Correct calibration procedure for the Q-switched ruby laser and checking the treatment irradiation pattern

Abstract

Background and aims: There are many Q-switched lasers. The Q-switched ruby laser is the one most popularly used in dermatology, aesthetic surgery and plastic surgery, to remove pigmented lesions or tattoos. Correct and regular calibration of such a system is essential. However, some clinics fail to perform this with the excuse of having no measuring instrument (MI) in their offices or treatment rooms in some of their hospitals or clinics, or even the case of well-known medical universities in Japan. The present article explains the precise calibration procedure and beam pattern checking for the Q-switched ruby systems in the first author's clinic.

Rationale: In the case of treatment with a medical laser, the calibration and the irradiated pattern (IP) check of the laser being used for treatment are the most important factors for treatment efficacy and safety. If these factors change, the treatment result could be different from that expected. Such kind of data are not acceptable as scientific information for a presentation or published paper. With such unreliable results and incorrect beam pattern, replicating such a study would be impossible

Regular calibration check: In our clinic, we have 2 Q-switched ruby laser systems. On a daily basis, the beam patterns, both the optical axis of the beam and its treatment footprint, are checked on dedicated printed sheets and footprint paper, respectively, at the beginning of the day and after the last procedure. Every two weeks we calibrate our systems in-house using a precise MI. Every six months we calibrate the systems in-house with the MI, and then we send the systems back to the manufacturers for calibration. Once every year, we have our MI calibrated by an accredited facility in Japan. In this way, we are not only ensuring accurate and safe treatment for our patients, but we are also producing accurate system and treatment data which can be replicated by others, the basis of evidence-based medicine.

Introduction

In 1974, The first author visited Professor Leon Goldman, the Godfather of laser dermatology, at the Medical Laser Center of the University of Cincinnati and studied laser treatment technology. Six months later, he returned to Japan with the intent of purchasing the same type of medical ruby laser system which was used at Cincinnati. Unfortunately the company which made Goldman's laser machine had gone out of business. The first author was therefore forced to purchase an industrial ruby laser system from Korad Co. Ltd. in the USA, and modify it for medical use by himself.

In 1975, Ohshiro and his medical staff simultaneously founded the Ohshiro Clinic and the Japan Medical Laser Laboratory (JMLL). In order to obtain a good, consistent treatment result safely and surely, we recognized that we needed to achieve the precise output power from the laser system and deliver an accurate and homogeneous beam pattern for the irradiated area. To get such consistently good performance, we precisely maintained and managed the laser system in JMLL and at the same time, we performed accurate and careful treatments in the Ohshiro Clinic.

At the beginning, we used a normal millisecond domain pulsed ruby laser for the treatment of pigmented nevi, but as time passed and new systems were developed, our first pioneering ruby laser was replaced by nanosecond domain Q-switched ruby laser systems with which we now treat our patients.

In this paper, we would like to explain about our experiences and methods of the calibration and checking for our two Q-switched ruby laser systems and also the maintenance of the systems we use for system checks and beam measurement.

The comprehensive timetable is as follows:

1. 1: A daily check of the optical axis of the beam at the beginning and end of each day and a daily check of the beam irradiation pattern at the beginning and end of each day.

2. 2: An in-house calibration performed every 2 weeks with the MI.

3. 3: A 6-monthly calibration performed both in-house with our MI and also externally by the system manufacturers, with repair if required.

4. 4: Annual calibration of the in-house MI by an accredited facility in Japan. We therefore have to keep good relationships with the manufacturers and the accredited facility in Japan.

Through this rigorous maintenance and calibration schedule, we are able to maintain our Q-switched ruby laser systems, allowing them to deliver an accurate and aligned beam with precise and known parameters. We recommend that this should be performed for all Q-switched laser systems, by all clinics using lasers in medicine and surgery.

