In treating bladder cancer, which nodes should the treatment field include?

When treating bladder cancer, the inclusion of the obturator, external, and internal iliac nodes in the treatment field is essential due to the typical lymphatic drainage patterns associated with the bladder. The bladder's primary lymphatic drainage routes lead to these nodal regions.

The obturator nodes are particularly critical as they are the first echelon of lymph nodes receiving drainage from the bladder. Additionally, the external and internal iliac nodes serve as significant sites for metastasis in bladder cancer, particularly as the disease progresses. Involving these nodes increases the likelihood of effectively treating potential micrometastases that may not be clinically apparent.

The other nodal groups listed in the answer choices may contribute to lymphatic drainage, but they either do not encompass the most relevant areas or do not adequately capture the primary drainage routes. Therefore, the combination of the obturator, external iliac, and internal iliac nodes represents the most comprehensive approach in targeting possible metastatic spread in bladder cancer.