- Email: [email protected]
Comparison of Heart Dose in Early Stage Left Sided Breast Cancers Treated with IORT or EBRT-DIBH
Volume 99 Number 2S Supplement 2017
Poster Viewing
E1
Poster Viewing 2000
2001
Evaluation of Radiation-Induced Cardiac Toxicity in Breast Cancer Patients Treated with Trastuzumab-Based Chemotherapy M.L. Abouegylah,1,2 L.W. Salama,1 M. Elebrashi,1 S. Edgington,3 K. Remillard,4 A. Niemierko,4 M. Farouk,5 M. Alm El-Din,6 B. Napolitano,4 J.A. Wolfgang,7 A.S.A. Ismail,5 and A.G. Taghian1; 1 Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, 2Faculty of medicine, Alexandria University, Alexandria, Egypt, 3Massachusetts general hospital, Boston, MA, 4Massachusetts General Hospital, Boston, MA, 5Alexandria University, Alexandria, Egypt, 6 Tanta University, Tanta, Egypt, 7Massachusetts General Hospital, Harvard Medical School, Boston, MA
Reduced Mean Cardiac Dose: An Additional Benefit of Hypofractionated Whole Breast Radiotherapy? M. Ahmad,1 P.N. Barry Jr,1 M. Moler,2 J. Gaskins,3 and A.E. Dragun1; 1 University of Louisville School of Medicine, Louisville, KY, 2University of Pikeville, Kentucky College of Osteopathic Medicine, Pikeville, KY, 3 University of Louisville, Louisville, KY
Purpose/Objective(s): Patients with Her2 positive breast cancer treated with trastuzumab have a higher rate of cardiotoxicity(CT), particularly when combined with chemotherapy. Breast radiation to the left side might increase the risk for CT from cardiac exposure to radiation The aim of our study is to evaluate the contribution of radiotherapy (RT) in the development of CT in breast cancer patients receiving chemotherapy with trastuzumab. We hypothesize that the risk of CT is based on the volume and location of the heart exposed to radiation Materials/Methods: 205 patients were treated with RT and trastuzumab in our institute from 2001 to 2014; The RT plans for 108 patients with left side disease were recalled from archives. The heart, each chamber and the left anterior descending artery (LAD) were independently contoured. New dose-volume histograms (DVH) were generated. Their serial echocardiograms and or radioisotope scans were also studied, which included a baseline pretreatment scan. Patients lacking follow up cardiac scans were excluded from the analysis. CT was defined as a >10% decrease in the left ventricular ejection fraction (LVEF) from baseline, development of wall motion abnormality, and myocardial ischemia diagnosed by EKG. The crude rates of CT for left and right side were compared using Fisher’s exact test. The DVH data indices for the left side cases were correlated with the predefined cardiac events using actuarial Cox regression analysis The Equivalent Uniform Dose (EUD) was the primary index that was extracted from individual DVHs. The EUD model converts an inhomogeneous dose distribution within a structure of interest into a biologically equivalent uniform dose distribution. Right side cases were used as control to assess the combined effect of RT and trastuzumab on developing CT Results: Patients in the 2 groups were well balanced regarding demographics and clinical characteristics with median follow up of 81 months in left side and 84 months for the right side. Compared to the right sided, the left side cases showed statistically significant increase in wall motion abnormalities: 13 patients in the left side (12%) and one patient in right side (w1%) (pZ0.002). Cardiac ischemia diagnosed by EKG were found in 11 patients in left side (10%) and one patient in the right side (w1%) (pZ0.006). On Cox regression analysis, the EUD to the left ventricle (LV), LAD and heart was statistically significantly associated with decrease in LVEF by >10% (p Z0.04) for LAD and LV, and (pZ0.05) for the heart Other DVH parameters like V5, V10, V20, mean and maximum dose for the heart, LAD and each chamber were not statistically significant as risk factors for CT Conclusion: RT to the left breast increases the risk of CT, mainly the wall motion abnormalities and ischemia diagnosed by EKG when combined with Trastuzumab. The EUD index of LV, LAD and heart could be considered as a parameter to describe the risk of radiationinduced CT. Author Disclosure: M.L. Abouegylah: None. L.W. Salama: None. M. Elebrashi: None. S. Edgington: None. K. Remillard: None. A. Niemierko: None. M. Farouk: None. M. Alm El-Din: None. B. Napolitano: None. J.A. Wolfgang: None. A.A. Ismail: None. A.G. Taghian: Research Grant; Impedimed. Honoraria; UpToDate. Consultant; VisionRT.
