60 Gy isodose volumes in carcinoma of the cervix and their relation to the geometry of uterine tube and ovoids.
The International Commission on Radiation Units and Measurements recommends the use of 60 Gy isodose volumes for reporting doses in the intracavity treatment of carcinoma of the uterine cervix. This study was aimed at determining the variation in isodose volumes while using different sizes of intrauterine tubes and ovoids, with different applicator geometries. It was based on the treatment plans of 175 patients with cervical cancer, treated with low dose rate intracavitary brachytherapy with or without additional external beam radiotherapy. The volumes encompassed by the 60 Gy isodose curves were calculated using the Nucletron planning system. Applicator positions in 15 patients who were treated to the same point A dose, using 6 cm intrauterine tube and medium ovoids, were recorded. This was to discover how variations in applicator geometry influences isodose volumes. The 60 Gy isodose volumes increased with increasing point A dose. For a constant point A dose prescription, reference isodose volume increased with ovoid applicator size used, but showed no consistent variation with the length of intrauterine tube. There were individual variations in the isodose volumes within a standard set-up (same sized intrauterine tube and ovoids and same point A dose), due to variations in applicator geometry. Displacement of the ovoids changed the volumes encompassed by the reference isodose. There are significant variations in the volumes encompassed by the 60 Gy isodose during intracavitary treatment using a standard set-up, while treatment using applicators of different sizes can give equivalent values of 60 Gy isodose volume. 60 Gy isodose volumes may hence be useful in dosimetric comparisons but have a limited role in predicting clinical response.
Jacob
R
R
Department of Radiotherapy, Royal Marsden Hospital, London, UK.
Bidmead
A M
AM
Blake
P R
PR
D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods*; D005260:Female; D006801:Humans; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy*