Differences between cytotoxicity in photodynamic therapy using a pulsed laser and a continuous wave laser: study of oxygen consumption and photobleaching

Oxygen consumption at the targeted site has a significant effect on dosimetry in photodynamic therapy (PDT). However, oxygen consumption in PDT using a pulsed laser as a light source has not been clarified. We therefore investigated the dependence of cytotoxicity on the oxygen consumption and the photosensitizer photobleaching of PDT using a pulsed laser by comparing with that using a continuous wave (CW) laser. Mouse renal carcinoma cells (Renca) were incubated with a second-generation photosensitizer, PAD-S31. The cells were then irradiated with either a 670-nm nanosecond pulsed light from the 3rd harmonics of a Nd:YAG laser-pumped optical parametric oscillator with a peak fluence rate of ~1 MW/cm² at 30 Hz or a 670-nm CW diode laser with a total light dose of 40 J/cm². Regardless of laser source, cytotoxic effects exhibited cumulative dose responses to the photosensitizer ranging from 12 to 96 g/ml. However, cytotoxic effect of PDT using the pulsed light was significantly less than that using the CW light with the photosensitizer concentrations of 24 and 48 g/ml under identical fluence rates. During PDT, the cells exposed to the pulsed light consumed oxygen more slowly, resulting in a lower amount of oxygen consumption when compared with PDT using CW light. In accordance with oxygen consumption, the pulsed light induced significantly less photobleaching of the photosensitizer than the CW light did. These results indicate that the efficiency of PDT using pulsed light is less when compared with CW light, probably being related to suppressed oxygen consumption during the pulsed light irradiation.     

Total effective fluence: a useful concept in photodynamic therapy

Photodynamic therapy is generally carried out using a laser, usually a dye laser with the wavelength tuned to suit the particular sensitizer. The availability of broad-band sources for use in photodynamic therapy is challenging the role of the laser, since the non-laser sources are more portable and less expensive. Also, the wavelengths utilized may easily be changed by optical filtering. However, the use of a broad-band source introduces serious problems with dosimetry. The concept of the total effective fluence takes account of the incident spectral irradiance from the light source, optical transmission through tissue (preferably including backscatter), and absorption by the sensitizer. Application of the concept to various light sources demonstrates the potential value of this simple concept.     

Treatment of port wine stains with photodynamic therapy, using pulsed dye laser as a light source, compared with pulsed dye laser alone: a pilot study

BACKGROUND AND OBJECTIVES: Laser-induced photo thermal damage has been combined with photodynamic therapy (PDT) using a systemic photosensitiser to treat vascular lesions. The efficacy of PDT using systemic 5-aminolaevulinic acid (5-ALA) as the photosensitiser and pulsed dye laser (PDL) as the light source in port wine stains (PWS) is unknown. STUDY DESIGNS/MATERIALS AND METHODS: We conducted an internally controlled pilot study comparing the efficacy of PDT using PDL as a light source, to PDL alone in the treatment of PWS. RESULTS: The PWS improved slightly in all patients but no significant difference was found between the three treatment arms in terms of lesional lightening or incidence and severity of side effects. CONCLUSIONS: There was no evidence of increased efficacy of PDT using PDL as a light source compared to PDL alone. There was also no significant difference in adverse events. Further studies using different treatment regimens over longer periods of time may be warranted.     

Light dose fractionation versus single-dose irradiation in photodynamic therapy of tumours

The effect of photoirradiation fractionation on photodynamic therapy of Sarcoma 180 in mice was investigated. Photofrin II (10 mg/kg bodyweight) and different schedules of light dose fractionation were used. The inhibition of tumour growth was comparable when a dose of 1×300 J/cm² or 2×150 J/cm² was applied. However, the skin photoreaction and the normal tissue reactions in the irradiated area were weaker with the second schedule of irradiation. The best effect was reached with 6×50 J/cm², doses being given at 5-hour intervals between the 24th and 48th hours after drug administration. Despite the small total dose in the case of irradiation with 6×35 J/cm², the effect on the tumour was comparable with that reached using the first two schedules of treatment (total irradiation dose 300 J/cm²). With multiple photoirradiation fractionation the photodynamic therapeutic effect is considerably greater than with a single or double fractionation of irradiation using the same total dose. With the multiple light dose fractionation the normal tissue reactions in the irradiated areas are more weakly expressed than with a single or double fractionation of irradiation using the same total dose. The multiple photoirradiation fractionation allows a reduction in the total light dose necessary to achieve the same biological effect as with single or double irradiation.     