Materials and Methods

1. 1: The optical axis check and the irradiated pattern check on the treatment day

   Before the daily treatment, we check the optical axis of both of our Q-switched ruby laser systems (Nippon Sekigaisen Ltd. Japan, wavelength of 694.3 nm, energy density range 3-10 J/cm², pulse width 20 nsec, repetition rate 1 Hz, spot size 5 mm ϕ, Figure 1) in the early morning and the evening of each treatment day. The circle of the head of the distance gage should be settled inside the circle of the printed paper and should not touch the circle of the printed paper (Figure 2). We irradiate black footprint paper with the lasers at 8 J/cm² at spot sizes of 7 and 5 mm in diameter early every morning before any patients are treated. The medical doctor should confirm the irradiation pattern (IP) for a good circular shape and beam homogeneity (i.e., no hotspots). The doctor should also check the IP at the end of the working day with the laser set at 8 J/cm² and a spot size of 7 mm in diameter.

2. 2:The two-weekly calibration

   In the Ohshiro Clinic, every 2 weeks both Q-switched ruby laser systems are calibrated in-house using the a Laser Power/Energy Meter 30A-P-17 (OPHIR JAPAN LTD., Figure 3) as our MI. We check the output power at 7.5 J/cm² and 5 J/cm². We set the systems at 7.5 J/cm² and use a 5 mm diameter spot size for the calibration.

3. 3:The six-monthly calibration by two parties (in-house at the Ohshiro clinic and JMLL and externally at the manufacturers)

   We ask the manufacturer to check our Q-switched ruby laser systems, twice a year in June and December after we have checked the systems inhouse using our own MI. Both parties should separately calibrate the systems using their own MIs.

4. 4:The annual calibration of our MI by the accredited facility

   We use an OPHIR MI to check the accuracy of the system parameters for both lasers. Once a year, we return our MI to OPHIR JAPAN LTD., which is the accredited facility in Japan, for a calibration check.

Figure 1:

Nippon Sekigaisen Ltd. 694.3nm, 3-10J/cm², 20nsec, 1Hz, 5mmϕ,

Figure 2:

Relationship of the distance gage and the circle of the printed paper.

Figure 3:

Right side is the Laser Power/Energy Meter 30A-P-17. Left side is the Display Monitor NOVA. (OPHIR JAPAN LTD.)

Results

1. 1:The optical axis check and the irradiated pattern check on the treatment day

   Figure 4 shows the check sheet of the optical axis and the irradiated pattern of one of our Q-switched ruby lasers. The room temperature (RT), the room humidity (RH), Output Power (OP), the morning beam axis (MBA), the evening beam axis (EBA), the morning irradiation pattern (MIP) and the evening irradiation pattern (EIP) are all shown on the sheet.

2. 2:The two-weekly calibration

   We calibrate both Q-switch Ruby laser systems at 7.5 J/cm² and 5 J/cm² every two weeks, using the Laser Power/Energy Meter 30A-P-17.

   Table 1-1, Table 1-2 and Table 1-3 are the Calibration Sheets of the two-weekly calibrations. The calibration date is shown at the top right of each Table.

   The Name of the Laser Device, Set Value (J/cm2), Irradiated area Diameter (ID, mm), Lower Value (LV, J), Standard Value (SV, J), Measuring Value (MV, J), Measuring Rate of the Output Power (MR, %) are written in the appropriate table cells. As we are calibrating two Q-switched ruby lasers, we have designated them as No.1 Q-ruby and No.2 Q-ruby, and we put the appropriate system name in the table.

3. 3:The six-monthly calibration by two parties (Ohshiro clinic and JMLL side and the manufacturer's side)

   Twice a year, in June and December, following inhouse calibration of both systems with our MI, we return the systems to the manufacturers and ask them to check the systems independently. The 2 parties should separately calibrate the laser systems using their own MIs.

   Table 2-1 and Table 2-2 show examples of the measurement records of the six- monthly calibration by the two parties. The calibration date is shown at the top right of each Table.

