Comparison of Static Fields IMRT and Helical IMRT for Accelerated Partial Breast Irradiation

Purpose/Objective(s) To compare two different intensity-modulated radiation therapy (IMRT) techniques for accelerated partial breast irradiation (aPBI). Materials/Methods All patients analyzed were enrolled in a prospective controlled Phase 3 trial. The treatment plan of 10 patients treated with aPBI after conservative surgery for breast cancer were reviewed: all patients had surgical clips in the tumor bed, CTV was obtained with an isotropic expansion of surgical clips of 1 cm clipping the volume 3 mm inside skin profile or at chest wall; PTV was obtained with an isotropic expansion of CTV clipping the volume 3 mm inside skin profile and not allowing for more than 4 mm inside lung. We chose all left sided breast cancer volumes to assess the ability to spare heart. 30 Gy in 5 nonconsecutive fractions were given to all patients. All patients were originally treated with a static 4 field IMRT technique (SFI): treatment plans were replanned with helical IMRT (HI), using a 2.5 cm field width. We performed a comparison of target coverage and organs at risk sparing of the two treatment plans obtained for each patients; t-test of average values of the chosen parameters was performed. Results HI showed better target coverage than SFI with the average percentage of PTV receiving ≥95% of prescribed dose (28.5 Gy) of 99,4% (range 98.0%-100%) and 97.9% (range 95.5%-99.7%) respectively (p = 0.01) and the average lowest dose to PTV (defined as the dose received by the 98% of PTV) of 2938 cGy and 2868 cGy (p = 0.03). The average maximum dose was not different between the two treatment modalities (3176 cGy for HI and 3212 cGy for SFI; p = 0.4). The comparison of the two treatment modalities about the organs at risk sparing (percentage of heart receiving ≥3 Gy, dose received by 10% of heart, % of homolateral uninvolved breast receiving > 15 Gy, % of contralateral breast receiving > 1 Gy; % of homolateral lung receiving > 10 Gy; % of contralateral lung receiving > 5 Gy) did not show any statistically significant difference between the two treatment modalities. In addition, the average treatment time was not found to be different between the two treatment modalities. Conclusions SFI and HI are both capable to achieve good target coverage with excellent organs at risk sparing; HI seems to be able to give a slightly better target coverage with no increase of dose to organs at risk and with no increase in the treatment time.