Affirmative paper for pressure based compression from the Norwegian screening

Recently, a paper from the Norwegian screening program appeared online in which they compared three different compression paddles. A fixed study paddle with pressure indication was compared to a conventional flex paddle and a conventional fixed paddle without pressure indication.

Pain experience (NRS) was collected in 4,675 women. Between the flex paddle and the  study paddle no significant difference was found (2.5), but between the conventional fixed paddle and the fixed study paddle with pressure indicator, a significant difference was found in favor of the pressure based study paddle.

In this paper the mean pain score appeared to be halfway between no pain and mild pain. It is of course very difficult to find a pain relieving effect at all, if pain scores are as low as in Norway during the course of this study. We were very happy that the results in pain comparison between the conventional flex paddle and the fixed study paddle with pressure indication showed no differences. A conventional flex paddle adjusts to the shape of the breast and therefore avoids the incising effects of the edge near the thorax. The problem with the flex paddle is that in circumstances where compressions are much higher than in Norway (like in the Dutch breast cancer screening), breast tissue can be pushed out the field of view. However, in moderate compression as can be seen in this study, the use of a flex paddle is preferred. This was a reason for Sigmascreening to develop a flex paddle version with pressure indication. The first trials with this new type show very promising results. So it seems that the combination of a flex paddle with the moderate and safe pressures of the Sigma paddle is the ideal combination.

Furthermore, we noticed that the paddle was used during a pre-study period. The authors state: “The substantially higher compression force and pressure used in the pre-study period indicates a study effect – the radiographers adapted the compression force needed to obtain 10 kPa also in the room without a pressure indicator.” This suggests that the pain reducing effect of the pressure indication was (in part) already achieved before the start of the study. 

As far as we can see, in this study the compression parameters show realistic compression values when pressure based compression is evaluated, with pressure around the 10 kPa, “which is currently considered a better metric related to experienced pain, than force”. The results in table 2 show exactly what should be expected in pressure based compression. The pressure is around 10 kPa with a very small standard deviation as compared to the conventional paddle. The standard deviation in force in the study paddle with pressure indicator, is considerably higher than in conventional paddles, as expected when taking breast size into account.

Another intriguing remark is being made about the faster performance of the study with the pressure based paddle as compared to the conventional paddles. They relate the higher inclusion of women in the study paddle group to the fact that the examinations were generally performed faster when using the study paddle with pressure indicator, compared to the conventional flexible and fixed paddles. In a first come first serve set-up a remarkable difference of 1.9 was found. In several trials we noticed  a substantial workflow improvement with the help of a pressure indicating paddle. Therefore, we completely agree with the authors that in pressure based mammography the LED information “can facilitate the communication between radiographers and women, and help women easier accept the applied force and/or pressure.”

The remarks about the radiation dose has to be considered in the usual way of working. In this study a slightly higher mean glandular dose was found (1.37 mGy versus 1.42 mGy) in the pressure based study paddle. In all relevant international studies from the US and Europe the mean glandular dose is equal or higher and the mentioned difference in this paper may be significant but clinically irrelevant.

Our conclusion is that the range of the pain relieving effects of pressure based compression depends on the historical way of working, which leads to already low pain scores. The combination of a flex paddle with pressure sensing, is very promising. On top of this, pressure based way of working goes beyond pain and discomfort. It also reduces variations, improves workflow and facilitates a better communication with the patient.