Target Volume Coverage and Organ at Risk Doses for Left-sided Whole-breast Irradiation With or Without Internal Mammary Chain Irradiation: A Comparison Between Three Techniques Representing the Past and the Present

Quality assurance of internal mammary node irradiation in the DBCG IMN2 study

PURPOSE/OBJECTIVE

The Danish Breast Cancer Group (DBCG) IMN2 study investigated the gain from internal mammary node irradiation (IMNI) in node-positive breast cancer patients. IMNI was indicated in right-sided patients, but not in left-sided. Target volume delineations were based on bony landmarks in contrast to the contemporary vessel-based ESTRO consensus guideline. Our objective was to compare IMNI doses in right-sided versus left-sided patients.

MATERIAL/METHODS

Treatment plans and delineated structures including CTVn_IMN (IMN_old) from 2008 to 2014 were collected from the DBCG RT Nation study. During the study period, IMN_old was only delineated in right-sided patients. Right and left-sided CTVn_IMN structures were auto-segmented following the ESTRO guidelines (IMN_ESTRO). Due to cranial discordance between IMN_old and IMN_ESTRO, the IMN_ESTRO models were separated into IMN_ESTRO_cranial and IMN_ESTRO_intercostal space(IC)1-3, IC1-4, and IC4_only.

RESULTS

Treatment plans for 2837 patients were available (62.5 % of patients in the IMN2 study). In right-sided patients, the median IMN_old dose coverage (92.4 %) was higher than IMN_ESTRO (71.7 %), p < 0.001. Dose coverage in IMN_ESTRO_IC1-3 was comparable to IMN_old. Comparing IMN_ESTRO_IC1-3 in all patients by laterality, the median CTVn_V90% was 94.6 % (IQR 64.8-100.0) in right-sided patients and 20.4 % (IQR 0.9-55.8) in left-sided patients, p < 0.001. For right-sided patients, median CTV_V90% was 82.3 % in IMN_ESTRO_IC4_only. Median mean heart doses were lower in right-sided patients (1.2 Gy) than in left-sided (2.3 Gy), p < 0.001. Median mean lung doses were higher in right-sided patients (16.0 Gy) than in left-sided (12.7 Gy), p < 0.001.

CONCLUSION

For IMN_ESTRO_IC1-3, we found a significantly higher IMN dose coverage in right-sided than in left-sided patients supporting treatment according to study guidelines in the DBCG IMN2 study.

Dosimetric Analyses of the Three Radiation Techniques Used in the EORTC 22922/10925 IM-MS Breast Cancer Trial

PURPOSE

The aim of the current study is to compare the dosimetry of 3 radiation therapy (RT) techniques used in the EORTC 22922/10925 trial for irradiating the internal mammary (IM) and medial supraclavicular nodes (MS) using a treatment planning system available nowadays for dose calculation.

METHODS

We performed a retrospective dosimetry analysis of anonymised data; thus, ethics approval was not required. Ten cases of left-sided breast were randomly selected for RT planning to a total dose of 50 Gy in 25 fractions. The treatment planning was done according to the trial's protocol and under the supervision of the EORTC trial's coordinators. Doses to planning target volumes (PTV) and to organs at risk (OARs) are reported. Data is presented in descriptive statistics.

RESULTS

A total of 10 cases and 40 treatment plans (4 plans per case: standard-plan A, modified standard-plan B, individualised-plan C and breast-only-plan D). For all planning techniques, the mean dose to the PTV of the left breast (plan A-D) and the PTV-MS (plan A-C) exceeded 95% of the prescribed dose (>47.5 Gy). The individualised technique (plan C) had a lower coverage for PTV-IM, with a mean of 87% of the prescribed dose compared to ∼102% for plans A and B. The dose to OARs varied between techniques, with the mean heart dose being higher in the standard and modified standard techniques (18.3 and 16.6 Gy, respectively) compared to the individualised technique (9.5 Gy).

CONCLUSIONS

The 3 RT techniques used in the trial varied in target coverage and OARs dose. Our results may help to understand the observed larger absolute benefit of individualised IM-MS treatment planning in terms of breast cancer outcomes.

