- Email: [email protected]
High power interstitial laser therapy in congenital vascular malformations
ARTICLE IN PRESS
Medical Laser Application 20 (2005) 291–295 www.elsevier.de/mla
High power interstitial laser therapy in congenital vascular malformations Dietmar Cholewaa,, Frank Wackerb, Andre´ Rogganc, Ju¨rgen Waldschmidta a
Department of Paediatric Surgery, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany Department of Radiology, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany c Institute of Medical Physics and Laser Medicine, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany b
Received 1 July 2005; accepted 28 August 2005
Abstract Recently, it has been shown that coagulation volumes of interstitial laser therapy (ILT) can be enlarged by introducing a diffuser tip applicator into a cooling catheter system in the treatment of liver, breast and lung neoplasm. The aim of this study was to prove if coagulation volumes in ILT of congenital vascular malformations (CVMs) can also be enlarged by using this system. Cooled laser applicators were used in eight patients with CVM. The procedures were executed with an Nd:YAG laser 1064 nm. The laser power was 25 W. The applicator was introduced into a thermostable Teflon cooling catheter. Cooling flow was 50 ml/min. For online thermo-monitoring, we used three timeoptimized MR sequences in an open magnetic resonance imaging (MRI) unit. The volume of MRI-changes ranged from 12 up to 36 ml (mean: 20.5 ml). In comparison with previous results in 600 mm bare fibre treatment (mean spot volume 1.9 ml), treatment spots were 10 times higher in the cooled applicator system. In certain large and deep seeded CVM, ILT becomes more effective with cooled laser applicator systems. r 2005 Elsevier GmbH. All rights reserved. Keywords: Congenital vascular malformation; Interstitial laser therapy
Introduction Interstitial laser therapy (ILT) is a well-known established option in the treatment of congenital vascular disease (CVD). Waldschmidt and Berlien introduced the Nd:YAG ILT of CVD into the paediatric surgery clinic [1,2]. Recently, after the high incidence of ILT in adulthood, technical improvements occurred in the field of colon liver metastasis. By now, the largest volumes of coagulation in ILT of tumours can be achieved by diffusing applicators introduced into Corresponding author. Chirurgische Universita¨tskinderklinik,
Inselspital Bern, 3010 Bern, Switzerland. Tel.: +41 31 632 9256; fax: +41 31 632 9292. E-mail address: [email protected] (D. Cholewa). 1615-1615/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.mla.2005.08.002
a cooled catheter system. Consequently, we investigate the application of cooled laser applicators in ILT as well for giant congenital vascular malformations (CVMs) in an open magnetic resonance imaging (MRI). We wanted to know if the volumes of MRI-changes in CVM can be increased by using high laser power in a cooled catheter system (high power interstitial laser therapy – HPILT).
Material and methods Between 1996 and 2000 a total of eight MR-guided HPILT laser interventions were carried out in the treatment of children with CVMs. Reasons for the intervention were always malformation-related symptoms. All treated CVMs
ARTICLE IN PRESS 292
D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
showed an infiltrating and a displacing growth. All treatments were carried out in general anaesthesia. All children received perioperative antibiotic prophylaxis for 3 days (Cefotiam 50 mg/kg b.w. d and Gentamycin 5 mg/ kg b.w. d). The applications were executed with an Nd:YAG laser (1064 nm, Fibertom 5100, Dornier, Germany) located in the MR control room and equipped with a fibre of 12 m length. MR imaging before, during, and after ILT was performed on a 0.2 T system (Magnetom OPEN, Siemens, Germany) using a large standard surface coil. After MR-guided marking of the skin, the entry site was sterilized and draped. The titanium alloy needle (Somatex, Germany) was advanced under MR guidance until the tip was positioned as distal as possible from the insertion site. Finally, the Teflon catheter system was introduced and the needle was withdrawn. The therapy was stopped at one location if no further signal reduction was observed for a period of 2 min. Application time for single treatment spot differed from patient to patient and ranged between 5 and 15 min (11 min). Laser light was transmitted to tissue with a scattering dome diffusing applicator (Huettinger, Germany). The