Dose verification in carcinoma of uterine cervix patients undergoing 3D conformal radiotherapy with Farmer type ion chamber

Abstract

External beam radiotherapy (EBRT) for carcinoma of uterine cervix is a basic line of treatment with three dimensional conformal radiotherapy (3DCRT) in large number of patients. There is need for an established method for verification dosimetry. We tried to document absorbed doses in a group of carcinoma cervix patients by inserting a 0.6 cc Farmer type ion chamber in the vaginal cavity. A special long perspex sleeve cap is designed to cover the chamber for using in the patient's body. Response of ionization chamber is checked earlier in water phantom with and without cap. Treatment planning was carried out with X-ray computed tomography (CT) scan and with the chamber along with cap in inserted position, and with the images Xio treatment planning system. Three measurements on 3 days at 5-6 fraction intervals were recorded in 12 patients. Electrometer measured charges are converted to absorbed dose at the chamber center, in vivo. Our results show good agreement with planned dose within 3% against prescribed dose. This study, is a refinement over our previous studies with transmission dosimetry and chemicals in ampules. This preliminary work shows promise that this can be followed as a routine dose check with special relevance to new protocols in the treatment of carcinoma cervix with EBRT.

On-line estimations of delivered radiation doses in three-dimensional conformal radiotherapy treatments of carcinoma uterine cervix patients in linear accelerator

“…In vivo dose estimates obtained in this study are in good agreement with the accuracy levels obtained through various methods (done in pelvic malignancies) which are published in literature. [9101213151617] Our experience is limited to only symmetric fields where the central axis goes through the “ion chamber centre” in the exit position. If it is an asymmetric field or very long elongated field, the calibration cannot be extrapolated.…”

“…[11] In this direction, a few reports describe in vivo dosimetry with chemical dosimeter and IC by placement of detectors in vaginal cavity of patients receiving external beam radiotherapy treatment for carcinoma uterine cervix. [1213] As the above method needs patient's consent and was time consuming, better methodology was found necessary. The present work illustrates our attempt in positioning an ion chamber, positioned on locally fabricated mount fixed at EPID level, along the beam central axis, and estimating the in vivo dose at isocenter in a group of carcinoma of uterine cervix patients treated with 3DCRT by accounting water equivalent path length principle.…”

Simultaneous measurement of In vivo and transit mid-plane doses with ionization chambers in gynecological malignancy patients undergoing three-dimensional conformal radiotherapy

“…Srinivas et al [ 4 16 ] studied the in vivo dose measurements in the vaginal cavity by inserting the different detectors. An ion chamber (0.6 cc Farmer type with protective cap) in 12 cervical carcinoma patients undergoing 3DCRT[ 16 ] treatment to the pelvic site demonstrated good agreement between planned vs prescribed dose which was within 3%.…”

“…In some of the studies, the in vivo dose was measured by inserting an ionization chamber directly into the natural body cavity (e.g., esophagus, rectum, or vagina) with a protective cap which comes in the region of the treatment portals. [ 13 14 15 16 ] The temperature of the cavity (which is the surrogate of the body temperature) where the chamber is placed is taken into account for temperature correction factor that needs to be applied to the charge collected by the chamber. The dose is then calculated by application of all chamber-related correction factors (e.g., calibration factor, temperature, pressure, and beam quality) to the collected charge.…”

“…Few studies described methods to assess in vivo mid-plane dose in patients through transit signal measured by an ionization chamber positioned at the EPID level while actual treatment is going on. [ 3 13 14 16 17 18 19 ]…”