MUCOSAL REGENERATION DURING RADIOTHERAPY

Background and purpose: Regeneration of the aerodigestive mucosa is kn own to occur during conventionally fractionated radiotherapy. The circ umstances surrounding its time of onset and magnitude are not well und erstood, however. Material and methods: Mucosal reactions were observe d in 100 patients undergoing conventionally fractionated treatment at 2 Gy/day over 7 weeks and 88 receiving accelerated treatment 1.8 Gy tw ice daily over 3(1/2) weeks on the Trans Tasman Radiation Oncology Gro up head and neck cancer trials. Similar observations in 61 patients tr eated palliatively at dose rates between 0.8 and 240 Gy/h using ten 3. 0-4.2 Gy fractions over 2 weeks are compared. Results: Several finding s emerged from these studies: 1. Reactions evolved more quickly at oro pharyngeal sites than in the hypopharynx. 2. Reactions at both sites e volved more rapidly at greater rates of dose accumulation. 3. The timi ng of reactions suggested the presence of a strong regenerative mucosa l response that started before the manifestation of 'patchy' (grade II ) mucosal reactions, 4. The regenerative response was strong enough to 'make good' damage accumulated at a rate of 2 Gy/day in over a third of cases. 5. The linear quadratic model without time correction failed to provide an adequate prediction of the frequency or intensity of mu cosal reactions produced by any of the regimes. A simple model of the regenerative response is presented. Conclusions: This study suggests t hat the timing and magnitude of the regenerative response vary between sites and individuals but are linked to the amount of epithelial cell ular depletion occurring during treatment.