laser power was 25 W. The applicator had an active length of 2 mm (outer diameter 1.1 mm, core diameter 400 mm) and was introduced into the thermostable Teflon cooling catheter (Somatex, Germany) of 1.9 mm inner diameter. The remaining space between the scattering dome and catheter allowed a cooling flow of 50 ml/min. Sterile isoosmolar solution served as the cooling fluid. Conventional T1-weighted spin echo sequences (TR: 450 ms; TE: 5 ms; matrix: 256 256; layer: 7–10 mm; two signals acquired) and T2-weighted turbo spin echo sequences (TR: 5000 ms; TE: 117 ms; matrix: 256 256; layer: 7–10 mm; one signal acquired) were obtained plainly in the transverse and sagittal or coronal planes for all patients pre- and post-operatively. Optimal entry position and angle to the lesion were determined by an external marker and a biplanar short gradient echo sequence adjacent to the axis of the needle (FLASH; TR: 66 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; one signal acquired). A gradient echo sequence with three slices parallel to the needle course was applied for the interactive MR-guided puncture (FLASH; TR: 66 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; measuring time: 10 s; one signal acquired). Targeting success was confirmed by acquiring an additional plane along the needle orthogonally to the guiding plane. To monitor ILT, T1-weighted gradient echo (TR: 132 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; measuring time: 19 s; one signal acquired) and fast spin echo sequences (TR: 540 ms; TE: 24 ms; echo train: 5; matrix: 256 256; layer: 10 mm; measuring time: 18 s; one signal acquired) were repeatedly acquired during and after laser application. The T1-weighted images were analysed for regions with signal intensity changes. The maximum area of signal
reduction was measured online in the central plane using scanner image software. MR follow-up studies using the above-mentioned T1- and T2-weighted sequences were performed immediately, after 48 h and 6 weeks after ILT. The total volumes of the vascular lesions were determined before and 6 weeks after the intervention. The post-therapeutic images were compared to the online images acquired during laser application. No other therapy was performed during the 6-week follow-up.
Results We treated five girls and three boys with CVM. Their ages ranged from 5 to 15 years. All CVMs were of extratruncular types (four venous, two arteriovenous and two haemolymphatic). MRI passive tip tracking through the titanium alloy provided optimal diffuser positioning in all applications. Online thermometry was possible in all 40 therapy spots. Intraprocedural T1weighted scans revealed signal reduction in all 40 laser applications. The hypointense region increased during the active laser time with a maximum diameter of 45 mm. All regions showed recurrence of the T1 signal after switching off the laser. We neither observed a strong irreversible signal loss at the catheter system nor any peripheral reaction. This was assumed to indicate no vaporization due to carbonization. The T2-weighted sequences acquired immediately after therapy revealed alterations, which showed good correlation with the extent of temperature sensitive intraprocedural T1weighted images. The preoperative CVM volume ranged from 850 to 2100 ml (mean 1417 ml). The 6-week followup revealed a reduction in tumour size in all patients (mean 89.4%). Clinical symptoms (pain in six, bleeding in two) improved in seven out of eight patients. In two of these patients, the symptoms (bleeding) were completely resolved after therapy. We did not observe intraoperative bleeding complications or catheter system-related problems as leakage or fibre breakage. On average, first MR-signal alterations were found after 210 s. The volume of MRI-changes ranged from 12 up to 36 ml (mean: 20.5 ml). With respect to our former results [3] in bare fibre treatment of CVM (mean spot volume 1.9 ml), treatment spots were 10 times higher in cooled applicator system (Figs. 1a and b; Table 1).
Discussion CVM may become symptomatic due to expansive volume enlargement, compression and infiltration of adjacent structures. CVMs are divided into groups according to the Hamburg classification [4]. Type, localization and extension are decisive factors for the
ARTICLE IN PRESS D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
Fig. 1. Maximal T1-MRI signal alteration in retroperitoneal venous CVM (*) in (a) high power ILT and (b) low power ILT.
