Effect of laser therapy on bone tissue submitted to radiotherapy: experimental study in rats.

OBJECTIVE: The aim of this study was to investigate the effect of laser therapy (lambda = 780 nm) on bone tissue submitted to ionizing radiation. BACKGROUND DATA: The biostimulation effect of laser in normal bone tissue has already been demonstrated successfully; however its effect on bone tissue submitted to radiotherapy has not yet been studied. METHODS: Twenty-two Wistar rats were randomly divided into four groups: group I, control (n = 4), submitted only to radiotherapy; group II, laser starting 1 day prior to radiotherapy (n = 6); group III, laser started immediately after radiotherapy (n = 6); group IV, laser 4 weeks after radiotherapy (n = 6). The source of ionizing radiation used was Cobalt 60, which was applied in a single dose of 3000 cGy on the femur. The laser groups received seven applications with a 48-h interval in four points per session of DE = 4 J/cm(2), P = 40 mW, t = 100 sec, and beam diameter of 0.04 cm(2). All animals were killed 6 weeks after radiotherapy. RESULTS: Clinical examination revealed cutaneous erosions on experimental groups (II, III, and IV) starting at the 6th week after radiotherapy. The radiographic findings showed higher bone density in groups II and IV (p < 0.05) compared to the control group. The results further showed an increase of bone marrow cells, and number of osteocytes and Haversian canals in experimental groups II and IV (p < 0.05). It was also found an increase of osteoblastic activity, in groups II, III, and IV (p < 0.05). CONCLUSION: Laser therapy on bone tissue in rats presented a positive biostimulative effect, especially when applied before or 4 weeks after radiotherapy. However, the use of laser in the parameters above should be used with caution due to epithelial erosions.

Long-term changes in the haversian systems following high-dose irradiation. An ultrastructural and quantitative histomorphological study.

The effects of high-dose irradiation on the morphology of haversian bone were studied, over a fifty-two-week period, in seventy-seven adult rabbits, after the administration of a single dose of radiation (therapeutic x-ray; twenty-five, fifty, or 100 gray) to one knee joint. The specimens of bone were examined with microangiography, light and transmission electron microscopy, and histomorphometry. Analysis was performed on the haversian bone in the subchondral bone plate of weight-bearing portions of the femoral condyles. Microangiography demonstrated dilatation of the microvasculature four weeks after irradiation. Beginning at twelve weeks, there was a marked decrease in vascularity; no obvious recovery of the subchondral bone had occurred by fifty-two weeks. At four weeks, morphological analysis revealed two changes in the haversian canals: simple occlusion of the haversian vessels with loss of cells in the canal, and dilatation of the capillaries with abnormal resorption of the perivascular bone matrix by osteoclasts. The abnormal bone resorption was not coupled with subsequent new-bone formation, resulting in increased porosity. Beginning at four weeks, a progressive decrease in the number of haversian vessels and in cellularity became prominent. The decrease in cellularity involved all types of cells, including endothelial cells, pericytes, perivascular mesenchymal cells, osteoblasts, osteocytes, and osteoclasts. The loss of perivascular cells was often but not always associated with occlusion of the haversian vessels. Histomorphometry revealed both time-dependent and dose-dependent decreases in capillary density (the number of intraosseous capillaries per unit area) and in the number of osteocytes in the subchondral bone plate. The porosity of the same areas showed a significant increase by four weeks (p < 0.001 after administration of twenty-five gray and p < 0.01 after administration of both fifty and 100 gray), but between twelve and fifty-two weeks, there was only a slight additional increase. Statistical analysis revealed significant correlations between capillary density and osteocyte survival (p < 0.001) and between capillary density and porosity (p < 0.001). The portion of the subchondral bone plate that was located farthest from the non-irradiated normal bone showed progressive damage and no sign of recovery at fifty-two weeks.

[The pathogenesis of osteoradionecrosis]. / La pathogénie de l'ostéoradionécrose.