Purpose/Objective(s): Mean heart dose (MHD) has been widely accepted as a predictor of long term cardiac toxicity. Additionally, it is known that MHD from whole breast radiation is largely attributable to internal lowisodose scatter. The goal of the present study was to evaluate the impact of different whole breast radiation regimens on MHD on patients enrolled in a phase 2 institutional protocol. Materials/Methods: Patients with left-sided Stage 0-II breast cancer who were treated on an institutional protocol in which they received onceweekly whole-breast irradiation (WHBI) to a dose of 2850-3000cGy in 5 fractions were the subject of this analysis. These patients were subsequently re-planned, and MHD was re-calculated using two alternative radiation regimens: conventionally-fractionated (CFRT) and daily hypofractionated (HFRT) radiotherapy (5000cGy in 25 fractions and 4256cGy in 16 fractions, respectively). Ideal MHD was defined as less than 200cGy, which is consistent with established heart dose objectives. Results: A total of 228 plans were generated from 76 patients with leftsided Stage 0-II breast cancer who were treated on a phase 2 protocol. Most of these patients were postmenopausal females (87%) with ER positive tumors (75%) in the outer quadrant of the breast (69%). All patients underwent breast conservation surgery, and the majority did not receive systemic therapy (75%). Of the 76 patients treated with WHBI, 69 (91%) had a MHD less than 200cGy. When the same 76 patients were replanned, only 58 (76%) of CFRT plans and 42 (55%) of HFRT plans had MHDs that were less than 200cGy. The average MHDs were 1.14Gy, 1.62Gy, 1.97Gy for the WHBI, HFRT, and CFRT regimens. Using the reported 7.4% increase in coronary event rate per Gy established by Darby et al, the detected increase in MHD for HFRT corresponds to a 3.5% (CI: 1.4% to 6.9%) elevated risk of coronary events and for CFRT a 6.1% (CI: 2.4% to 12.0%)elevated risk of coronary events, both relative to WHBI. Conclusion: WHBI is an emerging strategy in the treatment of early-stage breast cancer that may offer improved MHD and thus theoretically reduced estimated risk of coronary event relative to traditional regimens. More study is needed to determine whether MHD vs. anatomic dose-volume metrics is the best method of estimating late-cardiac risk in the era of emerging alternative fractionation schemes. Author Disclosure: M. Ahmad: None. P.N. Barry: I only receive my base salary. I do not receive additional compensation.; Radiation Oncology, UofL SOM. M. Moler: None. J. Gaskins: None. A.E. Dragun: None.
2002 Comparison of Heart Dose in Early Stage Left Sided Breast Cancers Treated with IORT or EBRT-DIBH C. Alonso,1 S. Showalter,2 B. Neal,1 B. Libby,1 and E.M. Janowski1; 1 Department of Radiation Oncology, University of Virginia, Charlottesville, VA, 2Department of Surgery, University of Virginia, Charlottesville, VA Purpose/Objective(s): A recent pooled analysis has suggested a possible improvement in overall survival among breast cancer patients treated with intraoperative radiation therapy (IORT) compared to patients treated with external beam whole breast irradiation. This survival benefit is thought to be derived, at least partially, from decreased cardiac toxicity among IORT patients. However, these findings lack the supporting dosimetric data to validate their conclusion. The purpose of this study is to compare heart dose between patients treated with lumpectomy and either intraoperative radiation therapy with CT-guided HDR brachytherapy (Precision Breast
E2
International Journal of Radiation Oncology Biology Physics
IORT; PB-IORT) or deep inspiratory breath hold external beam radiation therapy (EBRT-DIBH) for early stage left sided breast cancers at our institution. Materials/Methods: We retrospectively identified the 17 patients with left sided breast cancers treated with PB-IORT on a phase I clinical trial. 