Organ Doses in Interventional Radiology Procedures: Evaluation of Software

XA0101660 IAEA-CN-85-226 ORGAN DOSES IN INTERVENTIONAL RADIOLOGY PROCEDURES: EVALUATION OF SOFTWARE

I. Tort, R. Ruiz-Cruces, M. Perez-Martinez, F. Carrera, C. Ojeda, A. Diez de los Rios Research Group of Radiation Protection, Radiology Department, University of Malaga, Spain

Abstract

Interventional Radiology (IR) procedures require large fluoroscopy times and important number of radiological images, so the levels of radiation to patient are high, which leads us to calculate the organ doses. The objective of this work is to estimate and make a comparison of the results given by the different software that we have to do the calculation of organ doses in complex procedures of IR. To do this, 28 patients have been selected, distributed in the 3 procedures with highest doses. The determination of organ doses and effective doses has been made using the projections utilized and different software, based on MonteCarlo Methods: Eff-dose, PCXMC and Diasoft. We have obtained dispersion in the average organ dose between the 3 programs very high. In many cases, it is higher than 25% and in some particular cases, is greater than 100%. Dispersion obtained in effective doses is not so high, being under 20% in all cases. This shows that a better solution is needed to solve the problem of the organ doses calculation, being necessary a more accurate method that brings us to a trustworthy approach to reality, and, by the moment, we do not dispose of it.

1. Introduction and objective

Procedures in Interventional Radiology (IR) require long time of fluoroscopy and an important number of radiological images, being very high the level of radiation doses given to patient. This leads us to determine the dose received in organs, because in some cases can be very high. Although the probability of the stochastic effects to appear always exists, deterministic effects only exist if certain threshold doses are surpassed, that are different for each organ. In the IR procedures, it is interesting to estimate if the doses given are higher than the limits we have for deterministic effects. The objective of this paper is to estimate the organ doses and to analyze the results given by different software available to carry out the calculation of organ doses in complex procedures in IR.

2. Material and methods

To do this study, 28 patients have been selected, distributed in the 3 procedures considered to have the higher risk that are:

1. Abdominal aortic aneurysm endoprothesis treatment (AAA) 2. Transjugular intrahepatic portosystemic shunts (TIPS) 3. Mesenteric arteriography with venous return (AMRT).

Measures have been obtained using a transmission ionization chamber Diamentor M2 (PTW- Freiburg) placed at the exit of the X-ray tube of the IR equipment (Siemens Digitron 3), which has allowed us to obtain the Dose-Area product (DAP) of the irradiated field. Following data have been collected: - Total DAP (in fluoroscopy and radiography) Characteristics of patient (age, sex, weight, and height) - Projections utilized, as well as the anode angle - Radiological technique (kV and mAs) - Total time of radioscopy Total number of images obtained

325 IAEA-CN-85-226 The posterior determination of organ doses and effective dose has been done knowing in each case the projections applied, and using different software based on Monte Carlo Methods: Eff- dose, PCXMC and Diasoft.

Eff-Dose asks for data on kV, total filtration of the beam, DAP, and projections utilized. In this work, the closer simple projection and similar to the irradiated field in each procedure has been selected, following the methodology described by Ruiz-Cruces et al. [1-3]

PCXMC asks for more information to carry out the dosimetric estimation, requesting the DAP, projections, kV, anode angle, total filtration of beam, age of the patient, source-patient distance, size of the irradiated field by means of coordinates (X, Y, Z), number of energy levels and number of photons in each level (maximum 50000). Moreover, it allows us to adjust the field with rotation degrees, which is an advantage from the previous program. [4]

Diasoft asks for the same parameters than Eff-Dose: kV, total filtration of the beam, DAP, projections utilized, as well as the source-patient distance. [5] This program has the possibility of being executed directly connected to the transmission ionization chamber of PTW Freiburg.

3. Results

Table I shows the organs with doses that have a relative error higher than 25% for each procedure, with its dose value, calculated as the dose obtained with the different programs as well as the average that results. For the AAA and AMRT there are only 2 and 4 organs in each case with this characteristic, meanwhile for the number increases until 19. It is important also that there are 5 organs in this last procedure that have a relative error that surpass 100%. This error appears as a consequence of the disparity of results between those ones given by PCXMC and the other two of them. The values given by Eff-Dose and DiaSoft are almost equal for all the procedures.

Table II shows the effective doses obtained with the three programs, the average value and its standard deviation, expressed also as a relative error. The values given by Eff-Dose and DiaSoft are almost totally equal for all the procedures, but on the other hand, the calculation made by PCXMC is very different from the other ones. The standard deviation between the results of the three programs varies from 6 to 8, and the relative error from 15 to 17%.

