Transcript
Woman: Thank you very much. This lecture was going to be originally presented by Amanda but she couldn't come. So I'm here to talk to you about it a little bit. So this is a Google Earth picture from Mexico City. Here you have the downtown, the airport. And in south, near the freeway to Acapulco, it's National Neurology and Neurosurgery Institute. The country has a population of over 100 million persons. And the institute give surveys to people from all over the country that has a neurological disease. And some of these people with present with trigeminal neuralgia. The prevalence of the trigeminal neuralgia is 4 to 5 for every 100,000 persons. The ratio between men and women are two to three.
The stereotactic radiosurgery is the less invasive alternative for treatment of drug-resistant trigeminal neuralgia. In the Institute, there have been 24 treatments of this kind. The protocol that we follow when we do this kind of treatment is that we give up prescription dose that goes from 80 to 90 Gy to the isocenter. We use circular collimators that goes from diameter of 4.0 millimeters to 7.5 millimeters. Typically, we use eight to seven arcs. And we are very careful with the Isodose lines. As we don't want to induce radiation complications, we are very careful that the 40 Gy isodose line be outside of the brainstem. But to have a more probability of success, we are careful to have the 27 Gy isodose line, should encompass the brainstem.
So, as we need... Oh sorry, this should be an arrow, but sorry. As we need a good characterization of the radiation beam because we are giving a very high dose to a very small volume. So we need a very good characterization of the radiation beam. To characterize this small radiation beam, we need an adequate measuring device. The dosimetric measurements should be done accurately. So we are sure that we are giving the dose where we want. In this walk, we mentioned tissue maximum ratio, out of axis ratio, output factors, and were compared with other dosimeters. And we are proposing to use a radiochromic film. We're proposing to use GafChromic EBT radiographic film. It has been calibrated. And one of the advantages of this kind of dosimeter is that it does not need any developing process. So we are taking out one variable of all the equations for the dosimetry.
Now, they have an energy-independent dose response. But one of the disadvantages is that it needs color stabilization. The manufacturer says that the color stabilization takes place in two hours. But we have found that an inlet in the literature supported that it needs at least six hours of stabilization. For low doses, we are just to confirm that it needs more time. So you would need to be a little bit careful when using this kind of film. But the principal advantage is that it has a high spatial resolution. So that's why we are proposing it. So this is the experiment. We did the calibration of the film in phantom water. And we use our LINAC accelerator. It has a nominal energy of 6MV. And we used a circular collimator of 7.5 millimeters of diameter. Their calibration was down from 0.0 cGy to 0.1 cGy to 450 cGy. And we digitalized the films without a transmission commercial scanner.
The parameters for digitalization are six, 100 dots per inch, and we use the three color components red, green, and blue. Each color component set has 16 bits depth. As a validation dosimeter, we use a solid-state dosimeter to be able to act, to have the reason to trust in our measurements in the EBT. Here's the picture of the experiment with the solid-state dosimeter. And here we have the results. We did a comparison of the out of axis ratio with four dosimeters. We used a pinpoint ionization chamber, the GafChromic EBT, the radiographic film, and the Diode. The biggest differences are with the pinpoint demonstration chamber and it was a result we expected because we have partial volume effect with this kind of detector. We have a very good agreement between the GafChromic and the X-OMAT. I'm not sure if you can appreciate from the graph, but the best accordance is between the GafChromic and the Diode.
We also measured TMR with Diode and GafChromic and we see a very good accordance. The output factor was compared also between the EBT and the Diode. And they show a difference that is 1.64%. So we validate the measurements with the EBT. The largest differences between EBT and Diode are less than 1%. Out of axis ratio 0.87% and TMR is 0.82%. So by this way, we trusted in the measurements. And we introduced information of the EBT radiochromic film to the brain scan planning system. And we compared between the X-OMAT radiographic film. We did this comparison because we used to do the small beam radiation dosimetry with this kind of detector. So this is the plan we use for the trigeminal neuralgia. We use 10 non-coplanar arcs, and we use the 7.5 collimator.
So, those are the profiles of the dose measurements. You can see that there are differences between the radiographic film and the EBT and the Diode had a very good agreement. This is a histogram of the differences between the EBT and the radiographic film. The mean of the differences is 1.3 and the standard deviation is 3.56. So we can see that there is a little bit of overestimation of the radiographic film. But if we see the things we've covered, we can see that we can trust in the EBT radiochromic film. The EBT and the Diode showed consistent results. The penumbra region is overestimated by the radiographic film and the gradient region is underestimated. This can mean that maybe the eyes of those lines that we are carrying a lot, they are not what we are thinking they are. So this can mean that we have complications. And maybe this can mean that we don't have the success we are expecting.
This reason of the differences between the EBT and X-OMAT can be explained because the X-OMAT is energy-dependent. Something that we are starting to concert, it's that same processes are disappearing. In our hospital, there is the tendency to go to digital radiography. So we are beginning to be a little bit worried about what is going to happen to film processes. So we are looking for two alternatives. The results suggest that small beam radiation dosimetry should be done with radiographic film detectors. And we recommend to the EBT radiochromic output factor because the EBT has been its tissue equivalent. In literature, there have been differences in some statistical differences. And sometimes it is attributed to the output factor. So we have found differences in the output factor between the Diode and the EBT. So we suggest to use the EBT one. And that's all I have to say. I have to say thank you to Amanda because she trusted me to give this lecture, to BrainLab, to the Instituto Nacional, and the help of Dra. González, Dr. Moreno, and Dr. Gutierrez. And these are pictures of the team in the radiosurgery unit. Thank you very much.
