Dose Calculation Accuracy of Radiotherapy Treatment Planning Systems in Out-of-Field Regions

long with chemotherapy and surgery, radiotherapy remains as an important modality in tumor treatment, as it is used to treat approximately 50% of all patients with localized cancer [1-3]. However, the use of radiotherapy inevitably leads to exposing the organs/ tissues that are entirely or partially excluded from the treatment volume [4]. Therefore, out-of-field regions receive dose values due to secondary radiation sources, including scattered radiation from collimators and beam modifiers, photon leakage through the treatment head of the linear accelerator (Linac), and internal patient radiation scattering [5]. In a study by Kase, et al. [6], it was found that the radiation scattering from patient is the main cause of dose near the edge of treatment field, while the leakage radiation has the main contribution at large distances from the edge of treatment field. Although dose value in out-of-field region is smaller than that in-field region, these doses can induce secondary malignancies with a long-latency period (particularly in radiosensitive tissue/organs) [7-8]. Furthermore, knowledge of the peripheral dose can be of very interest when considering radiation therapy for patients with pregnancy or patients with cardiac pacemaker. Therefore, accurate measurement of the peripheral dose to normal tissue outside the target volume is essential, to have an adequate clinical decision for patients with implanted electronic devices or pregnant patients as well as more accurate estimation of the radiation-induced secondary cancer risk.