Electronic brachytherapy for postsurgical adjuvant vaginal cuff irradiation therapy in endometrial and cervical cancer: A retrospective study

A dosimetric comparison of brachytherapy sources for endometrial cancer: an electronic brachytherapy and an iridium-192 source with multichannel cylinders and a three-dimensional technique

BACKGROUND AND PURPOSE

Ir192 vaginal brachytherapy (IBT) is commonly used for patients with postoperative endometrial cancer (EC). We devised a novel multichannel vaginal applicator that could be equipped with an electronic brachytherapy (EBT) device. We aimed to explore the differences in physical parameters between the EBT and IBT.

MATERIALS AND METHODS

This retrospective study included 20 EC patients who received adjuvant IBT from March 1, 2023, to May 1, 2023. Multichannel vaginal cylinders were used, and three-dimensional plans were generated. We designed an electronic multichannel vaginal applicator model and simulated a three-dimensional EBT plan. In order to ensure comparability, D90 of the CTV for the EBT plan was normalized to be equivalent to that of the IBT plan for the same patient.

RESULTS

Twenty EBT plans were compared with 20 IBT plans. Results showed, the mean D90 value of clinical target volume (CTV) was 536.1 cGy for both treatment plans. For the mean dose of CTV, the EBT was significantly greater (738.3 vs. 684.3 cGy, p = 0.000). There was no significant difference in CTV coverage between the EBT and IBT plans. For high-dose areas (V200% and V150%), the EBTs were significantly greater. There were no significant differences in the maximum doses to the vaginal mucosa between the EBT and IBT, whether at the apex or in the middle segment. For the bladder and rectum, both the low-dose area and high-dose area were significantly lower in the EBT plans. For the conformity index, there was no significant difference between the EBT and IBT plans. For the dose homogeneity index, the EBT value was lower.

CONCLUSION

In conclusion, under the premise of a three-dimensional brachytherapy plan, for patients receiving multichannel vaginal applicator brachytherapy, compared with IBT, EBT could reduce the dose to the surrounding organs at risk while maintaining the dose in the target area.

Electronic brachytherapy for gynecological cancers - a systematic review

Background

The purpose of this manuscript is to provide an in-depth literature review of the management of endometrial and cervical cancers with electronic brachytherapy.

Materials and methods

An extensive literature search was performed and 9 articles were selected based on preset criteria.

Results

The reviewed studies provided dosimetric and clinical results. Patient populations were diverse and prescribed doses varied. When treatment plans were compared to those using cobalt 60 (⁶⁰Co) and iridium 192 (¹⁹²Ir) sources researchers found lower or equivalent doses in organs at risk while the doses at the applicator surface were significantly higher for electronic brachytherapy. In the eligible studies, a total of 72 patients received treatment with AxxentXoft vaginal applicator, 29 were treated with the Intrabeam vaginal applicator, and 8 with AxxentXoft cervical applicator.

Conclusions

All authors found that electronic brachytherapy was safe and well tolerated as higher mucosal doses did not present as adverse clinical effects. Electronic brachytherapy for gynecological cancers has the potential to achieve equivalent tumor control while minimizing bowel and urinary toxicity thus improving the quality of life. More clinical data is needed to stratify patients who would benefit the most.

Benchmarking failure mode and effects analysis of electronic brachytherapy with data from incident learning systems

PURPOSE

Failure modes and effects analysis (FMEA) is a prospective risk assessment tool for identifying failure modes in equipment or processes and informing the design of quality control systems. This work aims to benchmark the performance of FMEAs for electronic brachytherapy (eBT) of the skin and for breast by comparing predicted versus actual failure modes reported in multiple incident learning systems (ILS).

METHODS AND MATERIALS

Two public and our institution's internal ILS were queried for Xoft Axxent eBT-related events over 9 years. The failure modes and Risk Priority Numbers (RPNs) were taken from FMEAs previously performed for Xoft eBT of nonmelanoma skin cancer and breast intraoperative radiation therapy (IORT). For each event, the treatment site and primary failure mode was compared with the failure modes and RPNs from that site's FMEA.

RESULTS

49 events involving Xoft eBT were identified. Thirty-one (63.3%) involved breast IORT, and 18 (36.7%) involved the skin. Three events could not be linked to an FMEA failure mode. In 87.7% of events, the primary failure mode ranked in the FMEA top 10 by RPNs. In 83.3% of skin events, the failure modes ranked in the top 10 by RPN or severity. In 90.3% of IORT events, the failure modes ranked within the top 10 by RPN or severity.

CONCLUSIONS

Evaluating FMEA failure modes against ILS data demonstrates that FMEA is effective at predicting failure modes but can be dependent on user experience. ILS data can improve FMEA by identifying potential failure modes and suggesting realistic occurrence, detectability, and severity values.

Adjuvant electronic brachytherapy for endometrial carcinoma: A 4-year outcomes report

PURPOSE

The purpose of the study was to report the outcomes of a single-center adjuvant electronic brachytherapy (e-BT) experience for patients with endometrial carcinoma.

