Preoperative versus postoperative radiotherapy for locally advanced gastroesophageal junction and proximal gastric cancers: a comparison of normal tissue radiation doses.

Locoregional relapse occurs in over half of gastric cancer patients who undergo potentially curative resection. Adjuvant chemoradiation reduces locoregional relapse, but often requires irradiating large fields and is limited by poor patient tolerance. This study explores the potential dosimetric benefit in reducing the radiation dose to normal structures by treating gastroesophageal (GE) junction/proximal gastric cancers with preoperative rather than adjuvant radiotherapy. Five cases of GE junction/proximal gastric cancer patients treated postoperatively with curative intent were selected. The actual target contours were then modified to reflect hypothetical target volumes which would have been used had the patients been treated preoperatively. Hypothetical preoperative treatment plans were generated for each patient based on these modified contours. The hypothetical preoperative treatment plans were then compared to the actual postoperative plans with respect to dose-volume parameters including lung mean dose, lung V20, heart V20 and V30, and mean doses to abdominal structures. Target volumes were smaller with preoperative treatment, with an average reduction of 23%. Comparative dose-volume histogram (DVH) analysis showed the resultant composite lung doses were reduced in the preoperative plans by 50-79%. In all patients, the proportion of lungs receiving at least 20 Gy (V20) was substantially reduced using preoperative treatment (1.9% vs. 9.7% in the 3-D conformal patient; mean of 3.1% vs. 17.6% in the intensity modulated radiation therapy patients). Likewise, the volume of heart receiving at least 30 Gy was dramatically reduced in all preoperative plans (15.8% vs. 35.4%). Doses to the kidneys, liver and spinal cord were comparable in both approaches. Preoperative treatment of GE junction and proximal gastric cancer patients offers the potential to decrease the radiation dose received by normal thoracic structures.