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Left Anterior Descending Artery Avoidance for Patients Receiving Breast Irradiation
Volume 96 Number 2S Supplement 2016 receiving 20 Gy) to the ipsilateral lung and on mean dose to the contralateral lung. Results: One hundred forty-four studies from 28 countries reported mean ipsilateral lung dose (MLDipsi) from 481 regimens. MLDipsi averaged over these regimens was 8.9 Gy (IQR 5.5-12.5 Gy). For a given regimen (tangential irradiation of the breast or chest wall in the supine position and without breathing adaptation) there was considerable variation in MLDipsi between different countries. In 119 regimens from 72 studies and 27 countries, the average MLDipsi in each country varied from 0.4 Gy (Canada) to 13.5 Gy (Spain). For whole breast or chest wall radiation therapy (in the supine position and without breathing adaptation) the average MLDipsi was 8.4 Gy (IQR 5.9-11 Gy) from 241 regimens. When the axilla or supraclavicular fossa was also included, the average MLDipsi increased to 11.7 Gy (IQR 9.0-14.3). The addition of the internal mammary chain increased it further to 13.6 Gy (IQR 10.0-18.0 Gy). Comparing different techniques for irradiation of the whole breast or chest wall, breathing adaptation reduced MLDipsi from 8.4 (241 regimens with no breathing adaption) to 6.3 Gy (20 regimens with breathing adaption). Treatment in alternative positions reduced MLDipsi to 1.6 Gy (prone, based on 17 regimens) and 0.9 Gy (lateral decubitus, based on 2 regimens). The highest MLDipsi were reported for intensity modulated radiation therapy, 9.1 Gy, based on 74 regimens and volumetric modulated arc therapy, 9.9 Gy, based on 42 regimens. Similar dose differences between techniques were observed for V20Gy. 60 studies reported mean contralateral lung dose (MLDcont) in 221 regimens. The average MLDcont was 2.4 Gy (IQR 0.4-3.8 Gy). For treatment of the whole breast or chest wall in the supine position, tangential radiation therapy delivered average MLDcont 0.7 Gy (IQR 0.2-0.6). The highest MLDcont were received from 3D conformal rotational therapy (4.6 Gy), IMRT (3.1 Gy) and VMAT (2.9 Gy). Conclusion: Lung doses from breast cancer radiation therapy vary substantially worldwide, even between studies describing apparently similar regimens. Inclusion of the regional lymph nodes considerably increased the MLDipsi relative to irradiation of the whole breast only. IMRT and VMAT regimens tended to deliver higher MLDcont than other regimens. Author Disclosure: M.C. Aznar: None. F.K. Duane: None. Z. Wang: None. S.C. Darby: None. C.W. Taylor: None.
2074 Left Anterior Descending Artery Avoidance for Patients Receiving Breast Irradiation J.T. Dilworth,1 L. Zamdborg,2 K.G. Blas,2 I.S. Grills,1 M. Teahan,2 M.S. Jawad,1 M. Wallace,1 and P.Y. Chen1; 1Beaumont Health System, Royal Oak, MI, 2Beaumont Health, Royal Oak, MI Purpose/Objective(s): Dose to the left anterior descending artery (LAD) contributes to cardiac toxicity for patients receiving left whole breast irradiation (WBI). We investigated if prospective contouring and avoidance of the LAD during treatment planning reduces LAD dose. Materials/Methods: Between January 2014 and January 2016, 189 patients with left-sided breast cancer who received WBI with or without internal mammary lymph node (IMN) coverage at a single institution were reviewed. All patients received non-contrast CT-based, inverseplanned, multi-segment, 3D-conformal treatment. Active breathing control (ABC) was used in 79% of patients. If the patient could not tolerate or was determined not to benefit from breath hold, ABC was not used. The LAD was contoured prospectively for 53 patients. While the LAD was not implemented as an optimization parameter, beam angle modification was used to avoid the LAD while ensuring appropriate target coverage. Dose-volume-histograms from these patients were compared to 156 patients for whom the LAD was contoured retrospectively after treatment completion. To account for differences in fractionation, median (med) and maximum (max) doses were expressed in EQD2, using the equation EQD2 Z D{[(D/n) + a:b]/[2 + a:b]}, where D is the composite dose (including that contributed by the boost, if given), n is the number of fractions given for the breast tangents, and a:b is the alpha/beta ratio,
