Absorbed Energy Dose Research Articles

The device forlight therapy with absorbed energy dose measuring

Light therapy conducting always connected with need to set optimal intensity of irradiating signal, modulation frequency and exposure. The better option is determination of dose absorbed by patient skin surface and frequency of the maximal absorption. At the same time the dose of falling signal energy is measured to protect patient from harmful effects (e.g. burns) of laser radiation. The authors developed a structural scheme of the device for light therapy and proposed an algorithm for converting and measuring signals by high-sensitive optical modulation radiometer. The scheme provides patient irradiation, measuring the dose of the absorbed energy in the irradiated areas of human body, for example, biologic active point, and determination of the maximal absorption frequencies. It increases the efficacy of the therapeutic procedure and allows to predict the result of treatment.

“Green” molecular weight degradation of chitosan using microwave irradiation

Chitosan degradation in 0.1 M acetic acid solution by microwave radiation alone (without any additives and initiators) is reported. At the condition of reduced thermal effects of microwave heating degradation manifested most of typical features associated with mechanical (and or mechanochemical) degradations induced by shear forces, in this particular case oscillating molecules. At the absorbed energy dose of 9 MJ kg−1 chitosan in 1% w/v solution degrades within 20 min to the weight average molecular weight of 30 kDa.Comparative evaluation of degradation yield of chain scission (Gs) with other high energy radiations such as ultraviolet- and gamma radiation showed microwave to be the least efficient, but considering the environmental impact and low running costs it presents a viable alternative to obtain targeted molecular weights of charged polysaccharides.

Experimental simulation and theoretical analysis of the thermal deformation of dielectric plates under submicrosecond radiation heating

The flexural deformation of dielectric plates subjected to submicrosecond thermal stresses generated by volume and surface sources is studied. The action of such stresses is simulated by laser irradiation of colored glass plates with different optical absorption factors. Such an approach to simulating the thermomechanical action of radiation on dielectric materials allows researchers to visualize the qualitative and quantitative thermoelastic response of the plates to the action of pulsed sources of thermal stresses with different spatial parameters. For volume sources of thermal stresses, it is shown that the thermal deformation of a dielectric plate can be viewed as a set of quasi-harmonic extension-compression wave processes combined with the quasi-static bend of the plate. Under the action of surface sources of submicrosecond thermal stresses, the deformation mechanism is a superposition of the thermal deformation of a thin surface layer and a pulse wave process resulting in the bend of the plate when the pulses reverberate between the surfaces of the plate. Approximate analytical models of thermal deformation due to pulsed thermal disturbances are suggested that make it possible to predict the extent of bend versus the absorbed energy dose under the action of both volume and surface sources of thermal stresses.

The influence of non-radioactive iodine (127I) on the outcome of radioiodine (131I) therapy in patients with Graves’ disease and toxic nodular goitre

The aim of the study was to achieve an effective target dose in the thyroid by increasing the effective half-life (Teff) of (131)I by use of iodide ((127)I) two days after (131)I therapy in patients with hyperthyroidism with low Teff. The study was carried out in two groups. Group A - 41 patients, and Group B - 14 patients, all the patients were with hyperthyroidism with Teff less than 3 days qualified for (131)I therapy. Only group A patients received 600 μg of iodide a day for 3 days, two days after (131)I therapy. Radioiodine uptake (RAIU) after 24 and 48 hours, thyroid scintiscan and ultrasonography were done before and after 12 months of (131)I therapy. In group A a significant increase was seen in the Teff (5 days on average) resulting in an increase in the energy target dose by 28% and 37%, in patients with Graves' disease (GD) and toxic nodular goitre (TNG), respectively. After one year of therapy 50% of GD and 93% of TNG patients achieved euthyroidism; 28% of GD and 3% of TNG patients were in hypothyroidism. In Group B, all the patients had radioiodine treatment failure and received a second therapeutic dose of (131)I. Administration of (127)I after (131)I treatment can lead to an increase in its effective half-life. This will also increase the absorbed energy dose in thyroid tissue, thereby improving therapeutic outcome without administration of a higher or second dose of (131)I. This may minimize whole-body exposure to radiation and reduces the cost of treatment.