17 patients with left-sided tumors who had undergone lumpectomy and adjuvant EBRT-DIBH during a similar time period were identified for comparison. Dosimetric data was obtained for mean and maximum heart and left anterior descending artery (LAD) doses. T-testing analysis was performed, and biologically effective doses (BED) were calculated using an alpha/beta ratio for heart of 2 Gy. Results: Mean heart dose was found to be significantly lower in the EBRTDIBH group compared to the IORT group (0.61 vs. 0.87 Gy, pZ0.006). Nominal maximum heart dose was significantly higher in the EBRT-DIBH group (11.37 vs. 4.81 Gy, pZ0.004). BED for maximum heart dose was similar between the EBRT-DIBH and IORT groups, 16.63 vs. 19.36 Gy, respectively (pZ0.64). No difference was found in mean left anterior descending (LAD) artery dose: 2.18 Gy in the EBRT-DIBH group and 1.89 Gy in the IORT group (pZ0.446). The maximum LAD doses were 9.63 Gy and 3.62 Gy in the EBRT-DIBH and IORT groups, respectively (pZ0.016). Conclusion: Heart doses were found to be low in both groups. Expected increase in cardiac risk at these doses is minimal. It is unlikely that there will be a clinically significant difference in cardiac toxicity in patients treated with EBRT-DIBH or PB-IORT. Author Disclosure: C. Alonso: None. S. Showalter: None. B. Neal: None. B. Libby: None. E. Janowski: None.
incidence of VUS quadrupled from 2.2% in first half to 9.2% in the latter half of the study period (p<0.03). Similarly, the utilization of multigene panel testing increased 11-fold during this time period (1.6% vs. 18.3%, p<0.001). Conclusion: As expected, mastectomy rates were highest among patients with positive mutation results. A VUS result did not appear to impact locoregional therapy choice, with a similar proportion of patients opting for BCT compared to those with a negative result. Given the unknown prognostic significance of VUS and the changing landscape of genetic testing, these data highlight the continuing need for functional testing methods to allow objective interpretation and communication of VUS results to newly diagnosed breast cancer patients. Author Disclosure: A.Y. Ho: None. K. Amoroso: None. M. Wilgucki: None. K. Vora: None. B.B. Arnold: None. S.N. Powell: None. M. Morrow: ; Society of Surgical Oncolgy. M.E. Robson: Honoraria; AstraZeneca. Advisory Board; AstraZeneca, McKesson.
2003 Prevalence and Impact of Variants of Uncertain Significance on Local Therapy Decision-Making in Newly Diagnosed Breast Cancer Patients A.Y. Ho,1 K. Amoroso,2 M. Wilgucki,2 K. Vora,2 B.B. Arnold,1 S.N. Powell,2 M. Morrow,2 and M.E. Robson2; 1Cedars Sinai Medical Center, Los Angeles, CA, 2Memorial Sloan Kettering Cancer Center, New York, NY Purpose/Objective(s): The commercialization of next-generation sequencing for genetic testing has enhanced the identification of variants of uncertain clinical significance (VUS), introducing new complexities for breast cancer patients making decisions about locoregional therapy. Our purpose was to evaluate whether pre-surgical knowledge of a pathogenic mutation or VUS influenced the type of locoregional therapy received. Materials/Methods: Data was collected from a prospective database of 691 patients who underwent peri-diagnostic genetic counseling and testing at a single, high-volume cancer center between 3/2012-5/2016. Patients diagnosed with metastatic disease
2004 In Vivo Dosimetry for Single Fraction Intraoperative Electron Radiation Therapy for Early Stage Breast Cancer R.B. Ash; Valley Radiotherapy Associates, Orange, CA, St. Joseph Hospital, Orange, CA Purpose/Objective(s): Patients with early stage breast cancer are offered adjuvant breast radiation to reduce the likelihood of recurrence. This is usually in the form of whole breast radiation. Recent data shows that partial breast radiation may be appropriate in some patients with early stage disease. Partial breast radiation, in the form of intraoperative radiotherapy (IORT) is one form of partial breast radiation. Little data has been published on in vivo dosimetry for IORT using electrons. We set out to prospectively measure the dose at three points within the tumor cavity using in vivo dosimeters (nanodots) for patients receiving single fraction IORT using electrons. Materials/Methods: Eligible patients with early stage breast cancer undergoing breast conservation and single fraction IORT were assessed. Following lumpectomy and sentinel node evaluation, the tumor bed was prepared for IORT. A chest wall shield was placed with in-vivo dosimeters (nanodots) placed above and below the shield. The tumor bed was then approximated and intraoperative ultrasound was used to determine depth from top of tumor cavity to top of shield. A 3rd in-vivo