长脉冲Nd:YAG激光非侵入性治疗皮肤浅表静脉畸形

目的前瞻性研究长脉冲1064nm Nd:YAG激光非侵入性治疗皮肤浅表静脉畸形的疗效。方法22例不同部位皮肤浅表静脉畸形患者接受长脉冲1064nm Nd:YAG激光治疗,6mm直径光斑,7～8ms双脉宽,脉冲间隔20ms,140～150J/cm2能量,接触式冷却,治疗间隔3周至1个月,治疗后1、6个月随访,评价病灶清除率分为五级。结果22例患者完成治疗,最多治疗5次。随访6个月,96.3%浅表静脉畸形获得76%～100%的清除,37%获得病灶的完全清除,未见复发。治疗部位无一例发生紫癜,治疗后8例(38.1%)出现红斑,1d至1个月消退。无色素改变和形成。结论长脉冲1064nm Nd:YAG激光能有效安全地治疗皮肤浅表静脉畸形,选择性地清除浅表血管,并使用接触冷却系统保护表皮,减少紫癜发生及色素改变和瘢痕的形成,达到理想的美容效果。     

Effects of laser parameters on pulsed Er-YAG laser skin ablation

Previous studies demonstrated that pulsed 2.94m Er-YAG laser radiation allows a precise etching of organic tissue with only minimal thermal damage. This makes the Er-YAG laser a promising tool for the careful removal of superficial skin lesions. In order to provide optimized laser parameters for potential clinical use and to enhance our understanding of the mid-infrared ablation process, we measured the ablation rate, temperature profile and damage zones for various pulse numbers, radiant energies and pulse repetition rates. Ablation is very efficient (about 6m J^–1 cm² for high radiant exposure) and the crater depth is exactly (1Hz) or nearly (2 Hz) linearly related to the radiant exposure. In contrast, no significant effects of the laser parameters on the thermal damage of the epidermis and the crater bottom were observed. In conclusion, for a future clinical use high radiant energies should be applicable without the disadvantage of enhanced damage.     

Near infra-red diode laser for photodynamic tumour therapy using bacteriochlorina

Clonogenic cell survivals were performed in order to assess the feasibility of tumour cell kill with an experimental diode laser emitting 250 mW of light at λ = 779 nm using the photosensitizer bacteriochlorina(BCA). The AlGaAs diode laser is based on organometallic vapour epitaxial crystal growth technology. The electrical to optical conversion efficiency amounts to 21% and the beam divergence is 47° by 7.0° full width at half maximum. BCA was proved to be an effective non-toxic photosensitizer in vitro and in vivo. It has a major absorption peak at 760 nm where tissue penetration of light is optimal. Clonogenic T24 human bladder carcinoma cell survivals were photosensitizer concentration and light dose dependent. A 0.1% survival rate was obtained with an illumination intensity of 50 mWcm⁻² for 90 s (4.5 Jcm⁻²) and a BCA concentration of 6 μgml⁻¹. Illumination without BCA at energy levels exceeding the PDT levels with a factor 10, or BCA alone without illumination had no effect on the cells in the clonogenic cell survivals. The combination of BCA with a near infra-red diode laser is most promising for photodynamic tumour therapy as a result of the reliability, compactness and relatively low price of the illumination device, the high transmittance of near infra-red light in tissue and the tumour killing potential of BCA.     