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taken as 2 for late effects of heart and coronary vessels. EQD2 values between groups were compared groups using the Wilcoxon Rank Sum test. Results: One hundred sixty-eight patients received WBI with (59%) or without (41%) a cavity boost and without IMN coverage. Compared to patients with retrospectively contoured LADs, patients with prospectively contoured LADs had a lower med LAD EQD2 (190.4 cGy vs 141.8, P<0.001) and a lower max LAD EQD2 (522.1 vs 284.6 cGy, P<0.001). The med heart EQD2 in this group was 75 cGy versus 61.6 cGy (P<0.001), respectively. Twenty-one patients with IMN coverage had a higher med/max LAD EQD2 (419.2 cGy/1402.8 cGy) and a higher med heart EQD2 (128.9 cGy) compared to those without IMN coverage (all P values <0.001). When considering only patients receiving IMN irradiation, prospectively contouring the LAD did not significantly impact the med or max LAD EQD2 or med heart EQD2. All comparisons were statistically similar independent of the use of active breathing control. Conclusion: Prospective contouring of the LAD and simple beam modifications can help reduce LAD dose during WBI. LAD dose reduction in the setting of IMN coverage may require incorporating the LAD as an optimization parameter during inverse treatment planning. Ongoing studies correlating LAD dosimetry and long-term cardiac toxicity may establish a dose constraint objective in this setting. Author Disclosure: J.T. Dilworth: None. L. Zamdborg: None. K.G. Blas: None. I.S. Grills: Stock; Greater Michigan Gamma Knife. M. Teahan: None. M.S. Jawad: None. M. Wallace: None. P.Y. Chen: Stock; Greater Michigan Gamma Knife.
2075 External Beam Accelerated Partial Breast Irradiation Versus Hypofractionated Whole-Breast Irradiation in T1N0, ER Positive Patients R.J. Kumar, A. Goel, E.K. Wei, L.X. Yang, and J.W. Lee; California Pacific Medical Center, San Francisco, CA Purpose/Objective(s): The aim of this study was to compare outcomes between external beam accelerated partial breast irradiation (APBI) and hypofractionated whole breast irradiation. Accelerated partial breast irradiation has been compared to whole breast irradiation in the past, but these studies have included brachytherapy and conventional whole breast fractionation. Relatively few comparisons have been made between external beam APBI and hypofractionated whole breast irradiation. In this single institution retrospective cohort study, patients aged 40 or greater with T1N0, ER positive breast cancer were examined for local recurrence, distant recurrence, and survival. Materials/Methods: Patients aged 40 years or greater with T1N0, ER positive breast cancer were identified who received lumpectomy followed by radiation treatment at a single institution between 2008 and 2014. A total of 390 patients were included in the study. Of these, 96 patients received external beam accelerated partial breast irradiation with 38.5 Gy in 10 fractions given twice daily over 5-6 days. 294 patients received hypofractionated whole breast radiation therapy with 42.56 Gy given in 16 fractions of 266 cGy with or without a 1-3 fraction boost. Local recurrence, distant recurrence, and survival were analyzed. Statistical analysis was performed with a Fisher’s Exact test. Multivariate logistic regression was used to compare both treatment groups while adjusting for possible confounding variables. Results: At a median follow up of 4.2 years, incidence of local recurrence was 1.04% in the APBI group compared to 1.70% in the hypofractionated group (P Z 0.99). The incidence of distant recurrence was 3.13% in the APBI group and 1.70% in the hypofractionated group (P Z 0.41). Overall survival was 97.92% and 97.96% in the APBI and hypofractionated groups respectively (P Z 0.99). Treatment groups were similar with respect to age (P Z 0.08), histology (0.35), and margin status (P Z 0.63). The two treatment groups had a different distribution of grade (P Z 0.04), but this was addressed in the multivariate analysis.
