A Dosimetric Comparison of Intensity Modulated Radiation Therapy and Intensity Modulated Proton Therapy Accelerated Partial Breast Irradiation with Emphasis on Left Anterior Descending Coronary Artery Doses

Committee/Faculty

Presenting Author(s)

MN

My-Lien Nguyen, n/a

Resident
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: I do not have any relevant financial / non-financial relationships with any proprietary interests.

Co-Author(s)

AS

Alexis Schutz

Resident
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: Disclosure information not submitted.
HP

Hanh Pham

Dosimetrist
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: Disclosure information not submitted.
HJ

Hayden Jackson

Medical Student
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: Disclosure information not submitted.
WD

William Dooley

Attending Physician
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: Disclosure information not submitted.
CH

Christina Henson

Primary Investigator, Attending Physician
University of Oklahoma Health Sciences Center
Oklahoma City, Oklahoma, United States

Disclosure: Disclosure information not submitted.

Purpose: Radiation dose to the left anterior descending coronary artery (LADCA) is thought to correlate with stenosis and subsequent cardiac disease following irradiation for breast cancer. Though previous studies have shown a dosimetric advantage to proton therapy in decreasing heart dose in patients receiving comprehensive nodal irradiation, little data is available on the potential benefit of proton therapy for early breast cancer. In this retrospective study, we examine LADCA dose in patients with left sided breast cancer treated with accelerated partial breast irradiation (APBI) using intensity modulated proton therapy (IMPT) as compared to intensity modulated radiation therapy (IMRT).

Methodology: From January 2019 to July 2021, 34 patients were treated at our institution with adjuvant IMPT APBI following lumpectomy for Stage 0-IA left sided breast cancer. All patients treated were female with median age of 70. Histology included ductal carcinoma in situ or invasive carcinoma. LADCA was contoured via contouring atlas by Feng et al [1]. Comparison IMRT plans were generated either at the time of treatment planning or retrospectively. The prescription dose was 3000 cGy in 5 fractions delivered every other day prescribed to the clinical target volume (CTV) for IMPT and planning target volume (PTV) for IMRT.

Results: Dose to 0.02cc (D0.02) of the LADCA for IMPT ranged from 0.1 cGy to 4910 cGy. D0.02 for the LADCA for IMRT ranged from 0.3 cGy to 5490 cGy. Mean D0.02 to the LADCA for IMPT and IMRT were 518 cGy and 824 cGy, respectively, with p-value = 0.013. All doses were adjusted to account for equivalent dose in 2 Gy fractions (EQD2). Of the 34 patients, 3 patients (8.8%) had an EQD2 maximum dose to the LADCA greater than 20 Gy with both IMRT and IMPT which is above the threshold recommended by the Danish Breast Cancer Cooperative Group (DBCG) [2]. One patient (2.9%) had an above threshold EQD2 maximum dose with IMRT but not IMPT.

Conclusions: Our study shows that even with APBI in early breast cancer patients, we must be mindful of dose to the LADCA. LADCA D0.02 for IMPT was significantly lower than IMRT, showing a potential for advantage in IMPT in treating this subset of patients.

References: [1] Feng, M., Moran, J. M., Koelling, T., Chughtai, A., Chan, J. L., Freedman, L., et al (2011). Development and Validation of a Heart Atlas to Study Cardiac Exposure to Radiation Following Treatment for Breast Cancer. International Journal of Radiation Oncology Biology Physics, 79(1), 10–18.

[2] Thomsen, M., Berg, M., Zimmermann, S., Lutz, C., Makocki, S., Jensen, I., et al (2021). Dose constraints for whole breast radiation therapy based on the quality assessment of treatment plans in the randomised Danish breast cancer group (DBCG) HYPO trial. Clinical and Translational Radiation Oncology, 28, 118–123.