Table III shows the standard deviation end the average relative error of the organ doses in each procedure. It stands out the relative error of 56% in the case of TIPS, meanwhile in the other two procedures the relative errors are 16 and 14% in each case. The results given by PCXMC are very different in some particular cases, making that the average relative error to be as high as showed.

326 IAEA-CN-85-226

Table I. Organ doses with relative error higher than 25% for each procedure

Procedure Organ Dose Dose Dose Dose Relative Eff- DiaSoft * PCXMC* Average* Error (%) Dose* AAA Adrenals 106,90 106,90 209,26 141,02 42 Lung 7,21 7,21 12,09 8,84 32 Adrenals 389,36 389,40 142,52 307,09 46 Breast 3,36 3,36 1,43 2,72 41 Bladder 129,84 129,80 42,92 100,85 50 Stomach 107,39 107,40 33,31 87,70 52 UL1 83,37 83,37 46,12 70,95 30 LLI 14,37 14,37 57,52 28,75 87 Heart 18,87 18,87 7,08 14,94 46 Kidney 606,02 606,00 237,74 483,25 44 Liver 159,83 159,80 53,53 124,39 49 TIPS Lung 21,63 | 21,63 7,83 17,03 47 Ovaries 12,48 12,48 68,07 31,01 103 Pancreas 175,21 175,20 53,61 134,67 52 Spleen 356,39 356,40 117,83 276,87 50 Testes 0,20 0,19 10,09 3,49 164 Thymus 2,39 2,39 0,54 1,77 60 Thyroid 0,27 0,27 0,00 0,18 140 Urinary 2,55 2,55 35,28 13,64 107 bladder Uterus 9,67 9,67 56,45 25,26 107 Esophagus 25,17 25,17 3,81 18,05 68 Adrenals 59,49 59,49 128,45 82,48 48 AMRT Breast 0,64 0,64 1,29 0,86 44 Heart 3,59 3,59 6,38 4,52 36 Lung 249,78 249,80 214,28 4,68 44 * Given in mGy

Table II. Dispersion obtained in effective dose for each procedure

Effective Dose(mSv2 Procedure Eff- DiaSoft PCXMC Average Standard Relative Dose Deviation Error (%) AAA 75,68 75,68 57,48 69,6 10 15 TIPS 51,18 51,18 37,81 46,7 8 17 AMRT 40,30 40,29 29,91 36,8 6 16

Table III. Standard deviation and average relative error of the entire organ doses in each procedure

Procedure Standard deviation* Relative error (%)* AAA 14 16 TIPS 37 56 AMRT 6 14 * Average for all the organs

327 IAEA-CN-85-226 4. Discussion and recommendations

To have three different programs to carry out the same calculations should imply first a way to arise a more accurate result. However, as it can be seen in this work, this is not in this way.

The results given by the three programs are very different, so in general, the dispersion error is very high.

First, we have Eff-Dose y DiaSoft that provide values that are practically equal, which implies that two of them can be utilized indiscriminately.

On the other hand, PCXMC, which results are very different from the other two programs, has the advantage of be able to adjust better the angle of the field for each projection.

All we have said shows that a better solution is needed to solve the problem of the calculation of organ doses, being necessary a more accurate method to be closer to reality, and by the moment, we do not have this method.

As a recommendation, we propose as lesser solution to calculate an average using the three programs, obtaining an estimated value with its relative error.

References

[1] RUIZ-CRUCES R.; PEREZ MARTINEZ, M.; MARTIN PALANCA, A; FLORES, A.; CRISTOFOL, J.; MARTINEZ MORILLO, M.; DIEZ DE LOS RIOS,A., Patient dose in radiologically guided vascular procedures: Conventional versus digital systems, Radiology 205(1997): 385-394 [2] RUIZ-CRUCES R.; GARCIA GRANADOS J.; DIAZ ROMERO, F.J.; HERNANDEZ ARMAS, J., Estimation of effective dose in some digital angiographic and interventional procedures, British Journal of Radiology, 71(1998),42-47. [3] NBH, National Institute of Radiation Hygiene; Eff-Dose software: Estimation of effective and organ doses. Bronshoj, Denmark (1995) Version 1.02. [4] TAPIOVARA, M.; LAKKISTO,M.; SERVOMAA, A., PCXMC: A PC-based Monte Carlo program for calculating patient doses in medical X-ray examinations, Helsinki (1997) 1-55. [5] DiaSoft Version 5.0. Users' manual. PTW, Freiburg (2000).

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