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OBJECTIVE: The aim of this study was to determine whether significant fiducial marker migration occurs between the periods of prostatic marker insertion and computed tomography (CT) performed for radiotherapy planning and if a waiting period is necessary. MATERIAL AND METHODS: Thirty-nine patients with prostate adenocarcinoma underwent fiducial marker insertion before radiotherapy between June 2013 and December 2015. Three markers were inserted by one radiologist under the guidance of transrectal ultrasonography. All patients underwent CT three hours after insertion to confirm the number and position of fiducial markers. Radiotherapy planning CT was performed on an average of 11 days (range 7-20) after insertion. CT images were imported into treatment planning system to analyze the position of fiducial markers. Point- based marker match algorithm was used to find the distance of marker migration. The mean and maximum distances between each fiducial markers were calculated. RESULTS: The mean distance of migration was 1.029±0.42 mm (range 0.23-1.93 mm) and the maximum distance was 1.361±0.59 mm (range 0.25-2.74 mm). The distance of marker migration was not statistically significant for the groups organized according to the timing of marker insertion, prostate volume, patient age, prostate specific antigen level and Gleason score. CONCLUSION: According to our results significant fiducial marker migration did not occur during the interval between insertion and treatment planning CT. It should be taken into consideration that performing simulation on the same day as marker insertion might prevent increased cost and delayed radiation therapy by saving the patients from extra visits to the clinic.
RESUMO
BACKGROUND: The study aimed to calculate chest-wall skin dose associated with different frequencies of bolus applications in post-mastectomy three-dimensional conformal radiotherapy (3D-CRT) and to provide detailed information in the selection of an appropriate bolus regimen in this clinical setting. METHODS: CT-Simulation scans of 22 post-mastectomy patients were used. Chest wall for clinical target volume (CTV) and a volume including 2-mm surface thickness of the chest wall for skin structures were delineated. Precise PLAN 2.11 treatment planning system (TPS) was used for 3D-CRT planning. 50 Gy in 25 fractions were prescribed using tangential fields and 6-MV photons. Six different frequencies of bolus applications (0, 5, 10, 15, 20, and 25) were administered. Cumulative dose-volume histograms were generated for each bolus regimen. The minimum, maximum and mean skin doses associated with the bolus regimens were compared. To test the accuracy of TPS dose calculations, experimental measurements were performed using EBT gafchromic films. RESULTS: The mean, minimum and maximum skin doses were significantly increased with increasing days of bolus applications (p < 0.001). The minimum skin doses for 0, 5, 10, 15, 20, and 25 days of bolus applications were 73.0% +/- 2.0%, 78.2% +/- 2.0%, 83.3% +/- 1.7%, 88.3% +/- 1.6%, 92.2% +/- 1.7%, and 93.8% +/- 1.8%, respectively. The minimum skin dose increments between 20 and 25 (1.6% +/- 1.0%), and 15 and 20 (4.0% +/- 1.0%) days of bolus applications were significantly lower than the dose increments between 0 and 5 (5.2% +/- 0.6%), 5 and 10 (5.1% +/- 0.8%), and 10 and 15 (4.9% +/- 0.8%) days of bolus applications (p < 0.001). The maximum skin doses for 0, 5, 10, 15, 20, and 25 days of bolus applications were 110.1% +/- 1.1%, 110.3% +/- 1.1%, 110.5% +/- 1.2%, 110.8% +/- 1.3%, 111.2% +/- 1.5%, and 112.2% +/- 1.7%, respectively. The maximum skin dose increments between 20 and 25 (1.0% +/- 0.6%), and 15 and 20 (0.4% +/- 0.3%) days of bolus applications were significantly higher than the dose increments between 0 and 5 (0.2% +/- 0.2%), 5 and 10 (0.2% +/- 0.2%), and 10 and 15 (0.2% +/- 0.2%) days of bolus applications (p < or = 0.003). The TPS overestimated the near-surface dose 10.8% at 2-mm below the skin surface. CONCLUSION: In post-mastectomy 3D-CRT, using a 1-cm thick bolus in up to 15 of the total 25 fractions increased minimum skin doses with a tolerable increase in maximum doses.
