Geometrical considerations in dose volume analysis in intracavitary treatment.
OBJECTIVE
The present work was aimed at to study the relationship between the volume enclosed by reference isodose surface and various geometrical parameters of the intracavitary applicator in treatment of carcinoma of cervix.


METHODS
Pearshape volume of the reference isodose derived from the Total Reference Air Kerma (TRAK) and the product of its dimensions, height H, width W and thickness T which is dependent on the applicator geometry, were estimated for 100 intracavitary applications treated by Selectron LDR machine. Orthogonal radiographs taken for each patient were used for measurement of actual geometric dimensions of the applicator and carrying out the dosimetry on TP-11 treatment planning system. The dimensions H, W and T of reference isodose surface (60 Gy) were also noted.


RESULTS
Ratio of the product HWT and the pearshape volume was found mainly to be a function of colpostat separation and not of other geometrical parameters like maximum vertical and anterio-posterior dimension of the applicator. The ratio remained almost constant for a particular combination of uterine tandem and colpostat. Variation in the ratios were attributed to the non-standard geometry.


CONCLUSIONS
The ratio of the volume of reference isodose surface to the product of its dimensions in the applicator depends upon the colpostat separation.
Deshpande
D D
DD
Department of Medical Physics, Tata Memorial Hospital, Bombay, India.
Shrivastava
S K
SK
Pradhan
A S
AS
Viswanathan
P S
PS
Dinshaw
K A
KA
D001918:Brachytherapy / Q000295:instrumentation / Q000379:methods* / Q000706:statistics & numerical data; D002277:Carcinoma / Q000000981:diagnostic imaging / Q000532:radiotherapy; D003037:Cobalt Radioisotopes / Q000008:administration & dosage; D005260:Female; D006801:Humans; D010347:Patient Care Planning; D011859:Radiography; D011867:Radioisotope Teletherapy; D011879:Radiotherapy Dosage; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy
D003037:Cobalt Radioisotopes