293
therapy protocol which is interdisciplinary and multimodal. Conservative, interventional and open surgical procedures are applied. CVMs which have a clear boundary to the surrounding structures or which have large arteriovenous shunts should be resected surgically, possibly with a selective embolization directly prior to surgery. But, in case of a diffuse and infiltrating tumour growth, there is a risk of damage to neighbouring structures, resulting in a high recurrence rate due to the lack of radical surgery. This was the cause for investigating less invasive palliative procedures such as ILT for these forms of CVM. ILT is a minimally invasive treatment procedure to create thermal lesions in pathological tissue and has frequently been applied for different indications. Monochromatic light of a wavelength of 1064 nm deeply penetrates into biological tissue in which photon absorption and heat conduction lead to photochemical and hyperthermic effects. For ILT, a quartz fibre is directly positioned within the tumour or vascular malformation and a near infrared laser is used at moderate power settings. The distal fibre end can be prepared as a bare fibre with a forward directed radiation characteristic. The advantage of the bare fibre is its small diameter (o1 mm, including coating) allowing the use of thin puncture needles for placement; its disadvantage is its tendency to induce carbonization due to high power densities at the fibre tip [5]. Alternatively, the distal end can be prepared in order to diffusely distribute the laser light within the region of interest (diffusing tip, scattering applicator). The power density is essentially reduced by the large radiating surface, allowing the application of higher total energies through a larger contact surface without carbonization [6,7]. Consequently, larger volumes of denaturation may be achieved. Maximum volumes of coagulation in tumours treatment were achieved by using scattering applicators in cooled catheter systems [8,9]. The catheter system allows the application of high Nd:YAG laser power of 25 W and long application-time. It has not been examined yet if it is would be possible to increase coagulation volumes around the laser applicator using the same systems in the interstitial laser treatment of CVM. While MRI is sensitive to thermal-related changes it has already proven to be an effective method to monitor interstitial laser coagulation [10,11]. We had the opportunity to test if the active volume can be enlarged by using scattering applicator in a cooled catheter system in an open MRI unit. The introduction of open systems offers access to patients and interactive management directly in the magnetic field. Thus, ILT can be optimized by the registered volume of T1 volume changes. T1-MRI signal alterations correlate with the biological tissue changes [12]. The intended optimal tissue temperature for the maximum coagulated volume ranges from 45 to 80 1C. Temperature above 90 1 results
ARTICLE IN PRESS 294
Table 1.
D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
MRI-signal changes in interstitial laser therapy with different applicators High power ILT
Low power ILT
Applicator Cooling medium Cooling flow Core diameter Laser power Laser spots
Nd:YAG 1064 nm (Fibertom 5100; Dornier, Germany) Diffuser tip (Huettinger, Germany) Sterile NaCl 0.9% 50 ml/min 400 mm 25 W n ¼ 40
Nd:YAG 1064 nm (Fibertom 5100; Dornier, Germany) Bare fibre (Dornier, Germany) None None 600 mm 5W n ¼ 164
First MRI-signal alteration after Minimum Maximum Mean
90 s 500 s 210 s
35 s 180 s 87 s
Kind of MRI-signal changes Reversible Irreversible Mixed
40 None None
75 13 76
Maximum diameter
45 mm
27 mm
Volume of MRI changes Minimum Maximum Mean
12 ml 36 ml 20.5 ml
0.5 ml 6 ml 1.9 ml
Laser
in tissue shrinking, exsiccation and carbonization. Carbonization means total absorption of further laser light. Thus, no further effect beside the fibre is possible except heat conduction. In case of large amounts of light energy in the absorption area, vaporization becomes visible in MRI-images as an irreversible zone of signal loss or reduced intensity. In a previous study, we saw all these MRI-changes in signal intensity in bare fibre treatment of CVM. Due to carbonization, treatment spot size was limited to volumes of about 2 ml. Frequent bare fibre replacement and new positioning is necessary to treat adapted volumes of CVM. As an improvement the simultaneous application of multiple fibres is used. This technique provides lesion volumes between 4 and 12 ml with four fibres, but it requires a high number of punctures [13]. By now, the largest volumes of coagulation have been achieved with diffusing applicators introduced into a cooled catheter system. In vitro experiments showed coagulation volumes of up to 30 ml in porcine liver [14–16]. The application of the cooled diffusing tip for the MR-controlled treatment of liver tumours revealed a significant increase in lesion volume in comparison with the non-cooled laser applicators [9]. In certain cases, it may be disadvantageous to perform multiple repositioning with the bare fibre and it might be better to have a larger single spot size. In this study, we focussed on the size of coagulation volumes of ILT using a high laser power in a cooling catheter system. The protective catheter prevents direct
contact of the laser applicator with the patient and enables complete removal of the applicator even in the unlikely event of damage to the fibre during treatment. The catheter is transparent for laser light and resistant to heat up to 400 1C. The system is fully compatible with MR imaging systems. Magnetic markers on the laser applicator facilitate visualization and positioning. The disadvantages of the system are its larger diameter and the risk of haemorrhage. We did not observe any bleeding complications in our cases. Obviously, tissue edges are sealed totally by laser coagulation, no bleeding from the puncture channel was observed during removal of the system. Based on cooling effect the increase of temperature increases slowly. Thus, MRI signal intensity changes in a cooled catheter system occurred later than in bare fibre treatment. As no irreversible MRI signal intensity changes occurred, we may state that no carbonization occurred. This means that tissue temperature in CVM around the catheter system was below 100 1C. The absence of carbonization around the catheter leads to a persistently high penetration depth of Nd:YAG laser light of a long time period of several minutes. Therefore, a 10-fold enlargement of the coagulation volume compared to single bare fibre treatment of CVM could be realized. With comprehensive cooling of the laser applicator in CVM tissue the laser power can be raised up to 25 W, applying this energy for a long period of 10 min minimum. The centrifugal temperature changes persist in the ideal
ARTICLE IN PRESS D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
therapeutic index and lead to large coagulation volumes. Although we have no direct histological proof of the correlation between MR-signal changes and tissue coagulation of the malformations, HPILT improves the treatment options in some forms of CVM, particularly in large extratruncular malformations with infiltrating growth.
