To my knowledge, there is limited data in the setting of lung cancer that informs ipsilateral lung constraints, outside of mesothelioma protocols. One study by Ramella et al., PMID 19619955 described an ipsilateral V20 of 52% and V30 of 39% as predictive of grade 2 or higher pneumonitis for patients...

I have never used an ipsilateral lung constraint for conventionally fractionated lung RT in a patient with two lungs.

No. Unless there is reason to believe that there is a large difference in ventilation/perfusion between the two lungs.

I agree with the other answers. However, in cases where ventilation in the ipsilateral lung is severely compromised due to tumor obstruction, like in the case of a total or near total lung collapse, I apply constraints to the contralateral lung that are similar to those of mesothelioma patients. Oft...