How do you approach external beam RT to the thyroid bed for resected recurrent thyroid cancer in a patient with previous history of 150mCi of radioactive iodine?  

This is a terrific question and speaks to ALARA; I know of no data or dosimetric capacity to accurately estimate a biological effect (dose-wise) from an unsealed radiopharmaceutical on OAR. Keep in mind that dose limits for I-131 are due more on bone marrow toxicity than local effects. Previously, ...

I think the first question is, would you sacrifice target coverage? Without knowing the specifics of the case...I highly doubt you would. Working from there, you can't go wrong with minimizing the dose to cervical esophagus.  This is a different situation from a spinal cord that received EBRT...

I have not considered prior RAI a contraindication or complicating factor when planning. Would use routine conventionally fractionated normal tissue constraints, with a close eye on optimization to make sure OARs with potential prior RAI dose are being kept ALARA (which is good practice anyway), but...

The absorbed radiation dose with 150 mCi as suggested by this study, which used several techniques to model the absorbed dose, to surrounding structures of interest are probably on the order of 200 - 400 cGy (Shahbazi-Gahrouei and Ayat, PMID 25709539). Although measurements of absorbed dose have the...

Ignore the RAI.