|Year : 2020 | Volume
| Issue : 1 | Page : 38-42
Installation, commissioning, and performance evaluation of Bhabhatron-II TAW – An Indian-made telecobalt unit
Shashi Bhushan Sharma, Gautam Sarma, Mithu Barthakur, Pranjal Goswami, Bhaveshwar Yadav, Shachindra Goswami
Department of Radiation Oncology, Dr. B. Borooah Cancer Institute, Guwahati, Assam, India
|Date of Submission||11-Jun-2020|
|Date of Decision||24-Jun-2020|
|Date of Acceptance||29-Jun-2020|
|Date of Web Publication||25-Sep-2020|
Mr. Shachindra Goswami
Department of Radiation Oncology, Dr. B. Borooah Cancer Institute, Guwahati, Assam
Source of Support: None, Conflict of Interest: None
Aim: The aim of this study was to report commissioning and performance evaluation of Bhabhatron-II TAW (an Indian made machine). Materials and Methods: Commissioning comprises of following quality assurance (QA) (a) electrical QA, (b) mechanical QA, (c) radiation QA and (d) survey of installation. Electrical QA were done for various components of the unit for its functionality. Mechanical QA were done and the measured data were verified as per guidelines of Atomic Energy Regulatory Board (AERB), India and vendor's specified values. Cylindrical ionization chamber, electrometer, ready pack films, water phantom, thermometer and barometer were used during radiation QA and survey of installation procedures. Moreover, the data so generated were fed to treatment planning system (TPS) for dose calculation and also kept in proper tabular manner for clinical use. Results: Couch and collimator parameters were found to comply the tolerance criteria. Source strength of 172.2 roentgen per minute at 1 meter (RMM) was measured with an absolute dose rate of 225.76 cGy/min at dmax for 10cm x 10cm field size at normal treatment distance (NTD). Shutter timer error of 0.004 min was measured and incorporated in the clinical data. A maximum of 3.66 % variation was noted for 300 (15W × 20) physical wedge transmission factor between measured and vendor specified value. Radiation leakage through beam limiting device (BLD) and outside BLD were found to be within the limits prescribed by AERB. Conclusion: Commissioning is a prerequisite process after installation of a radiation therapy machine for medical purpose. Bhabhatron-II machine has several advantages over other telecobalt machine. Features like high source storage capacity of machine head, one pair of asymmetric jaw, closure of jaws to 0 cm x 0 cm during radiation emergency and presence of one motorized wedge filter makes it unique and yet cost effective telecobalt machine..
Keywords: Bhabhatron-II TAW, commissioning, performance evaluation, quality assurance
|How to cite this article:|
Sharma SB, Sarma G, Barthakur M, Goswami P, Yadav B, Goswami S. Installation, commissioning, and performance evaluation of Bhabhatron-II TAW – An Indian-made telecobalt unit. J Radiat Med Trop 2020;1:38-42
|How to cite this URL:|
Sharma SB, Sarma G, Barthakur M, Goswami P, Yadav B, Goswami S. Installation, commissioning, and performance evaluation of Bhabhatron-II TAW – An Indian-made telecobalt unit. J Radiat Med Trop [serial online] 2020 [cited 2023 Mar 26];1:38-42. Available from: http://www.jrmt.org/text.asp?2020/1/1/38/296108
| Introduction|| |
Cancer is a major public health problem and the incidence is increasing worldwide. About 65% of all cancer deaths globally occurred in low- and middle-income countries (LMICs) in 2012., This is projected to increase to 75% by 2030., An estimated 18.1 million new cancer diagnoses and 9.6 million cancer deaths happened in 2018., As per the WHO estimation, this will increase to 29.5 million new cancer diagnoses and 16.5 million cancer-related deaths annually by 2040. In high-income country like the United States, 1,806,590 new cancer cases and 606,520 cancer deaths are projected to occur in 2020. Patients with cancer in LMICs have a poorer prognosis because of relatively low awareness, late diagnosis, and the lack of access to affordable curative services., More than 50% of all cancer patients require radiation therapy during their course of illness., The main hurdle to improve access to cancer care in LMICs is the high cost of modern radiotherapy machines. Among all the external-beam teletherapy machines available, telecobalt machines are the cheapest. Although telecobalt machines have some shortcomings, they have the advantages of (i) low cost, (ii) low maintenance cost, (iii) lower power need (iv), less machine downtime, and (v) constancy of beam quality. They are suitable for treatments of commonly encountered type of cancers in LMICs.
Before using any radiation facility for medical purpose, every machine needs to undergo commissioning as a prerequisite procedure. Commissioning is the process during which structures, systems, and components of a nuclear and radiation facility, on being constructed, are made functional and verified to be in accordance with design specifications and to have met the performance criteria.
