Cobalt-60 Source Loading: Necessity of
A Rigid Protocol
Ravi Kant1, Geomcy George2*, Shekhar Dwivedi1, Mahajan MK1, Shahid KM1 and Yadvinder S1
1Advanced Cancer Diagnostic, Treatment and Research Centre, Bathinda, India
2Believers Church Medical College Hospital, Thiruvalla, India
Submission: July 01, 2019; Published: July 25, 2019
*Corresponding Address: Geomcy George, Department of Radiation Oncology, Believers Church Medical College Hospital, St. Thomas Nagar, P.O. Box-31, Kuttapuzha, Thiruvalla, Kerala, India
How to cite this article:Ravi Kant, Geomcy George, Shekhar Dwivedi, Mahajan MK, Shahid KM, et al. Cobalt-60 Source Loading: Necessity of A Rigid
002 Protocol. Canc Therapy & Oncol Int J. 2019; 14(4): 555893. DOI:10.19080/CTOIJ.2019.13.555893
Aim: To look if calculating the gantry angle position helps in source loading.
Materials and Methods: The study was conducted in Advanced Cancer Diagnostic, Treatment and research Centre- Bathinda, India at the time of source loading in the Bhabhatron – II TAW teletherapy unit. There is no rigid protocol for calculating the angle in which source loading needs to be done. The study looks at various gantry angle positions in which source loading was attempted and failed and describes how to calculate the position in which source loading needs to be done; based on which successful loading was done.
Result: Calculating the gantry angle position helps reduce source loading errors.
Conclusion: By following a rigid protocol, the number of trials undertaken for the cobalt-60 source loading could be reduced, thus limiting the radiation exposure to all involved.
Telecobalt units are widely used in developing countries for cancer treatment and are preferred over medical linear accelerators because of:
i) Low cost,
ii) Low maintenance cost,
iii) Lower power requirements, and
iv) Less down time . Bhabha Atomic Research Centre, Mumbai, India has designed and developed a prototype telecobalt unit, which has been named Bhabhatron‐I . After receiving feedback on the operations of this unit, a modified model was developed, Bhabhatron‐II
Cobalt-60 source loading is a routinely practiced procedure for more than six decades now. This procedure involves a close co-operation between Service Engineer, Medical Physicist, Radiation Therapy Technologist and radiation oncologist. For a smooth operation and reasonably low radiation exposure to the personnel, a workable and time-tested protocol might be more beneficial than an experience based on ‘hit and trial’ method.
The present study is an attempt to that context evolved during the experience of various problems faced during Cobalt-60 source loading in the Bhabhatron-II-TAW teletherapy unit at Advanced Cancer Diagnostic, Treatment and Research Centre- Bathinda.
The study was conducted in Advanced Cancer Diagnostic, Treatment and research Centre- Bathinda, India at the time of source loading in the Bhabhatron – II TAW teletherapy unit. There is no rigid protocol for calculating the angle in which source loading needs to be done. The room preparation was done before source loading. The surface of the floor was flat. Gamma zone monitor in the room was in working condition. There was proper lightening in the room. The various acceptance tests for the treatment unit including electrical and mechanical of the machine were completed. Usual protocols have been defined for the teletherapy unit having the swivel function of the head of the gantry which facilitates rotation of the Gantry head to face towards the floor. Bhabhatron-II unit is not having swivel function in its Gantry Head necessitating for an alternate solution. The Source flask was shifted into the telecobalt roomby hydraulic trolley. Alignment with head of the Gantry was
achieved. The gantry angle for source loading was preferred in
anti-clockwise direction as the position in clockwise direction
interfered with the electrical connections of the couch.
The Gantry angles from serial no. 1 to 3 were randomly
selected by the engineers while the 4th one was calculated as
shown in table 1 and detailed in figure 1. The selection of the
angle of 230.10 was calculated using trigonometry and calculus
Flask source drawer center to floor distance (CG) =68.6cm
Gantry source drawer (Gθ=2700) to floor distance (BF)
=120cm, Gantry rotation center (axis) to floor distance
AE = (AH-EH)
AE = (120cm-68.6cm)
AE =51.4cm, AC=80cm
Cos θ = AE/CA
Cos θ = (51.4)/80
Θ = cos-1(0.6425)
Θ =50.020 (Approx. 500)
Finally we got the optimized gantry angle i.e. (θ1+θ2+θ)o =
At the distance values of the center of the source drawer flask
to floor, the derived values of Gantry angle are shown in table
2. The SD error is 0.10 The Gantry motion tolerance suggested
by the manufacturers was 0.20. Hence the optimized Gantry
angle for the current source loading operation was 2300. The total time taken for the procedure comprising of 4 attempts was
1hour 50minutes out of which, the 4th attempt made at Gantry θ
=230.1o took 7 minutes only.
The review of literature showed limited material regarding
detailed guidelines for source loading in teletherapy units. The
extra time taken and also causing Radiation exposure by carrying
out the ‘Hit & Trial’ method based on working experience by
service engineers at the time of source loading warrants a rigid
protocol for source loading to be adopted. The result of this
study documents that by following a rigid protocol, the number
of trials undertaken for the cobalt-60 source loading could have
been reduced. In this exercise from 4 to 1 (75%), overall time
taken can also be reduced from 120 minutes to 20 minutes
and thus also limiting the radiation exposure to all personnel
involved; thereby making this procedure more friendly as per
the ALARA principle.