Interobserver variations of target volume delineation and its impact on irradiated volume in accelerated partial breast irradiation with intraoperative interstitial breast implant

Brachytherapy in India: Learning from the past and looking into the future

India has a longstanding tradition in the practice of brachytherapy and has actively contributed to the scientific literature by conducting prospective studies, clinical audits, developing innovative techniques, and performing randomized studies. Indian investigators have also contributed to international collaborative research, education, training programs along with guideline development for brachytherapy in cervix and head and neck cancers. The present article summarizes the key contributions to scientific literature, current infrastructure, skill set for brachytherapy, existing challenges, and strategy to further strengthen brachytherapy practice in the next decade.

What is the dosimetric impact of isotropic vs anisotropic safety margins for delineation of the clinical target volume in breast brachytherapy?

PURPOSE

The purpose of the study was to report dosimetric differences for breast brachytherapy plans optimized for clinical target volume (CTV) generated using conventional isotropic expansion of tumor bed volume (TBV) and Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) recommendations to expand the TBV anisotropically to achieve a total safety margin of 2 cm (resection margin size + added safety margin).

METHODS

Institutional records of 100 patients who underwent accelerated partial breast irradiation using multicatheter interstitial brachytherapy from May 2015 to March 2020 were reviewed retrospectively. Two sets of CT-based plans were made, one with 1-cm isotropic margins around the tumor bed (CTV_ISO) and the other with anisotropic margins (CTV_GEC). Plans were evaluated and compared using the American Brachytherapy Society and GEC-ESTRO guidelines.

RESULTS

The median TBV was 36.97 cc. The median margin widths were as follows: anterior 1.2, posterior 1.0, superior 1.0, inferior 0.9, medial 1.2, and lateral 1.2 cm. The mean tumor bed coverage index was 0.94; 0.93 [p.066], the CTV coverage index 0.86; 0.84 [p 0.001], the dose homogeneity index (DHI) 0.77; 0.75 [p < 0.001] and the conformity index 0.66; 0.64 [p < 0.001] in CTV_ISO and CTV_GEC plans, respectively. In smaller volume implants (TBV< 35 cc), the DHI was 0.76; 0.75 [p 0.008] and the conformity index was 0.66; 0.62 [p < 0.001], whereas in larger volumes >35 cc, the CTV coverage index was 0.86; 0.84 [p 0.003] and the DHI 0.78; 0.76 [p 0.001] in CTV_ISO and CTV_GEC plans, respectively.

CONCLUSIONS

In this cohort of patients who underwent accelerated partial breast irradiation, plans with anisotropic margins had lower conformity, the impact of which was predominantly seen in smaller implants. Rest of the dosimetric constraints were achieved in both the plans as per the American Brachytherapy Society and GEC-ESTRO guidelines.

Coverage with dosimetric concordance index (CDCI): a tool for evaluating dosimetric impact of inter-observer target variability in brachytherapy

Purpose

The aim of this study was to propose an index for evaluating dosimetric impact of inter-observer target delineation variability in brachytherapy.

Material and methods

The coverage with dosimetric concordance index (CDCI) is expressed as CDCI_common and CDCI_pair. The CDCI_common is the mean coverage of target volume with common volume irradiated by prescription dose among all observers and represents the condition of worst target coverage. CDCI_pair is the generalized form of CDCI, which is mean target coverage with common prescription volume obtained between all possible pairs of observers and represents more realistic coverage of target with dosimetric concordance. The index was used to evaluate the dosimetric impact of target delineation variability in optimized conformal plans on target volumes of five radiation oncologists for twenty patients of multi-catheter interstitial partial breast brachytherapy.

Results

The mean decline of 5.6 ±3.2% and 11.3 ±5.7% in CDCI_pair and CDCI_common, respectively, was observed comparing to coverage index (CI) of target volume in all patients due to inter-observer target variability. CDCI_common and CDCI_pair were found to have significant linear correlation (r = 0.964, p < 0.000). The difference between CDC and CI increased with the mean relative target volume among observers. Significant correlation (r = 0.962, p < 0.000) was also noted for the difference (Δ) in CDCI_common and CDCI_pair with CI of target volume.

Conclusions

The recommended indices and difference between the dosimetric coverage of target volume (CI) with CDCI (ΔCDCI) can be used for evaluating dosimetric impact of the inter-observer target delineation variability.

Impact of inter-observer variations in target volume delineation on dose volume indices for accelerated partial breast irradiation with multi-catheter interstitial brachytherapy

PURPOSE

To investigate dosimetric impact of inter-observer variation in clinical target volume(CTV) delineation for patients undergoing interstitial partial breast brachytherapy.

