Esophageal gel-shifting technique facilitating eradicative boost or reirradiation to upper mediastinal targets of recurrent nerve lymph node without damaging esophagus
A 73-year-old male patient with chronic cardiac dysfunction was referred for radiotherapy of a single metastasis to right RNLN. He had been diagnosed 3 years earlier with intrathoracic lower esophageal squamous cell cancer, and underwent esophagectomy with lower mediastinal and abdominal lymph nodal dissection under thoraco-laparotomy with left-sided intra-thoracic gastric tube reconstruction for stage IV, pT3N4M0. Lymph nodal dissection was not performed in the upper mediastinum because of underlying cardiac failure. Six months after the surgery, FDG-PET revealed lymph node relapse in the paraaortic and subcarinal region, and he received 64 Gy of external beam irradiation in 2-Gy fractions for 6 weeks and 4 days. Three months before the referral, right RNLN metastasis was detected close to the esophagus (Fig. A). Because this area had been involved in the previous prescribed field of 42 Gy, external beam retreatment was not considered.\nThe size of the tumor had continued to increase during the period until brachytherapy (Fig. B). The prepared gel was injected, and pooling of the gel and the shifting effect were confirmed on X-ray CT imaging (Fig. C). We prescribed 18 Gy in one fraction (42.0 GyELQ2, α/β=10) to 80% of the PTV volume (Fig. D), with 16 Gy (60.8 GyELQ2, α/β=3) of tracheal D2cc and 6.8 Gy (13.3 GyELQ2, α/β=3) of esophageal D2cc (Fig. A). The previous irradiated dose to the corresponding area was 20 Gy. In a simulation without gel shifting, D2cc of the esophagus was calculated as 15 Gy (31.3 GyELQ2, α/β=3). The enhancement factor for gel shifting was calculated as 2.34 (31.3 GyELQ2, α/β=3/13.3 GyELQ2, α/β=3) for D2cc, and 3.72 (65.6 GyELQ2, α/β=3/17.6 GyELQ2, α/β=3) for D1cc. Thus, accumulated esophageal D2cc and D1cc were 51.3 Gy and 85.6 Gy without gel shifting, which decreased to 33.3 Gy and 37.6 Gy, respectively, after gel injection (Fig. B).