silicon and Rectal-Neoplasms

Interfraction dose accumulation is necessary to evaluate the dose distribution of an entire course of treatment by adding up multiple dose distributions of different treatment fractions. This accumulation of dose distributions is not straightforward as changes in the patient anatomy may occur during treatment. For this purpose, the accuracy of nonrigid registration methods is assessed for dose accumulation based on the calculated deformations fields.. A phantom study using a deformable cubic silicon phantom with implanted markers and a cylindrical silicon phantom with MOSFET detectors has been performed. The phantoms were deformed and images were acquired using a cone-beam CT imager. Dose calculations were performed on these CT scans using the treatment planning system. Nonrigid CT-based registration was performed using two different methods, the Morphons and Demons. The resulting deformation field was applied on the dose distribution. For both phantoms, accuracy of the registered dose distribution was assessed. For the cylindrical phantom, also measured dose values in the deformed conditions were compared with the dose values of the registered dose distributions. Finally, interfraction dose accumulation for two treatment fractions of a patient with primary rectal cancer has been performed and evaluated using isodose lines and the dose volume histograms of the target volume and normal tissue.. A significant decrease in the difference in marker or MOSFET position was observed after nonrigid registration methods (p < 0.001) for both phantoms and with both methods, as well as a significant decrease in the dose estimation error (p < 0.01 for the cubic phantom and p < 0.001 for the cylindrical) with both methods. Considering the whole data set at once, the difference between estimated and measured doses was also significantly decreased using registration (p < 0.001 for both methods). The patient case showed a slightly underdosed planning target volume and an overdosed bladder volume due to anatomical deformations.. Dose accumulation using nonrigid registration methods is possible using repeated CT imaging. This opens possibilities for interfraction dose accumulation and adaptive radiotherapy to incorporate possible differences in dose delivered to the target volume and organs at risk due to anatomical deformations.

Topics: Computer Simulation; Cone-Beam Computed Tomography; Humans; Models, Biological; Phantoms, Imaging; Radiation Dosage; Radiotherapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Rectal Neoplasms; Rectum; Silicon; Urinary Bladder

Results are presented of a cohort study on the incidence of cancers and crude death rates in ferrochromium and ferrosilicon workers. The whole cohort was observed from 1 January 1953 to 31 December 1985. Two sets of results are presented; one restricted to workers first employed before 1960 and one to workers first employed before 1965. The latter cohort consists of 1235 workers. The total mortality in the whole cohort was low (SMR = 81) as was the overall incidence of cancers (SIR = 84). There was an overall deficit of deaths and cases of cancer in the ferrosilicon group. An excess of lung cancer (SIR = 154) and cancer of the prostate (SIR = 151) was observed in the ferrochromium workers employed before 1965. Cancer of the kidney was also in excess (SIR = 273) in the ferrochromium group, with a mean "latency time" of 39 years. Two cases of malignant melanomas had occurred versus 0.19 expected in a small subgroup of workers in electrical shops and an electric power station.

Topics: Chromium; Female; Humans; Incidence; Iron; Male; Metallurgy; Neoplasms; Norway; Occupational Diseases; Rectal Neoplasms; Silicon; Time Factors