Tandem-ring dwell time ratio in Nigeria: dose comparisons of two loading patterns in standard high-dose-rate brachytherapy planning for cervical cancer

Active small bowel sparing in intracavitary brachytherapy for cervical cancer

OBJECTIVE

To propose and evaluate an active method for sparing the small bowel in the treatment field of cervical cancer brachytherapy by prone position procedure.

METHODS

The prone position procedure consists of five steps: making bladder empty, prone-positioning a patient on belly board, making the small bowel move to abdomen, filling the bladder with Foley catheter and finally turning the patient into the supine position. The proposed method was applied for the treatment of seven cervical cancer patients. Its effectiveness was evaluated and a correlation between the patient characteristics and the volumetric dose reduction of small bowel was also investigated. Brachytherapy treatment plans were built before and after the proposed method, and their dose-volume histograms were compared for targets and organs-at-risk. In this comparison, all plans were normalized to satisfy the same D90% for high-risk clinical target volume.

RESULTS

For the enrolled patients, the average dose of small bowel was significantly reduced from 75.2 ± 4.9 Gy before to 60.2 ± 4.0 Gy after the prone position procedure, while minor dosimetric changes were observed in rectum, sigmoid and bladder. The linear correlation to body mass index, thickness and width of abdominopelvic cavity and bladder volume were 76.2, 69.7, 28.8 and -36.3%, respectively.

CONCLUSIONS

The application of prone position procedure could effectively lower the volumetric dose of the small bowel. The dose reduction in the small bowel had a strong correlation with the patient's obesity and abdominal thickness. This means the patients for whom the proposed method would be beneficial can be judiciously selected for safe brachytherapy.

Assessment of cartesian co-ordinates-based bladder and rectal dose and variability with tandem-ring angles first Nigerian experience in high-dose-rate brachytherapy

OBJECTIVE:

This study assessed bladder and rectal dose based on Cartesian-coordinates in intracavitary brachytherapy and examined the variations resulting from use of tandem-ring (T-R) of different angles.

METHODS:

Cartesian-co-ordinates of bladder and rectum points were derived on orthogonal-radiographs of 90 patients who had high-dose-rate brachytherapy for cervical cancer at the Department of Radiation Oncology, University College Hospital, Ibadan, Nigeria. The patients were classified in three groups of 30, based on T-R angles 30°, 45° and 60° used, bearing same lengths and diameters across sets. The measured co-ordinates and the related percentage doses to points of interest in the two organs were analysed using EViews and SPSS statistical softwares.

RESULTS:

The mean rectal point dose (RPD) obtained was 68.97 ± 13.57 % of the prescribed doses as against 56.57 ± 11.83% for bladder point dose. While the maximums of the mean RPD were 95.7, 90.5 and 82.5% for T-R angles 30°, 45° and 60° respectively; corresponding values for the bladder point were 72.8, 87.8 and 62.3%.

CONCLUSION:

The baseline data obtained in this study served as guidelines for subsequently achieving acceptable values of bladder point dose and RPD at University College Hospital, Nigeria. Special attention should be paid to the application of 2 cm-tandems in relation to the RPD.

ADVANCES IN KNOWLEDGE:

This is one of the few studies assessing the influence of T-R angles on organs-at-risk. The increase in RPD with the use of intrauterine tandem-2 cm is found to be most pronounced with T-R 30⁰, and this trend reduced with larger angles.

Comparison of dose volume parameters evaluated using three forward planning - optimization techniques in cervical cancer brachytherapy involving two applicators

Purpose

This study is intended to compare dose-volume parameters evaluated using different forward planning- optimization techniques, involving two applicator systems in intracavitary brachytherapy for cervical cancer. It looks for the best applicator-optimization combination to fulfill recommended dose-volume objectives in different high-dose-rate (HDR) fractionation schedules.

Material and methods

We used tandem-ring and Fletcher-style tandem-ovoid applicator in same patients in two fractions of brachytherapy. Six plans were generated for each patient utilizing 3 forward optimization techniques for each applicator used: equal dwell weight/times (‘no optimization’), ‘manual dwell weight/times’, and ‘graphical’. Plans were normalized to left point A and dose of 8 Gy was prescribed. Dose volume and dose point parameters were compared.

Results

Without graphical optimization, maximum width and thickness of volume enclosed by 100% isodose line, dose to 90%, and 100% of clinical target volume (CTV); minimum, maximum, median, and average dose to both rectum and bladder are significantly higher with Fletcher applicator. Even if it is done, dose to both points B, minimum dose to CTV, and treatment time; dose to 2 cc (D_2cc) rectum and rectal point etc.; D_2cc, minimum, maximum, median, and average dose to sigmoid colon; D_2cc of bladder remain significantly higher with this applicator. Dose to bladder point is similar (p > 0.05) between two applicators, after all optimization techniques.

Conclusions

Fletcher applicator generates higher dose to both CTV and organs at risk (2 cc volumes) after all optimization techniques. Dose restriction to rectum is possible using graphical optimization only during selected HDR fractionation schedules. Bladder always receives dose higher than recommended, and 2 cc sigmoid colon always gets permissible dose. Contrarily, graphical optimization with ring applicators fulfills all dose volume objectives in all HDR fractionations practiced.

Routine use of ultrasound guided tandem placement in intracavitary brachytherapy for the treatment of cervical cancer - a South Indian institutional experience

PURPOSE

Intracavitary brachytherapy necessitates the insertion of a tandem applicator through the cervical os into the uterine cavity. Blind insertion of the tandem may result in suboptimal tandem placement. This decreases the control of the tumor locally and may result in uterine perforation. Although routine real time ultrasound guided tandem placement has shown better results, it is seldom practised. The aim of this work is to evaluate the role of routine real-time intraoperative trans-abdominal ultrasound guided tandem placement in intracavitary brachytherapy for the treatment of cervical cancer.

MATERIAL AND METHODS

This is a prospective single institutional study conducted from April 2013 to May 2015. A total of 96 patients of locally advanced cervical cancer were treated with routine ultrasound guided brachytherapy amounting to a total of 282 intracavitary applications.

RESULTS

In 78 of the study patients, the cervical os could be easily identified visually, which was then confirmed with ultrasound guidance. In another 12 patients, though the os could be identified visually, uterine sounding was only possible under ultrasound guidance. In another 4 patients, the cervical os could not be identified visually as the cervix was flushed with vagina and ultrasound guidance was necessary for accurate os identification. In 2 of the study patients, intraoperative ultrasound helped in identifying the patients suitable for interstitial brachytherapy rather than intracavitary brachytherapy. Out of the 96 study patients, the length of the uterine canal changed in 15 patients during the subsequent brachytherapy application.

CONCLUSIONS

This procedure is strongly advocated for proper placement of the tandem applicator and to avoid perforations. It is an accurate, fast, easily available, and cost-effective method. Hence, it can be incorporated in intracavitary applications for cervical cancers even in the developing countries where cost, accessibility, and time are important issues.