The photodynamic effect of a pulsed dye laser on human bladder carcinoma cells in vitro

Summary The photodynamic effect of a pulsed flashlamp pumped dye laser on cultured human bladder carcinoma cells was studied. MGH-U1 cells were incubated for 1 h in dihaematoporphyrin ether (DHE) and then exposed to green laser light (504 nm, 20 Hz) for varying laser power densities (50–100 mW/cm² and exposure times (2–15 s), representing incident pulse energy fluences of 2.5–5 mJ/cm² and energy densities of 0.1–1.5 J/cm². The cell survival was measured by clonogenic assay and controls exposed to either laser light alone or DHE in the dark showed no cytotoxicity. Sensitised cells were killed by energy densities of less than 1 J/cm² (LD₉₀=0.54 J/cm²). This demonstrates the probable effectiveness of a pulsed dye laser for photodynamic therapy provided that pulse fluence are below the saturation threshold of the photosensitiser (10 mJ/cm²).     

Histologic evaluation of the pulsed Nd:YAG laser for laser lipolysis

BACKGROUND AND OBJECTIVES: Laser lipoplasty with pulsed Nd:YAG laser, widely used in Europe and Latin America, has recently been introduced in Japan and the USA. We report histologic analyses of the effects of the laser on human fat tissue. STUDY DESIGN/MATERIALS AND METHODS: Freshly excised human skin and subcutaneous fat were irradiated with the pulsed Nd:YAG laser (SmartLipo, DEKA, Italy). A 1,064 nm laser at 40 Hz and 150 mJ and 100 microseconds-long pulses were used. Methods of exposure were the same as in the clinical application. In the control group, the specimens were cannulated by the handpiece without irradiation. The tissue was studied by scanning electron microscopy and hematoxylin eosin staining. RESULTS: Scanning electron microscopy after irradiation showed greater destruction of human adipocytes than in the control. Degenerated cell membrane, vaporization, liquefaction, carbonization, and heat-coagulated collagen fibers were observed. CONCLUSIONS: Our study showed that the SmartLipo appeared to be histologically effective for destruction of human fat tissue.     

Laser therapy of varicosities with the flashlamp-pumped pulsed dye laser

The flashlamp-pumped pulsed dye laser with an output wavelength of 585 nm and a pulse duration of 450m was used to treat 102 areas of blue and red varicosities in the lower limbs of female patients. Varicosities could be divided into two groups, early red varicosities and more developed blue varicosities. Forty-two areas of blue varicosities were treated with a single pulse, and only 20% of these were eliminated. Blue varicosities were then treated in three treatment sessions, 3 weeks apart, and none of them could be occluded. Red varicosities responded better; all of the varicosities treated were occluded in three treatment sessions separated by 3 weeks. The use of two consecutive pulses with only 6.5 Jcm^–2 in a single treatment session resulted in only 54% of the varicosities being eliminated. Finally, seven areas of red varicosities were treated in a single treatment with an argon laser at 2 W; only 10–20% of these lesions responded. The pulsed dye laser is therefore of most use in treating red varicosities.     

The pulsed dye laser versus the Q-switched Nd:YAG laser in laser-induced shock-wave lithotripsy

To date, there are two fairly well-established alternatives for laser-induced shock-wave lithotripsy in clinical practice. The Q-switched Nd:YAG laser is distinguished by the high-stone selectivity of its coupler systems. The necessity of a coupler system and its fairly small conversion rate of light energy into mechanical energy present serious drawbacks. Furthermore, the minimal outer diameter of the transmission system is 1.8 mm. The pulsed-dye laser can be used with a highly flexible and uncomplicated 200-micron fiber. However, the laser system itself is more complicated than the Q-switched Nd:YAG laser and requires a great deal of maintenance. Biological evaluation of damage caused by direct irradiation shows that both laser systems produce minor damage of different degrees. YAG laser lithotripsy with the optomechanical coupler was assessed in 31 patients with ureteral calculi. The instability and limited effectiveness of the fiber application system necessitated auxiliary lithotripsy methods in 14 cases. Dye-laser lithotripsy is currently being tested in clinical application. Further development, such as systems for blind application or electronic feedback mechanisms to limit adverse tissue effects, have yet to be optimized. Nevertheless, laser-induced shock-wave lithotripsy has the potential to become a standard procedure in the endourologic management of stone disease.     