   The name of the MI, Name of the Laser Device, Set Value (J/cm²), Irradiated Diameter (ID, mm), Lower Value (LV, J), Standard Value (SV, J), Measuring Value (MV, J), and the Measuring Rate of the Output Power (MR, %) are filled in to the appropriate table cells In the example shown, we have illustrated the data of only the No. 2 Q-ruby System. We found an unstable MR in Table 2-1, especially in the Set Value of 5 J/cm² of our in-house MI. We therefore asked the manufacturer to check and repair the system. When the system was returned to us, we checked the MV and MR of the laser system again. Finally we got the good result seen in Table 2-2. When the comparison of the measurement of the data from the two parties is within ±3%, our in-house MI could be acceptable for the calibration.

4. 4:The annual calibration of the MI by the accredited facility

   Once a year, we ask OPHIR JAPAN LTD, an accredited MI calibration facility in Japan, to calibrate our MI Figure 5 is the copy of the Certificate of Calibration issued by OPHIR Japan LTD, which annually certifies and guarantees the accuracy of the MI. On the right hand side of Figure 3, showing the in-house MI components is the power meter called Laser Star, and on the left hand side of the figure is the display monitor called NOVA. Figure 6 is the head characteristics report from the power meter, and Figure 7 is the characteristics report of the display monitor. Figure 8 (power meter) and Figure 9 (display monitor) show the calibration seals fixed to the MI components and provided for the user by OPHIR Japan LTD after the annual MI calibration check.

Figure 4:

the daily check sheet of the Q-switched ruby laser. RT: Room Temperature. RH: Room Humidity. OP: Output Power. MBA: Morning Beam Axis. EBA: Evening Beam Axis. MIP: Morning Irradiation Pattern. EIP: Evening Irradiation Pattern.

Table 1-1: Measuring Sheet by every two weeks. ID: Irradiated Diameter. LV: Lower Value. SV: Standard Value. MV: Measuring Value. MR: Measuring Rate of the Output Power=MV*100/SV.

						24th Nov. 2012
Name of Laser	Set Value (J/cm2)	ID. (mm)	LV (Joule)	SV (Joule)	MV (Joule)	MR (%)
No.1 Q-Ruby	5	5	0.88.	0.98	0.98	100.0
	7.5	5	1.33	1.47	1.41	95.9
No.2 Q-Ruby	5	5	0.88.	0.98	0.89	90.8
	7.5	5	1.33.	1.47	1.35	91.8

Table 1-2: Measuring Sheet by every two weeks. ID: Irradiated Diameter. LV: Lower Value. SV: Standard Value. MV: Measuring Value. MR: Measuring Rate of the Output Power=MV*100/SV.

						07th Dec. 2012
Name of Laser	Set Value (J/cm2)	ID. (mm)	LV (Joule)	SV (Joule)	MV (Joule)	MR (%)
No.1 Q-Ruby	5	5	0.88.	0.98	0.92	93.9
	7.5	5	1.33.	1.47	1.44	98.0
No.2 Q-Ruby	5	5	0.88.	0.98	0.84	85.7
	7.5	5	1.33.	1.47	1.24	84.4

Table 1-3: every two weeks Calibration Sheet by. ID: Irradiated Diameter. LV: Lower Value. SV: Standard Value. MV : Measuring Value. MR: Measuring Rate of the Output Power=MV*100/SV.

						21th Dec. 2012
Name of Laser	Set Value (J/cm2)	ID. (mm)	LV (Joule)	SV (Joule)	MV (Joule)	MR (%)
No.1 Q-Ruby	5	5	0.88	.0.98	.0.91	.92.9
	7.5	5	1.33	1.47	1.39	.94.6
No.2 Q-Ruby	5	5	0.88	.0.98	.0.95	.96.9
	7.5	5	1.33	1.47	.1.42	.96.6

Table 2-1: Six monthly Measuring Record at pre-repair condition. MI: Measuring Instrument. ID: Irradiated Diameter. LV: Lower Value. SV: Standard Value. MV: Measuring Value. MR: Measuring Rate of the Output Power=MV*100/SV.

