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ORIGINAL ARTICLE
Year : 2016  |  Volume : 12  |  Issue : 2  |  Page : 1056-1059

Radiological safety features of indigenously developed radiotherapy simulator


1 Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, Anushaktinagar, Mumbai, Maharashtra, India
2 Divison of Remote Handling and Robotics, Bhabha Atomic Research Centre, Trombay, Mumbai, Maharashtra, India
3 Panancea Medical Technologies Limited, Bangalore, Karnataka, India

Date of Web Publication25-Jul-2016

Correspondence Address:
Rajesh Kumar
Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS Building, Anushaktinagar, Mumbai - 400 085, Maharashtra
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.150412

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 > Abstract 


Objective: To study the radiological safety feature of indigenously developed radiotherapy simulator.
Materials and Methods: A comprehensive study for radiological safety features of the unit were carried out as per the standard protocol/guidelines. NERO mAx X-ray test device was used for KVp, mA, mAs, and X-rays output related test of the units along with other required test device.
Results: All the measurement results indicate that all the tested parameters of this simulator are well within the prescribed tolerance limit.
Conclusion: The simulator is safe for routine clinical use.

Keywords: Quality assurance, radiological safety, radiotherapy simulator


How to cite this article:
Kumar R, Kar DC, Sharma SD, Ilpakurty R, Subrahmanyam GV. Radiological safety features of indigenously developed radiotherapy simulator. J Can Res Ther 2016;12:1056-9

How to cite this URL:
Kumar R, Kar DC, Sharma SD, Ilpakurty R, Subrahmanyam GV. Radiological safety features of indigenously developed radiotherapy simulator. J Can Res Ther [serial online] 2016 [cited 2020 Apr 3];12:1056-9. Available from: http://www.cancerjournal.net/text.asp?2016/12/2/1056/150412




 > Introduction Top


Radiotherapy simulator is a device which has mechanical and radiation beam geometry identical to that of a teletherapy machine and imaging system similar to that of a diagnostic imaging unit. It plays major role for accurate radiotherapy planning and dose delivery. It is used to determine patient positioning and beam parameters. Among the medical centers with teletherapy facilities in our country, many do not have radiotherapy simulator for accurate delivery of radiation therapy. There is wide gap between the demand and availability of radiotherapy facilities in the country. Considering the growing requirement for such machines, a digital radiotherapy simulator was developed by Bhabha Atomic Research Centre and its technical specifications are given in [Table 1]. This paper describes the radiological safety features of this radiotherapy simulator.
Table 1: Technical specification of indigenously developed radiotherapy simulator

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 > Materials and Methods Top


A comprehensive study for radiological safety features of the unit were carried out as per the standard protocol/guidelines.[1],[2],[3],[4],[5],[6] NERO mAx X-ray test device (Victoreen Inc) was used for KVp, mA, mAs, and X-rays output related test of the units. Central beam alignment was evaluated using a collimator and beam alignment test tools. Accuracy of tube accelerating voltage was tested for 45–150 kVp. Accuracy of timer was evaluated for set time 0.1–1 sat 60 kVp and 100 mA. Linearity of mA loading were studied for set mA ranges from 20 to 320 mA with fixed kVp of 80 and time 1 s. Linearity of mA loading was estimated using coefficient of linearity (COL). Linearity of timer was tested for time setting from 280 to 1,000 ms by keeping constant value of kVp and mA at 50 and 200, respectively.

Accuracy of mA setting for set value ranges from 50 to 400 mA was evaluated. Output consistency for different kVp and mAs setting were evaluated. X-ray beam output at 1 m in mR/mAs at 80 kV for field size of 20 × 20 cm 2 were measured for different combination of current and time. The output consistency was estimated by determining the coefficient of variation (COV). Measurement of half-value thickness for 70 kV X-ray tube voltages was measured. Attenuation curves were plotted by varying the thickness of the aluminum filter, and measuring the exposure. The thickness of aluminum was increased in 0.5 mm steps until the measured exposure was well below half of the reading corresponding to no added filter. The total filtration was derived from the standard data set from the measured half value layer (HVL) value. Aluminum equivalent of table top was also measured. Radiation leakage from X-ray tube housing was measured using 40 cc cylindrical ionization chamber with UnidoseE electrometer. Radiation levels at 5 cm from the surface of high tension transformer were measured using a pressurized ion chamber-based survey meter. Exposure rate at table top in fluoroscopy mode was also measured using the above mentioned survey meter. Image quality of simulator was access using a high contrast resolution test tools and Leeds tools.


