Dosimetry Contribution:Comparison between DVH-based doses and ICRU point-based doses to the rectum and the bladder using CT-based high-dose rate brachytherapy to the cervix
Introduction
Intracavitary brachytherapy is an integral part of the management of carcinoma of the cervix. It is possible to achieve a high therapeutic index with brachytherapy by delivering a high dose to the tumor and by sparing adjacent organs like the bladder and the rectum.1 Traditionally, the doses to the bladder and the rectum were quantified using the bladder and rectal reference points defined by the International Commission on Radiation Units and Measurements (ICRU) in Report No. 38.2
The ICRU bladder point is located on a radiograph by inserting a Foley catheter and the Foley balloon is filled with a 7-cm3 radiopaque fluid. The catheter is pulled down to bring the balloon against the urethra. The bladder reference point is at the center of the balloon on an anteroposterior radiograph. On the lateral radiograph, the bladder reference point is located on an anteroposterior line drawn through the center of the balloon, at the posterior surface.
The ICRU rectal reference point is located at the lower end of intrauterine source or the middle of the intravaginal source on an anteroposterior radiograph. On a lateral radiograph, an anteroposterior line is drawn through from the lower end of intrauterine source and the rectal reference point is located 5 mm behind the posterior vaginal wall on this line.
With the advent of volumetric imaging and 3-dimensional planning in intracavitary brachytherapy, doses to the organs at risk (OARs), namely, the bladder, the rectum, and the sigmoid are quantified using dose-volume histograms. The recommendations for dose reporting for 3-dimensional image-based brachytherapy have been published by the GEC ESTRO (Groupe Europeen de Curietherapie and the European Socie Ty for Radiotherapy and Oncology) group.3, 4 The acceptable isoequivalent dose limits to the bladder and the rectum are 90 and 75 Gy, respectively, which include doses from teletherapy and brachytherapy.
Although there is widespread use of ICRU point-based dose reporting to the OARs in intracavitary brachytherapy, one cannot deny the inherent weakness of ICRU-based points in predicting the late toxicities.5, 6 Point-based dose reporting does not properly characterize the absorbed dose heterogeneity in the organ walls. Certain segments of the OARs, namely, the posterior recto sigmoid walls and the anterosuperior bladder walls, receive much lower doses. Hence, it is recommended to report the dose-volume values in the high-dose region. The minimum doses to 0.1-, 1.0-, and 2.0-cc volumes of OARs that receive the maximum dose are represented by D0.1cc, D1cc, and D2cc, respectively.
The differences between volumetric doses and point-based doses to the bladder and the rectum have been reported earlier in several studies.7, 8, 9 The best correlation was found between the D2cc dose and ICRU point doses.10, 11, 12 In the present study, we compared the 0.1-, 1.0-, 2.0-cc doses to the bladder and the rectum with the corresponding ICRU point doses using CT-based planning.
Section snippets
Patient selection
CT datasets of 136 consecutive intracavitary brachytherapy insertions between January and May 2015 were analyzed. The total external beam radiotherapy dose was 50 Gy to the whole pelvis. The patients also received weekly doses of cisplatin 40 mg/m2.
Technique of intracavitary application
The procedure of intracavitary insertion was performed under general anesthesia in the operating room. The bladder was left to drain by catheterizing the bladder using a Foley catheter. The Foley bulb was filled with 3 mL of iodinated contrast and
Correlation between volume-based dose and ICRU point dose to the bladder
Mean doses of 0.1, 1.0, and 2.0 cc to the bladder were found to be 2.02, 1.57, and 1.35 times the ICRU point dose. The maximum doses of 0.1, 1.0, and 2.0 cc received by the bladder were found to be 5.83, 4.27, and 2.35 times the average ICRU point dose. From the previous results, it is clear that the ICRU point underestimated the dose to the bladder.
The difference between the average 0.1-cc dose to the bladder and the average ICRU point dose was 5.28 Gy (Table 1, Table 2). The difference
Discussion
Bladder and rectal toxicity is a major concern in the intracavitary brachytherapy of carcinoma of the cervix. With the advent of 3-dimensional image-guided brachytherapy it is possible to limit the doses to the OARs without compromising the dose to the tumor. Traditionally, ICRU point-based dose reporting to the bladder and the rectum was used as a surrogate to assess bladder and rectal toxicities, respectively. In recent times, many centers have started reporting volume-based doses to the
Conclusions
For many decades, ICRU reference points for the bladder and the rectum were used to quantify doses to OARs in the intracavitary brachytherapy of carcinoma of the cervix. Because studies have shown that ICRU points may not represent the actual organ doses, it is better to evaluate volume-based doses to the bladder and the rectum. Contouring of OARs on CT and evaluating dose-volume histograms is essential to determine normal tissue tolerance limits in the era of image-guided brachytherapy.
Acknowledgments
The authors thank Dr. TN.Vijaysri, Department of Radiation Oncology, Government Royapettah Hospital, Mrs.Vijayalakshmi, Department of Radiation Oncology, Government Royapettah Hospital, and Mrs. Kumari, Department of Radiation Oncology, Government Royapettah Hospital.
References (24)
- et al.
The American Brachytherapy Society recommendations for high-dose-rate brachytherapy for carcinoma of the cervix
Int. J. Radiat. Oncol. Biol. Phys
(2000) - et al.
Recommendations from gynaecological (GYN) GEC ESTRO working group (II): concepts and terms in 3D image-based treatment planning in cervix cancer brachytherapy—3D dose volume parameters and aspects of 3D image-based anatomy, radiation physics, radiobiology
Radiother. Oncol
(2006) - et al.
Recommendations from Gynaecological (GYN) GEC-ESTRO Working Group (I): concepts and terms in 3D image-based 3D treatment planning in cervix cancer brachytherapy with emphasis on MRI assessment of GTV and CTV
Radiother. Oncol
(2005) - et al.
Unique role of proximal rectal dose in late rectal complications for patients with cervical cancer undergoing high dose-rate intracavitary brachytherapy
Int. J. Radiat. Oncol. Biol. Phys
(2003) - et al.
High-dose-rate brachytherapy in the treatment of uterine cervix cancer. Analysis of dose effectiveness and late complications
Int. J. Radiat. Oncol. Biol. Phys
(2001) - et al.
Comparison between CT-based volumetric calculations and ICRU reference-point estimates of radiation doses delivered to bladder and rectum during intracavitary radiotherapy for cervical cancer
Int. J. Radiat. Oncol. Biol. Phys
(2005) - et al.
Correlation between (ICRU) point doses and CT based 3D image planning of intracavitary brachytherapy for cervical cancer
Int. J. Radiat. Oncol. Biol. Phys
(2008) - et al.
Image-based three-dimensional treatment planning of intracavitary brachytherapy for cancer of the cervix: Dose-volume histograms of the bladder, rectum, sigmoid colon, and small bowel
Brachytherapy
(2007) - et al.
Point vs. volumetric bladder and rectal doses in combined intracavitary-interstitial high-dose-rate brachytherapy: Correlation and comparison with published Vienna applicator data
Brachytherapy
(2008) - et al.
The use of a transverse CT image for the estimation of the dose given to the rectum in intracavitary brachytherapy for carcinoma of the cervix
Radiother. Oncol
(1998)
Image-guided intracavitary high-dose-rate brachytherapy for cervix cancer: A single institutional experience with three-dimensional CT-based planning
Brachytherapy
Maximum and mean bladder dose defined from ultrasonography: Comparison with the ICRU reference in gynaecological brachytherapy
Radiother. Oncol
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