							18th Dec. 2012
Name of MI	Name of Laser	Set Value (J/cm2)	ID. (mm)	LV (Joule)	SV (Joule)	MV (Joule)	MR (%)
Ohshiro's MI	No.2 Q-Ruby	5	5	0.88	.0.98	0.90	91.7
		7.5	5	1.33	1.47	1.30	88.3
Trader's MI	No.2 Q-Ruby	5	5	0.88	.0.98	0.84	85.6
		7.5	5	1.33	1.47	1.27	86.2

Table 2-2: Six monthly Measuring Record at post-repair condition. MI: Measuring Instrument. ID: Irradiated Diameter. LV: Lower Value. SV: Standard Value. MV: Measuring Value. MR: Measuring Rate of the Output Power=MV*100/SV.

							18th Dec. 2012
Name of MI	Name of Laser	Set Value (J/cm2)	ID. (mm)	LV (Joule)	SV (Joule)	MV (Joule)	MR (%)
Ohshiro's MI	No.2 Q-Ruby	5	5	0.88	.0.98	1.01	102.9
		7.5	5	1.33	1.47	1.45	98.5
Trader's MI	No.2 Q-Ruby	5	5	0.88	.0.98	1.03	104.9
		7.5	5	1.33	1.47	1.45	98.5

Figure 5:

the copy of the certificate of completion of calibration issued by OPHIR Japan LTD. as the accredited facility in Japan.

Figure 6:

he head characteristic report of Laser Star

Figure 7:

the analog performance report of Display Monitor NOVA

Figure 8:

the calibration seal of Laser Star

Figure 9:

the calibration seal of Display Monitor NOVA

Discussion

Every month, nearly 2,000 outpatients consult our clinic for treatment of their skin lesions. That is why we must calibrate every machine every two weeks. We have over 30 kinds of laser systems, 3 full-time doctors, over 15 part-time doctors, 9 laser engineers, over 12 full- and part-time nurses and other support staff. Nowadays we have 4 Q-switched laser systems, comprising our 2 ruby lasers, 1 Nd:YAG laser and 1 Alexandrite laser. These four laser systems are checked every two weeks on the same day.

In Table 1-1, Table 1-2 and Table 1-3, we fired our 2 ruby systems (No 1 and No 2) at 7.5 J/cm² with a 5 mm diameter irradiated area. In the case of a Q-switched ruby laser, the 100% level of the output power (Standard Value: SV) of the laser is calculated to be 1.47 J as follows:

7.5 J/cm² × {3.142 (π) × 0.125 . } cm^2. = 1.47 J

where 7.5 J/cm² is the set energy density, and 0.125 is the square of the radius of the irradiated area.

We performed calibration 3 times for our No.2 Q-ruby laser system using our in-house MI on 24^th Nov. 2012, and the measuring value (MV) became 1.35 J. (mean value of the three calibration values). The measuring rate of the output power (MR) of our laser system was calculated to be 91.8% as follows:

We set the tolerance range of the MR (TR) from 90% to 100% from our clinical experience. 91.8% (MR) falls between 90% and 100%, so No 2 Q-ruby was acceptable for clinical use on 24^th Nov. 2012. However, on 07^th Dec. 2012, the MR of the No.2 Q-ruby was 84.4% as seen from. Table 1-2. We therefore asked the manufacturer to check and repair this system. As seen in Table 1-3, we achieved an MR value of 96.6% for No.2 Q-ruby system on December 21^st, 2012. So, we could therefore use the system for treatment on the same day. This shows how very important it is to check the Output Power (MV) and MR of Q-switched ruby laser systems every two weeks, when the volume of use is as great as it is in our clinic.