 > Results and Discussion Top


[Figure 1] shows the image acquired for beam alignment test. It can be inferred from the image that both ball are exactly coinciding with each other and beam alignment found to be well below the acceptable values of 1.5°. [Figure 2] presents the congruence between set and observed values of delineating wire for field size ranges from 5 × 5 cm 2 to 15 × 15 cm 2. It can be inferred that they are in well agreement with each other. [Figure 3] shows the image of Leeds phantom acquired from the simulator. The 13th circle for low contrast resolution which is corresponding to the contrast value of 0.022 and 10th line pattern for high contrast resolution which is corresponding to the 1.4 lp/mm are visible in the image. [Table 2] shows the test result of set and measured kVP values. It can be observed that the variation between measured and set kVP values are ranges from −0.1 to 1.1 kVp, which is well within the tolerance limit value of ± 5kVp. [Table 3] represents the variation between measured and set value of the timer. The tolerance values for the variation between measured and set timing is ± 10%, while the evaluated variation was not detectable. [Table 4] shows the test result for mA loading linearity. The estimated COL was found to be 0.004 up to 100 mA and 0.006 for 160-320 mA setting. Results of linearity of timer can be seen in the [Table 5]. The evaluated values of COL were found to be 0.006, which is well within the tolerance limit values of 0.1. Variation between measured and set value of mA is listed in [Table 6]. Evaluated percentage error was found to be in range of 0.38-1%. [Table 7] shows the results of output consistency. It can infer from the table that a COV value varies from 0.001 to 0.005 in respect to the tolerance limit of 0.05. X-rays output in term of mR/mAs at 80 kV for field size of 20 × 20 cm 2 at different mA setting is given in the [Table 8]. It can be seen from the table that measured values have COV of about 0.02, which is less than the tolerance limit value of 0.05. The measured values of HVL for 70 kV was found to be 4.08 mm of aluminum (Al). The corresponding total filtration was estimated from the standards result and found to be 7.6 mm Al. The Al equivalent of table top was measured and found to be 0.5 mm. Radiation leakage level at 1 m from focus was measured and found to 122 mR in 1 h for 320 mA-min and 73.44 mR in 1 h for 180 mA-min. This value is well within the tolerance limit of 115 mR in 1 h for 180 mA-min. The radiation level at 5 cm from the surface of high tension transformer was 0.1 mR in 1 h for 5mA and 60 min setting.
Figure 1: Image showing the results of beam alignment test of simulator

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Figure 2: Image showing the results of congruence test for set and observed values of delineating wire for field size (a) 5 × 5 cm2 (b) 10 × 10 cm2 (c) 12 × 12 cm2 (d) 15 × 15 cm2

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Figure 3: Image of Leeds phantom acquire by simulator

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Table 2: Accuracy of tube accelerating voltage (kVp)

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Table 3: Accuracy of timer setting

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Table 4: Test result for linearity of mA loading station

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Table 5: Test result for linearity of timer

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Table 6: Variation of set and measured mA values

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Table 7: Measurements of output consistency

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Table 8: X-ray beam output at 1m in mR/mAs at 80 kV for field of 20×20 cm2

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 > Conclusions Top


Radiological safety features of this simulator were studied to evaluate its performance for comparison with the standards. Measurement results indicate that all the tested parameters of this simulator arewell within the prescribed tolerance limit. The simulator is safe for routine clinical use.

 
 > References Top

1.
Type approval tests for simulator, BARC/RP and AD/MPSS/QA/SIM, Radiological Physics and Advisory DivisionBhabha Atomic Research Centre, Mumbai.  Back to cited text no. 1
    
2.
Type approval tests for Diagnostic X-ray Machine, BARC/RP and AD/MPSS/TA/XD-4, Radiological Physics and Advisory Division Bhabha Atomic Research Centre, Mumbai.  Back to cited text no. 2
    
3.
European Commission. European guidelines on quality criteria for diagnostic radiographic images. EUR 16260ISBN 92-827-7284-5, Brussels; 1996.  Back to cited text no. 3
    
4.
Quality assurance handbook. Middleton (WI): RMI; 1992.  Back to cited text no. 4
    
5.
American Association of Physicists in Medicine Medical Physics Monograph 4; 1977.  Back to cited text no. 5
    
6.
International Electrotechnical Commission, Particular requirements for the safety of radiotherapy simulators, IEC- 60601-2-29 (1991).  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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