Zusammenfassung High Power Interstitial Laser Therapie bei vaskula¨ren Malformationen In den letzten Jahren konnte in der Behandlung von Leber- Brust- und Lungenneoplasmen gezeigt werden, dass man die lokalen Koagulationsvolumen bei der interstitiellen Lasertherapie dadurch erho¨hen kann, dass man den Applikator in ein ku¨hlendes Kathetersystem platziert. Ziel dieser Arbeit war es nachzuweisen, ob die Koagulationsvolumina bei der interstitiellen Lasertherapie (ILT) von kongenitalen vaskula¨ren Malformationen ebenfalls dadurch vergro¨ssert werden ko¨nnen, dass man dieses System benutzt. Wir wendeten das geku¨hlte Applikatorsystem bei acht Patienten an. Die Applikation erfolgte mit einem Nd:YAG Laser 1064 nm. Die Laserleistung betrug 25 W. Der Applikator wurde in einen thermostabilen Teflonkatheter platziert. Der Ku¨hlstrom betrug 50 ml/min. Zum Online Thermomonitoring nutzten wir drei zeitoptimierte MR Sequenzen in einer offenen MRT Einheit. Die Volumina der MRVera¨nderungen lagen zwischen 12 und 36 ml (mean 20.5 ml). Vergleicht man das mit fru¨heren Resultaten der ungeku¨hlten 600 mm bare fibre Therapie (mean 1.9 ml) sind die Behandlungsspots im geku¨hlten System um das zehnfache ho¨her. Deshalb kann die Therapie von bestimmten ausgedehnten und tiefsitzenden CVMs durch die Anwendung eines geku¨hlten Laserapplikatorsystems effektiviert werden. r 2005 Elsevier GmbH. All rights reserved. Schlu¨sselwo¨rter: Kongenitale Interstitielle Lasertherapie
vaskula¨re
Malformationen;
References [1] Berlien HP, Waldschmidt J, Mu¨ller G. Laser treatment of cutaneous and deep vessel anomalies. In: Waidelich W, editor. Laser optoelectronics in medicine. Berlin, Heidelberg, New York: Springer; 1988. p. 526–8. [2] Philipp C, Berlien HP, Po¨tke M, Waldschmidt J. Ten years of laser treatment of congenital vascular disorders – technical techniques and results. Proc SPIE 1994;2327: 44–53.
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[3] Cholewa D, Wacker F, Roggan A, Waldschmidt J. Magnetic resonance imaging: controlled interstitial laser therapy in children with vascular malformations. Lasers Surg Med 1998;23:250–7. [4] Belov S. Classification of congenital vascular defects. Int Angiol 1990;9:141–614. [5] Noelsoe CP, Torp-Pedersen S, Burcharth F, Horn T, Pedersen S, Christensen NH, et al. Interstitial hyperthermia of colorectal liver metastases with US-guided Nd:YAG laser with a diffuser tip: a pilot clinical study. Radiology 1993;187:333–7. [6] Nolsoe C, Torp-Pedersen S, Olldag E, Holm HH. Bare fibre low power Nd:YAG laser interstitial hyperthermia. Comparison between diffuser tip and non-modified tip, an in vitro study. Lasers Med Sci 1992;7:1–7. [7] Roggan A, Albrecht D, Berlien HP, Beuthan J, Fuchs B, Germer C, et al. Application equipment for intraoperative and percutaneous laser-induced interstitial thermotherapy. In: Mu¨ller G, Roggan A, editors. Laser-induced interstitial thermotherapy. Bellingham: SPIE Press; 1995. p. 224–48. [8] Vogl T, Mu¨ller PK, Hammerstingl R, Weinhold N, Mack MG, Philipp C, et al. Malignant liver tumours treated with MR imaging-guided laser-induced thermotherapy: technique and prospective results. Radiology 1995;196: 257–65. [9] Roggan A, Knappe V, Mack M, Vogl TJ, Albrecht D, Germer CT, et al. Experimental study and first clinical results with a cooled applicator system for interstitial laser coagulation. Proc SPIE 1998;3249:85–93. [10] Jolesz FA, Bleier AR, Jakab P, Ruenzel PW, Huttl K, Jako GJ. MR imaging of laser–tissue interactions. Radiology 1988;168:249–53. [11] Leung DA, Debatin JF, Wildermuth S, Heske N, Dumoulin CL, Darrow RD, et al. Real-time biplanar needle tracking for interventional MR imaging procedures. Radiology 1995;197:485–8. [12] Wacker F, Cholewa D, Doede T, Waldschmidt J, Wolf KJ. LITT-Monitoring im offenen MRT bei 0.2 Tesla mo¨glich? In: Waidelich W, Waidelich R, Waldschmidt J, editors. Laser