The microradiographic analysis of thick sections of fragments removed from irradiated patients suffering from osteoradionecrosis has made it possible to bring to the fore two types of bone resorption caused by cells: an osteoclastic one not followed by a relevant osteogenesis, and another, pathognomonic of postradic complications, linked with an altered activity of the osteocytes. Those cells, which have been affected, because of a progressive infection, are responsible for an irreversible widening of the osteoplasts, set in the properly vascularized bone regions, in particular in the wall of haversian canals. The coalescence of widened osteoplats causes polycylic cavities which is a typical feature of osteoradionecrosis. A third type of bone postradic damage consists in a massive demineralization, related to the presence of saliva or pus.

Radiation dose factors for alpha-emitters in osteons and some considerations on dose non-uniformity ratios and relative distribution factors.

Dose factors for locations within a tissue-filled cylindrical cavity bounded by an infinite medium of bone labelled with an alpha-emitter are calculated by means of a Monte Carlo procedure. The calculational approach is general and allows us to determine dose factors for specific distances or target volumes defined by concentric cylinders, as well as various source geometries including surface sources, buried surface sources, infinite and bounded volume sources, and also comprises plane (trabecular) surfaces as a limiting case. Values for the dose factors and the contribution of cross-fire traversals are calculated mainly for 239Pu and 226Ra and a typical Haversian canal diameter of 30 microns in beagles and 70 microns in humans. Also tables are given that allow dose factors to be derived for the relevant range of alpha-particle energies, diameters and target distances. The dose non-uniformity factors (local dose rate/average skeletal dose rate) for 239Pu are 27.2 in humans and 14.0 in beagles. The corresponding values for 226Ra are in the ranges 1.18-1.26 (humans) and 0.90-0.97 (beagles) for a 222Rn retention between 10-30%. The relative distribution factors 239Pu/226Ra are 21.5-23.0 for humans and 14.5-15.6 for dogs. General expressions for calculating non-uniformity factors and relative distribution factors are derived and implications are discussed in the light of some experimental findings.

Investigations of 90Sr in dogs. I. Pathogenesis of radiation-induced bone tumors.

Purebred beagle dogs given 90Sr and unirradiated controls were studied for over two decades. Pregnant females were fed different doses of 90Sr from day 21 post-conception until the offsprings reached an age of 540 days. In an additional experiment two dose levels were given in a single intravenous dose to dogs 540 days old. Radiographically the earliest skeleton lesions were characterised by small linear, solitary, cortical lucencies. These as well as tumors were more frequently noted in the higher exposure levels. They affected the appendicular skeleton almost as frequently as the axial skeleton. The lesions were predominantly found in the diaphysis, at the angle and near the acetabulum in the tubular bones, mandible and pelvis, respectively. The lesions within the diaphysis originated in the cortical bone. Histologically these lesions were characterised by different types of porosities. These could be empty or filled by a defect and/or immature, dysplastic fibrous repair tissue, within the frame of which malignant transformations seemed to take place as evidenced by malignant clones and micro-osteosarcomas. A comparison is made of the histologic events in dogs and mice and a tentative pathogenesis of 90Sr induced bone tumors is discussed.

Plugged haversian canals and local dose in radium cases.

Haversian canal plugging is a common lesion in bone from human radium cases, signaling vascular damage. Its incidence is correlated with the whole body radium dose. However, since the vascular supply to bone forms an extensive anastomotic plexus facilitating propagation of vascular damage from a primary site of high radium content, we do not know if the degree of plugging is related to the local bone dose. In this report, we compare the incidence of plugging of osteons in different regions (16 sections) of humeri of three radium cases with terminal 226Ra body contents of 0.203, 1.03 and 15.4 muCi to the local dose of radium in adjacent bone sections. While the first and third subjects had received 226Ra only, the second had had a large intake of 228Ra as well. The background incidence of plugging in 35 "normal" humeri from dissecting room populations (45-90 yr) ranged from 0 to 1%, with an average of 0.3%. The least squares linear regression equation for the relation between the percent of canals plugged (PCP) and dose, PCP = (0.00214 +/- 0.00014) rad + (3.26 +/- 3.6), predicts for our three radium cases a development of about 0.002% plugs/rad. The correlation coefficient was very high (r = 0.97, n = 16, P less than 0.01). When normalized to radiation dose from the two decay series, 226Ra and 228Ra appear to be equally effective in producing plugged canals.