METHODS

Five radiation oncologists delineated CTV in twenty patients who underwent multi-catheter partial breast brachytherapy. Five treatment plans for each patient were graphically optimized for CTV of all observers and evaluated using coverage index(CI), external volume index(EI), overdose volume index(OI) and conformal index(COIN). In addition, volume enclosed by prescription isodose(V₁₀₀), its spatial concordance(CI_common), mean coverage of all CTVs with common volume of prescription dose(V_{100_common}) and mean CTV coverage for all pairs of observer with common prescription volume of respective pairs(V_{100_pair}) were also computed.

RESULTS

The mean ± standard deviation(SD) of CI and COIN ranged from 0.756 ± 0.076 to 0.840 ± 0.070 and 0.591 ± 0.090 to 0.673 ± 0.06 respectively. When a plan made for CTV of individual observer was evaluated on CTV of all observers, the maximum variations(ρ < 0.05) in the mean CI,COIN,OI and EI were 10.6%,11.4%,10.6% and 72.7% respectively. The observed mean ± SD of V₁₀₀, CI_common of V₁₀₀, CTV coverage with V_{100_common} and V_{100_pair} was 160.7 ± 52.1, 0.70 ± 0.09, 73.1 ± 8.1% and 77.9 ± 7.3% respectively.

CONCLUSION

Inter-observer variation in delineation of CTV showed significant dosimetric impact with mean CTV coverage of 73.1% and 77.9% by common and paired prescription dose volume respectively among all observers.

Case report of a dose-volume histogram analysis of rib fracture after accelerated partial breast irradiation: interim analysis of a Japanese prospective multi-institutional feasibility study

We initiated the first multi-institutional prospective study of accelerated partial breast irradiation for early breast cancer in Japan. Our early clinical results showed that the treatment methods were technically reproducible between institutions and showed excellent disease control at a median follow-up of 26 months in our previous report. At present, total 46 patients from six institutions underwent the treatment regimen from October 2009 to December 2011, and the median follow-up time was 60 months (range, 57-67 months). In 46 patients, we experienced one patient who had rib fracture as a late complication. The dose-volume histogram (DVH) result of this patient was analyzed. The D_0.01cc, D_0.1cc, and D_1cc values of the patient were 913, 817, and 664 cGy per fraction, respectively. These values were the highest values in 46 patients. The average D_0.01cc, D_0.1cc, and D_1cc values of the other 45 patients were 546, 500, and 419, respectively, cGy per fraction. From this result, DVH values showing high-dose irradiated volume (D_0.01cc, D_0.1cc, and D_1cc) seem to be a good predictive factor of rib fracture for accelerated partial breast irradiation. However, further investigation is necessary because of the small number of patients investigated.

Advantages of intraoperative implant for interstitial brachytherapy for accelerated partial breast irradiation either frail patients with early-stage disease or in locally recurrent breast cancer

Purpose

To describe the intraoperative multicatheter implantation technique for accelerated partial breast irradiation (APBI) delivered with high-dose-rate brachytherapy (HDR-BT). Secondarily, to evaluate outcomes and toxicity in a series of 83 patients treated with this technique at our institution.

Material and methods

Retrospective analysis of a series of patients treated with HDR-BT APBI after intraoperative multicatheter interstitial implant between November 2006 and June 2017 at our institution. We assessed cosmesis, toxicity, overall survival (OS), and disease-free survival (DFS).

Results

Eighty-three patients were included: 59 patients (71.1%) with primary early-stage breast cancer and 24 (28.9%) with locally recurrent breast cancer. Tumorectomy was performed in all cases, with intraoperative tumor margin assessment and sentinel node biopsy. Median age was 82 years (range, 44-92). The total prescribed dose was 32 Gy (8 treatment fractions) in 60 patients (72.3%), and 34 Gy (10 fractions) in 23 patients (27.7%). Median follow-up was 40 months (range, 1-136 months). Three-year OS and DFS in the recurrent and primary cancer groups were 87% vs. 89%, and 96 % vs. 97.8%, respectively. Five patients died from non-cancer related causes. No local relapses were observed. Rates of acute and late toxicity were low in both groups. The cosmesis was good or excellent in most of patients treated for primary disease; in patients who underwent salvage brachytherapy for local recurrence, cosmesis was good in 49 patients and fair in 6.

Conclusions

This technique, although time-consuming, achieves good local disease control with a satisfactory toxicity profile in both early-stage and local recurrent breast cancer patients. It may be especially suitable for frail patients.