Phillip Pifer, MD, FSCAI, MD, PhD
PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): As the field of radiation oncology moves toward 3D planning for post-mastectomy radiotherapy, contouring guidelines from cooperative groups including RTOG and ESTRO have been published to help guide clinical practice. However, considerable variation exists in the recommended dorsal border for the chest wall CTV. We aimed to quantify the impact of this variation on doses to critical organs and examine patterns of chest wall recurrence relative to the pectoralis muscle with the hypothesis that the majority of recurrences in the modern era occur anterior to the rib surface wherein a reduction in the dorsal chest wall CTV border might decrease normal tissue exposure to heart and lung.
Materials/Methods: We retrospectively created treatment plans for 5 women treated with post-mastectomy radiotherapy to the left chest wall, undissected axilla, supraclavicular, and internal mammary lymph nodes. The chest wall was contoured using varying dorsal borders for CTV recommended in the literature: (1) anterior pleural surface (RTOG), (2) anterior surface of pectoralis major (ESTRO), and (3) anterior rib surface (institutional practice). Plans were generated for 50Gy in 25 fractions with goals of meeting the criteria for target volume coverage recommended in the NSABP-B51. Doses to organs-at-risk were compared using paired-sample t-tests. To assess institutional chest wall recurrence, we used a prospectively maintained breast cancer database. From 2005-2017, we identified 17 patients with chest wall recurrences. The location of each recurrence, as noted on pre-operative imaging and/or post-operative pathology, were quantified relative to the recommended CTV borders.
Results: Comparing plans generated for the RTOG versus EORTC contouring guidelines, the mean lung V20Gy, heart mean dose, and left anterior descending artery mean dose were 33.5% versus 29.4% (p<0.01), 5.2Gy versus 3.2Gy (p=0.02), and 27.3Gy versus 17.8Gy (p=0.04), respectively. Comparing plans generated for the RTOG versus our institutional variation the mean lung V20Gy, heart mean dose, and left anterior descending artery mean dose were 33.5% versus 31.4% (p=0.01), 5.2Gy versus 3.8Gy (p=0.03), and 27.3Gy versus 22.6Gy (p=0.12), respectively. Institutional patterns of chest wall recurrence were as follows: 64.7% had recurrence isolated to tissue anterior to the pectoralis muscle, 23.5% were located both anterior to and between the pectoralis muscles, and only 11.8% of recurrences were isolated to the tissue between the pectoralis major and minor. No chest wall recurrences were noted deep to pectoralis minor.
Conclusion: Recommended variations in the dorsal chest wall CTV border have significant impact on doses to heart and lung. While limited by small numbers, our institutional patterns of recurrence would support a more anterior dorsal border for the chest wall CTV consistent with older literature; wherein continued study and international consensus is needed to help better guide clinical practice and trial design.
The asset you are trying to access is locked. Please enter your access key to unlock.