Adaptive off-line protocol for prostate external radiotherapy with cone beam computer tomography
- PDF / 777,017 Bytes
- 7 Pages / 595.276 x 790.866 pts Page_size
- 99 Downloads / 178 Views
radiation therapy is routinely used in radical treatment of prostate cancer. Several studies have shown that dose escalation may improve the clinical outcome of prostate radiotherapy [8]. Dose escalation almost inevitably leads to increasing probability of rectum injury unless technologically advanced techniques are used. For a given total dose, the dose delivered to the rectum depends on the margin between the clinical target volume (CTV) and the planning target volume (PTV). In general, the smaller the margin, the smaller the rectum dose. The CTV–PTV margin depends on target motion, patient setup, and target delineation uncertainty. To reduce the CTV– PTV margin required for setup errors and organ motion, several adaptive radiation therapy protocols have been introduced. For compensation of the setup uncertainty the Shrinking Action Level or No Action Level protocols are widely used [1, 3]. In centers where these protocols are implemented, the typical CTV–PTV margin is 1.0 cm. However, some reports suggest larger margins should be added, especially if extracapsular invasion of tumor is suspected [15]. Further diminishing the CTV–PTV margin requires controlling of the prostate movement in relation to bony structures. New radiotherapy technologies introduced in the late 1990s enabled measuring the interfraction of prostate movement. These were computer tomography on rails installed in the treatment room and cone beam computer tomography systems (CBCT) [7, 10, 11, 12]. Using these technologies, the first adaptive strategies were introduced. According to these
M. Piziorska1 · P. Kukołowicz1 · A. Zawadzka1 · M. Pilichowska2 · P. Pęczkowski2 1 Medical Physics Department, Center of Oncology, Warsaw 2 Radiotherapy Department, Center of Oncology, Warsaw
Adaptive off-line protocol for prostate external radiotherapy with cone beam computer tomography
strategies, the treatment was initiated with a conventional CTV–PTV margin, e.g., 1 cm [6]. Next volumetric imaging was performed during the first few fractions (first 4–6 fractions). Based on the image data, the average CTV was defined, and a new adapted plan was prepared with a smaller CTV–PTV margin. If this adaptive protocol was used, the typical CTV– PTV margin was 0.7 cm in each direction. Only systematic error is corrected in these strategies. In Munich where helical tomotherapy is used supported by the daily megavoltage computerized tomography prior to irradiation the CTV–PTV margin is decreased to 3 mm in all directions and to 5 mm in the craniocaudal direction [4]. In the newest adaptive procedures, online techniques were implemented. They enabled compensation of both systematic and random errors. In these techniques, the position of the prostate is identified by the position of the gold markers inserted into the prostate gland [2]. Using this method, the CTV–PTV margin was decreased to 0.5 cm (0.3 cm dorsally) in Charité–University of Berlin [5]. Nearly continuous localization of prostate in relation to the machine isocenter may be obtained with electromagnetic act
Data Loading...