Bhabhatron-II Tungsten, Asymmetric, and Motorized Wedge (TAW) is an Indian-made telecobalt machine. It was designed and manufactured by Bhabha Atomic Research Centre, India. It complies with the radiological safety standards of the International Electrotechnical Commission (IEC). Many cancer centers of LMICs have recently installed Bhabhatron-II TAW for cancer treatment. In this study, we will discuss the various parameters related to commissioning and performance evaluation of Bhabhatron-II TAW installed at Dr. Bhubaneswar Borooah Cancer Institute, Guwahati, a tertiary cancer institute of India. When comparing with other telecobalt machines, Bhabhatron-II TAW machine has some unique features like high-source loading capacity of 250 Roentgen per minute at 1 m (RMM) in the machine head, one pair of asymmetric Y-jaw as Y1 and Y2, capability of automatically closing of jaws to 0 cm × 0 cm in case of source stuck, and one motorized wedge of 60° inside the collimator head of the machine.
This study was approved by the expedited review board of the Institutional Ethics Committee.
| Materials and Methods|| |
During installation and commissioning of the Bhabhatron-II TAW telecobalt machine, a series of Quality Assurance (QA) checks were performed in compliance with Atomic Energy Regulatory Board (AERB), India. The QA involves (a) electrical QAs, (b) mechanical QAs, (c) radiation QAs, and (d) survey of installation. Post commissioning and acceptance tests, geometrical and beam data were fed to the treatment planning system for dose calculation. These data were preserved in proper tabular format as a baseline for future quality control (QC) program. Future QC programs were planned as per the literature published by the American Association of Physicist in Medicine Report No. 46.
Electrical QAs are performed with visual and functional observations. In mechanical QAs, the parameters of optical field size verifications, mechanical isocenter with respect to the rotation of gantry and collimators, accuracy of alignment lasers, optical distance indicator (ODI) accuracy, movements of couch (treatment table) in various directions, collimator and gantry angle accuracy, parallelism and orthogonality of jaws, etc., were checked for their specified tolerance prescribed by AERB, India.
Radiation QA involves the measurements of shutter timer error, optical and radiation field congruence, isocenter accuracy, absolute radiation output of the unit, etc., For carrying these QA tests, the following equipments are used:
- Cylindrical ion chamber of 0.6 cc volume (make: PTW) with electrometer
- Water phantom (30 cm × 30 cm × 30 cm) with a waterproof sleeve
- Calibrated thermometer and barometer
- Ionization-based survey meter (Fluke Biomedical System, Model: 451)
- Radiochromic ready-packed verification film (Kodak X-OMAT V Film)
- Slab phantom of 1-cm thick slabs.
Optical field size verification
Optical field size was verified for field sizes 5 cm × 5 cm, 10 cm × 10 cm, 15 cm × 15 cm, 20 cm × 20 cm, 25 cm × 25 cm, 30 cm × 30 cm, and 35 cm × 35 cm using a graph sheet at 80 cm source to surface distance (SSD) keeping and gantry and collimator 0°. Deviations were noted for the field sizes.
Tolerance: For ≤10 cm × 10 cm: ±1 mm and for >10 cm × 10 cm: ±2 mm
Mechanical Isocenter check (with respect to collimator rotation)
Mechanical isocenter check was performed by placing a graph sheet on the flat couch at 80 cm SSD with gantry 0°. Optical crosshair was initially matched with a point on the graph sheet and then the collimator was rotated in clockwise and counterclockwise direction with its extreme limits. The deviation of the crosshair was observed throughout the procedure and the maximum deviation was noted.
Tolerance: Within 4-mm diameter circle.
Mechanical Isocenter check (with respect to gantry rotation)
A pin with a sharp tip was attached on the couch edge and its tip was matched with isocenter. Now, the gantry was rotated ± 180° and deviation was noted throughout the 360° rotation of gantry.
Tolerance: Within 4-mm diameter sphere.
Laser alignment test
Laser alignment test tool was placed on the couch and was aligned with help of crosshair and ODI. Deviation of the three lasers (sagittal, coronal, and transverse) was checked with the test tool.
Tolerance: ±1.5 mm.
Roentgen per minute at one meter measurement
The 0.6 cc ionization chamber with the buildup cap was placed at isocenter with its long axis parallel to the gantry axis of rotation. The ionization chamber was exposed for 1 min for a field size of 20 cm × 20 cm and electrometer reading was noted.
Tolerance: ±10% from quoted value.
Congruence between Optical and Radiation field
For this test, a 30 cm × 30 cm ready-packed film pinpricked at the optical field (10 cm × 10 cm) borders was placed on the couch at 80 cm SSD. After putting sufficient buildup, the film was exposed to the optically defined field sizes to get an optimal optical density of one. After developing the film, the deviation between the optical and radiation field was noted for all the edges. This procedure can be repeated for different field sizes.
Tolerance: For ≤10 cm × 10 cm: ±1 mm and for >10 cm × 10 cm: ±2 mm
Shutter timer error measurement
For the measurement of shutter timer error, the experimental setup was done as per the International Atomic Energy Agency (IAEA) Technical Report Series (TRS)-398 document. Electrometer reading R1 for T = 2 min of exposure was noted and then meter reading R2 for exposure time of T/2 + T/2 min was noted without resetting the electrometer. From the collected readings, shutter timer error was calculated using the following formula.
