Magnitude and Implications of Interfraction Variations in Organ Doses during High Dose Rate Brachytherapy of Cervix Cancer: A CT Based Planning Study

Santam Chakraborty,Firuza D Patel,Vijay M Patil,Suresh C Sharma,Arun S Oinam

doi:10.1155/2014/687365

Santam Chakraborty, Firuza D Patel + Show 3 more

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https://doi.org/10.1155/2014/687365

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Abstract

Background. Quantifying the interfraction dose variations in the organs at risk (OAR) in HDR intracavitary brachytherapy (HDR ICBT). Methods. Rectum and bladder were contoured in 44 patients of cervical carcinoma on CT after each fraction of HDR ICBT (9 Gy/2 fractions). Interfraction dose variations (VARact) were calculated. Rigid image registration of consecutive fraction images allowed quantification of the hypothetical variation in dose (VARhypo) arising exclusively due to changes in applicator placement and geometry. VARhypo was regressed against the VARact to find out to what extent the applicator variation could explain the VARact in the OAR. The rest of the variation was assumed to be due to organ deformation. Results. The VARact in the dose to 2 cc of bladder and rectum were 1.46 and 1.16 Gy, respectively. Increased dose was seen in 16 and 23 patients in the subsequent fraction for bladder and rectum, respectively. Doses to OAR would have exceeded constraints in 16% patients if second fraction was not imaged. VARhypo explained 19% and 47% of the VARact observed for the bladder and rectum respectively. Conclusions. Significant interfraction variations in OAR doses can occur in HDR ICBT. Organ deformations are mostly responsible for this variation.

Highlights

Quantifying the interfraction dose variations in the organs at risk (OAR) in HDR intracavitary brachytherapy (HDR Intracavitary brachytherapy (ICBT))
The mean equivalent dose at 2 Gy per fraction (EQD2) bladder D2 cc was 25.27 Gyα/β=3 and 23.82 Gyα/β=3 in the first and second fraction ICBT respectively
The mean EQD2 for the rectal D2 cc was 9.92 Gyα/β=3 and 10.52 Gyα/β=3 in the first and second fraction ICBT, respectively

Summary

Introduction

Quantifying the interfraction dose variations in the organs at risk (OAR) in HDR intracavitary brachytherapy (HDR ICBT). While high dose rate ICBT (HDR ICBT) has become popular due to its logistical advantages over low dose rate ICBT (LDR ICBT), it necessitates dose fractionation in order to reduce normal tissue complications [1] This results in inadvertent changes in the position/geometry of the applicator. In addition there are interfraction deformations in organs at risk (OAR) due to movement, shape changes, and variable filling of these hollow organs. These in turn result in organ dose variations, which have important implications in dose reporting. Data from some of the recent series have highlighted the problem of interfraction dose variation in HDR brachytherapy using volumetric imaging modalities [12,13,14]

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