When the measuring rate of the output power (MR) exceeds 100%, the risk of the treatment causing some kind of unexpected overtreatment-related side effect becomes higher. When the MR is 100%, the best treatment result can be achieved. When the MR becomes closer to 90%, the safety range gets wider and the effect of the treatment becomes lower, so finally we set the tolerance range of the MR (TR) from 90% to 100%. When the calibration results are within the TR, the system can be used for treatment on that day. When we encounter any trouble with the system, we should calibrate and check the irradiated pattern tentatively. When we find that the output power falls outside of the TR we should ask the manufacturer to check and repair the laser system. Because the MR can be changed easily by the room temperature (RT) and the room humidity (RH), we should control the RT between 21°C and 28°C and adjust the RH using the air conditioner to between 30% and 50%.

We ask the manufacturer to check our Q-switched Ruby laser system, twice a year in June and December. The two parties should separately calibrate the laser system using their own MI, and we should compare the calibration data. Of course we calibrate both systems, but in the interests of space we have shown the data from only our No.2 Q-ruby Laser System. As explained, we found an unstable MR on the in-house MI as shown in Table 2-1, especially at the Set Value 5 J/cm². In the case of this laser system, instability was seen at the low rather than the high output settings, so we requested the manufacturer to repair the system, following which we checked the MV and MR again and finally we got the good result seen in Table 2-2. When the comparison of the data of both parties is within ±3%, our in-house MI could be acceptable for calibration. As already stated, we set the tolerance range of the MR (TR) from 90% to 100% but when we consider the ±3% allowance level of the MI, the tolerance range of the MR (TR) should be change between 90% and 103%. On the other hand the lower threshold of 90% cannot be changed to 87%, because we must consider the treatment efficacy. We send our MI to an accredited Japanese facility.

After the facility has successfully tested the MI we are able to receive the Certificate of Calibration (Figure 5), the characteristics report of the display monitor (Figure 6) and the power meter (Figure 7), and the facility affixes a calibration seal to the back of the power meter case (Figure 8) and the display monitor (Figure 9). If anyone attempts to open either of these components, the seal will be broken and the calibration data will no longer be valid.

On a daily basis, before treatment starts, we have to check the optical axis of both our Q-switched ruby laser systems. After setting the head of the handpiece distance guide inside one of the circles on the printed paper, we fire the laser onto the paper. If the optical axis of the beam is correctly set, the laser beam should impact the center of the printed cross within the circle on the paper (Figure 10). However, if the optical axis is misaligned, the laser beam will impact outside of the center of the printed cross (Figure 11) In such a case, we must send the system back to the manufacturer to check both the optical alignment of the beam for any misalignment of the optical pathway, and the correct set-up of the distancing guide of the handpiece in case it has somehow become twisted or bent out of its correct shape.

Figure 10:

the laser beam should attack to the center to the cross mark of the printed paper.

Figure 11:

the laser beam should attack to the outside of the center of the cross mark of the printed paper.

To make sure the lasers operate in a uniform environment without spikes or troughs in room temperature and humidity which could adversely affect the performance of the systems, the treatment room temperature (RT) is controlled between 21°C and 28°C and the room humidity (RH) is controlled with an air conditioner to keep it between 30% and 50%

The black material used for coating the footprint paper and printing the alignment paper consists of fine carbon particles. When the laser beam strikes the black coating, the carbon coating or printing is instantly vaporized to show the beam impact, revealed by the white paper beneath the coating. If the optical axis is in good alignment, a white circular pattern appears on the footprint paper, and the center of the cross shape within the circle is targeted on the printed paper. The impacts of the morning beam axis (MBA) and the evening beam axis (EBA) can be seen in Figure 12. The morning IPs (MIP) and evening IPs (EIP) are shown in Figure 13. The physician should confirm an almost true circular shape for the IP and the beam homogeneity. The doctor should also check the irradiation pattern at 5 J/cm² for a spot size 7 mm in diameter at the end of working day, to make sure no problems have occurred with the IP results during the day. Figure 13 shows no difference in the IPs between the MIP and EIP. Because of the scatter effect at the beam periphery, it is almost impossible to obtain an absolutely perfect circular pattern, but when the pattern is very obviously irregular, as in Figure 14, we should return the laser system to the manufacturer for repair. In any case, the physician must judge the correctness of the irradiated pattern based on his or her clinical experience.