dosimeter was placed on the surface of the tumor bed. After 2100 cGy was delivered, the dosimeters were retrieved and the three dose points recorded. Energies, cone size, cone angles and presence/absence of bolus were also recorded. Regression coefficient was used to determine dose as a function of the above factors. Results: Nanodots for a total of 136 patients were evaluated. Cone size ranged from 4.5- 7.5 cm. The majority of cases (86%) used cone size >/Z 5.0 cm. Energies used included 6 (54.4%), 9 (38.2%), and 12 (7.4%) Mev. 58% of cones used had 0 degree angle. The mean surface dose was 1983 cGy (range 1706-2321), the mean dose above the shield was 1396.7 (range 2.4-2702) and the mean dose below the shield was 34.66 (1.4-748.3). Using the regression coefficient, surface dose was dependent on energy and cone size (PZ 0.26, 0.28 respectively) but not cone angle (pZ 0.06). The dose above shield did not appear to be dependent on energy, cone size or angle, (pZ 0.62, 0.21, 0.28 respectively). The dose below shield does not appear to be dependent on the cone size or angle (pZ 0.21, 0.19), but is dependent on energy (pZ0.0). Conclusion: Our data shows that surface dose and dose below shield is consistent. Surface dose appears to be dependent on energy and cone size while dose below the shield seems to be dependent on energy. Dose above the shield was quite variable and not dependent on either three factors. The variability may be due to various issues including shield placed below chest wall muscle, off centering of dosimeters and inaccurate measurement of depth to chest wall. The top of the shield may also not be an appropriate surrogate for the base of the tumor bed. Author Disclosure: R.B. Ash: None.
Poster Viewing
E1
Poster Viewing 2000
2001
Evaluation of Radiation-Induced Cardiac Toxicity in Breast Cancer Patients Treated with Trastuzumab-Based Chemotherapy M.L. Abouegylah,1,2 L.W. Salama,1 M. Elebrashi,1 S. Edgington,3 K. Remillard,4 A. Niemierko,4 M. Farouk,5 M. Alm El-Din,6 B. Napolitano,4 J.A. Wolfgang,7 A.S.A. Ismail,5 and A.G. Taghian1; 1 Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, 2Faculty of medicine, Alexandria University, Alexandria, Egypt, 3Massachusetts general hospital, Boston, MA, 4Massachusetts General Hospital, Boston, MA, 5Alexandria University, Alexandria, Egypt, 6 Tanta University, Tanta, Egypt, 7Massachusetts General Hospital, Harvard Medical School, Boston, MA
Reduced Mean Cardiac Dose: An Additional Benefit of Hypofractionated Whole Breast Radiotherapy? M. Ahmad,1 P.N. Barry Jr,1 M. Moler,2 J. Gaskins,3 and A.E. Dragun1; 1 University of Louisville School of Medicine, Louisville, KY, 2University of Pikeville, Kentucky College of Osteopathic Medicine, Pikeville, KY, 3 University of Louisville, Louisville, KY
Purpose/Objective(s): Patients with Her2 positive breast cancer treated with trastuzumab have a higher rate of cardiotoxicity(CT), particularly when combined with chemotherapy. Breast radiation to the left side might increase the risk for CT from cardiac exposure to radiation The aim of our study is to evaluate the contribution of radiotherapy (RT) in the development of CT in breast cancer patients receiving chemotherapy with trastuzumab. We hypothesize that the risk of CT is based on the volume and location of the heart exposed to radiation Materials/Methods: 205 patients were treated with RT and trastuzumab in our institute from 2001 to 2014; The RT plans for 108 patients with left side disease were recalled from archives. The heart, each chamber and the left anterior descending artery (LAD) were independently contoured. New dose-volume histograms (DVH) were generated. Their serial echocardiograms and or radioisotope scans were also studied, which included a baseline pretreatment scan. Patients lacking follow up cardiac scans were excluded from the analysis. CT was defined as a >10% decrease in the left ventricular ejection fraction (LVEF) from baseline, development of wall motion abnormality, and myocardial ischemia diagnosed by EKG. The crude rates of CT for left and right side were compared using Fisher’s exact test. The DVH data indices for the left side cases were correlated with the predefined cardiac events using actuarial Cox regression analysis The Equivalent Uniform Dose (EUD) was the primary index that was extracted from