4 research outputs found
High-precision prostate cancer irradiation by clinical application of an offline patient setup verification procedure, using portal imaging
Purpose: To investigate in three institutions, The Netherlands Cancer Institute (Antoni van Leeuwenhoek Huis [AvL]), Dr. Daniel den Hoed Cancer Center (DDHC), and Dr. Bernard Verbeeten Institute (BVI), how much the patient setup accuracy for irradiation of prostate cancer can be improved by an offline setup verification and correction procedure, using portal imaging. Methods and Materials: The verification procedure consisted of two stages. During the first stage, setup deviations were measured during a number (N(max)) of consecutive initial treatment sessions. The length of the average three dimensional (3D) setup deviation vector was compared with an action level for corrections, which shrunk with the number of setup measurements. After a correction was applied, N(max) measurements had to be performed again. Each institution chose different values for the initial action level (6, 9, and 10 mm) and N(max) (2 and 4). The choice of these parameters was based on a simulation of the procedure, using as input preestimated values of random and systematic deviations in each institution. During the second stage of the procedure, with weekly setup measurements, the AvL used a different criterion ('outlier detection') for corrective actions than the DDHC and the BVI ('sliding average'). After each correction the first stage of the procedure was restarted. The procedure was tested for 151 patients (62 in AvL, 47 in DDHC, and 42 in BVI) treated for prostate carcinoma. Treatment techniques and portal image acquisition and analysis were different in each institution. Results: The actual distributions of random and systematic deviations without corrections were estimated by eliminating the effect of the corrections. The percentage of mean (systematic) 3D deviations larger than 5 mm was 26% for the AvL and the DDHC, and 36% for the BVI. The setup accuracy after application of the procedure was considerably improved (percentage of mean 3D deviations larger than 5 mm was 1.6% in the AvL and 0% in the DDHC and BVI), in agreement with the results of the simulation. The number of corrections (about 0.7 on the average per patient) was not larger than predicted. Conclusion: The verification procedure appeared to be feasible in the three institutions and enabled a significant reduction of mean 3D setup deviations. The computer simulation of the procedure proved to be a useful tool, because it enabled an accurate prediction of the setup accuracy and the required number of corrections
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Single dose irradiation response of pig skin: a comparison of brachytherapy using a single, high dose rate iridium-192 stepping source with 200 kV X-rays
An experimental brachytherapy model has been developed to study acute and
late normal tissue reactions as a tool to examine the effects of
clinically relevant multifractionation schedules. Pig skin was used as a
model since its morphology, structure, cell kinetics and radiation-induced
responses are similar to human skin. Brachytherapy was performed using a
microSelectron high dose rate (HDR) afterloading machine with a single
stepping source and a custom-made template. In this study the acute
epidermal reactions of erythema and moist desquamation and the late dermal
reactions of dusky mauve erythema and necrosis were evaluated after single
doses of irradiation over a follow-up period of 16 weeks. The major aims
of this work were: (a) to compare the effects of iridium-192 (192Ir)
irradiation with effects after X-irradiation; (b) to compare the skin
reactions in Yorkshire and Large White pigs; and (c) to standardize the
methodology. For 192Ir irradiation with 100% isodose at the skin surface,
the 95% isodose was estimated at the basal membrane, while the 80% isodose
covered the dermal fat layers. After HDR 192Ir irradiation of Yorkshire
pig skin the ED50 values (95% isodose) for moderate/severe erythema and
moist desquamation were 24.8 Gy and 31.9 Gy, respectively. The associated
mean latent period (+/- SD) was 39 +/- 7 days for both skin reactions.
Late skin responses of dusky mauve erythema and dermal necrosis were
characterized by ED50 values (80% isodose) of 16.3 Gy and 19.5 Gy, with
latent periods of 58 +/- 7 days and 76 +/- 12 days, respectively. After
X-irradiation, the incidence of the various skin reactions and their
latent periods were similar. Acute and late reactions were well separated
in time. The occurrence of skin reactions and the incidence of effects
were comparable in Yorkshire and Large White pigs for both X-irradiation
and HDR 192Ir brachytherapy. This pig skin model is feasible for future
studies on clinically relevant multifractionation schedules in a
brachytherapy setting