can be set precisely and reliably day after day through the course of treatment. The patient’s skin may be tattooed and frequently marked to guide the treatment setup from day to day, and measurements will be taken of the patient's body to reconfirm the computer plan and to allow final computerized calculations of radiation dose.

Custom treatment devices are often used. Some of these - face masks, foam plastic cushions to the shape of the patient's body -- ensure that body position can be accurately duplicated, allowing all treatments to precisely target the same point. Others - lead alloy blocks - are shaped to exclude as much normal tissue as possible.