Abstract
BackgroundTo quantify the incidental irradiation dose to esophageal lymph node stations when irradiating T1-4N0M0 thoracic esophageal squamous cell carcinoma (ESCC) patients with a dose of 60 Gy/30f.MethodsThirty-nine patients with medically inoperable T1–4N0M0 thoracic ESCC were treated with three-dimensional conformal radiation (3DCRT) with involved-field radiation (IFI). The conformal clinical target volume (CTV) was re-created using a 3-cm margin in the proximal and distal direction beyond the barium esophagogram, endoscopic examination and CT scan defined the gross tumor volume (GTV) and a 0.5-cm margin in the lateral and anteroposterior directions of the CT scan-defined GTV. The PTV encompassed 1-cm proximal and distal margins and 0.5-cm radial margin based on the CTV. Nodal regions were delineated using the Japanese Society for Esophageal Diseases (JSED) guidelines and an EORTC-ROG expert opinion. The equivalent uniform dose (EUD) and other dosimetric parameters were calculated for each nodal station. Nodal regions with a metastasis rate greater than 5% were considered a high-risk lymph node subgroup.ResultsUnder a 60 Gy dosage, the median Dmean and EUD was greater than 40 Gy in most high-risk nodal regions except for regions of 104, 106tb-R in upper-thoracic ESCC and 101, 104-R, 105, 106rec-L, 2, 3&7 in middle-thoracic ESCC and 107, 3&7 in lower-thoracic ESCC. In the regions with an EUD less than 40Gy, most incidental irradiation doses were significantly associated with esophageal tumor length and location.ConclusionsLymph node stations near ESCC receive considerable incidental irradiation doses with involved-field irradiation that may contribute to the elimination of subclinical lesions.
Highlights
Radiotherapy has been indicated as a definitive treatment for unresectable or medically inoperable tumors in esophageal squamous cell carcinoma (ESCC) patients
Recent clinical trials employing threedimensional conformal radiotherapy (3DCRT) without intentional elective nodal irradiation have shown the rate of isolate out-field nodal failure was only 2-8% [6,7,8]
The reasons for the discrepancy between the risk of microscopic disease in surgical series and the low incidence of isolate out-field nodal failure in radiation series include but not limited to the following: (1) high incidences of local failure and distant metastases, which may mask regional nodal failure because many patients die before their regional nodal disease becomes clinically apparent, (2) patients undergoing radiation series often have severe co-morbidity such that there may not be enough time for micrometastases to develop into a clinically detectable nodal failure, (3) untreated or inadequately treated micrometastases in the out-field nodes may not result in clinical nodal failures and they may be sources of distant metastases later, and (4) micro-metastases may be adequately controlled by the incidental nodal irradiation
Summary
Radiotherapy has been indicated as a definitive treatment for unresectable or medically inoperable tumors in ESCC patients. In two retrospective studies that included over 1000 patients, ENI (elective nodal irradiation) for esophageal squamous cell carcinoma (ESCC) was suggested because a high lymph node metastasis rate was noted [4,5]. Recent clinical trials employing threedimensional conformal radiotherapy (3DCRT) without intentional elective nodal irradiation have shown the rate of isolate out-field nodal failure (which was defined as a recurrent esophageal lesion and regional nodes that occurred inside the PTV) was only 2-8% [6,7,8]. Greater than 8 cm of normal tissue can exist between the gross tumor and micro-metastatic skip areas secondary to this extensive lymphatic network [9] This phenomenon is inconsistent with the low incidence of isolate out-field nodal failure reported in 3D-CRT studies. To quantify the incidental irradiation dose to esophageal lymph node stations when irradiating T1-4N0M0 thoracic esophageal squamous cell carcinoma (ESCC) patients with a dose of 60 Gy/30f
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