whole_HamiltonChrisS1998.pdf (17 MB)
Reflectance spectrophotometry in the assessment of radiation erythema
thesisposted on 2023-05-26, 22:08 authored by Hamilton, CS
This thesis describes the dose response relationships, qualitative and quantitative observations of cutaneous erythema in 236 patients treated on three prospective clinical radiobiological studies, utilising Fractionated Low Dose Rate (FLDR) and Fractionated High Dose Rates (FHDR) external beam radiotherapy. ‚Äö Patients with incurable, locally advanced head and neck cancer and bone and soft tissue metastases from a variety of other solid malignancies, were treated on a modified Caesium 137 teletherapy unit , at dose rates ranging from 0.8 to 8.2 Gy/hr in 10 fractions over 12 to 14 days (FLDR). ‚Äö Patients with bony and soft tissue metastasis from a variety of solid malignancies were treated on a Clinac 1800 (6 MV photons), utilising four fractionation schedules (5, 10, 12 and 20) over 5 to 35 days (FHDR). ‚Äö Patients with localised carcinoma of the prostate were treated on a Clinac 1800 (6 MV photons), in 30 - 32 fractions over 45 to 55 days (FHDR). Skin reactions were quantitatively assessed using a reflectance spectrophotometer and graded qualitatively using a modified EORTC/RTOG grading scale (FLDR). Qualitative skin scoring was unreliable and subject to considerable inter- and intra-observer variation. Qualitative scores were over estimated (relative to reflectance observations) in female patients and at nonUV exposed anatomical sites. Pre-treatment reflectance readings were significantly higher in male patients and in anatomical sites which had previously heavy UV exposure. Pronounced dips in erythema readings during the second week of therapy and \reciprocal vicinity\" effects adjacent to the treatment field undetected by the naked eye were observed in a subset of patients. Peak erythema values were found to provide the best measure of radiation effect. Peak erythema was found to depend on biologically effective skin dose patient age sex and treatment site. Considerable inter- and intrapatient heterogeneity (both before and during treatment) was demonstrated. No dose-rate effect was seen in the FLDR group and a negative dose response relationship was demonstrated for 0.8 Gy/hr patients. FHDR data was under-predicted by the Linear Quadratic model at doses less than 1.5 Gy/fraction. This finding is potentially explained by the \"Induced Repair Model\" of Joiner et al. For doses above 2 Gy/fraction a reasonable fit was obtained giving an a/13 ratio in the range of 4-8 and a repair half time of 0.05- 0.15 hours. This short VA value is not consistent with other reports and may reflect multi-component cellular repair processes. This study also suggests that radiation-induced erythema is not exclusively related to basal cell kill."
Rights statementCopyright 1995 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (M.D.)--University of Tasmania, 1998.