Efficacy and Safety of the Addition of Internal Mammary Irradiation to Standard Adjuvant Radiation in Early-Stage Breast Cancer: A Systematic Review and Meta-Analysis

Background: Existing data on adding internal mammary nodal irradiation (IMNI) to the regional nodal fields are inconsistent. Methods: Randomized trials investigating the addition of IMNI to standard adjuvant radiation were identified. Hazard ratios (HRs) and 95% confidence intervals (CI) were extracted for overall-survival (OS), breast cancer specific-survival (BCSS), and disease-free survival (DFS) as well as distant-metastasis free survival (DMFS). The odds ratios (ORs) for regional and loco-regional recurrence, non-breast cancer mortality, secondary non-breast cancer, contralateral breast cancer, and cardiovascular morbidity and mortality were also extracted. Results: Analysis included five trials comprising 10,994 patients, predominantly with higher risk, lymph node positive disease. Compared to the control group, IMNI was associated with significant improvement in OS (HR = 0.91, p = 0.004), BCSS (HR = 0.84, p < 0.001), DFS (HR = 0.89, p= 0.01), and DMFS (HR = 0.89, p = 0.02). IMNI was also associated with reduced odds for regional (OR = 0.58, p < 0.001) and loco-regional recurrence (OR = 0.85, p = 0.04). The odds for cardiotoxicity were not statistically significantly higher (OR = 1.23, p = 0.07). There were comparable odds for cardiovascular mortality (OR = 1.00, p = 1.00), non-breast cancer mortality (OR = 1.05, p = 0.74), secondary cancer (OR = 0.95, p = 0.51), and contra-lateral breast cancer (OR = 1.07, 95% 0.77−1.51, p = 0.68). Conclusions: Compared to the control group, the addition of IMNI in high-risk patients is associated with a statistically significant improvement in survival, albeit with a magnitude of questionable clinical meaningfulness.

The association of internal mammary and medial supraclavicular lymph node radiation technique with clinical outcomes: Results from the EORTC 22922/10925 randomised trial

BACKGROUND AND PURPOSE

The multicentre EORTC 22922/10925 trial (ClinicalTrials.gov, NCT00002851) was conducted between 1996 and 2004. The trial evaluated the effect of irradiation of the internal mammary and medial supraclavicular lymph node chains (IM-MS) vs no further radiation therapy (RT) on survival and cause of death in breast cancer stage I-III patients. At 15.7 years of median follow-up, a significant reduction of breast cancer specific mortality (BCSM) and any recurrence, not translating in improved overall survival (OS), and low absolute rates of side effects were found. The aim of the current analysis was to evaluate the association of RT techniques of IM-MS lymph node irradiation with long-term outcomes.

PATIENTS AND METHODS

Three RT techniques were used for IM-MS: a standard technique using a fixed set-up combining photon/electron beams to the IM and tangential fields to the breast or chest wall vs a standard-modified technique with minor adaptation for beam settings vs a more individualised technique based on individual localisation of the IM. Techniques used were fixed per institution over the duration of the trial. We performed an exploratory and descriptive analysis of the outcomes after 15 years follow-up for the three RT techniques.

RESULTS

Between July 1996 and January 2004, 46 radiation oncology departments from 13 countries accrued 4004 patients. Median follow-up was 15.7 years. The number of patients treated by each technique was 2440 (61%) by standard vs 635 (16%) by standard-modified vs 929 (23%) patients by individualised technique. The absolute improvements of oncological outcomes in terms of disease-free survival (DFS), OS and BCSM with IM-MS RT compared to no IM-MS RT were 6.8%, 4.9% and -5.8% for the individualised technique, vs 1.6%, 2.9% and -4.3% for modified standard and -1.4%, 1.1% and -3% for standard technique, respectively. The increase in 15-year rates of side effects due to IM-MS RT, both scored longitudinally and cross-sectionally, were similar among the techniques.

CONCLUSION

Even though a straightforward comparison by technique is not possible because of variations in baseline characteristics between institutions, our findings suggest that the use of more individualised RT techniques is associated with higher rates of oncological improvements without increased risks for late side effects.