Long-term follow-up results of intensity-modulated radiotherapy with helicoïdal tomotherapy for non-metastatic breast cancers: Single centre experience

Determinants of radiation dose to immune cells during breast radiotherapy

BACKGROUND

The immune system has been identified as an organ at risk in esophageal and lung cancers. However, the dosimetric impact of radiotherapy on immune system exposure in patients treated for breast cancer has never been studied.

METHODS

A monocentric retrospective dosimetric study included 163 patients treated at the Institut Curie (Paris, France) between 2010 and 2016 with locoregional helical tomotherapy after conservative surgery or total mastectomy. The effective dose to the immune system (EDIC) was calculated based on diverse dosimetric parameters. The clinical and volumetric determinants of EDIC in adjuvant radiotherapy of breast cancer were analyzed.

RESULTS

The median EDIC for the population was 4.23 Gy, ranging from 1.82 to 6.19 Gy. Right-sided radiotherapy and regional lymph node irradiation were associated with significantly higher EDIC in univariate (4.38 Gy vs. 3.94 Gy, p < 0.01, and 4.27 Gy vs. 3.44 Gy, p < 0.01, respectively) and multivariate analyses (p < 0.01 and p < 0.01). Liver overexposure was the main contributor to EDIC increase in right-sided breast cancer patients (+0.38 Gy [95%CI: +0.30; +0.46]), while the integral total dose increase was the main contributor to EDIC increase in cases of regional node irradiation (+0.63 Gy [95%CI: +0.42; +0.85]).

CONCLUSION

The EDIC score during adjuvant radiotherapy after breast cancer was statistically significantly higher in the case of right-sided radiotherapy and regional lymph node irradiation. Liver irradiation is the main contributor to immune system exposure in adjuvant irradiation of right-sided breast cancer. Populations in which an association between EDIC and survival would exist have yet to be identified but could potentially include patients treated for triple-negative breast cancer with a poor response to neoadjuvant chemoimmunotherapy.

Dosimetric evaluation of the benefit of deep inspiration breath hold (DIBH) for locoregional irradiation of right breast cancer with volumetric modulated arctherapy (VMAT)

INTRODUCTION

Right-lateralized cardiac substructures can be substantially exposed during right breast cancer (R-BC) radiotherapy. The cardiac benefit of deep inspiration breath hold (DIBH) is established in combination with volumetric modulated arctherapy (VMAT) for left breast cancer with regional node irradiation but is unknown for R-BC. This study evaluated the dosimetric benefit of DIBH for locoregional irradiation of R-BC with VMAT.

MATERIAL AND METHODS

All patients treated for R-BC with adjuvant locoregional DIBH-VMAT in the Department of Radiation Oncology of the Institut Curie (Paris, France) until December 2022 were included, corresponding to 15 patients. FB- and DIBH-VMAT plans were compared both for a normofractionated regimen (50 Gy/25fx) used for treatment and a replanned hypofractionated regimen (40 Gy/15fx). Dose to the heart, cardiac substructures (sinoatrial node (SAN), atrio-ventricular node (AVN), right coronary artery, left anterior descending coronary artery, left ventricle), ipsilateral lung and liver were retrieved and compared.

RESULTS

Mean heart dose (MHD) was 3.33 Gy with FB vs. 3.10 Gy with DIBH on normofractionated plans (p = 0.489), and 2.58 Gy with FB vs. 2.41 Gy with DIBH on hypofractionated plan (p = 0.489). The benefit of DIBH was not significant for any cardiac substructure. The most exposed cardiac substructure were the SAN (mean dose of 6.62 Gy for FB- and 5.64 Gy for DIBH-VMAT on normofractionated plans) and the RCA (mean dose of 4.21 Gy for FB- and 4.06 Gy for DIBH-VMAT on normofractionated plans). The maximum benefit was observed for the RCA with a median individual dose reduction of 0.84 Gy on normofractionated plans (p = 0.599). No significant dosimetric difference were observed for right lung. Liver mean dose was significantly lower with DIBH with median values decreasing from 2.54 Gy to 0.87 Gy (p = 0.01).

CONCLUSION

Adding DIBH to efficient cardiac-sparing radiotherapy techniques, such as VMAT, is not justified in the general case for locoregional R-BC irradiation. Specific R-BC patient subpopulations who could benefit from additional DIBH combination with locoregional VMAT are yet to be identified.

Association Between Cardiac Radiation Exposure and the Risk of Arrhythmia in Breast Cancer Patients Treated With Radiotherapy: A Case–Control Study

Background

Previous studies suggested that radiation therapy (RT) for breast cancer (BC) can induce cardiac arrhythmias and conduction disorders. However, the association with mean heart dose and specific cardiac substructures doses was less studied.

Materials and Methods

We conducted a nested case–control study based on French BC patients, enrolled in the European MEDIRAD-BRACE study (https://clinicaltrials.gov, Identifier: NCT03211442), who underwent three-dimensional conformal radiation therapy (3D-CRT) between 2009 and 2013 and were retrospectively followed until 2019. Cases were incident cases of cardiac arrhythmia. Controls without arrhythmia were selected with propensity-scored matching by age, duration of follow-up, chemotherapy, hypertension, and diabetes (ratio 1:4 or 5). Doses to the whole heart (WH), left and right atria (LA and RA), and left and right ventricles (LV and RV) were obtained after delineation with multi-atlas-based automatic segmentation.

Results

The study included 116 patients (21 cases and 95 controls). Mean age at RT was 64 ± 10 years, mean follow-up was 7.0 ± 1.3 years, and mean interval from RT to arrhythmia was 4.3 ± 2.1 years. None of the results on association between arrhythmia and cardiac doses reached statistical significance. However, the proportion of right-sided BC was higher among patients with arrhythmia than among controls (57% vs. 51%, OR = 1.18, p = 0.73). Neither mean WH dose, nor LV, RV, and LA doses were associated with an increased risk of arrhythmia (OR = 1.00, p > 0.90). In contrast, the RA dose was slightly higher for cases compared to controls [interquartile range (0.61–1.46 Gy) vs. (0.49–1.31 Gy), p = 0.44], and a non-significant trend toward a potentially higher risk of arrhythmia with increasing RA dose was observed (OR = 1.19, p = 0.60). Subanalysis according to BC laterality showed that the association with RA dose was reinforced specifically for left-sided BC (OR = 1.76, p = 0.75), while for right-sided BC, the ratio of mean RA/WH doses may better predict arrhythmia (OR = 2.39, p = 0.35).

Conclusion

Despite non-significant results, our exploratory investigation on BC patients treated with RT is the first study to suggest that right-sided BC patients and the right atrium irradiation may require special attention regarding the risk of cardiac arrhythmia and conduction disorders. Further studies are needed to expand on this topic.