PV QA 4 - Poster Viewing Q&A 4
Purpose/Objective(s): Deep inspiration breath hold (DIBH) technique has been effective to reduce cardiac dose for left sided breast cancer treatment. However there are limited data on the setup reproducibility with DIBH technique. Herein we report the daily setup reproducibility and variation of DIBH using daily mega voltage (MV) imaging based on a large network of data.
Materials/Methods: 109 left breast cancer patients from 10 hospital sites across XXX network were treated using DIBH technique with daily MV imaging from May 2016 to July 2017. All patients had visual coaching via iPod device as well as voice coaching for DIBH for CT simulation and treatment. The same procedure and technique for DIBH CT simulation and treatment planning have been shared between physicists and physicians across the network. For each patient, BMI, age, surgery type (lumpectomy or mastectomy), regional and internal mammary nodes (IMN) involvement, MV imaging procedure used, number of total portal images and inter-fraction directional shifts were collected. For the statistical analyses, we separated all patients into two groups in each of the following three categories; 1) obese (BMI ≥ 30) vs. non- obese, 2) surgery type: mastectomy vs. lumpectomy, 3) internal mammary node (IMN) treatment vs. no IMN treatment.
Results: 1833 treatments and 2818 MV portal images were analyzed. Minimum mean distance from heart to the tangential field edge was 2.5 mm (ranges 0- 12 mm). The group mean inter-fraction directional shifts were as following: 1) 0.7 mm (superior; SD =2.26), 0.8 mm (inferior; SD = 2.21), 2) 0.65 mm (left; SD =1.60), 0.64 mm (right; SD =1.62), 3) 0.89 mm (anterior; SD=1.96), 0.83 mm (posterior; SD=2.03). However between hospitals, there was found a difference in mean inter-fraction directional shift (p < 0.001). Any inter-fraction directional shift for ≥ 2mm, ≥ 3mm, ≥ 4mm, ≥ 5mm, ≥ 10mm was found to be 52.9 %, 37.6 %, 30.9 %, 21.9 %, 3.7 % of total fractions, respectively. In the stratified analysis, obese patients had larger directional shifts (p < 0.05) and highly associated with number of fractions for ≥ 5mm in any directional shift compared to non-obese patients (29 % vs. 17 %; p =0.04).
Conclusion: To the best of our knowledge, this is the first and the largest study that reports the daily setup reproducibility and variation using MV images and patient’s visual feedback. DIBH setup for left breast cancer treatment at our large cancer center network was reproducible with any mean directional shifts less than 1.0 mm, although there was some inter-fraction variation between hospital sites. Consideration of daily imaging for obese patients should be taken to ensure the benefit of DIBH for that population. Also, if the distance of heart to the edge of the tangential treatment field is relatively close, it would be more beneficial to have daily imaging because 53 % of patients still had ≥ 2 mm shift.
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