The stereotactic radiosurgery is the less invasive alternative for treatment of drug-resistant trigeminal neuralgia. In the Institute, there have been 24 treatments of this kind. The protocol that we follow when we do this kind of treatment is that we give up prescription dose that goes from 80 to 90 Gy to the isocenter. We use circular collimators that goes from diameter of 4.0 millimeters to 7.5 millimeters. Typically, we use eight to seven arcs. And we are very careful with the Isodose lines. As we don't want to induce radiation complications, we are very careful that the 40 Gy isodose line be outside of the brainstem. But to have a more probability of success, we are careful to have the 27 Gy isodose line, should encompass the brainstem.
So, as we need... Oh sorry, this should be an arrow, but sorry. As we need a good characterization of the radiation beam because we are giving a very high dose to a very small volume. So we need a very good characterization of the radiation beam. To characterize this small radiation beam, we need an adequate measuring device. The dosimetric measurements should be done accurately. So we are sure that we are giving the dose where we want. In this walk, we mentioned tissue maximum ratio, out of axis ratio, output factors, and were compared with other dosimeters. And we are proposing to use a radiochromic film. We're proposing to use GafChromic EBT radiographic film. It has been calibrated. And one of the advantages of this kind of dosimeter is that it does not need any developing process. So we are taking out one variable of all the equations for the dosimetry.
Now, they have an energy-independent dose response. But one of the disadvantages is that it needs color stabilization. The manufacturer says that the color stabilization takes place in two hours. But we have found that an inlet in the literature supported that it needs at least six hours of stabilization. For low doses, we are just to confirm that it needs more time. So you would need to be a little bit careful when using this kind of film. But the principal advantage is that it has a high spatial resolution. So that's why we are proposing it. So this is the experiment. We did the calibration of the film in phantom water. And we use our LINAC accelerator. It has a nominal energy of 6MV. And we used a circular collimator of 7.5 millimeters of diameter. Their calibration was down from 0.0 cGy to 0.1 cGy to 450 cGy. And we digitalized the films without a transmission commercial scanner.
The parameters for digitalization are six, 100 dots per inch, and we use the three color components red, green, and blue. Each color component set has 16 bits depth. As a validation dosimeter, we use a solid-state dosimeter to be able to act, to have the reason to trust in our measurements in the EBT. Here's the picture of the experiment with the solid-state dosimeter. And here we have the results. We did a comparison of the out of axis ratio with four dosimeters. We used a pinpoint ionization chamber, the GafChromic EBT, the radiographic film, and the Diode. The biggest differences are with the pinpoint demonstration chamber and it was a result we expected because we have partial volume effect with this kind of detector. We have a very good agreement between the GafChromic and the X-OMAT. I'm not sure if you can appreciate from the graph, but the best accordance is between the GafChromic and the Diode.
We also measured TMR with Diode and GafChromic and we see a very good accordance. The output factor was compared also between the EBT and the Diode. And they show a difference that is 1.64%. So we validate the measurements with the EBT. The largest differences between EBT and Diode are less than 1%. Out of axis ratio 0.87% and TMR is 0.82%. So by this way, we trusted in the measurements. And we introduced information of the EBT radiochromic film to the brain scan planning system. And we compared between the X-OMAT radiographic film. We did this comparison because we used to do the small beam radiation dosimetry with this kind of detector. So this is the plan we use for the trigeminal neuralgia. We use 10 non-coplanar arcs, and we use the 7.5 collimator.
So, those are the profiles of the dose measurements. You can see that there are differences between the radiographic film and the EBT and the Diode had a very good agreement. This is a histogram of the differences between the EBT and the radiographic film. The mean of the differences is 1.3 and the standard deviation is 3.56. So we can see that there is a little bit of overestimation of the radiographic film. But if we see the things we've covered, we can see that we can trust in the EBT radiochromic film. The EBT and the Diode showed consistent results. The penumbra region is overestimated by the radiographic film and the gradient region is underestimated. This can mean that maybe the eyes of those lines that we are carrying a lot, they are not what we are thinking they are. So this can mean that we have complications. And maybe this can mean that we don't have the success we are expecting.
This reason of the differences between the EBT and X-OMAT can be explained because the X-OMAT is energy-dependent. Something that we are starting to concert, it's that same processes are disappearing. In our hospital, there is the tendency to go to digital radiography. So we are beginning to be a little bit worried about what is going to happen to film processes. So we are looking for two alternatives. The results suggest that small beam radiation dosimetry should be done with radiographic film detectors. And we recommend to the EBT radiochromic output factor because the EBT has been its tissue equivalent. In literature, there have been differences in some statistical differences. And sometimes it is attributed to the output factor. So we have found differences in the output factor between the Diode and the EBT. So we suggest to use the EBT one. And that's all I have to say. I have to say thank you to Amanda because she trusted me to give this lecture, to BrainLab, to the Instituto Nacional, and the help of Dra. González, Dr. Moreno, and Dr. Gutierrez. And these are pictures of the team in the radiosurgery unit. Thank you very much.