Image-guided brachytherapy for cervical cancer: Analysis of D2 cc hot spot in three-dimensional and anatomic factors affecting D2 cc hot spot in organs at risk

Dosimetric evaluation of the feasibility of utilizing a reduced number of interstitial needles in combined intracavitary and interstitial brachytherapy for cervical cancer

PURPOSE

To evaluate the ability of the Venezia advanced multichannel tandem and ring applicator to consistently produce dosimetrically comparable plans utilizing a reduced number of needle channels, to reduce the risk of secondary complications when boosting cervical cancer treatments with high dose rate (HDR) brachytherapy.

METHODS

We evaluated 26 fractions from 13 patients who were treated with HDR brachytherapy using the Venezia (Elekta) applicator. The original plans included a full load of 12-16 needles, including both parallel and 30-degree oblique needles. We replanned each original to nine new configurations, with a reduced number of two, three, four, or six needles. Comparisons included differences in percentage dose coverage to 90% of the high-risk clinical target volume, and percentage dose to 2 cm³ of the bladder, rectum, sigmoid, and bowel. We considered new plans "passing" if they remained within our standards (D90 > 100%; D2 cm³  < 85% bladder, <65% rectum, sigmoid, bowel) or did not perform worse than original.

RESULTS

Removing only the two most anterior or the two most posterior needles from both sides showed 80.8% and 61.5% overall passing rate. Removal of the most anterior and posterior four needles together showed 65.4% overall passing rate. Removing all oblique needles showed 19.2% overall passing rate. Removing only left-sided or only right-sided oblique needles showed 46.2% and 23.1% overall passing, respectively. Removing only right-sided or only left-sided parallel needles separately showed 19.2% and 34.6% overall passing, respectively. Removing all parallel needles showed 11.5% overall passing rate.

CONCLUSIONS

As only two replans required a full needle load to maintain dosimetric quality and 40 (76.9%), 36 (34.6%), 18 (69.2%), and 10 (19.2%) replans passed with 2, 3, 4, and 6 needles removed respectively, this indicates the potential for using a lesser number of interstitial needles during combined intracavitary and interstitial HDR brachytherapy while maintaining dosimetric quality.

Selection of brachytherapy applicators based on tumor size and shape for cervical cancer: simulation analysis of pear-shaped isodose dimensions

The purpose of study is to measure Point A pear-shaped isodose dimensions of the conventional intracavitary brachytherapy with various sizes of colpostats and analyze which size of tumor is the optimal for 3-D interstitial brachytherapy. CT simulation was performed with Fletcher type applicator using various sizes of colpostats (2.0, 2.5, and 3.0 cm diameter). The Manchester standard loading (dwell time) system was used to generate pear-shaped isodose envelopes with high-dose rate iridium-192 according to the colpostat sizes. The size of the pear-shaped envelope was measured at 5 different levels: A-level (center of the colpostats), B-level (top of the colpostats), C-level (between B and D), D-level (Point A), and E-level (1.0 cm above Point A). In this study, it was assumed that uterine tandem was located at the center of tumor. For width of pear-shape: At the A-level, 6.4, 7.3, and 8.0 cm for 2.0, 2.5, and 3.0 cm colpostats, respectively. At the B-level, 5.8, 6.4, and 6.8 cm for 2, 2.5, and 3.0 cm colpostats, respectively. At the C-level, 4.6, 4.8, and 4.8 for 2.0, 2.5, and 3.0 cm colpostats, respectively. At the D-level, 4.0 cm for all different size. At the E-level, 3.8 cm for all 3 different size colpostats. A-level was the largest dimension of pear-shape. However, it was located in the upper vagina below the main cervical mass. The center of the effective pear-shape size for tumor was between the C and D levels. For thickness, all 5 different levels were ranging 3.7 to 4.0 cm. For height, the length of height was dependent on the tandem length. Therefore, the pear-shape envelope was able to accommodate up to 4.0 cm diameter volume. According to our analysis of conventional pear-shape dimension, 3-D interstitial brachytherapy should be considered for tumors larger than 4.0 cm for symmetrical tumor.

Pulsed-dose rate image-guided adaptive brachytherapy in cervical cancer: Dose-volume effect relationships for the rectum and bladder

PURPOSE

To establish dose-volume effect correlations for late bladder and rectum side effects in patients treated for locally advanced cervical cancer with concomitant chemoradiation followed by pulsed-dose rate image-guided adaptive brachytherapy.

MATERIAL AND METHODS

The dosimetric data, converted in 2 Gy equivalent, from 217 patients were confronted to late morbidity defined as any event lasting or occurring 90 days after treatment initiation. Toxicity was assessed using the CTC-AE 3.0. Probit analyses and Log rank tests were performed to assess relationships.

RESULTS

One hundred and sixty-one urinary and 58 rectal events were reported, affecting 98 (45.1%) and 51 (23.5%) patients, respectively. Cumulative incidences for grade 2-4 bladder and rectal morbidity were 24.3% and 9.6% at 3 years, respectively. Significant relationships were observed between grade 2-4 and 3-4 events and D0.1cm(3) and D2 cm(3) for the bladder and between grade 1-4 and 2-4 event probability and rectal D2 cm(3). The effective doses for 10% grade 2-4 morbidity were 65.3 Gy (59.8-81.3), and 55.4 Gy (15.7-63.6), respectively, for the rectum and bladder. Without considering urinary and rectal incontinence, for which the pertinence of correlating them with D2 cm(3) is questionable, ED10 were 68.5 Gy (62.9-110.6) and 65.5 Gy (51.4-71.6 Gy). When sorting patients according to D2 cm(3) levels, patients with high D2 cm(3) had significantly lower morbidity free survival rates for grade 1-4 and 2-4 urinary and rectal morbidity.

CONCLUSION

Significant dose-volume effect relationships were demonstrated between the modern dosimetric parameters and the occurrence of late rectal and urinary morbidity in patients treated with pulsed-dose-rate brachytherapy. Further studies are required to refine these relationships according to clinical cofactors, such as comorbidities.