Safety Margins for Geometrical Uncertainties in Radiotherapy

Cancer is the unrestricted growth of cells in an organism, which can eventually destroy organs that are needed for survival of the organism. Throughout human history, cancer has been one of the major medical causes of death. At the moment, there are about 840.000 cancer fatalities in Europe per year. It is estimated that in the westem world approximately 1 in 3 people will develop some kind of tumor during their lifetime, and more than 1 in 5 will die of it. Although significant progress has been achieved in the fight against cancer in the last decades, still about half of the cancers cannot be cured. Currently, the three main therapies for cancer are surgery (removing the tumor), radiotherapy (killing the tumor cells with radiation), and chemotherapy (the use of anti-cancer mugs). The first two are especially used for tumors that are well localized. Surgety is straightforward but catmot always be applied, for instance when the tumor is localized in or close to a vital organ. Futthermore, invisible, microscopic extensions of the tumor might be trtissed. In radiotherapy, those tumor extensions can be treated more easily. Moreover, this therapy may be less demanding on the patient and hospitalization is usually not necessaty. When microscopic tumor cells have spread from the primary tumor site to different parts of the body, chemotherapy can be applied. The blood circulation is used to transpoti the drugs are transported through the body. In many cases, the difterent therapies are combined to improve the treatment outcome. Radiotherapy is used for about half of all cancer patients. With radiotherapy, ionizing radiation in the fotm of high energy photons, electrons or protons is aimed at the tumor. These particles deposit some of their energy in the tumor cells, which can cause ionization of DNA or surrounding molecules. This can induce irreparable genetic damages in the tumor cells that either kill the cell directly or result in the socalled apoptosis, i.e. cellular suicide. However, since radiation may kill healthy cells as well, one has to be careful to deliver the radiation dose in the right place. Basically, there are two ways the radiation can be delivered: by brachytherapy or by external beam radiotherapy

High-precision prostate cancer irradiation by clinical application of an offline patient setup verification procedure, using portal imaging

Purpose: To investigate in three institutions, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis [AvL]), Dr. Daniel den Hoed Cancer Center (DDHC), and Dr. Bernard Verbeeten Institute (BVI), how much the patient setup accuracy for irradiation of prostate cancer can be improved by an offline setup verification and correction procedure, using portal imaging. Methods and Materials: The verification procedure consisted of two stages. During the first stage, setup deviations were measured during a number (N(max)) of consecutive initial treatment sessions. The length of the average three dimensional (3D) setup deviation vector was compared with an action level for corrections, which shrunk with the number of setup measurements. After a correction was applied, N(max) measurements had to be performed again. Each institution chose different values for the initial action level (6, 9, and 10 mm) and N(max) (2 and 4). The choice of these parameters was based on a simulation of the procedure, using as input preestimated values of random and systematic deviations in each institution. During the second stage of the procedure, with weekly setup measurements, the AvL used a different criterion ('outlier detection') for corrective actions than the DDHC and the BVI ('sliding average'). After each correction the first stage of the procedure was restarted. The procedure was tested for 151 patients (62 in AvL, 47 in DDHC, and 42 in BVI) treated for prostate carcinoma. Treatment techniques and portal image acquisition and analysis were different in each institution. Results: The actual distributions of random and systematic deviations without corrections were estimated by eliminating the effect of the corrections. The percentage of mean (systematic) 3D deviations larger than 5 mm was 26% for the AvL and the DDHC, and 36% for the BVI. The setup accuracy after application of the procedure was considerably improved (percentage of mean 3D deviations larger than 5 mm was 1.6% in the AvL and 0% in the DDHC and BVI), in agreement with the results of the simulation. The number of corrections (about 0.7 on the average per patient) was not larger than predicted. Conclusion: The verification procedure appeared to be feasible in the three institutions and enabled a significant reduction of mean 3D setup deviations. The computer simulation of the procedure proved to be a useful tool, because it enabled an accurate prediction of the setup accuracy and the required number of corrections