American Cancer Society estimates
The American Cancer Society estimates there will be 220 900 new cases of prostate cancer diagnosed and 28 900 deaths from this disease in the United States in 2003.1 For patients with nonmetastatic prostate cancer, multiple options for management exist 2 including observation,surgery, external beam radiation therapy (EBRT), brachyther apy, or hormonal manipulation with or with- out surgery or radiation therapy (RT).
During the past 50 years, EBRT has been a mainstay in the management of prostate cancer and continues to be used in the treatment of almost 1/3 of all patients receiving definitive therapy.8 Increasing numbers of patients receiving EBRT have been treated with conformal techniques using 3-dimensional (3D) data sets (i.e., CT scans) and now intensity modulated rather than conventional techniques.
The adoption of the prostate specific antigen (PSA) test and its implementation into clinical practice as a screening tool and prognostic and therapeutic measure has increased the number of patients diagnosed and subsequently treated for nonmetastatic disease.9, 10 Importantly pretreatment PSA level has been shown to be the strongest independent predictor of treatment outcome (especially PSA control) after both surgery and radiation. Biochemical disease free survival (bNED control) is defined by a nonrising post-treatment PSA level, while a rising post-treatment PSA level is an early surrogate to a clinical failure many years later. Here we discuss the evolution of EBRT RT tecniques In 2004, there are several different EBRT techniques including conventional EBRT, 3 dimensional conformal radiation therapy (3DCRT), and IMRT. Planning for patients treated with conventional RT is the least complex of these techniques. These patients undergo simulation (planning) and treatment in the supine position. Custom immobilization devices are not commonly utilized. Rectal and bladder contrast and retrograde urethrograms to aid in the localization of the prostate are not mandatory during the simulation.
Treatment fields are usually based upon bony landmarks without the aid of a CT scan. A description of conventional technique used at Fox Chase in the past has been described before. Radiation dose distributions for conventional treatment plans are typically generated in a single plane and the dose is prescribed at the isocenter and normalized at the 100% isodose line. For patients treated with 3DCRT or IMRT, the planning begins first by defining treatment volumes including both the target (prostate) and the surrounding normal structures (bladder and rectum most importantly) based on a 3D data set. Target volumes are defined according to the International Commission on Radiation Units and Measurements (ICRU) report 50. The gross tumor volume (GTV) is considered to be all known disease defined by the planning CT, pertinent imaging or physical exam. The clinical target volume (CTV) is defined as the GTV and any areas containing microscopic disease. In this case, the entire prostate is considered the CTV. Finally, the planning target volume (PTV) is the CTV plus a margin to account for the uncertainties of daily treatment setup and internal organ motion.
DCRT is the process where the radiation dose is planned and delivered so the high dose volume conforms to an accurately defined target volume. This process minimizes the volume of normal tissue receiving a clinically significant radiation dose thereby reducing the probability of normal tissue com plications.
The volume of normal tissue can be further reduced with better target delineation and immobilization of the target (prostate) allowing smaller PTV expansion (i.e., treatment margins).
