Effect of Gastric Filling on Radiation Therapy in Patients with Gastrointesinal Cancer

Abstract

In the treatment of gastrointestinal (GI) cancers, radiotherapy (RT) is frequently delivered with 3-dimensional conformal RT (3DCRT) or intensity modulated RT (IMRT) techniques. These tumors are highly sensitive to neighboring organs’ movement. Differences in gastric or bowel filling may alter the position of target volumes and cause the risk of missing the target volumes and increase the organs at risk (OAR) doses. Thus, it is very important to ensure the same conditions of the patient during simulation and in all RT fractions. In this study, we tried to determine the optimal RT technique (3DCRT or IMRT) in patients with upper GI cancers and investigated the effect of gastric filling (empty-ES vs. full-FS) on target coverage and OARs doses. Ten patients with either gastric (n=5) or pancreatic cancer (n=5), who were treated with adjuvant RT following surgery were included. Two computed tomography (CT) images were taken with ES and FS. The first scan was taken after at least 2 hours fasting. Then the patients drank 1.5 L (50.7 fl oz) of water in 30 minutes and second CT images were taken. Following delineation of target volumes and OARs, 3DCRT [2 different 3 fields (3-field and 3-field 1) and 4-field] and IMRT (5- and 7-fields) plans were generated in each CT images. Firstly, it was evaluated whether there was a difference between planning techniques in terms of ES or FS. Secondly, CT images of each patient including ES and FS were fused and dose volume parameters were analyzed. We also obtained dosimetric measurements with thermoluminescence dosimetry (TLD) and Gafochromic EBT3 films using Alderson rando phantom. Calculations of treatment planning system (TPS) did not indicate a marked difference in target coverage in relation to gastric filling (ES vs. FS) for each planning technique (3DCRT vs. IMRT). As for ES plans best target coverage is achieved with 7-field IMRT for pancreatic cancer and 4-field 3DCRT for gastric cancer. IMRT plans yielded better results concerning OAR doses, especially liver and bowel doses. If patients were treated with FS instead of ES, target volume doses were significantly decreased for both cancers (p=0.043). For 7-field IMRT plans, the differences between TPS calculations and measurements by TLDs and Gafchromic EBT3 films were higher in plans for ES than plans for FS (1.15% - 8.08% and 1.20% - 3.99% for ES whereas 1.49% - 5.49% and 0.65% - 3.34% for FS, respectively) IMRT technique produced better dose distributions than 3DCRT regarding target volumes and OARs. The most important point for the accuracy and reproducibility of the treatment is that the ensuring same gastric filling during the treatment. For this purpose, each center should prepare a suitable treatment protocol, instruct the patient in detail and monitor its implementation. Funded by The Scientific and Technological Research Council of Turkey’s #S115S913 grant.