Can point doses predict volumetric dose to rectum and bladder: a CT-based planning study in high dose rate intracavitary brachytherapy of cervical carcinoma?

Abstract

Objective: Point doses, as defined by the International Commission on Radiation Units and Measurements (ICRU), are classically used to evaluate doses to the rectum and bladder in high dose rate intracavitary brachytherapy (HDR-ICBT) in cervical cancer. Several studies have shown good correlation between the ICRU point doses and the volumetric doses to these organs. In the present study we attempted to evaluate whether this correlation could be used to predict the volumetric doses to these organs. Methods: A total of 150 HDR-ICBT insertions performed between December 2006 and June 2008 were randomly divided into two groups. Group A (n550) was used to derive the correlation between the point and volumetric doses using regression analysis. This was tested in Group B (n5100) insertions using studentised residuals and Bland-Altman plots. Results: Significant correlations were obtained for all volumetric doses and ICRU point doses for rectum and bladder in Group A insertions. The strongest correlation was found for the dose to 2 cc volumes (D 2cc ). The correlation coefficients for bladder and rectal D 2cc versus the respective ICRU point doses were 0.82 and 0.77, respectively (p,0.001). Statistical validation of equations generated in Group B showed mean studentised residual values of 0.001 and 0.000 for the bladder and rectum. However, Bland-Altman analysis showed that the error range for these equations for bladder and rectum were ¡64% and ¡41% of the point A dose, respectively, which makes these equations unreliable for clinical use. Conclusion: Volumetric imaging is essential to obtain proper information about volumetric doses.

The dosimetric impact of vaginal balloon-packing on intracavitary high-dose-rate brachytherapy for gynecological cancer

“…Notably, the ICRU bladder point dose was often deceptively within normal limits (< 80% of the prescribed dose), but the image-based D2 cc was over 100% of the prescribed dose. The disconnection between ICRU point doses and image-based dosimetry has been previously noted [14], and image-based dosimetry has been shown to be more clinically relevant in terms of side effects [15]. Our current study further underscores the importance of volume-based dosimetry in brachytherapy planning.…”

Volumetric (3D) bladder dose parameters are more reproducible than point (2D) dose parameters in vaginal vault high-dose-rate brachytherapy

“…Some studies suggest a tendency in the correlation1920, whereas others do not21. Although our findings support the adoption of CT-based planning in VCB, its generalization to HDR in the intact uterus should be supported by specific studies.…”

Bladder–Rectum Spacer Balloon versus Vaginal Gauze Packing in High Dose Rate Brachytherapy in Cervical Cancer: A Randomised Study (Part II)

“…OAR, namely the bladder, rectum and sigmoid, were contoured on computed tomography at each fraction, as recommended by the GEC-ESTRO guidelines [2]. Applicators were reconstructed on the computed tomography scan on the multiplanar reconstruction views, as previously described [14,15]. A dose of 9 Gy was prescribed to point A. Doses to 0.1, 1, 2 and 5 cm 3 volumes for the bladder, rectum and sigmoid were documented at each fraction.…”