in der Medizin/in Medicine, vol. 8. Berlin, Heidelberg, New York: Springer; 1997. p. 23–9. [13] Albrecht D, Germer CT, Isbert C, Ritz JP, Roggan A, Mueller G, et al. Interstitial laser coagulation: evaluation of the effect of normal liver blood perfusion and the application mode on lesion size. Lasers Surg Med 1998;23:40–7. [14] Dowlatshahi K, Bangert JD, Haklin MF, Rhodes CK, Weinstein RS, Economou SG. Protection of fibre function by para-axial fluid flow in interstitial laser therapy of malignant tumors. Lasers Surg Med 1990;10(4):322–7. [15] Orth K, Russ D, Duerr J, Hibst R, Steiner R, Beger HG. Thermo-controlled device for inducing deep coagulation in the liver with the Nd:YAG laser. Lasers Surg Med 1997;20(2):149–56. [16] Sturesson C, Andersson-Engels S. Tissue temperature control using a water-cooled applicator: implications for transurethral laser-induced thermotherapy of benign prostatic hyperplasia. Med Phys 1997;24(3):461–70.
Medical Laser Application 20 (2005) 291–295 www.elsevier.de/mla
High power interstitial laser therapy in congenital vascular malformations Dietmar Cholewaa,, Frank Wackerb, Andre´ Rogganc, Ju¨rgen Waldschmidta a
Department of Paediatric Surgery, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany Department of Radiology, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany c Institute of Medical Physics and Laser Medicine, University Hospital Benjamin Franklin, Hindenburgdamm 30, 12220 Berlin, Germany b
Received 1 July 2005; accepted 28 August 2005
Abstract Recently, it has been shown that coagulation volumes of interstitial laser therapy (ILT) can be enlarged by introducing a diffuser tip applicator into a cooling catheter system in the treatment of liver, breast and lung neoplasm. The aim of this study was to prove if coagulation volumes in ILT of congenital vascular malformations (CVMs) can also be enlarged by using this system. Cooled laser applicators were used in eight patients with CVM. The procedures were executed with an Nd:YAG laser 1064 nm. The laser power was 25 W. The applicator was introduced into a thermostable Teflon cooling catheter. Cooling flow was 50 ml/min. For online thermo-monitoring, we used three timeoptimized MR sequences in an open magnetic resonance imaging (MRI) unit. The volume of MRI-changes ranged from 12 up to 36 ml (mean: 20.5 ml). In comparison with previous results in 600 mm bare fibre treatment (mean spot volume 1.9 ml), treatment spots were 10 times higher in the cooled applicator system. In certain large and deep seeded CVM, ILT becomes more effective with cooled laser applicator systems. r 2005 Elsevier GmbH. All rights reserved. Keywords: Congenital vascular malformation; Interstitial laser therapy
Introduction Interstitial laser therapy (ILT) is a well-known established option in the treatment of congenital vascular disease (CVD). Waldschmidt and Berlien introduced the Nd:YAG ILT of CVD into the paediatric surgery clinic [1,2]. Recently, after the high incidence of ILT in adulthood, technical improvements occurred in the field of colon liver metastasis. By now, the largest volumes of coagulation in ILT of tumours can be achieved by diffusing applicators introduced into Corresponding author. Chirurgische Universita¨tskinderklinik,
Inselspital Bern, 3010 Bern, Switzerland. Tel.: +41 31 632 9256; fax: +41 31 632 9292. E-mail address: [email protected] (D. Cholewa). 1615-1615/$ - see front matter r 2005 Elsevier GmbH. All rights reserved. doi:10.1016/j.mla.2005.08.002
a cooled catheter system. Consequently, we investigate the application of cooled laser applicators in ILT as well for giant congenital vascular malformations (CVMs) in an open magnetic resonance imaging (MRI). We wanted to know if the volumes of MRI-changes in CVM can be increased by using high laser power in a cooled catheter system (high power interstitial laser therapy – HPILT).
