Dit artikel is een vertaling van Reproduceren van gegevens, zo gemakkelijk is het niet!

Reproduction of data seems easy. Just copy the measurement-setup and parameters and of you go. But which parameters can be influenced? What to do about parameters that cannot be influenced?

One in nine Dutch women develops breast cancer. The conventional treatment is breast amputation with lymph nodes extraction. This surgery has several negative side-effects. Besides the emotional and esthetic damage post-op complication do occur. This is why researchers all over the world are looking for breast-saving-treatments.

Laser ablation is such a possible new treatment to remove the breast tumor. The laser is positioned near the tumor through the skin. The laser increases the local temperature. Temperature above 45 degrees centigrade damage cells in general. Thus also cancer cell will suffer DNA damage. It is very important to minimize the damage of normal well-functioning cells. Important parameters to obtain minimal damage are among other things: the power of the laser, the directivity of the laser, the heat coefficient, size of the tumor. This research is in its start-up. Using the experiment described below the researcher hopes to get more insight in breast tumors and laser ablation. Liver tumors are already treated with laser ablation.

Radiofrequent-abblation (RFA) is a different new possible treatment. RFA with a 460kHz frequency produces heat and this heat destroys the tumor just as the laser does. More research is done on the use of RFA than on the use of laser ablation. The ultimate researcher’s goals is to compare the RFA-results with the result of the laser. For this experiment, the researcher can use a laser, temperature sensor and a PC. The most important part is the breast tissue itself. Because of medical-ethical considerations it is not possible to use human breast tissue. The first possible candidate is chicken tissue. This tissue does not have enough similarities with human breast tissue, but it is easy to obtain and it is cheap. The researcher did not use the temperature sensor, since the chicken tissue was used to get an indication of the laser’s power and the size of the created lesion. After this experiment the quest for a good substitute for human breast tissue started. Human breast tissue consists of a lot of glands. Finally the researcher found a candidate: a cow’s udder.

The udders is cut into four pieces to be able to reproduce the measurements. The researcher positions four temperature sensor on such piece. Three of those sensors lie in a straight line at 1,2 and 3 centimeter distance of the laser. The fourth sensor is positioned in front of the laser. These sensors register the temperature as a function of time. A second piece is positioned on top of this sensors. These sensors are connected with the PC. The temperature of the breast tissue has to be 35 degrees centigrade to simulate breast tissue as well as possible. To make this happen the researcher uses a thermo-matras and a bag with hot water to prevent to much cooling. The laser is switched on during a certain period. Unfortunately the piece of breast tissue cannot be reused.

The idea is to compare the result of the laser with the RFA. To be able to do this the first important step is to be able to reproduce the data of the laser. According to the researcher, the current results are not reproducible yet. But how does the researcher know that his results are not reproducible? Beforehand he has an idea about the outcome of his experiment. This idea comes from comparable experiments. The data of this specific experiment are not reproducible because the same temperature sensor displays different temperature curves using different pieces of breast tissue. The researcher suggests several possible causes for this.

• The stucture of the pieces of breast tissue differs. For instance blood vessels could influence the heat coefficient. This could possibly explain the different temperature curves.
• The temperature sensor are moved when the researches puts the second piece of breast tissue on the first one. Thus the researcher never has an exact idea about the distance between the laser tip and the temperature sensors.

The researcher has no idea about the possible influence of the difference in structure on the temperature curve. Since it is not possible to reuse the pieces of breast tissue the researcher is now working on a solution to take the displacement of the sensors into account. He has a rough idea about the influence of this possible displacement on the temperature curve. If the sensor is positioned closer to the laser tip the measured maximum temperature will be higher. But it is not clear how much higher. Is a displacemant of 0,5 centimeter allready detectable?

If the researcher is able to fixate the sensors this will not be a guarantee that he will me be to reproduce the measurements. A lot of different possible influences can cause reproduction problems:

• The power of the laser fluctuates as a function of time
• The presence of the researcher influences the temperature
• Touching of the sensor heats them. This causes a change in temperature curve.
• The color of the researchers’ eyes.

It is not plausible that this last item influences the measurement, but how does the researcher know which parameters influence his research?

From the above it is clear that is not simple to reproduce an experiment. The researcher already has some idea about the outcome of his experiment even before he conducted it. But how does he know that these results are applicable to his research? And which parameters do influence his research?

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Dit artikel werd aangemaakt op maandag 20 augustus 2007 om 15:38 en werd geplaatst in Achtergrond, Chirurgie, Onderzoek, english. U kunt de reacties van dit artikel volgen via de RSS 2.0 feed. Je kan een reactie plaatsen, of een trackback doen van je eigen site.

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