Objective Versus Subjective Assessment of Single Photon Emission Computed Tomography (SPECT) Cardiac Perfusion Scans to Assess for Radiation Therapy (RT) Induced Cardiac Injury
Presenter: Robert G. Prosnitz, MD
Presenter's Affiliation: Duke University Medical Center, Durham, NC
Type of Session: Plenary
- Radiation therapy has been used in the treatment of breast cancer for many years.
- Multiple clinical trials that compared surgery to surgery plus radiation have consistently demonstrated that the addition of radiation therapy decreases the chances for a local tumor recurrence.
- However, the addition of radiation to surgery has only recently been shown to improve survival in breast cancer patients.
- Early radiation techniques delivered a considerable amount of radiation to a patient's heart when they had left side breast cancers.
- In left sided cases, radiation therapy was responsible for decreasing a patient's chances of dying from breast cancer, but increased a patient's chances of dying from a cardiac complication.
- Newer radiation techniques have been developed which greatly decrease the amount of heart treated in left sided breast cancer cases.
- SPECT scans help quantify decreases in cardiac perfusion from a variety of insults.
- After radiation therapy to the left breast/chest wall, it has been reported that 20% to 70% of women experience perfusion defects seen on SPECT.
- From 1998 to 2005, a prospective IRB approved study of cardiac toxicity following radiation therapy for breast cancer was performed at Duke University Medical Center.
- All patients had left sided breast cancers.
- SPECT perfusion defects were scored either subjectively (based on the analysis of the nuclear medicine attending's read of the serial scans) or objectively (based on a computer algorithm and statistical analysis the of serial scans).
- SPECT scanning was done before and then serially after radiation therapy.
- 152 patients were enrolled, but all patients with abnormal pre-RT SPECT scans were excluded leaving 79 patients evaluable.
- The cumulative incidence of SPECT perfusion defects seen in this study was higher than hypothesized.
- The likelihood of developing a SPECT perfusion scan was related to the volume of the heart muscle in the radiation treatment fields.
- 30% of the patients with <1% of the heart muscle in the radiation field developed a SPECT perfusion defect while >90% of the patients with a >10% of heart muscle in the radiation field developed a SPECT perfusion defect.
- The median breast radiation dose was 47 Gy.
- The mean volume of heart in the radiation field was 8% (range 0-36%).
- Although the subjective and objective analyses of the serial SPECT scans produced fairly similar results, there were 15 patients that were deemed to have a perfusion defect on computer based analysis who were not identified by the nuclear medicine attending as having any abnormalities on SPECT.
- When examining these 15 patients, the mean volume of heart in the field was 11%, and 4 of these 15 patients eventually did go on to have subjective perfusion defects noted on SPECT.
- Visible perfusion defects are common after modern radiation therapy.
- Objective, quantitative methods for determining perfusion defects may improve detection of defects.
- The true incidence of perfusion defects following radiation therapy may be higher than was previously reported.
- The long term significance of perfusion defects in not known, and further study of this modality for predicting cardiac morbidity and mortality is warranted.
- When possible, incidental irradiation of cardiac tissues should be avoided.
The authors presented a well constructed and interesting piece of research about the likelihood of developing perfusion defects on SPECT imaging following radiation therapy for left sided breast cancers. The authors should be commended for initiating this research shortly after the value of SPECT imaging was elucidated. It has been well established that older radiation techniques which treated significant volumes of the heart muscle can lead to increased risks of cardiac morbidity and mortality. It is currently unclear if these abnormalities on SPECT scans will translate into clinically significant changes. These patients should be followed long term to determine if SPECT scans help to predict which patients are likely to have cardiac problems in the future. Patients who develop abnormalities on SPECT may need to be counseled strongly to modify cardiac risk factors. Longer follow-up time with serial SPECT imaging may allow us to have a better idea about the utility of this test following radiation therapy. This research also highlights the correlation between the volume of heart treated and the risk of perfusion abnormalities. Radiation oncologists must continue to develop treatment plans which spare as much cardiac tissue as is possible.