METHODS AND MATERIALS

Patients were retrospectively assessed. Intracavitary e-BT was applied through a cylindrical applicator (diameters 2.5-3.5 cm). e-BT single doses ranged between 4 and 7 Gy (EQD2 ∼ 6-12, α/β of 10 Gy and an relative biological effectiveness of 1.3) at 5-mm depth. Adverse events are reported at first week, 1-3 months, 3-12 months, 12-24 months, and >24 months. The overall survival, disease-free survival, distant disease control rate, and local control rate were estimated using the Kaplan-Meier method.

RESULTS

Twenty-nine patients were assessed. The median age was 68 [48-86] years. External beam radiotherapy was added in n = 8 (27.6%) patients. Staging was 13.8% for T1a, 51.7% for T1b, 24.1% for T2, 6.9% for T3a, and 3.4% for T3b. Grading was G3 in 51.7% (n = 15), G2 in 20.7% (n = 6), and G1 in 27.6% (n = 8). Median followup was 47 months [5-88]. Overall Grade 1, 2, and 3 toxicity was 89.7% (n = 26), 17.2% (n = 5), and 6.9% (n = 2), respectively. No Grade 3 cystitis or proctitis or any Grade 4 or 5 toxicity occurred during followup. No local recurrences were detected. Estimated distant disease control rate was 92.1% (n = 2, distant metastasis at 7 and 11 months). Estimated 4-year overall survival was 84.8% (n = 4 events, two unrelated to disease) and disease-free survival was 84.6%.

CONCLUSIONS

Our data suggest that e-BT resembles a very-low-toxicity profile and a high local control rate in the adjuvant scenario for patients with endometrial carcinoma.

Investigation of a source model for a new electronic brachytherapy tandem by film measurement

PURPOSE

To investigate the accuracy of a vendor-supplied source model for a new Xoft Axxent 0-degree titanium tandem by film measurement.

METHODS

We measured the anisotropy factors at varying distances and angles from the tandem in water using radiochromic film (Gafchromic EBT3) and an Epson Perfection v750 desktop flatbed scanner (US Epson, Long Beach, CA). A 0-degree tandem was placed vertically in a water phantom. Four pieces of film, each at varying depths, were positioned orthogonal to the longitudinal axis of the tandem for azimuthal anisotropy measurements. Polar anisotropy measurements were taken with the film aligned parallel to the tandem. An absolute dose calibration for the film was verified with a PTW 34013 Soft X-Ray Chamber. The film measurements were analyzed using different color channels. The measured polar anisotropy for varying source positions was compared to the vendor's data. Azimuthal anisotropy was measured as a function of the radius and angle, and normalized to the mean value over all angles at the specified radius.

RESULTS

The azimuthal anisotropy of the tandem and source was found to be consistent for different positions along the tandem's longitudinal axis and at varying distances from the tandem. Absolute dose using a calibrated parallel plate chamber showed agreement to within 2% of expected TPS values. The custom tandem, which has a thicker tip than the wall, was attenuating the 50 kV photons more than expected, at the angles where the photons had more wall material to traverse. This discrepancy was verified at different distances from the tandem and with different measurement techniques. As distance increased, anisotropy values had better agreement.

CONCLUSIONS

We quantified the agreement between the measured and provided anisotropy factors for a new Xoft Axxent 0-degree titanium tandem. Radiochromic film response at low kV energy was also investigated. Our results showed that vendor-supplied TG-43 values were appropriate for clinical use at majority of the angles. A rigorous quality assurance method for new electronic brachytherapy sources and applicators, along with complete knowledge of all dosimetric measuring tools, should be implemented for all parts of the verification and commissioning process.

Dosimetric comparison of brachytherapy sources for high-dose-rate treatment of endometrial cancer: (192)Ir, (60)Co and an electronic brachytherapy source

OBJECTIVE

To compare high-dose-rate (HDR) brachytherapy systems with (192)Ir, (60)Co and electronic brachytherapy source (EBS) for treatment of endometrial cancers.

METHODS

Two additional plans were generated per patient fraction using a (60)Co source and Xoft-EBS on 10 selected patients, previously treated with a vaginal cylinder applicator using a (192)Ir source. Dose coverage of "PTV_CYLD", a 5-mm shell surrounding the cylinder, was evaluated. Doses to the following organs at risk (OARs) the rectum, bladder and sigmoid were evaluated in terms of V35% and V50%, the percentage volume receiving 35% and 50% of the prescription dose, respectively, and D2cm(3), the highest dose to a 2-cm(3) volume of an OAR.

RESULTS

Xoft-EBS reduces doses to all OARs in the lower dose range, but it does not always provide better sparing of the rectum in higher dose range as does evaluation using D2cm3. V150% and V200% for PTV_CYLD was up to four times greater for Xoft-EBS plans than for plans generated with (192)Ir or (60)Co. Surface mucosal (vaginal cylinder surface) doses were also 23% higher for Xoft-EBS than for (192)Ir or (60)Co plans.

CONCLUSION

Xoft-EBS is a suitable HDR source for vaginal applicator treatment with advantages of reducing radiation exposure to OARs in the lower dose range, while simultaneously increasing the vaginal mucosal dose.

ADVANCES IN KNOWLEDGE

This work presents newer knowledge in dosimetric comparison between (192)Ir or (60)Co and Xoft-EBS sources for endometrial vaginal cylinder HDR planning.