595 nm脉冲染料激光单独或联合剥脱性激光治疗寻常疣的临床观察

目的 探讨595 nm脉冲染料激光单独或联合剥脱性激光(CO2激光或Er:YAG激光)治疗寻常疣的临床效果.方法 自2016年9月至2018年9月,中国医学科学院整形外科医院激光中心收治10例寻常疣患者(21个疣体),采用595 nm脉冲染料激光单独或联合剥脱性激光治疗1～3次,记录每次治疗结束后2～4周疣体面积变化,...     

A comparison of novel light sources for photodynamic therapy

A diode laser, light-emitting diode (LED) array bandwidth 25 nm, full width half maximum (FWHM) and filtered arc lamp (bandwidth 40 nm, FWHM), all with peak emission at about 650 nm, suitable for the photosensitizer tetra(meta-hydroxyphenyl)chlorin (mTHPC), were compared with a copper vapour laser pumped dye laser, using depth of necrosis in normal rat liver as a measure of photodynamic effect. A three-way comparison between a DL10K dye laser, the LED array and the filtered arc lamp resulted in mean depths of necrosis of 4.64, 4.29 and 4.04 mm, respectively, at 20 J cm^-2, the values for the laser and arc lamp being significantly different at the 5% level. A further comparison of a narrower linewidth DL20K dye laser with the LED array, using a light dose of 20 J cm^-2, showed a significant difference between the mean depths of necrosis of 4.97 and 4.05 mm, respectively (p=0.01). A final study, comparing the DL20K dye laser with the diode laser and a light dose of 10 J cm^-2, demonstrated no significant difference in depths of necrosis (3.23 and 3.25 mm, respectively). The results obtained in the three studies are attributed to the relative bandwidths of light emission for the various sources. A simple mathematical model is presented explaining the results in terms of the relative activation of the photosensitizer and the consequent threshold fluence required for the induction of necrosis. It is concluded that, in order to achieve the same depth of effect as a laser when using the broad band sources, the incident fluence would have to be approximately doubled. However, when the low cost and ease of use of the non-laser sources are taken into consideration, these devices are likely to find widespread applications in clinical photodynamic therapy.     

Correlations between light penetration into skin and the therapeutic outcome following laser therapy of port-wine stains

. For several years the flashlamp-pumped pulsed dye laser (FPDL) has been the favoured method for the treatment of port-wine stains (PWS). The therapeutic outcome of FPDL laser therapy depends on the anatomical location of the PWS and is mainly attributed to morphological parameters such as size and depth of the PWS blood vessels. The aim of this study was to show a correlation between the therapeutic outcome following FPDL therapy and the optical properties of the skin overlying the PWS vessels. For this purpose the therapeutic outcome following FPDL treatment (585 nm; 0.45 ms) of 884 PWS situated on different body sites was evaluated by judging the grade of fading of PWS colour. On the other hand the light penetration into 123 skin samples (thickness 0.10–1.35 mm) was determined between 450 nm and 1030 nm and compared with the PWS laser therapy outcome for equal locations by statistical analysis. PWS on the neck, trunk, arms or legs yielded a higher mean grade of fading as compared to PWS on the head. Within the face, a wide range of fading was evident. The light penetration into skin increased linearly with increasing wavelength and location-dependent differences were found. The attenuation coefficient was 22.8±5.3 mm⁻¹ at 585 nm. No significant or strong correlation was observed between the therapeutic outcome of PWS laser therapy and the light penetration into skin. However, a correlation was obvious by plotting the respective profile plots. Therefore, among other effects, in particular morphological parameters of PWS vessels, the optical properties of the skin contribute to a small extent to the clinical outcome of PWS laser therapy. Paper received 2 May 2001; accepted after revision 21 June 2001.