Proton therapy for reducing heart and cardiac substructure doses in Indian breast cancer patients

Abstract

Purpose: Indians have a higher incidence of cardiovascular diseases, often at a younger age, than other ethnic groups. This higher baseline risk requires consideration when assessing additional cardiac morbidity of breast cancer treatment. Superior cardiac sparing is a critical dosimetric advantage of proton therapy in breast cancer radiotherapy. We report here the heart and cardiac-substructure doses and early toxicities in breast cancer patients treated post-operatively with proton therapy in India’s first proton therapy center. Materials and Methods: We treated twenty breast cancer patients with intensity-modulated proton therapy (IMPT) from October 2019 to September 2022, eleven after breast conservation, nine following mastectomy, and appropriate systemic therapy, when indicated. The most prescribed dose was 40 GyE to the whole breast/chest wall and 48 GyE by simultaneous integrated boost to the tumor bed and 37.5 GyE to appropriate nodal volumes, delivered in 15 fractions. Results: Adequate coverage was achieved for clinical target volume (breast/chest wall), i.e., CTV40, and regional nodes, with 99% of the targets receiving 95% of the prescribed dose (V95% > 99%). The mean heart dose was 0.78 GyE and 0.87 GyE for all and left breast cancer patients, respectively. The mean left anterior descending artery (LAD) dose, LAD D0.02cc, and left ventricle dose were 2.76, 6.46, and 0.2 GyE, respectively. Mean ipsilateral lung dose, V20Gy, V5Gy, and contralateral breast dose (Dmean) were 6.87 GyE, 14.6%, 36.4%, and 0.38 GyE, respectively. Conclusion: The dose to heart and cardiac substructures is lower with IMPT than published photon therapy data. Despite the limited access to proton therapy at present, given the higher cardiovascular risk and coronary artery disease prevalence in India, the cardiac sparing achieved using this technique merits consideration for wider adoption in breast cancer treatment.

Deep inspiratory breath-hold radiotherapy on a Helical Tomotherapy unit: Workflow and early outcomes in patients with left-sided breast cancer

“…We noted that reducing the EQD2 below the threshold for major events was not achieved for any patient for the heart and was achieved for the Mean LAD dose in 20% of cases and for the Max LAD (D0.02 cc) in 45% of cases. Unlike this, in our previously reported cohort of patients treated with proton therapy, the Dmean of heart (EQD2) was achieved in 100 %, Dmean LAD (EQD2) in 90 % and LAD D0.02 cc (EQD2) in 80 % of cases [15] . This underlines that while DIBH allows the reduction of heart and substructure doses, further reduction with proton therapy remains a desirable and achievable goal.…”

Proton Reirradiation for High-Risk Recurrent or New Primary Breast Cancer

“…Indeed, many studies have demonstrated that PBT results in a large reduction in cardiac and coronary artery radiation dose when compared to photon techniques, including three-dimensional conformal radiation therapy (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) [38][39][40][41][42][43][44]. Multiple studies have also demonstrated that PBT results in significantly reduced doses to cardiac tissues and substructures compared to photon techniques combined with deep inspiration breath hold (DIBH) [39][40][41].…”