Quad-shot RT
tumor
DISEASE, TUMOR
The gross tumor volume will be defined as the primary and/or nodal disease to be targeted. The clinical target volume will be defined as areas at risk of subclinical disease around the gross tumor volume that may be delineated at the discretion of the treating radiation oncologist. The planning target volume will be a 0.3- to 1-cm isotropic expansion from the gross tumor volume or clinical target volume (if present). Each cycle of QS RT will comprise 14.8 Gy in four fractions (3.7 Gy per fraction) delivered twice daily (at least 6 h apart) over two consecutive days before the administration of pembrolizumab. All patients will receive at least one cycle of QS RT; up to three QS cycles may be administered per protocol if deemed appropriate by the treating radiation oncologist. The first administration of QS RT will occur before cycle four (between cycles two and three or three and four) of pembrolizumab. If deemed appropriate by the treating radiation oncologist, a second QS may occur prior to pembrolizumab cycle eight (between cycles six and seven or seven and eight) and a third QS may occur prior to pembrolizumab cycle 13 (between cycles 11 and 12 or 12 and 13). Therefore, the total RT dose over the course of the study will depend on the number of QS RT treatments delivered: 14.8 Gy in four fractions for those who complete one QS RT cycle, 29.6 Gy in eight fractions for those who complete two QS RT cycles or 44.4 Gy in 12 fractions for those who complete three QS RT cycles. Upon planning the initial cycle of QS RT, a composite plan will be generated to assess the total dose to the target and organs at risk. Repeat CT simulation may be performed in order to plan subsequent cycles. QS RT will not be given on the same day as pembrolizumab infusion, and it is recommended to occur no more than 7 days prior to the next pembrolizumab infusion.