The estimation of lung dose from mid-perineum ionization chamber measurements in total body irradiations: a quality control check on dose delivery.
A series of patients (eleven males and eight females) receiving total body irradiation prior to bone marrow transplantation was monitored during treatment by recording the dose from an ionization chamber placed between the thighs in the mid-perineal region. The treatment was delivered by opposed lateral 6 MV photon beams. The patient was encompassed by the radiation field with the maximum collimator opening at a distance of 3.49 m from the X-ray focus to the patient mid-line. An analysis was made of the measured dose and the calculated percentage average lung dose for each patient in the series to seek a correlation between measured doses and patients' anatomical data so that estimates of delivered lung doses could be made. Whilst a global factor can be applied to measured dose to predict lung dose, it is concluded that perineal dose measurements distal to the region where dose is prescribed (mean lung dose) are sub-optimal for checks on target dose delivery. Entrance and exit dose measurements at the level of dose prescription (in the thorax) are preferable for more accurate predictions and quality control checks.
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Department of Radiation Oncology, St Vincent's Hospital, Sydney, New South Wales, Australia.
D005260:Female; D006801:Humans; D008168:Lung / Q000528:radiation effects*; D008297:Male; D010502:Perineum; D011786:Quality Control; D011874:Radiometry / Q000379:methods*; D011879:Radiotherapy Dosage; D014916:Whole-Body Irradiation / Q000379:methods*