individual DVHs. The EUD model converts an inhomogeneous dose distribution within a structure of interest into a biologically equivalent uniform dose distribution. Right side cases were used as control to assess the combined effect of RT and trastuzumab on developing CT Results: Patients in the 2 groups were well balanced regarding demographics and clinical characteristics with median follow up of 81 months in left side and 84 months for the right side. Compared to the right sided, the left side cases showed statistically significant increase in wall motion abnormalities: 13 patients in the left side (12%) and one patient in right side (w1%) (pZ0.002). Cardiac ischemia diagnosed by EKG were found in 11 patients in left side (10%) and one patient in the right side (w1%) (pZ0.006). On Cox regression analysis, the EUD to the left ventricle (LV), LAD and heart was statistically significantly associated with decrease in LVEF by >10% (p Z0.04) for LAD and LV, and (pZ0.05) for the heart Other DVH parameters like V5, V10, V20, mean and maximum dose for the heart, LAD and each chamber were not statistically significant as risk factors for CT Conclusion: RT to the left breast increases the risk of CT, mainly the wall motion abnormalities and ischemia diagnosed by EKG when combined with Trastuzumab. The EUD index of LV, LAD and heart could be considered as a parameter to describe the risk of radiationinduced CT. Author Disclosure: M.L. Abouegylah: None. L.W. Salama: None. M. Elebrashi: None. S. Edgington: None. K. Remillard: None. A. Niemierko: None. M. Farouk: None. M. Alm El-Din: None. B. Napolitano: None. J.A. Wolfgang: None. A.A. Ismail: None. A.G. Taghian: Research Grant; Impedimed. Honoraria; UpToDate. Consultant; VisionRT.
Purpose/Objective(s): Mean heart dose (MHD) has been widely accepted as a predictor of long term cardiac toxicity. Additionally, it is known that MHD from whole breast radiation is largely attributable to internal lowisodose scatter. The goal of the present study was to evaluate the impact of different whole breast radiation regimens on MHD on patients enrolled in a phase 2 institutional protocol. Materials/Methods: Patients with left-sided Stage 0-II breast cancer who were treated on an institutional protocol in which they received onceweekly whole-breast irradiation (WHBI) to a dose of 2850-3000cGy in 5 fractions were the subject of this analysis. These patients were subsequently re-planned, and MHD was re-calculated using two alternative radiation regimens: conventionally-fractionated (CFRT) and daily hypofractionated (HFRT) radiotherapy (5000cGy in 25 fractions and 4256cGy in 16 fractions, respectively). Ideal MHD was defined as less than 200cGy, which is consistent with established heart dose objectives. Results: A total of 228 plans were generated from 76 patients with leftsided Stage 0-II breast cancer who were treated on a phase 2 protocol. Most of these patients were postmenopausal females (87%) with ER positive tumors (75%) in the outer quadrant of the breast (69%). All patients underwent breast conservation surgery, and the majority did not receive systemic therapy (75%). Of the 76 patients treated with WHBI, 69 (91%) had a MHD less than 200cGy. When the same 76 patients were replanned, only 58 (76%) of CFRT plans and 42 (55%) of HFRT plans had MHDs that were less than 200cGy. The average MHDs were 1.14Gy, 1.62Gy, 1.97Gy for the WHBI, HFRT, and CFRT regimens. Using the reported 7.4% increase in coronary event rate per Gy established by Darby et al, the detected increase in MHD for HFRT corresponds to a 3.5% (CI: 1.4% to 6.9%) elevated risk of coronary events and for CFRT a 6.1% (CI: 2.4% to 12.0%)elevated risk of coronary events, both relative to WHBI. Conclusion: WHBI is an emerging strategy in the treatment of early-stage breast cancer that may offer improved MHD and thus theoretically reduced estimated risk of coronary event relative to traditional regimens. More study is needed to determine whether MHD vs. anatomic dose-volume metrics is the best method of estimating late-cardiac risk in the era of emerging alternative fractionation schemes. Author Disclosure: M. Ahmad: None. P.N. Barry: I only receive my base salary. I do not receive additional compensation.; Radiation Oncology, UofL SOM. M. Moler: None. J. Gaskins: None. A.E. Dragun: None.