Material and methods Between 1996 and 2000 a total of eight MR-guided HPILT laser interventions were carried out in the treatment of children with CVMs. Reasons for the intervention were always malformation-related symptoms. All treated CVMs
ARTICLE IN PRESS 292
D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
showed an infiltrating and a displacing growth. All treatments were carried out in general anaesthesia. All children received perioperative antibiotic prophylaxis for 3 days (Cefotiam 50 mg/kg b.w. d and Gentamycin 5 mg/ kg b.w. d). The applications were executed with an Nd:YAG laser (1064 nm, Fibertom 5100, Dornier, Germany) located in the MR control room and equipped with a fibre of 12 m length. MR imaging before, during, and after ILT was performed on a 0.2 T system (Magnetom OPEN, Siemens, Germany) using a large standard surface coil. After MR-guided marking of the skin, the entry site was sterilized and draped. The titanium alloy needle (Somatex, Germany) was advanced under MR guidance until the tip was positioned as distal as possible from the insertion site. Finally, the Teflon catheter system was introduced and the needle was withdrawn. The therapy was stopped at one location if no further signal reduction was observed for a period of 2 min. Application time for single treatment spot differed from patient to patient and ranged between 5 and 15 min (11 min). Laser light was transmitted to tissue with a scattering dome diffusing applicator (Huettinger, Germany). The laser power was 25 W. The applicator had an active length of 2 mm (outer diameter 1.1 mm, core diameter 400 mm) and was introduced into the thermostable Teflon cooling catheter (Somatex, Germany) of 1.9 mm inner diameter. The remaining space between the scattering dome and catheter allowed a cooling flow of 50 ml/min. Sterile isoosmolar solution served as the cooling fluid. Conventional T1-weighted spin echo sequences (TR: 450 ms; TE: 5 ms; matrix: 256 256; layer: 7–10 mm; two signals acquired) and T2-weighted turbo spin echo sequences (TR: 5000 ms; TE: 117 ms; matrix: 256 256; layer: 7–10 mm; one signal acquired) were obtained plainly in the transverse and sagittal or coronal planes for all patients pre- and post-operatively. Optimal entry position and angle to the lesion were determined by an external marker and a biplanar short gradient echo sequence adjacent to the axis of the needle (FLASH; TR: 66 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; one signal acquired). A gradient echo sequence with three slices parallel to the needle course was applied for the interactive MR-guided puncture (FLASH; TR: 66 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; measuring time: 10 s; one signal acquired). Targeting success was confirmed by acquiring an additional plane along the needle orthogonally to the guiding plane. To monitor ILT, T1-weighted gradient echo (TR: 132 ms; TE: 9 ms; FA: 801; matrix: 256 256; layer: 10 mm; measuring time: 19 s; one signal acquired) and fast spin echo sequences (TR: 540 ms; TE: 24 ms; echo train: 5; matrix: 256 256; layer: 10 mm; measuring time: 18 s; one signal acquired) were repeatedly acquired during and after laser application. The T1-weighted images were analysed for regions with signal intensity changes. The maximum area of signal
reduction was measured online in the central plane using scanner image software. MR follow-up studies using the above-mentioned T1- and T2-weighted sequences were performed immediately, after 48 h and 6 weeks after ILT. The total volumes of the vascular lesions were determined before and 6 weeks after the intervention. The post-therapeutic images were compared to the online images acquired during laser application. No other therapy was performed during the 6-week follow-up.
Results We treated five girls and three boys with CVM. Their ages ranged from 5 to 15 years. All CVMs were of extratruncular types (four venous, two arteriovenous and two haemolymphatic). MRI passive tip tracking through the titanium alloy provided optimal diffuser positioning in all applications. Online thermometry was possible in all 40 therapy spots. Intraprocedural T1weighted scans revealed signal reduction in all 40 laser applications. The hypointense region increased during the active laser time with a maximum diameter of 45 mm. All regions showed recurrence of the T1 signal after switching off the laser. We neither observed a strong irreversible signal loss at the catheter system nor any peripheral reaction. This was assumed to indicate no vaporization due to carbonization. The T2-weighted sequences acquired immediately after therapy revealed alterations, which showed good correlation with the extent of temperature sensitive intraprocedural T1weighted images. The preoperative CVM volume ranged from 850 to 2100 ml (mean 1417 ml). The 6-week followup revealed a reduction in tumour size in all patients (mean 89.4%). Clinical symptoms (pain in six, bleeding in two) improved in seven out of eight patients. In two of these patients, the symptoms (bleeding) were completely resolved after therapy. We did not observe intraoperative bleeding complications or catheter system-related problems as leakage or fibre breakage. On average, first MR-signal alterations were found after 210 s. The volume of MRI-changes ranged from 12 up to 36 ml (mean: 20.5 ml). With respect to our former results [3] in bare fibre treatment of CVM (mean spot volume 1.9 ml), treatment spots were 10 times higher in cooled applicator system (Figs. 1a and b; Table 1).