2074 Left Anterior Descending Artery Avoidance for Patients Receiving Breast Irradiation J.T. Dilworth,1 L. Zamdborg,2 K.G. Blas,2 I.S. Grills,1 M. Teahan,2 M.S. Jawad,1 M. Wallace,1 and P.Y. Chen1; 1Beaumont Health System, Royal Oak, MI, 2Beaumont Health, Royal Oak, MI Purpose/Objective(s): Dose to the left anterior descending artery (LAD) contributes to cardiac toxicity for patients receiving left whole breast irradiation (WBI). We investigated if prospective contouring and avoidance of the LAD during treatment planning reduces LAD dose. Materials/Methods: Between January 2014 and January 2016, 189 patients with left-sided breast cancer who received WBI with or without internal mammary lymph node (IMN) coverage at a single institution were reviewed. All patients received non-contrast CT-based, inverseplanned, multi-segment, 3D-conformal treatment. Active breathing control (ABC) was used in 79% of patients. If the patient could not tolerate or was determined not to benefit from breath hold, ABC was not used. The LAD was contoured prospectively for 53 patients. While the LAD was not implemented as an optimization parameter, beam angle modification was used to avoid the LAD while ensuring appropriate target coverage. Dose-volume-histograms from these patients were compared to 156 patients for whom the LAD was contoured retrospectively after treatment completion. To account for differences in fractionation, median (med) and maximum (max) doses were expressed in EQD2, using the equation EQD2 Z D{[(D/n) + a:b]/[2 + a:b]}, where D is the composite dose (including that contributed by the boost, if given), n is the number of fractions given for the breast tangents, and a:b is the alpha/beta ratio,
Poster Viewing
E31
taken as 2 for late effects of heart and coronary vessels. EQD2 values between groups were compared groups using the Wilcoxon Rank Sum test. Results: One hundred sixty-eight patients received WBI with (59%) or without (41%) a cavity boost and without IMN coverage. Compared to patients with retrospectively contoured LADs, patients with prospectively contoured LADs had a lower med LAD EQD2 (190.4 cGy vs 141.8, P<0.001) and a lower max LAD EQD2 (522.1 vs 284.6 cGy, P<0.001). The med heart EQD2 in this group was 75 cGy versus 61.6 cGy (P<0.001), respectively. Twenty-one patients with IMN coverage had a higher med/max LAD EQD2 (419.2 cGy/1402.8 cGy) and a higher med heart EQD2 (128.9 cGy) compared to those without IMN coverage (all P values <0.001). When considering only patients receiving IMN irradiation, prospectively contouring the LAD did not significantly impact the med or max LAD EQD2 or med heart EQD2. All comparisons were statistically similar independent of the use of active breathing control. Conclusion: Prospective contouring of the LAD and simple beam modifications can help reduce LAD dose during WBI. LAD dose reduction in the setting of IMN coverage may require incorporating the LAD as an optimization parameter during inverse treatment planning. Ongoing studies correlating LAD dosimetry and long-term cardiac toxicity may establish a dose constraint objective in this setting. Author Disclosure: J.T. Dilworth: None. L. Zamdborg: None. K.G. Blas: None. I.S. Grills: Stock; Greater Michigan Gamma Knife. M. Teahan: None. M.S. Jawad: None. M. Wallace: None. P.Y. Chen: Stock; Greater Michigan Gamma Knife.
2075 External Beam Accelerated Partial Breast Irradiation Versus Hypofractionated Whole-Breast Irradiation in T1N0, ER Positive Patients R.J. Kumar, A. Goel, E.K. Wei, L.X. Yang, and J.W. Lee; California Pacific Medical Center, San Francisco, CA Purpose/Objective(s): The aim of this study was to compare outcomes between external beam accelerated partial breast irradiation (APBI) and hypofractionated whole breast irradiation. Accelerated partial breast irradiation has been compared to whole breast irradiation in the past, but these studies have included brachytherapy and conventional whole breast fractionation. Relatively few comparisons have been made between external beam APBI and hypofractionated whole breast irradiation. In this single institution retrospective cohort study, patients aged 40 or greater with T1N0, ER positive breast cancer were examined for local recurrence, distant recurrence, and survival. Materials/Methods: Patients aged 40 years or greater with T1N0, ER positive breast cancer were identified who received lumpectomy followed by radiation treatment at a single institution between 2008 and 2014. A total of 390 patients were included in the study. Of these, 96 patients received external beam accelerated partial breast irradiation with 38.5 Gy in 10 fractions given twice daily over 5-6 days. 294 patients received hypofractionated whole breast radiation therapy with 42.56 Gy given in 16 fractions of 266 cGy with or without a 1-3 fraction boost. Local recurrence, distant recurrence, and survival were analyzed. Statistical analysis was performed with a Fisher’s Exact test. Multivariate logistic regression was used to compare both treatment groups while adjusting for possible confounding variables. Results: At a median follow up of 4.2 years, incidence of local recurrence was 1.04% in the APBI group compared to 1.70% in the hypofractionated group (P Z 0.99). The incidence of distant recurrence was 3.13% in the APBI group and 1.70% in the hypofractionated group (P Z 0.41). Overall survival was 97.92% and 97.96% in the APBI and hypofractionated groups respectively (P Z 0.99). Treatment groups were similar with respect to age (P Z 0.08), histology (0.35), and margin status (P Z 0.63). The two treatment groups had a different distribution of grade (P Z 0.04), but this was addressed in the multivariate analysis.