Long-Term Outcomes for Validation of Cardiac-Sparing Breast Cancer Treatment Techniques

Abstract

The association between radiation therapy (RT) and ischemic vascular disease (IVD) has been known for many decades. The publication in 2013 of a retrospective study linking RT for left breast cancer to IVD has inspired numerous dosimetric studies aimed at reducing cardiac doses. The cardiac risk has been attributed to attempts to treat internal mammary lymph nodes (IMLN), most commonly using an anterior beam that delivered high doses to the origins of major vessels and much of the myocardium. If a treatment technique is producing clinically significant IVD we should see a detrimental effect on survival for patients with left breast cancers compared to those with right breast cancers. In 1983 our facility began using CT images to guide treatment planning. Initially, conformal molded blocks shaped tangent fields to protect the cardiac profile as much as possible. Anterior or oblique internal mammary fields became very rare. Since 2001 we have used 3D conformal CT planning and multi-leaf collimators to the same purpose. Deep inspiration breath hold is used when indicated. Between 1983 and 2011 a total of 3474 patients (1735 R, 1739 L) with first primary pathologic stages 0-III breast cancers were treated with this philosophy. Treatment generally covered the whole breast with standard doses (typically 45 – 50 Gy) and a boost. Since 1982 patient data has been abstracted by certified cancer registrars from general medical records and RT summary letters, and maintained on an in-house registry system. The registry has current follow-up on 95.6% of all cases in this group and was the source of data for this study. The two groups proved to be very closely matched in patient and tumor characteristics. Survival estimates were calculated for 30 years following diagnosis using the Kaplan-Meier method on 1 day intervals (table). These were compared using the log-rank test. Throughout the 30-year period of analysis the P-value was never smaller than 0.23 (briefly, at 7 years). Clinically significant IMLN recurrence has been very rare. Cause-specific mortality declined substantially after about 15 years but all-cause mortality remained elevated. For any RT technique, the average heart dose is substantially smaller for right breast cancers than it would be for left breast cancers. The equivalent survival seen with these two groups suggests that relatively simple alterations to treatment plans can virtually eliminate excess cardiac mortality from left breast irradiation without adverse consequences.Tabled 1Abstract 2130; Table 1LateralityTime from Dx (Yrs)051015202530RightAt Risk173514988944691935811Survival100.00%87.35%73.30%59.03%46.65%35.84%22.15%Std Err of Survival0.00%0.81%1.28%1.79%2.52%3.80%6.18%LeftAt Risk173914929124691816614Survival100.00%87.29%71.97%59.14%45.73%34.19%28.80%Std Err of Survival0.00%0.81%1.28%1.77%2.58%3.52%6.49% Open table in a new tab