%0 Journal Article
%T Optimal Planning Target Volume Margins for Elective Pelvic Lymphatic Radiotherapy in High-Risk Prostate Cancer Patients
%A Benjamin K. Hinton
%A John B. Fiveash
%A Xingen Wu
%A Michael C. Dobelbower
%A Robert Y. Kim
%A Rojymon Jacob
%J ISRN Oncology
%D 2013
%R 10.1155/2013/941269
%X Purpose. High-risk prostate cancer patients often receive radiotherapy (RT) to pelvic lymphatics (PLs). The aim of this study was to determine the safety margin around clinical target volume for PL (PL-CTV) to construct planning target volume for PL (PL-PTV) and for planning elective PL irradiation. Methods and Materials. Six patients who received RT to PL as part of prostate cancer treatment were identified. To determine average daily shifts of PL, the right and left IVs were contoured at 3 predetermined slices on the daily MV scans and their daily shifts were measured at these 3 levels using a measuring tool. Results. A total of 1,932 observations were made. Daily shifts of IV were random in distribution, and the largest observed shift was 13.6£¿mm in lateral and 15.4£¿mm in AP directions. The mean lateral and AP shifts of IV were 2.1£¿mm (¡À2.2) and 3.5£¿mm (¡À2.7), respectively. The data suggest that AP and lateral margins of 8.9£¿mm and 6.5£¿mm are necessary. Conclusions. With daily alignment to the prostate, we recommend an additional PL-CTV to PL-PTV conversion margin of 9£¿mm (AP) and 7£¿mm (lateral) to account for daily displacement of PL relative to the prostate. 1. Introduction High-risk status in prostate cancer as defined by T stage, Gleason score, or presenting PSA confers a high probability of extraprostatic and lymphatic spread of cancer [1]. Radiotherapy (RT) in conjunction with neoadjuvant and concurrent long-term androgen suppression has been demonstrated to improve outcomes in such patients [2, 3]. The role of irradiating the pelvic lymphatics (PLs) is controversial [4, 5]. However, current NCCN guidelines suggest that patients with high-risk prostate cancer are candidates for RT to prostate, seminal vesicles, and PL. Technological advances have allowed for higher doses to be delivered to the target, while minimizing the potential for interfraction variations which could result from positioning errors or organ motion [6¨C10]. During IGRT of high-risk prostate cancers, image guidance is accomplished by aligning the prostate contour with the daily image of the prostate. Though there is potential for day-to-day movement of the PL relative to the prostate, the PL field is not subjected to daily imaging for a number of reasons. Most RT institutions make use of radioopaque fiducials implanted within the prostate gland and daily kV orthogonal imaging for image guidance. Even when imaging systems such as cone-beam CT is available, the whole pelvis is not imaged daily as the procedure is time consuming and exposes the patient to unnecessary radiation.
%U http://www.hindawi.com/journals/isrn.oncology/2013/941269/