Radioiodine therapy and thyrostatic drugs and iodine.

Radioiodine therapy is now the most common definite treatment for persistent hyperthyroidism. The outcome of radioiodine therapy depends mainly on the absorbed energy dose in the diseased thyroid tissue. The administered activity and the resulting target dose in the thyroid depend on both the biokinetics of radioiodine and the actual therapeutic effect of radioiodine in the thyroid. Thyrostatic drugs have a major influence on the kinetics of radioiodine in the thyroid and may additionally have a radioprotective effect. Pre-treatment with thyrostatic medication lowers the effective half-life and uptake of radioiodine. This can reduce the target dose in the thyroid and have a negative influence on the outcome of the therapy. Discontinuation of medication shortly before radioiodine administration can increase the absorbed energy dose in the thyroid without increasing the whole-body exposure to radiation as much as would a higher or second radioiodine administration. Furthermore, administration of non-radioactive iodine-127 2-3 days after radioiodine administration can also increase the effective half-life of radioiodine in the thyroid. Thus, improving the biokinetics of radioiodine will allow lower activities to be administered with lower effective doses to the rest of the body, while achieving an equally effective target dose in the thyroid.

Characterization of radioiodine therapy failures in Graves’ disease

Summary Aim of this study was a characterization of radioiodine therapy (RIT) failures in Graves’ disease without simultaneous Carbimazole. Method: 226 patients with a confirmed diagnosis of Graves’ disease received 686.8 ± 376.4 MBq of iodine-131 orally for thyroid ablation. Target dose was 250 Gy. All patients were followed up for 6 months. Therapy failures were compared with successes regarding possible influencing variables initial thyroid volume, thyroid function, immune activity (TRAb), 1-131 uptake, effective half-life, absorbed energy dose, age and gender. Results: 212 of 226 patients (93.8%) were treated successfully, 14 (6.2%) showed a hyperthyroidism relapse within 6 months which required a second radioiodine therapy. A success rate of 92.5% (62/67) could also be achieved with 67 patients who were hyperthyroid at the time of RIT. Compared to the therapy successes, the 14 failures achieved significantly lower absorbed doses (223.8 ±76.6 Gyvs. 285.2 ±82.1 Gy, ρ <0.005), but with no significant differences regarding age, thyroid volume, function or TRAb (all ρ >0.2). Of the 14 failures, η = 8 reached an absorbed dose <200 Gy and η = 1 a dose <250 Gy, although 5 of the failures reached an absorbed dose of >250 Gy. Stepwise logistic regression revealed only absorbed energy dose as a variable significantly influencing therapy success (p <0.005), but no influence of initial thyroid volume, function, TRAb value, age (all ρ >0.2) or gender (p = 0.13). Two-tailed Fisher’s exact test showed no significant influence of gender on success rates (failures/successes: male 1 /36, female 13/176, ρ = 0.48). Conclusions: Except for the absorbed energy dose, no other significant variable influencing the outcome of radioiodine therapy in Graves’ disease without simultaneous Carbimazole could be found. It should be noted, though, that 5 therapy failures (2.2%) reached an absorbed energy dose of >250 Gy.

Does thyroid stunning exist? A model with benign thyroid disease.