Discussion CVM may become symptomatic due to expansive volume enlargement, compression and infiltration of adjacent structures. CVMs are divided into groups according to the Hamburg classification [4]. Type, localization and extension are decisive factors for the
ARTICLE IN PRESS D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
Fig. 1. Maximal T1-MRI signal alteration in retroperitoneal venous CVM (*) in (a) high power ILT and (b) low power ILT.
293
therapy protocol which is interdisciplinary and multimodal. Conservative, interventional and open surgical procedures are applied. CVMs which have a clear boundary to the surrounding structures or which have large arteriovenous shunts should be resected surgically, possibly with a selective embolization directly prior to surgery. But, in case of a diffuse and infiltrating tumour growth, there is a risk of damage to neighbouring structures, resulting in a high recurrence rate due to the lack of radical surgery. This was the cause for investigating less invasive palliative procedures such as ILT for these forms of CVM. ILT is a minimally invasive treatment procedure to create thermal lesions in pathological tissue and has frequently been applied for different indications. Monochromatic light of a wavelength of 1064 nm deeply penetrates into biological tissue in which photon absorption and heat conduction lead to photochemical and hyperthermic effects. For ILT, a quartz fibre is directly positioned within the tumour or vascular malformation and a near infrared laser is used at moderate power settings. The distal fibre end can be prepared as a bare fibre with a forward directed radiation characteristic. The advantage of the bare fibre is its small diameter (o1 mm, including coating) allowing the use of thin puncture needles for placement; its disadvantage is its tendency to induce carbonization due to high power densities at the fibre tip [5]. Alternatively, the distal end can be prepared in order to diffusely distribute the laser light within the region of interest (diffusing tip, scattering applicator). The power density is essentially reduced by the large radiating surface, allowing the application of higher total energies through a larger contact surface without carbonization [6,7]. Consequently, larger volumes of denaturation may be achieved. Maximum volumes of coagulation in tumours treatment were achieved by using scattering applicators in cooled catheter systems [8,9]. The catheter system allows the application of high Nd:YAG laser power of 25 W and long application-time. It has not been examined yet if it is would be possible to increase coagulation volumes around the laser applicator using the same systems in the interstitial laser treatment of CVM. While MRI is sensitive to thermal-related changes it has already proven to be an effective method to monitor interstitial laser coagulation [10,11]. We had the opportunity to test if the active volume can be enlarged by using scattering applicator in a cooled catheter system in an open MRI unit. The introduction of open systems offers access to patients and interactive management directly in the magnetic field. Thus, ILT can be optimized by the registered volume of T1 volume changes. T1-MRI signal alterations correlate with the biological tissue changes [12]. The intended optimal tissue temperature for the maximum coagulated volume ranges from 45 to 80 1C. Temperature above 90 1 results
ARTICLE IN PRESS 294
Table 1.
