No abstract available

No abstract available

[en] In June 1975, the General Conference on measures and weights has internationally introduced the names of unit Gray for the activity of a radioactive substance. The reasons for this change - the valid units so far were Rad and Curie - and the international activities with regard to a general acceptance of these new units are reported on. (orig./AK)

No abstract available

[en] The research of the distribution of the absorbed dose along the perimeter and length of the polymer protective sheath on the basis of a halogen-free composition depending on the technological dose of radiation exposure of shipboard cable samples was performed. It has been established that irregularity of irradiation around the cable perimeter can reach 20…30% with a technological dose in the range of 1.25…0.5. The irradiation along the cable is more uniform and does not exceed 5% at a technological dose in the range of 1.25…0.567. With a reduction in the technological dose, the irregularity of radiation around the perimeter and length of the cable increases. It is established that with an average absorbed dose of 210 kGy, the protective polymer shell does not meet the requirements of the standard for relative elongation at break. Optimal and physical-mechanical characteristics of the polymer shell made of halogen-free material are provided under irradiation in the range of the absorbed dose of 160 to 170 kGy. (author)

No abstract available

[en] A sliding-window (SW) methodology for VMAT dose calculation was developed. For any two adjacent VMAT control points (CPs) n and n+1, the dose distribution was approximated by a 2-CP SW IMRT beam with the starting MLC positions at CP n and ending MLC positions at CP n+1, with the gantry angle fixed in the middle of the two VMAT CPs. Therefore, for any VMAT beam with N CPs, the dose is calculated with N-1 SW beams. VMAT plans were generated for ten patients in Pinnacle using 4° gantry spacing. For each patient, the VMAT plan was converted to a SW IMRT plan and dose was re-calculated. Another VMAT plan, with 1° gantry spacing, was created by interpolating the original VMAT beam. The original plans were delivered on an Elekta Versa HD and measured with Mapcheck2 using an in-house developed subarc method. For both the isodose distribution and DVH, there were significant differences between the original VMAT plan and either the SW or the interpolated plan. However, they were indistinguishable between the SW and interpolated plans. The average passing rate between the original VMAT plan and measurements was 84%. For both the interpolated and SW plans, the average passing rate was 96%. We conclude that the proposed SW approach improves VMAT dose calculation accuracy without increase in dose calculation time. (paper)

[en] Full text: IMRT planning supposes us to use as large amount of fields and field segments with complex shapes and segments with screened isocentre. This involves certain demands to the treatment planning system (TPS) dose calculation algorithm and brings us to a necessity of additional control. While introducing IMRT into practice we encountered some problems. In our Center we have the linear accelerator Elekta Precise Digital with 1 cm at isocentre MLC, TPS Precise Plan with facility to create IMRT plans, and standard dosimetric equipment: water and solid water phantoms, Keithly dosimeter with ionization chamber and a set of radiographic films. With the advent of the ability to create sophisticated dose distributions, requirements on accuracy of target and definition of critical structures increased. To combine the CT, MRI, PET, etc. data one needs special fusion programmes. Such programmes can be delivered by a TPS vendor or sold separately. In addition to the dose to point prescription dose-volume constrictions for target and critical structures appeared. They are described by so-called cost function. Dose in a point of beam intersection may differ from dose in point of prescription. For example, ICRU 2008 recommends prescribing dose to a volume rather them to a point. This mismatching may need special attitude, perhaps specific forms of delivered dose registration. We have created a set of tests to check parameters of TPS important for IMRT. Fields with narrow fragments are often used in IMRT planning. Collimator scattering contribution increases in this case. The difference between absolute dose calculations and measurements was no more than 4%. The next problem concerned the TPS ability to calculate dose distribution from screened isocentre fields correctly. This is because dose distribution is usually calculated relative to isocentre dose, which in this case is negligibly small and consequently uncertain. We verified that TPS calculation agreed well with measurement. The difference was less than 1% in simple geometries and up to 5% in complex geometries with heterogeneity. To apply an IMRT plan to a patient, one needs to verify it beforehand. As a patient-specific test we chose to perform absolute dose measurements in several critical points for single multisegment field and total dose measurements in water phantom in vertical and horizontal mode for all beams. Good agreement of calculation and measurements led us to transit from 2-D to 3-D conformal radiotherapy and to begin introducing IMRT in our clinical practice. To use IMRT in clinical practice more extensively, we need to work out a patient-specific QA protocol. In spite of the absence of required equipment and software for this QA we consider the use of IMRT in clinical practice possible because we made a basic set of tests. (author)

[en] Objective: In radiotherapy, it is important to conform the high dose volume to the planned target volume. A variable thickness paired wedge filter system was developed to compensate for dose inhomogeneity arising from field width segment variation in conformal irradiation. Materials and methods: The present study used a 6 MV linear accelerator equipped with multileaf collimator leaves and a paired wedge compensating filter system. The dose variation due to field width was measured in each field segment width. The variation in attenuation of the compensators was measured as a function of filter position. As the field width increases, the relative absorbed dose also increases; this is the point of requiring compensation, so it can be in reverse proportion. Results: As the field width increases, the relative absorbed dose also increases; this is why compensation is required and thus it must be in reverse proportion. Attenuation of the absorbed dose by the paired filters was in proportion to the filter position. The filter position to compensate for the difference of absorbed doses was defined by the square root of the field width. For a field varying in width from 4 to 16 cm, the variation in the absorbed dose across the field was reduced from 12% to 2.7%. Conclusion: This paired wedge filter system reduced absorbed dose variations across multileaf collimator shaped fields and can facilitate treatment planning in conformal therapy. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] Recently, the area of radiation usage is being enlarged by the industry's advancement over the world. And, the usage of radiation generator and radioisotope is increasing every year. So, they are researching actively how to protect operators from the radiation that causes direct or indirect harmfulness to radiation-related operators of the related institutions. Therefore, in case of operator's dose, not only the main dosimeter's correctness but also the reasonal evaluation to the read values becomes the important factor. From this view, LLD's application to the read dose value is being embossed more importantly than any other thing. So, this study tried to find out what change was generated in the personal dose and the group dose when LLD was applied based on the internal real operator's read value, for 3 years, 2005 - 2007, and find out the personal dose change after dividing them into the exposure group and the supervising group based on the common people's personal dose (1 mSv/y)