Because the retreatment dose is usually limited, radiation retreatment using conventional techniques is palliative in many cases (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11), although higher dose potentially curative re-irradiation has been applied in recurrent head/neck, gynecologic, prostate and breast neoplasms (12, 13, 14, 15, 16, 17, 18, 19, 20, 21).  One feature seen in re-irradiation for cure as opposed to palliation appears to be the feasibility of brachytherapy as part or all of the retreatment regimen, suggesting that the application of a more concentrated, high dose of radiation will be more likely to produce long-term disease-free survival or cure where “conventional” radiation has failed (13, 14, 15). In other curative intent retreatment cases, the limited tolerance to additional external beam irradiation is augmented by conservative surgery (12), or the addition of chemotherapy to the regimen, usually delivered concurrently, with occasional long-term survivors reported (16, 17, 18, 19, 20, 21).

When reirradiation +/- chemotherapy is done for cure, the complication list may be formidable, as illustrated by the head/neck retreatment series reported by DeCrevoisier, et al, describing an elevated incidence of severe soft tissue fibrosis, bone and soft tissue necrosis, and fatal carotid hemorrhage (16). Other investigators have also reported formidable head and neck cancer retreatment complications ( 17, 18, 21). Intensity modulated radiotherapy (IMRT) + chemotherapy salvage treatment may have a more favorable retreatment benefit to risk ratio for head and neck cancer relapse patients, presumably reflecting the more favorable dose sculpting characteristics of  IMRT, leading to better sparing of normal tissues compared with conventional techniques ( 19). In the case of salvage brachytherapy as potentially curative treatment of post-radiation recurrent prostate cancer, the risk of incontinence compared to de novo brachytherapy is substantially higher, at 24%, again illustrating the hazard of applying even localized additional high dose radiation therapy after primary radiotherapy relapse (14).

In summary, the scope of radiation relapse situations is varied, and their management challenging.  Due to limited normal tissue tolerance to additional radiation, conventional radiation retreatment is usually palliative, unless an intensification measure such as brachytherapy, chemotherapy or surgery is also possible. When reirradiation is done with curative intent, the risk of complications may be  significantly increased compared with de novo radiotherapy. Due to the wide variety of unique relapse scenarios, published medical literature often provides little guidance in these cases.