Abstract
Purpose: Whole breast irradiation is part of breast conservative management for early breast cancer; addition of boost dose to tumor bed improves local recurrence rates and is currently the standard of care. Randomized trials reported low a/b ratio for breast cancer that predict a radiobiological advantage for hypofractionation. Simultaneous boost radiation as a method of hypofractionation proved safe and effective for head and neck tumors. In this study we attempt to compare and analyze the dosimetric aspects of adding Simultaneous Integrated Boost (SIB) over Sequential Boost (SB) to a hypofractionated treatment schedule in breast cancer patients after BCS. Materials and methods: CT simulation data sets for 23 patients were selected for this planning study; Targets and OAR were delineated as per RTOG guidelines. Multiple dynamic field IMRT plans were generated for each patient. The prescribed dose was 40 Gy/15 fractions to whole breast (2.67 Gy/fraction) and 48 Gy/15fractions to lumpectomy cavity (3.2 Gy/fraction) for SIB, and 40 Gy/15 fractions followed by 10Gy/5 fractions for SB. Generated Treatment plans were evaluated by experienced radiation oncologist, and the best plan was selected for the dosimetric analysis. Results: The pre specified target coverage criteria were met for the lumpectomy cavity as well as whole breast in all plans. All quality indices for PTV coverage showed to be significantly improved with SIB for both whole breast and tumor bed volumes. SB technique showed more dose spillage outside the boost volume. SIB-IMRT was better in sparing OAR ,the volume of the ipsilateral lung V20 Gy was 19.8 % compared to 22.8 % (p = 0.04), maximum dose to LAD was 17.6 Gy Vs. 21.6 (p= 0.01) and contralateral breast mean dose was 0.36 Gy Vs. 1.27 Gy (p = 0.01) for SIB and SB respectively. Conclusions: Hypofractionated breast SIB is feasible with better PTV coverage and OAR. Along with further reduction of the overall period which may increase patient convenience and resource utilization benefit.
Highlights
Breast cancer is the leading cause of cancer related deaths in women worldwide [1]
All quality indices for Planning Target Volume (PTV) coverage showed to be significantly improved with Simultaneous Integrated Boost (SIB) for both whole breast and tumor bed volumes
SIB-Intensity Modulated Radiotherapy (IMRT) was better in sparing organs at risk (OAR),the volume of the ipsilateral lung V20 Gy was 19.8 % compared to 22.8 % (p = 0.04), maximum dose to Left Anterior Descending Artery (LAD) was 17.6 Gy Vs. 21.6 (p= 0.01) and contralateral breast mean dose was 0.36 Gy Vs. 1.27 Gy (p = 0.01) for SIB and Sequential Boost (SB) respectively
Summary
Breast cancer is the leading cause of cancer related deaths in women worldwide [1]. The main treatment is surgery, conservative breast surgery (BCS) followed by radiotherapy offers equivalent survival as modified radical mastectomy with better cosmetic outcomes. Adjuvant radiotherapy significantly improves the overall survival of breast cancer patients. This result can be augmented with further decreasing the dose to normal tissues such as heart, lung and use of IMRT and use of optimal fractionation schedules. Radiotherapy (IMRT) to breast cancer treatment further improved conformity and doses to normal tissue. IMRT improves dose homogeneity but might reduce the dose to the normal structures compared to conventional wedged fields [7,8]. The objective of this study is to analyze the quality of PTV coverage and doses to the organs at risk (OAR) associated with hypofractionated whole breast irradiation with simultaneous integrated boost (SIB) compared to sequential boost (SB) using dynamic field IMRT technique. In breast there are increasing clinical evidences suggesting similar advantages of SIB [9,10,11,12,13].
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