Anatomy-dependent lung doses from 3D-conformal breast-cancer radiotherapy.

This study aims to identify key anatomic features that govern the individual variability of lung doses from breast-cancer radiotherapy. 3D conformal, intensity-modulated and hybrid techniques with 50.4 Gy whole-breast dose were planned for 128 patients. From their CT images, 17 anatomic measures were assessed and tested as predictors for lung dose-volume characteristics. Tangential techniques yielded mean ipsilateral lung doses in the range of 3-11 Gy. This inter-patient variability was explained to almost 40% by central lung distance, and to almost 60% if this measure was complemented by midplane lung width and maximum heart distance. Also the variability in further dose-volume metrics such as volume fractions receiving 5, 20 or 40 Gy could be largely explained by the anatomy. Multi-field intensity-modulated radiotherapy reduced high-exposed lung volumes, but resulted in higher mean ipsilateral lung doses and larger low-dose burden. Contralateral lung doses ranged from 0.3 to 1 Gy. The results highlight that there are large differences in lung doses among breast-cancer patients. Most of this inter-individual variability can be explained by a few anatomic features. The results will be implemented in a dedicated software tool to provide personalized estimates of long-term health risks related to breast-cancer radiotherapy. The results may also be used to identify favourable as well as problematic anatomies, and serve as a quick quantitative benchmark for individual treatment plans.

Heart atlas for retrospective cardiac dosimetry: a multi-institutional study on interobserver contouring variations and their dosimetric impact.

PURPOSE: Cardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart's heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies. METHODS AND MATERIALS: The atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability. RESULTS: Contouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement. CONCLUSIONS: For the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.

WHAT ANATOMIC FEATURES GOVERN PERSONAL LONG-TERM HEALTH RISKS FROM BREAST CANCER RADIOTHERAPY?

Breast cancer radiotherapy may in the long term lead to radiation-induced secondary cancer or heart disease. These health risks hugely vary among patients, partially due to anatomy-driven differences in doses deposited to the heart, ipsilateral lung and contralateral breast. We identify four anatomic features that largely cover these dosimetric variations to enable personalized risk estimates. For three exemplary, very different risk scenarios, the given parameter set reproduces 63-74% of the individual risk variability for left-sided breast cancer patients. These anatomic features will be used in the PASSOS software to support decision processes in breast-cancer therapy.

INTER-PATIENT VARIABILITY IN DOSES TO NEARBY ORGANS IN BREAST-CANCER RADIOTHERAPY: INFERENCE FROM ANATOMIC FEATURES.

With improved cure rates and prolonged patient survival after breast-cancer radiotherapy, radiation-induced second cancers and heart diseases become increasingly important. The heart, lungs and contralateral breast are the most critical organs for these long-term effects. Doses to these organs and hence the risks differ between radiotherapy techniques and especially among patients. To address this variability, treatment plans were generated for 128 early-stage breast-cancer patients using intensity-modulated, 3D-conformal and hybrid radiotherapy. Twenty dedicated anatomic measures were assessed from CT data, such as the width and thickness of the treated breast or its distance from the heart. Their impact on doses to critical nearby organs was analysed. The majority of inter-patient variability can be covered with a few anatomic parameters. Patients can thus be stratified according to long-term risks already before treatment planning, and guidance can be provided towards a personalised selection of technique associated with the lowest risk.

Minimum breast distance largely explains individual variability in doses to contralateral breast from breast-cancer radiotherapy.

PURPOSE: To provide personalized estimates of doses to contralateral breast (CB) from breast-cancer radiotherapy. METHODS: Whole-breast irradiations using 3D conformal, intensity-modulated and hybrid techniques with 50.4 Gy prescribed dose were planned for 128 breast-cancer patients. From their CT images, 17 anatomic measures were assessed and tested by model fitting as predictors for CB dose-volume characteristics. RESULTS: Multi-field intensity-modulated radiotherapy (IMRT) yielded mean CB doses of 0.8-7.1 Gy, with no correlation to the studied anatomic parameters. Tangential whole-breast irradiation led to much lower mean CB doses, 0.2-1.6 Gy. About 60% of this inter-patient variability was explained by individual variations in a single anatomic measure, the minimum breast distance (MBD), defined as the CB distance from the tangent to the treated breast. Per 1 cm increase in MBD, the mean CB dose decreased by 10-15%. As an alternative to MBD, dose estimates could be based on the breast-to-breast distance, which is highly correlated with MBD. CONCLUSION: The results enable personalized assessment of CB doses from tangential whole-breast irradiation, based only on parameters assessable from CT data. This may help support clinical decision-making processes as well as analyse retrospective studies on CB risks.