With regard to the treatment of differentiated non-medullary thyroid carcinoma, there is controversy over whether radiation from a diagnostic radioiodine (131I) application really does have a suppressive effect on the uptake of subsequent therapeutic 131I (so-called thyroid stunning). However, inherent difficulties in exact remnant/metastatic tissue volumetry make it difficult to quantify how much diagnostic 131I is actually absorbed (absorbed energy dose) and hence to decide whether a threshold absorbed dose exists beyond which such stunning would occur. Since in benign thyroid disease the target volume can be readily quantified by ultrasonography, we sought to determine definitely whether stunning of thyroid cells occurs upon a second application of radioiodine 4 days following the first one. We therefore studied 171 consecutive patients with benign thyroid disease (diffuse goitre, Graves' disease, toxic nodular goitre) who received two-step 131I therapy during a single in-patient stay. For application of both calculated 131I activities we performed kinetic dosimetry of 131I uptake, effective half-life and absorbed dose. At the second application, patients showed significant stunning (a 31.7% decrease in 131I uptake, from 34.7% +/- 15.4% at first application to 23.7% +/- 12.3% at second application, P < 0.0005) without a significant difference in effective half-life (4.9 +/- 1.3 vs 5.0 +/- 1.7 days, P > 0.2). ANOVA showed that the extent of stunning was influenced significantly only by the absorbed energy dose at first application (F = 13.5, P < 0.0005), while first-application 131I activity, target volume, gender and thyroid function had no influence (all F < or = 0.71, all P > 0.4). There was no significant correlation between extent of thyroid stunning and first-application 131I activity ( r = 0.07, P > 0.3), whereas there was a highly significant correlation between thyroid stunning and first absorbed energy dose (r = 0.64, P < 0.00005), the latter correlation fitting a logarithmic model best. Multivariate factor analysis also revealed first absorbed energy dose to be the only decisive stunning factor. In conclusion, our study confirms that stunning exists in benign thyroid conditions and that it is a purely radiobiological inhibitory phenomenon related to absorbed dose.

Success rate of radioiodine therapy in Graves' disease: the influence of thyrostatic medication.

There is controversy whether simultaneous thyrostatic medication influences the outcome of radioiodine (131I) therapy in Graves' disease by reducing the absorbed energy dose of 131I when delivering a standard dose. We therefore sought to ascertain whether the outcome of ablative 131I therapy is in any way affected by simultaneous thyrostasis (carbimazole) by aiming for a constant absorbed dose of 200-250 Gy. We prospectively studied 207 patients with Graves' disease (106 with and 101 without simultaneous carbimazole at the time of 131I therapy). All patients were reexamined 3, 6, and 12 months after 131I therapy. The 101 nonthyrostatic patients showed a highly significantly greater success rate (93%) than the 106 thyrostatic patients (49%). Stepwise logistic regression demonstrated that failure was related to the administration of carbimazole during 131I therapy (P < 0.00005) and the absorbed dose (P < 0.025), but was not related to free T3, free T4, TSH receptor antibodies, or thyroid volume. The success rate was 100% in 93 nonthyrostatic patients with absorbed doses of 200 Gy or more, but was only 12.5% (1 of 8) for absorbed doses less than 200 Gy. Correlation between success and absorbed dose was significantly higher for nonthyrostatic than for thyrostatic patients (r = 0.93 vs. r = 0.24). Sixteen patients who discontinued thyrostasis 1-3 days before 131I therapy showed 94% successes. Simultaneous thyrostasis is the decisive factor against a successful 131I therapy even if the significantly reduced 131I uptake/half-life values under thyrostasis are compensated with a higher delivered dose to ensure a comparable absorbed dose, possibly due to the additionally effective radioprotective properties of carbimazole. Therefore, if clinically feasible, we recommend discontinuing thyrostasis at least 1 day before beginning 131I therapy, because even in hyperthyroid nonthyrostatic patients the success rate was 100%.

SYSTEMS APPROACH OF THEORETICAL MODELS IN RADIOBIOLOGY AND RADIOTHERAPY

Most of theoretical models encountered in radiobiology and radiotherapy use the absorbed energy dose (d) as the reference variable. By taking account of the nature of the elementary transformations which occur at molecular level in irradiated systems, it is shown that D is generally not a suitable variable, and that it is preferable to use a formalism in which the variables of radiation spectrum and intensity, and the time variable, are explicity separate. In parallel with the selection of suitable variables, a topological representation in the form of transformation graphs provides a clear schematization of the various processes and their respective roles. This representation, which includes physical, chemical and biological phenomena, clearly shows both the level of observations and the level of hypotheses. When searching for particular models one must first take into account the phenomenological requirements resulting from the observations which can be made, before introducing any complementary hypothe...