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26 Lasers Technology | Progress Report
Photodynamic therapy of skin cancer change on the amide II band (1580-1480 cm ),
−1
which indicates that gamma radiation induced
Photodynamic therapy (PDT) has become a changes on helical structure of collagen, and
promising alternative for treatment of skin these changes have a direct relation with
lesions such as squamous cell carcinoma. We the dose, however it does not interfere in the
propose a non-invasive method to monitor inorganic matrix of bone, since the content
the effects of PDT by using the optical atten- of carbonate was not altered after gamma
uation coefficient (OAC) calculated from opti- irradiation. The crystallinity index is useful
cal coherence tomography (OCT) images. We for evaluating the order, organization and
conducted a study on mice with chemically tension of the hydroxyapatite crystals. Crystal
induced neoplastic lesions and performed PDT growth and crystallinity of hard tissues can
on these lesions using local developed photo- be affected by factors such as the maturity
sensitizers cream (PI 0705591-9). The response degree of tissue or even due to the increase
of neoplastic lesions to therapy was monitored on its temperature. Our results evidenced
using, at the same time, macroscopic clinical that low doses of gamma radiation (0.01 kGy)
visualization, histopathological analysis, OCT decreases the crystallinity of bone; however
imaging, and OCT-based attenuation coef- doses higher than 0.1 kGy, did not promote
ficient measurement. Results with all four significant changes on the crystallinity index
modalities demonstrated a positive response when compared to the non-irradiated samples.
to treatment. The attenuation coefficient was In this way, we can infer that low doses of
found to be 1.4 higher in skin lesions than in gamma radiation have a significant effect on
healthy tissue and it decreased after therapy, the crystal characteristics of hydroxyapatite
demonstrating that the OAC is a potential tool from the bone and this effect, together with
to noninvasively assess the evolution of skin the effect on collagen secondary structure,
neoplastic lesions with time after treatment. can be the main reason for the changes on
the mechanical properties on sterilized bone
Effects of ionizing radiation (Co ) showed on literature.
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on biological hard tissues
Prevention of dental caries with lasers
Ionizing radiations, such as X-ray or Gamma
radiation, are well-recognized as effective Dental caries are a common oral disease which,
treatment and diagnostic methods for ma- viewed simply, is characterized by a deminer-
lignant diseases, as well as for sterilization alization of the dental hard tissue caused by
of tissues. However, these radiations can acids generated in the oral biofilm. Although
chemically alter the target tissue, and these a remarkable decline in the incidence of den-
changes can affect morphology, crystallinity, tal caries worldwide has been documented,
healing and mechanical properties of irradiat- it is still the most prevalent disease during
ed tissues, mainly considering enamel, dentin childhood and adolescence. On account of the
and bone. Bone samples were irradiate with widespread use of fluoride, lasers have been
0.01 kGy, 0.1 Gy and 1kGy a Co Gammacell tested to improve dental enamel properties in
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irradiator (1.43 kGy/h) while the irradiations order to enhance its resistance to demineral-
with 15kGy and 75kGy were performed at Co ization. We evaluated the effect of combining
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multipropose irradiator (6.0 kGy/h). ATR-FTIR laser irradiation (Nd:YAG and Er,Cr:YSGG) with
spectroscopy analysis showed a significant fluoride on an enamel microstructure and de-
Instituto de Pesquisas Energéticas e Nucleares
