Reducing secondary lung cancer risk by optimized planning of accelerated partial breast irradiation
OC-0102
Abstract
Reducing secondary lung cancer risk by optimized planning of accelerated partial breast irradiation
Authors: Hoekstra|, Nienke(1)*[n.hoekstra@erasmusmc.nl];Habraken|, Steven(1);Swaak - Kragten|, Annemarie(1);Breedveld|, Sebastiaan(1);Pignol|, Jean-Philippe(2);Hoogeman|, Mischa(1);
(1)Erasmus MC Cancer Institute, Radiation Oncology, Rotterdam, The Netherlands;(2)Dalhousie University, Radiotherapy, Halifax NS, Canada;
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Purpose or Objective
The survival benefit of adjuvant radiotherapy for low-risk breast cancer patients might be partially offset by the risk of radiation-induced lung cancer. Reducing dose to the lungs during treatment planning for external beam APBI mitigates this risk, but also results in higher doses to the ipsilateral breast if target coverage and dose to the contralateral breast are kept constant. This could lead to a higher risk of breast fibrosis. Our purpose is to quantify the trade-off between secondary lung cancer and fibrosis risks.
Material and Methods
We conducted a treatment planning study on 20 female patients eligible for APBI, comparing coplanar and non-coplanar techniques, namely VMAT and CyberKnife robotic radiotherapy. We created 11 Pareto-optimal plans per patient per technique using automated treatment planning with the same constraints but gradually shifting priority from maximum sparing of the lungs to maximum sparing of the breast tissue. The excess absolute risk of developing lung cancer was based on lung dose and calculated with the model described by Schneider et al. (2011) accounting for fractionation, repair and repopulation. The risk of breast fibrosis was calculated using the model from Avanzo et al. (2012) for APBI with complete repair.
Results
The dose parameters, secondary lung cancer risks and fibrosis risks are summarized in Table 1. Prioritizing lung sparing resulted in a substantial reduction of the mean lung dose to as low as 0.3 Gy, and a five-fold median reduction of the secondary lung cancer risk compared to prioritizing sparing of breast tissue. The associated increase in breast dose resulted in a very small absolute increase in fibrosis risk of 0.4%-point. Figure 1 shows the Pareto-fronts of all patients of the trade-off between mean lung dose and mean ipsilateral breast dose. The thick lines depict the means per technique. The use of non-coplanar beams created more planning flexibility compared to coplanar techniques, as shown by the wider Pareto-fronts. The non-coplanar technique resulted in better plans in all cases (Wilcoxon signed rank test p < 0.001), with a lower secondary cancer risk and also a lower fibrosis risk. Incidentally, the mean heart dose was also reduced for the plans prioritizing lung sparing.
Conclusion
The risk of secondary lung cancer of external beam APBI can be dramatically reduced by prioritizing lung sparing during treatment planning. The associated increase in breast dose does not lead to a relevant increase in fibrosis risk. Prioritizing lung sparing also reduced the mean heart dose. The use of non-coplanar beams systematically resulted in the lowest risks of secondary lung cancer and fibrosis.
Based on our results, we recommend prioritizing lung sparing to reduce the mortality risk from secondary lung cancer and cardiovascular disease for patients treated with APBI. A non-coplanar beam set-up can reduce these risks even further compared to a coplanar beam set-up.