2002 Comparison of Heart Dose in Early Stage Left Sided Breast Cancers Treated with IORT or EBRT-DIBH C. Alonso,1 S. Showalter,2 B. Neal,1 B. Libby,1 and E.M. Janowski1; 1 Department of Radiation Oncology, University of Virginia, Charlottesville, VA, 2Department of Surgery, University of Virginia, Charlottesville, VA Purpose/Objective(s): A recent pooled analysis has suggested a possible improvement in overall survival among breast cancer patients treated with intraoperative radiation therapy (IORT) compared to patients treated with external beam whole breast irradiation. This survival benefit is thought to be derived, at least partially, from decreased cardiac toxicity among IORT patients. However, these findings lack the supporting dosimetric data to validate their conclusion. The purpose of this study is to compare heart dose between patients treated with lumpectomy and either intraoperative radiation therapy with CT-guided HDR brachytherapy (Precision Breast
E2
International Journal of Radiation Oncology Biology Physics
IORT; PB-IORT) or deep inspiratory breath hold external beam radiation therapy (EBRT-DIBH) for early stage left sided breast cancers at our institution. Materials/Methods: We retrospectively identified the 17 patients with left sided breast cancers treated with PB-IORT on a phase I clinical trial. 17 patients with left-sided tumors who had undergone lumpectomy and adjuvant EBRT-DIBH during a similar time period were identified for comparison. Dosimetric data was obtained for mean and maximum heart and left anterior descending artery (LAD) doses. T-testing analysis was performed, and biologically effective doses (BED) were calculated using an alpha/beta ratio for heart of 2 Gy. Results: Mean heart dose was found to be significantly lower in the EBRTDIBH group compared to the IORT group (0.61 vs. 0.87 Gy, pZ0.006). Nominal maximum heart dose was significantly higher in the EBRT-DIBH group (11.37 vs. 4.81 Gy, pZ0.004). BED for maximum heart dose was similar between the EBRT-DIBH and IORT groups, 16.63 vs. 19.36 Gy, respectively (pZ0.64). No difference was found in mean left anterior descending (LAD) artery dose: 2.18 Gy in the EBRT-DIBH group and 1.89 Gy in the IORT group (pZ0.446). The maximum LAD doses were 9.63 Gy and 3.62 Gy in the EBRT-DIBH and IORT groups, respectively (pZ0.016). Conclusion: Heart doses were found to be low in both groups. Expected increase in cardiac risk at these doses is minimal. It is unlikely that there will be a clinically significant difference in cardiac toxicity in patients treated with EBRT-DIBH or PB-IORT. Author Disclosure: C. Alonso: None. S. Showalter: None. B. Neal: None. B. Libby: None. E. Janowski: None.
incidence of VUS quadrupled from 2.2% in first half to 9.2% in the latter half of the study period (p<0.03). Similarly, the utilization of multigene panel testing increased 11-fold during this time period (1.6% vs. 18.3%, p<0.001). Conclusion: As expected, mastectomy rates were highest among patients with positive mutation results. A VUS result did not appear to impact locoregional therapy choice, with a similar proportion of patients opting for BCT compared to those with a negative result. Given the unknown prognostic significance of VUS and the changing landscape of genetic testing, these data highlight the continuing need for functional testing methods to allow objective interpretation and communication of VUS results to newly diagnosed breast cancer patients. Author Disclosure: A.Y. Ho: None. K. Amoroso: None. M. Wilgucki: None. K. Vora: None. B.B. Arnold: None. S.N. Powell: None. M. Morrow: ; Society of Surgical Oncolgy. M.E. Robson: Honoraria; AstraZeneca. Advisory Board; AstraZeneca, McKesson.
