[en] Several treatment planning systems do not allow for variation of wedge factor with field size, and require the use of a single factor for each wedge at a given energy. This can lead to considerable errors. It would appear from the results in this note that the best approach for a treatment planning program would be to use values for three or four field sizes, including the largest and smallest sizes in clinical use, and to interpolate between these values on the basis of the equivalent square field sizes. (author)

No abstract available

[en] The research into direct and reverse problems in formation of spatial dose distribution was carried out. The stages of registration, formation of dose fields, their comparison and analytical presentation, as well as search for irradiation conditions, realizing the preset dose field were considered

[en] This technical note reports the design and use of a simple wedge technique which generates dose uniformity at the field junction, reduces dose variation resulting from clinical set-up error and allows simplicity and efficiency in every day use. Dose profiles taken in a phantom for two adjacent 8 cm x 25 cm fields with the J wedge in place show only small variations at the junction region at depths ranging from 2 cm to 10 cm. (U.K.)

[en] It is important to measure and protect from the radiation space dose and induced activity at the high energy medical linear accelerator facilities. These are to consider the additional risk to patients undergoing treatment, machine operators and staff members. Measurements of the space dose distribution and induced radioactivity at the 18 MeV medical linear accelerator facility in the Yonsei Cancer Center. 1. Exposure space dose for 300 rads monitor doses of 18 MeV electron are measured as 50 mR at 1 meter from patients. 2. Exposure space dose for 300 rads monitor doses of 10 MV X-ray are detected as 350 mR at 1 meter from phantom. 3. Induced radioactivity by photonuclear was measured as 0.65 mR/hr from collimater after 30 Gy(3000 rads) irradiated. 4. Analyzing the decay curves and energy spectrum of induced radioactivity, detected a few materials to be activated by photoneutron reaction, ⁶⁵Cu(γ · n) ⁶⁴Cu, ¹⁸⁶W(γ · n)¹⁸⁵W, ¹⁸¹Ta(γ · n) ¹⁸⁰Ta, ¹⁹⁹Au(γ · n) ¹⁹⁸Au. (Author)

[en] Traditionally, the shaping of non-uniform dose distributions has been performed by using wedges or compensating filters. The advent of high resolution multileaf collimators may largely eliminate the need for material attenuators for modification of the beam. This is achieved by a new technique for the shaping of arbitrary dose distributions by dynamic motion of the collimator leaves. By employing narrow elementary slit beams that correspond to the smallest possible opening of the multileaf collimator, the optimal density of such slit beams, i.e. opening density, can be determined automatically using a newly developed inversion algorithm. The present method has two major advantages (1) internal structures in the field can be created, controlled solely by steering the collimator leaves, (2) the opening density determined by the algorithm never gives rise to underdosage: this is important from a radiobiological point of view. (author)

[en] A simple, low-cost, multipurpose phantom has been designed for use with electronic portal imaging devices (EPIDS). Making use of the high spatial resolution of an EPID, together with the built in software tools for measuring distances, it is possible to verify X-ray/light field size and congruence, at any gantry angle, for fields up to 200 mm x 200 mm. Being of an accurate construction, it can help analyse the distance measuring capabilities of an EPID, ensuring that they are accurate and remain so with time. It can also be used to quantify, and monitor, image displacement and rotation with gantry angle. (author)

[en] Purpose: To determine the expected time to serum testosterone normalization after short-course neoadjuvant androgen deprivation therapy (NAAD) and three-dimensional conformal radiotherapy for patients with localized prostate cancer and to identify pretreatment predictors that correlated with the time to testosterone normalization. Methods: Between 1993 and 1999, 88 patients with localized prostate cancer, treated with NAAD and external beam radiotherapy, were prospectively monitored after treatment with sequential testosterone levels. NAAD was administered before and during the entire course of radiotherapy and discontinued at the end of treatment. The median duration of NAAD was 6 months. The actuarial rate of serum testosterone normalization from the end of treatment was evaluated, and the presence or absence of androgen deprivation-related symptoms was correlated with serum testosterone levels. Symptoms assessed included weight gain, loss of libido, breast tenderness, breast enlargement, hot flashes, and fatigue. Results: Serum testosterone levels returned to the normal range in 57 (65%) of the 88 patients and failed to normalize in 31 patients (35%). The median time to normalization was 18.3 months. The actuarial rate of normalization at 3, 6, 12, and 24 months was 10%, 26%, 38%, and 59%, respectively. In a multivariate analysis, a pretreatment testosterone level in the lower range of normal was the only variable that predicted for delayed testosterone normalization after NAAD (p=0.00047). Among 45 patients with information concerning androgen deprivation-related symptoms recorded 1 year after cessation of NAAD, 24 (53%) had normalized testosterone levels, but in 21 patients (47%), the levels had not yet returned to normal. At 1 year, only 1 (4%) of 24 patients whose testosterone level had returned to normal experienced NAAD-related symptoms compared with 14 (67%) of 21 patients who did not have normal testosterone levels (p<0.001). Conclusion: Testosterone levels often remain depressed for extended periods after cessation of short-course NAAD. Lower baseline testosterone levels predict for a delay in testosterone normalization, and the persistence of symptoms related to androgen deprivation correlates with low testosterone levels

[en] Three-dimensional (3-D) dose distribution as calculated in clinical practice for tangential breast treatment was verified through in vivo dosimetry. Clinical practice at Netherlands Cancer Institute implies use of 8MV X-ray beams, 2-D treatment planning system, collimator rotation and a limited set of patient data for dose calculations. By positioning diodes at the central beam axes as well as in the periphery of the breast the magnitude of dose values at the isocentre and in points situated in high-dose regions behind the lung could be assessed. The position of diodes was verified by means of an on-line portal imaging device. Reproducibility of these in vivo dose measurements was better than 2% (1SD). This study shows that on the average dose delivery at the isocentre is 2% less at the points behind the lung, 5.7% higher with respect to the calculated dose values. Detailed analysis of these in vivo dosimetry results, based on dose measurements performed with a breast shaped phantom, yielded the magnitudes of errors in predicted dose due to several limitations in dose calculation algorithms and dose calculation procedure. These limitations are each introducing an error of several percent but are compensating each other for the dose calculation at the isocentre. It is concluded that dose distribution in patient for this treatment technique and dose calculation procedure can be predicted with a 2-D treatment planning system in an acceptable way. A more accurate prediction of dose distribution can be performed but requires an estimation of the lack of scatter due to missing tissue, the change in the dose distribution due to oblique incident beams and incorporation of the actual output of the treatment machine in the assessment of the number of monitor units. (author). 28 refs.; 3 figs.; 4 tabs

[en] A multileaf collimator, in routine clinical use for both conventional and conformal radiotherapy for over four years, is described in detail. The collimator replaces the conventional treatment head of a Phillips SL series linear accelerator and comprises 80 tungsten leaves and two orthogonal pairs of back-up collimators. Each leaf projects a width of 1 cm in the isocentric plane, allowing shaped photon treatment beams of up to 40 cm square. The performance of the prototype and first production model have been thoroughly tested against the design specifications and the requirements of IEC standards. Radiation attenuation by the collimator components has been measured and substantially exceeds those requirements. (author)