Figure 12:

the burning shape on the morning beam axis(MBA) and the evening beam axis(EBA)

Figure 13:

Morning and Evening irradiated pattern are shown on the MIP and the EIP of the printed paper.

Figure 14:

the irregular shape of the irradiated pattern

The circle at the tip of the handpiece distancing guide should be carefully placed inside a circle on the printed paper and should not touch the sides of the circle (Figure 2). After placing the handpiece tip correctly, the laser is fired to irradiate the printed paper. In every case, we should note the date, the RT, the RH, the optical axis, and the irradiated pattern of the day in the daily check sheet (Figure 4).

When confirming the irradiated pattern using the footprint paper, the distance guides of 5 mm and 7 mm in diameter are used for testing, because 5 mm in diameter and 7 J/cm² or 7 mm in diameter and 5 J/cm² are often used for the treatment of abnormal melanin group lesions such as nevus of Ohta, or tattoo removal.

We have treated more than 4000 cases of nevus of Ohta over 38 years. From our experience, we have developed the following treatment method for nevus of Ohta with the Q-switched ruby laser system. Figure 15 and Figure 16 are the preoperative and postoperative views for an example of nevus of Ohta. Preoperatively, this patient was not happy going out with her nevus in this condition, so her long, white hair can be seen. We treated her with the Q-switched ruby laser system using the parameters of a spot size 7 mm in diameter and an energy density of 5 J/cm², or a 5 mm spot at 7 J/cm². The irradiated patterns which are shown in Figure 13 were used in the treatment. The treatment result was very good and a healthy skin tan could be seen together with well-cared for dark hair because she was no longer put off going out by the presence of her Ohta's nevus. The success of the procedure was due to the high degree of beam and system maintenance we regularly perform on our Q-switched ruby lasers, and indeed all lasers in the Ohshiro Clinic, to obtain the expected results in the treatment of pigmented lesions.

Figure 15:

Preoperative view of Ohta's nevus

Figure 16:

Postoperative view of Ohta's nevus

To treat the patient more safely and more surely, we should consider not only the calibration and the irradiation pattern of a laser, but many other factors must be kept in mind regarding the parameters and laser/tissue interaction. We recommend the reader to refer to the sets of the specialty-specific Guidelines published in this journal ^1-12), Smalley's paper on laser safety ¹³⁾ and the textbook ¹⁴⁾ of the International Laser License System (ILLiS):

http://islsminfo.com/certification-criteria.asp

Conclusions

In the case of the clinical or research use of Q-switched laser systems, the most important things to ensure safe and consistent treatment are the calibration of, and the irradiated pattern check for the laser systems. We recommend the following schedule to any clinic using Q-switched lasers in the treatment of patients:

• A daily check of the beam optical axis and irradiation pattern, at the beginning and end of the working day.

• To calibrate the laser systems every two weeks with accurate and tested in-house measuring equipment (MI).

• To calibrate the laser systems every six months in-house, and subsequently ask the manufacturers of the systems to calibrate, and if required, to repair the lasers.

• To calibrate the in-house MI once a year by periodically returning it to an accredited measurement and calibration facility in the country.

In this paper, we have explained about our method of the calibration and the irradiated pattern check for our Q-switched ruby laser systems and the care of the measuring instrument we use for in-house calibration. This process may seem quite complex, however it is an essential but simple routine which takes very little time to complete once it has become an accepted part of the daily work schedule. Most importantly, it keeps the laser systems performing accurately and delivering the parameters actually set, so that the clinician can get the clinical effect he or she wants. More importantly, with safe and effective treatment, the patients can be consistently satisfied with the treatment result.