Technical Considerations in Radiation Therapy for Gastroesophageal Junction Cancer

Incidence of distal and GOJ cancer have doubled over the past few years, mostly adenocarcinomas, and is associated with high mortality. chemoradiation therapy improves survival compared with surgery alone or with neoadjuvant chemotherapy followed by surgery, both in a neo and an adjuvant setting. This articles review technical considerations and data for radiation planning and field design for GE junction malignancies. Sim/CT Patient position is usually= arms placed overhead (ABC, T bar), with knee support underneath the legs for patient comfort. Patients are usually treated in the supine position, although some authors have advocated that patients with mid-esophageal tumor involvement should be simulated in the prone position to maximize distance between the target volumes and spinal cord. Motion of the thorax due to breathing can be monitored via 4D CT and gating, but the clinical benefit of respiratory motion is still not really understood. GTV Endoscopy reports as well as various imaging modalities, including barium swallow, CT, positron emission tomography (PET), and endoscopic ultrasonography (EUS), are useful to determine the gross tumor volume (GTV). PET has emerged as an important tool in staging esophageal and GE junction cancer patients, particularly in detecting occult stage IV disease. PET demonstrated improved accuracy compared with CT (82% vs 64%) for diagnosing patients with stage IV disease. EUS provides accuracy rates of 85%-90% for T stage and 75%-80% for N stage. CTV The extent of microscopic delineation of GOJ is a challenge due to the rich submucosal lymphatic network in both the oesophagus and stomach. A margin of 5 cm above and below the primary GTV is generally recommended to account for subclinical disease spread. Although not well defined, an approximate 1.5- to 2-cm radial margin expansion is recommended from the GTV to the CTV. PTV Intrafraction variations in target location, in large part due to organ motion during the respiratory cycle, or interfraction variability due to stomach filling can lead to variation in position of the CTV, thus PTV margin is added, In general, distal esophageal cancers appear to have greater respiratory motion than more proximal lesions, particularly in the cranial–caudal direction. RT adjuvant- post surgery, the recurrence rates are 30%-40% after R0 resection, thus giving emphasise towards additional adjuvant therapies. 3dCRT vs IMRT = CRT - improved dose conformality around target structures and normal-tissue sparing. IMRT- varying the dose intensity between each area of sub field, using inverse planning to provide steep dose gradients. 3d CRT- general approach is to use an initial anterior-posterior/posterior-anterior (AP/PA) approach with right anterior oblique/left posterior oblique fields to minimize dose to the heart/left ventricle, total dose for GE junction tumors ranges from 45 to 50.4 Gy. significant difference in mean heart dose (22.9 vs 28.2 Gy) and right coronary artery mean dose (23.8 vs 35.5 Gy) in favor of IMRT planning. This article also goes through ranges of OAR tol doses if you want to read more into it. Joseph M. Pepek, Christopher G. Willett, Brian G. Czito, Technical Considerations in Radiation Therapy for Gastroesophageal Junction Cancer, Seminars in Radiation Oncology, Volume 23, Issue 1, January 2013, Pages 51-59 this whole issue is devoted to Gastro-esophageal cancer if u want a look