A dose of 4 Gy is to be isocentrically delivered to a tumour with an 8 × 8 cm, C

Question

A dose of 4 Gy is to be isocentrically delivered to a tumour with an 8 × 8 cm, Co-60 beam using a technique called rotational therapy. In this technique, the treatment head rotates continuously around the patient while delivering the treatment. The dose rate in air at the isocentre is measured at 0.60 Gy/min. Under these conditions, the average or effective TAR is 0.760. For clinical reasons, three complete revolutions of the machine are required to deliver this treatment. Compute the rotational speed of the treatment head in rev/min.

Explanation / Answer

total dose=4

dose per minute=0.60

effective dose per minute=0.60*0.760=0.456

so total time taken to admister the doses=4/0.456=8.771 minutes

in that time machine need to complete 3 revolutions

then rotational speed=3/8.771=0.3420 rev/min

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