Comparative Analysis of Dose Distribution and Acute Toxicity with Intensity Modulated Radiation Therapy (IMRT) vs. Conventional Radiation Therapy in Gastric Carcinoma

Abstract

In the past decade, major change in the management of gastric carcinoma was brought about by the results of the Gastrointestinal Intergroup Trial that incorporated the role of adjuvant chemoradiation but at the expense of increased hematological and gastrointestinal toxicity. The aim of this study was to assess the efficacy of IMRT in reducing this toxicity. This is a retrospective analysis of 30 patients of gastric carcinoma (T3-4\N+) who received adjuvant chemoradiation at our institute. Most patients underwent radical total gastrectomy with D2 resection and received chemotherapy by the Mayo's regimen. Among these 15 patients underwent IMRT, and the other 15 received conventional radiation. Conventional radiation was done using three fields (Anterior and two wedged lateral pairs) to a dose of 45-50Gy in 25-28 fractions over 4.5-5 weeks. IMRT was delivered using 5-7 co-planar beams. The clinical target volume (CTV) encompassed the gastric bed, perigastric extension & the draining lymph nodes. Diagnostic scans, surgical clips and endoscopy findings guided CTV delineation. Planning target volume (PTV) was created with 1cm expansion in axial planes and 1.5-1.8 cm in craniocaudal direction, as per the diaphragmatic excursion. Dose of 45-50 Gy was prescribed to the 95% of the volume of CTV. Dosimetric comparison was done using DVH of both the groups. The mean doses received by the 33%, 50% and 66% of the volumes of organs at risk (OAR) were compared by the independent sample t - test. The clinical data was reviewed for the acute toxicities, which were graded according to the CTC version 3.0. IMRT reduced the mean doses to all the OAR's (kidneys, liver, small bowel & spinal cord) but it was statistically significant only for the small bowel, liver and spinal cord. Mean doses received by 50% of small bowel was 28.52Gy and 42.08Gy for IMRT and conventional radiation therapy groups respectively (p = 0.00). The corresponding doses for the liver were 18.04Gy and 31.88Gy respectively (p = 0.01). The Dmax to the spinal cord in both the groups were 30.61Gy and 45.04Gy respectively (p = 0.00). Acute toxicities were higher in the patients who underwent conventional radiation, with 11 (73 %) patients experiencing grade 2-3 gastrointestinal toxicity and 5 (33%) hematological toxicity. In the IMRT group, 2 patients (13%) had grade 2 gastrointestinal toxicity and 4 (26%) had grade 2 hematological toxicity. There was a significant reduction in the radiation doses to the OAR's with IMRT, which was reflected in the lesser acute toxicities seen in that group. This encouraging correlation can improve the tolerance of patients to chemoradiation which in turn can translate into better locoregional control and survival.