Dosimetry for intraoperative radiotherapy (IORT) after wide local excision for breast cancer using a 50 kV X-ray needle (Intrabeam) was performed in vivo using thermoluminescence dosimetry. Eight LiF:Mg,Ti chips were placed on the skin around the incision site after wide local excision while the tumour bed was irradiated to a prescribed dose of 5 Gy 10 mm from the applicator surface. The maximum and mean measured skin dose for 57 patients ranged from 0.64 to 7.1 Gy and 0.56 to 4.78 Gy, respectively, reflecting different tissue thicknesses overlying the applicator. The average maximum dose of 2.93+/-1.46 Gy was below the threshold for severe radiation skin toxicity.
The leakage radiation from electron applicators used with our linear accelerator has been measured. For the applicators 6 X 6 to 25 X 25 cm size, the leakage was measured in the plane of the patient and on the sides of the applicators with the available electron energies of 6, 9, 12, 15 and 18 MeV. The levels were significant. The highest leakage on the side was for the combination of 6 X 6-cm applicator and 9-MeV electrons (32%) and in the plane of the patient for 25 X 25-cm applicator with 18 MeV (10%) relative to the peak dose. Adding lead 1-2 mm, at appropriate locations inside the applicators has reduced the leakages to acceptable levels without affecting the beam parameters.
The effect of radiation in regard to breast carcinogenesis is well studied and analysed from data from atomic bomb survivors, patients treated for acute mastitis and tuberculosis patients monitored by fluoroscopy. Therefore the radiation received by the untreated breast during breast irradiation of the other breast, is of concern to clinicians. Using thermoluminescence dosimeters, we have measured the dose received by contraleteral breast of six patients during radiation therapy. Most of the dose received will be from the collimator scatter and leakage. We investigated the effect of an absorber, superflab, in reducing the skin dose to contralateral breast. With the overlaying of a cm superflab on the breast, the skin (surface) dose could be reduced by 40-75% of its original value. This is an effective and practical method of reducing significantly the dose to contralateral breast during breast conservation therapy. Superflab can be made conveniently at low cost.
The dose anisotropy around a (192)Ir HDR source in a water phantom has been measured using MOSFETs as relative dosimeters. In addition, modeling using the EGSnrc code has been performed to provide a complete dose distribution consistent with the MOSFET measurements. Doses around the Nucletron 'classic' (192)Ir HDR source were measured for a range of radial distances from 5 to 30 mm within a 40 x 30 x 30 cm(3) water phantom, using a TN-RD-50 MOSFET dosimetry system with an active area of 0.2 mm by 0.2 mm. For each successive measurement a linear stepper capable of movement in intervals of 0.0125 mm re-positioned the MOSFET at the required radial distance, while a rotational stepper enabled angular displacement of the source at intervals of 0.9 degrees . The source-dosimeter arrangement within the water phantom was modeled using the standardized cylindrical geometry of the DOSRZnrc user code. In general, the measured relative anisotropy at each radial distance from 5 mm to 30 mm is in good agreement with the EGSnrc simulations, benchmark Monte Carlo simulation and TLD measurements where they exist. The experimental approach employing a MOSFET detection system of small size, high spatial resolution and fast read out capability allowed a practical approach to the determination of dose anisotropy around a HDR source.
For single plane implants with gold seeds, assuming a matrix distribution for the seeds, the optimum separation of the matrix elements and the optimum ratio of the activity of the seeds in the area to that of those in the periphery, have been calculated, so that the uniformity of dosedistribution is within *lo%. Area dosages have also been computed and are tabulated.The dose variations in double plane implants and volume implants also have been studied and the results are presented. Dosage graphs have been given for both cases.The theoretical dose distributions have been verified for a few implants experimentally using LiF thermoluminescence dosimeters.
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