D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
MRI-signal changes in interstitial laser therapy with different applicators High power ILT
Low power ILT
Applicator Cooling medium Cooling flow Core diameter Laser power Laser spots
Nd:YAG 1064 nm (Fibertom 5100; Dornier, Germany) Diffuser tip (Huettinger, Germany) Sterile NaCl 0.9% 50 ml/min 400 mm 25 W n ¼ 40
Nd:YAG 1064 nm (Fibertom 5100; Dornier, Germany) Bare fibre (Dornier, Germany) None None 600 mm 5W n ¼ 164
First MRI-signal alteration after Minimum Maximum Mean
90 s 500 s 210 s
35 s 180 s 87 s
Kind of MRI-signal changes Reversible Irreversible Mixed
40 None None
75 13 76
Maximum diameter
45 mm
27 mm
Volume of MRI changes Minimum Maximum Mean
12 ml 36 ml 20.5 ml
0.5 ml 6 ml 1.9 ml
Laser
in tissue shrinking, exsiccation and carbonization. Carbonization means total absorption of further laser light. Thus, no further effect beside the fibre is possible except heat conduction. In case of large amounts of light energy in the absorption area, vaporization becomes visible in MRI-images as an irreversible zone of signal loss or reduced intensity. In a previous study, we saw all these MRI-changes in signal intensity in bare fibre treatment of CVM. Due to carbonization, treatment spot size was limited to volumes of about 2 ml. Frequent bare fibre replacement and new positioning is necessary to treat adapted volumes of CVM. As an improvement the simultaneous application of multiple fibres is used. This technique provides lesion volumes between 4 and 12 ml with four fibres, but it requires a high number of punctures [13]. By now, the largest volumes of coagulation have been achieved with diffusing applicators introduced into a cooled catheter system. In vitro experiments showed coagulation volumes of up to 30 ml in porcine liver [14–16]. The application of the cooled diffusing tip for the MR-controlled treatment of liver tumours revealed a significant increase in lesion volume in comparison with the non-cooled laser applicators [9]. In certain cases, it may be disadvantageous to perform multiple repositioning with the bare fibre and it might be better to have a larger single spot size. In this study, we focussed on the size of coagulation volumes of ILT using a high laser power in a cooling catheter system. The protective catheter prevents direct
contact of the laser applicator with the patient and enables complete removal of the applicator even in the unlikely event of damage to the fibre during treatment. The catheter is transparent for laser light and resistant to heat up to 400 1C. The system is fully compatible with MR imaging systems. Magnetic markers on the laser applicator facilitate visualization and positioning. The disadvantages of the system are its larger diameter and the risk of haemorrhage. We did not observe any bleeding complications in our cases. Obviously, tissue edges are sealed totally by laser coagulation, no bleeding from the puncture channel was observed during removal of the system. Based on cooling effect the increase of temperature increases slowly. Thus, MRI signal intensity changes in a cooled catheter system occurred later than in bare fibre treatment. As no irreversible MRI signal intensity changes occurred, we may state that no carbonization occurred. This means that tissue temperature in CVM around the catheter system was below 100 1C. The absence of carbonization around the catheter leads to a persistently high penetration depth of Nd:YAG laser light of a long time period of several minutes. Therefore, a 10-fold enlargement of the coagulation volume compared to single bare fibre treatment of CVM could be realized. With comprehensive cooling of the laser applicator in CVM tissue the laser power can be raised up to 25 W, applying this energy for a long period of 10 min minimum. The centrifugal temperature changes persist in the ideal
ARTICLE IN PRESS D. Cholewa et al. / Medical Laser Application 20 (2005) 291–295
therapeutic index and lead to large coagulation volumes. Although we have no direct histological proof of the correlation between MR-signal changes and tissue coagulation of the malformations, HPILT improves the treatment options in some forms of CVM, particularly in large extratruncular malformations with infiltrating growth.
Zusammenfassung High Power Interstitial Laser Therapie bei vaskula¨ren Malformationen In den letzten Jahren konnte in der Behandlung von Leber- Brust- und Lungenneoplasmen gezeigt werden, dass man die lokalen Koagulationsvolumen bei der interstitiellen Lasertherapie dadurch erho¨hen kann, dass man den Applikator in ein ku¨hlendes Kathetersystem platziert. Ziel dieser Arbeit war es nachzuweisen, ob die Koagulationsvolumina bei der interstitiellen Lasertherapie (ILT) von kongenitalen vaskula¨ren Malformationen ebenfalls dadurch vergro¨ssert werden ko¨nnen, dass man dieses System benutzt. Wir wendeten das geku¨hlte Applikatorsystem bei acht Patienten an. Die Applikation erfolgte mit einem Nd:YAG Laser 1064 nm. Die Laserleistung betrug 25 W. Der Applikator wurde in einen thermostabilen Teflonkatheter platziert. Der Ku¨hlstrom betrug 50 ml/min. Zum Online Thermomonitoring nutzten wir drei zeitoptimierte MR Sequenzen in einer offenen MRT Einheit. Die Volumina der MRVera¨nderungen lagen zwischen 12 und 36 ml (mean 20.5 ml). Vergleicht man das mit fru¨heren Resultaten der ungeku¨hlten 600 mm bare fibre Therapie (mean 1.9 ml) sind die Behandlungsspots im geku¨hlten System um das zehnfache ho¨her. Deshalb kann die Therapie von bestimmten ausgedehnten und tiefsitzenden CVMs durch die Anwendung eines geku¨hlten Laserapplikatorsystems effektiviert werden. r 2005 Elsevier GmbH. All rights reserved. Schlu¨sselwo¨rter: Kongenitale Interstitielle Lasertherapie
vaskula¨re
Malformationen;
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