RESUMEN
Purposes: The purpose of this study was to assess the internal rectal movement and to determine the factors related to extensive internal rectal movement using sequential simulation computed tomography (CT) images. Materials and Methods: From 2010 to 2015, 96 patients receiving long-course preoperative chemoradiotherapy were included in our retrospective study. The initial simulation CT (Isim-CT) and follow-up simulation CT (Fsim-CT) for a boost were registered according to the isocenters and bony structure. The rectums on Isim-CT and Fsim-CT were compared on four different axial planes as follows: (1) lower pubis symphysis (AXVERYLOW), (2) upper pubis symphysis (AXLOW), (3) superior rectum (AXHIGH), and (4) middle of AXLOW and AXHIGH (AXMID). The involved rectum in the planning target volume was evaluated. The maximal radial distances (MRD), the necessary radius from the end of Isim-CT rectum to cover entire Fsim-CT rectum, and the common area rate (CAR) of the rectum (CAR, (Isim-CT∩Fsim-CT)/(Isim-CT)) were measured. Linear regression tests for the MRDs and logistic regression tests for the CARs were conducted. Results: The mean ± standard deviation (mm) of MRDs and CAR <80% for AXVERYLOW, AXLOW, AXMID, and AXHIGH were 2.3 ± 2.5 and 8.9%, 3.0 ± 3.7 and 17.4%, 4.0 ± 5.2 and 27.1%, and 4.1 ± 5.2 and 25%, respectively. For MRDs and CARs, a higher axial level (AXVERYLOW/AXMID-HIGH, P = 0.018 and P = 0.034, respectively), larger bladder volume (P = 0.054 and P = 0.017, respectively), smaller bowel gas extent (small/marked, P = 0.014 and P = 0.001, respectively), and increased bowel gas change (decrease/increase, both P < 0.001) in rectum were associated with extensive internal rectal movement in multivariate analyses. Conclusions: As a result of following internal rectal movement through sequential simulation CT, the rectum above the pubis symphysis needs a larger margin, and bladder volume and bowel gas should be closely observed.
RESUMEN
Herein is reported our experience of radiation therapy using a real-time tumor-tracking and gated radiotherapy (RTRT) system for inoperable pancreatic cancer. Three unresectable pancreatic cancer patients were treated with intraoperative electron beam radiation therapy, at the time of open biopsy, and postoperative external beam radiation therapy using an RTRT system with a 2.0 mm diameter gold ball implanted into the pancreas. The total BED's (alpha/beta=10) was intended to be equivalent to that of delivering 60 Gy by 2.0 Gy/fraction, while the actual dose schedules were individualized. The movement of the pancreas was analyzed based on the 3-dimensional marker positions during the RTRT. The side effects and tumor responses were evaluated. During the RTRT course, the average movement of markers in the x (left to right), y (cranial to caudal) and z (dorsal to ventral) directions were 3.0 mm (1.7- 5.2 mm), 5.2 mm (3.5 - 6.8 mm) and 3.5 mm (2.7 - 5.1 mm), respectively. During and after the course of postoperative radiation therapy, no acute side effects of RTOG grade II or higher were detected. The objective tumor responses, as evaluated by CT scans 3 months after the treatment, were 2 partial responses and no response in one patient. Using the RTRT technique the margin of treatment planning and the possible errors in target localization were reduced, and the 3-dimensional movement of the internal marker implanted in the pancreas was able to be analyzed.