Radiation planning (CT simulation)

The therapeutic index is improved by increasing tumor control while reducing normal tissue complications. This conformal technique is accomplished in several ways.

Patients are first immobi- lized in the treatment position with a posterior body cast to reduce day to day patient motion and positioning error and tattoo marks and localization lasers are used to reproduce this position. The target (prostate) is reconstructed in 3 dimensions with treatment planning software from a computed tomographic (CT) scan imaged while the patient is in the body cast during the radiation planning (CT simulation). Third, multiple beams, which are directed at the target, are shaped to conform to the contours of the target from each beam’s eye view (BEV) (Figures 1 and 2). Treatment planning software with dosimetric algorithms is used to calculate the dose in 3 dimensions. Electronic portal imaging devices, ultrasound, and other techniques may be employed which allow daily confirmation of treatment portal locations reducing inter- fraction uncertainty.

The ultrasound localization device used at Fox Chase combines an abdominal ultra sound probe with a computer based targeting system. The unit is in the treatment room adjacent to the treatment couch and the patient is positioned on the treatment couch in a body cast and positioned using tattoo marks and localization lasers.

The prostate is im- aged with the ultrasound and the center of the organ determined. The treatment couch is then shifted so the center of the prostate is aligned with the center of the treatment field. This daily ultrasound procedure adds 5 min to the treatment time, is both non-invasive and painless and is performed by radiation therapist and checked by the treating physician. Dose volume histograms (DVHs) are used to aid in the quantitative analysis of 3D conformal treatment plans. Dose volume his- tograms are dimensional visual represen- tations of 3-dimensional volumes for the amount of radiation dose that the volume of a target or normal tissue organ receives.

Finally, multileaf collimation (MLC) or specific cerrobend blocks can be used to shape the treatment portal. The target is treated with multiple beams that conform to the shape as illustrated in Figure. Although not currently used, the Fox Chase Cancer Center (FCCC) 3D treatment technique has been described in previous reports.