2003 Prevalence and Impact of Variants of Uncertain Significance on Local Therapy Decision-Making in Newly Diagnosed Breast Cancer Patients A.Y. Ho,1 K. Amoroso,2 M. Wilgucki,2 K. Vora,2 B.B. Arnold,1 S.N. Powell,2 M. Morrow,2 and M.E. Robson2; 1Cedars Sinai Medical Center, Los Angeles, CA, 2Memorial Sloan Kettering Cancer Center, New York, NY Purpose/Objective(s): The commercialization of next-generation sequencing for genetic testing has enhanced the identification of variants of uncertain clinical significance (VUS), introducing new complexities for breast cancer patients making decisions about locoregional therapy. Our purpose was to evaluate whether pre-surgical knowledge of a pathogenic mutation or VUS influenced the type of locoregional therapy received. Materials/Methods: Data was collected from a prospective database of 691 patients who underwent peri-diagnostic genetic counseling and testing at a single, high-volume cancer center between 3/2012-5/2016. Patients diagnosed with metastatic disease
2004 In Vivo Dosimetry for Single Fraction Intraoperative Electron Radiation Therapy for Early Stage Breast Cancer R.B. Ash; Valley Radiotherapy Associates, Orange, CA, St. Joseph Hospital, Orange, CA Purpose/Objective(s): Patients with early stage breast cancer are offered adjuvant breast radiation to reduce the likelihood of recurrence. This is usually in the form of whole breast radiation. Recent data shows that partial breast radiation may be appropriate in some patients with early stage disease. Partial breast radiation, in the form of intraoperative radiotherapy (IORT) is one form of partial breast radiation. Little data has been published on in vivo dosimetry for IORT using electrons. We set out to prospectively measure the dose at three points within the tumor cavity using in vivo dosimeters (nanodots) for patients receiving single fraction IORT using electrons. Materials/Methods: Eligible patients with early stage breast cancer undergoing breast conservation and single fraction IORT were assessed. Following lumpectomy and sentinel node evaluation, the tumor bed was prepared for IORT. A chest wall shield was placed with in-vivo dosimeters (nanodots) placed above and below the shield. The tumor bed was then approximated and intraoperative ultrasound was used to determine depth from top of tumor cavity to top of shield. A 3rd in-vivo dosimeter was placed on the surface of the tumor bed. After 2100 cGy was delivered, the dosimeters were retrieved and the three dose points recorded. Energies, cone size, cone angles and presence/absence of bolus were also recorded. Regression coefficient was used to determine dose as a function of the above factors. Results: Nanodots for a total of 136 patients were evaluated. Cone size ranged from 4.5- 7.5 cm. The majority of cases (86%) used cone size >/Z 5.0 cm. Energies used included 6 (54.4%), 9 (38.2%), and 12 (7.4%) Mev. 58% of cones used had 0 degree angle. The mean surface dose was 1983 cGy (range 1706-2321), the mean dose above the shield was 1396.7 (range 2.4-2702) and the mean dose below the shield was 34.66 (1.4-748.3). Using the regression coefficient, surface dose was dependent on energy and cone size (PZ 0.26, 0.28 respectively) but not cone angle (pZ 0.06). The dose above shield did not appear to be dependent on energy, cone size or angle, (pZ 0.62, 0.21, 0.28 respectively). The dose below shield does not appear to be dependent on the cone size or angle (pZ 0.21, 0.19), but is dependent on energy (pZ0.0). Conclusion: Our data shows that surface dose and dose below shield is consistent. Surface dose appears to be dependent on energy and cone size while dose below the shield seems to be dependent on energy. Dose above the shield was quite variable and not dependent on either three factors. The variability may be due to various issues including shield placed below chest wall muscle, off centering of dosimeters and inaccurate measurement of depth to chest wall. The top of the shield may also not be an appropriate surrogate for the base of the tumor bed. Author Disclosure: R.B. Ash: None.