Output calibration for different field sizes
The measurements of the absolute absorbed dose for various field sizes were carried out as per the IAEA TRS-398 document. Output factors were calculated for various field sizes ranging from 5 cm × 5 cm to 30 cm × 30 cm.
Wedge (physical) factor
After output measurement, the same setup was used for the measurement of wedge transmission factor. Here, the electrometer readings were noted for 1 min of exposure for both the open field and wedge fields. The ratio of the electrometer reading with wedge and without wedge gives the wedge transmission factor for that particular wedge filter. Measurements were taken for 10 cm × 10 cm and maximum wedge fields.
During the ON and OFF position of the source, radiation leakage was measured as per the CODE NO. AERB/RF-MED/SC-1 (Rev. 1).
Radiation protection survey
Radiation protection survey was performed for maximum open-field size all around the installation and control console using an ionization-based survey meter for four gantry angles (0°, 90°, 180°, and 270°).
| Results|| |
Upon successful installation of the unit, all the required QAs were done for obtaining a license for clinical use.
Electrical quality assurance tests
Tests such as electrical interlocks, gantry head display, control console display, and control console functions were performed for the unit and results were satisfactory.
Mechanical quality assurance tests
Couch and collimator
All mechanical parameters for couch and collimator of the unit were performed and found to be within the specified limits of national competent authority [Table 1].
Radiation quality assurance tests
Roentgen per minute at one meter
RMM for the unit was found to be 172.2 RMM with an acceptable deviation of 7.62% from the quoted RMM from Board of Radioisotope and Technology, India.
Shutter timer error
It was 0.004 min [Table 2] which needs to be incorporated in the treatment time calculation.
The output (dose rate) for 10 cm × 10 cm was 225.76 cGy/min [Table 3]. The output of 10 cm × 10 cm was used as a baseline value for subsequent monthly measurements.
|Table 3: Absolute absorbed dose measurement as per the International Atomic Energy Agency Technical Report Series-398|
Click here to view
Optical and radiation field congruence
Congruence between optical and radiation field size for 5 cm × 5 cm and 10 cm × 10 cm was found to be ≤ 1 mm. For field sizes 15 cm × 15 cm and 20 cm × 20 cm, the deviation was ≤ 2 mm.
The wedge transmission factor (WF) for various wedges was determined and is tabulated in [Table 4]. A maximum variation of 3.66% between manufacturer specified value and measured WF was noted.
Maximum leakage radiation at 5 cm from source storage surface was found to be 1.5 mR/h (tolerance: ≤20 mR/h) and at 1 m from the source was 0.3 mR/h (tolerance: ≤2 mR/h) in source OFF condition. The maximum transmission through beam-limiting device in source ON condition was measured to be 1.3% (tolerance: 2%). Leakage radiation from the source housing in ON condition in the patient plane was found to be a maximum of 0.12% and average of 0.098% (tolerance: maximum 0.2%, average 0.1%). Leakage radiation from the source housing in ON condition at 1 m from the source in other than the patient plane was found to be 0.3% (tolerance: 0.5%). The maximum radiation during radiation protection survey around the bunker was found to be 1.3 mR/h which was a no occupancy area.
Proper radiation warning symbols were also placed at the maze entrance door and outside the treatment room. Gamma zone monitor was installed inside the bunker.
| Discussion|| |
Commissioning and performance evaluation are done to ensure radiation safety and accurate dose delivery of the machine. The guidelines for commissioning and performance evaluation can be obtained from IEC documents or respective national competent authority. However, data such as physical wedge filter transmission factor, couch transmission factor, and lead shielding tray transmission factor which are specific to the machine are provided by the vendor.
Our results were well within the acceptable criteria laid by AERB, India, and it also matched with the specifications provided by the vendor.
Some of the beam data such as percentage depth dose, tissue-to-air ratio, and Tissue-maximum ratio were taken from the published literature for dose calculations during clinical use.,
Six of seven physical wedge filter transmission factors have values ≤3% and maximum deviation was found to be 3.66% from vendor specifications. Akinlade et al. found that six wedges of seven wedge filters transmission factor values are ≤3% and maximum deviation of 6%. Mohib-UlHaq et al. reported that four wedges of seven wedge filters have transmission factor values ≤3% and maximum deviation of 5.01%. Tray transmission factors of shielding trays (plain and slotted) were measured and recorded as a baseline value for consistency check in future.
Bhabhatron-II TAW has a maximum source loading capacity which is 250 RMM. The source strength of our machine was 172.2 RMM. The reduction in source strength was due to the unavailability of high RMM source. Akinlade et al. reported loading source strength of 151.3 RMM.
| Conclusion|| |
Commissioning and performance evaluation are the prerequisites before starting clinical treatment. It is necessary to perform the commissioning and performance evaluation of the machine according to the guidelines laid by IEC or national competent authority. Bhabhatron-II TAW has many advantages in comparison to earlier telecobalt machines. Features such as high-source loading capacity of machine head (250 RMM), one pair of asymmetric jaw, closer of jaws to 0 cm × 0 cm, and one motorized wedge filter make Bhabhatron-II TAW a unique yet cost-effective telecobalt machine for LMICs.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4]