Re-treatment after full-course radiotherapy: Is it a viable option?

Rr-irradiation of previously treated areas may become necessary for recurre nt cancer, new primary tumours (common in head and neck cancer patients), o r nodal and metastatic disease. Factors that should be taken into account i n the decision to re-treat include: 1) previously treated volume (how much overlap is there with new treatment Gelds) and dose fractionation schedule. 2) which critical tissues or organs are at risk; 3) how much time has elap sed since first treatment; 1) whether there are any practical alternatives to re-irradiation? Rapidly proliferating tissues generally recover well fro m the initial radiotherapy and will tolerate re-irradiation to almost Full doses. Some slowly proliferating tissues are also capable of partial prolif erative and functional recovery, although this takes several months and som e residual damage remains. Preclinical data demonstrate that re-irradiation with reduced doses is possible in lung and spinal cord after intervals of 3-6 months. Other slowly proliferating organs, e.g. the kidneys, do not app ear to be capable of recovery. even after low, subtolerance doses. The larg est clinical experience of re-irradiation is for head and neck cancers. A r eview of this literature reveals that the most frequent normal tissue compl ication seen is trismus (lockjaw), which occurs in 16 to 30% of re-treated cases, with lower incidences of soft tissue or bone necrosis and fibrosis. Myelitis is rarely reported, even in the re-treatment situation. In general the highest incidence of local control for the lowest incidence of serious complications is achieved for combinations of external beam and brachyther apy, and for small, well-differentiated, new primary rumours rather than re current disease. Re-treatment with total doses < 55 Gy gives very poor loca l control rates. Re-treatment schedules with curative intent require a high re-treatment dose, which is accompanied by an increased risk of normal tis sue damage. To minimize serious complications, re-irradiation schedules req uire the best possible treatment planning (conformal therapy where possible ). Hyperfractionation or a combination of external beam and brachytherapy c ould also be beneficial.