Vishruta A. Dumane, Ph.D., Assistant Professor Radiation Oncology of the Icahn School of Medicine at Mount Sinai speaks about the ASTRO 2020 Abstract 2180 Low Dose Exposure to the Ipsilateral Lung while Sparing the Heart in Deep Inspiration Breath Hold.
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Purpose / Goal(s):
For patients with left-sided breast cancer, deep inspiration breath-hold (DIBH) has been studied, often with the objective of reducing the dose to the heart. The heart is forced away from the treatment fields with inspiration and widening of the chest wall; this, however, causes a rise in the amount of lungs exposed to a dose of radiation. Appropriate radiation plans seek to reduce the risk of maintaining ipsilateral lung V20Gy < 30 percent radiation pneumonitis (RP). The objective of this study was to test ipsilateral lung volumes exposed to 10Gy and 5Gy dose levels in tailored DIBH plans that meet the dose constraints of V20Gy while sparing the heart.
Methods/Materials:
For this retrospective analysis, twenty-three patients treated at our institution with DIBH from 2018-2019 were chosen. Sixteen breast and node patients were treated with a prescription dose of 50.4Gy in 28 fractions, and 7 patients with whole breast radiation were treated with 50Gy in 20 fractions. Patients were scheduled and handled using VisionRT for breath-hold control on a medical linear accelerator. Plans were formulated in such a way that 95 percent of the drug dose was covered by at least 95 percent of the breast and/or node preparation target volume (PTV), i.e. 95 percent for PTV D95 and V95. The dosimetric parameters reported were: absolute left lung volume, as well as 20Gy, V20Gy (percent), V10Gy (percent), and V5Gy (percent) volume covered. Mean heart dose, V20Gy (percent) and V5Gy (percent) were parameters reported for the heart.
Outcomes:
The ipsilateral lung V20Gy was held well below the 30 percent constraint in our optimized plans at 15.8 percent on average, while the V10Gy and V5Gy were both < 35 percent on average. The mean cardiac dose was well below 3Gy. The average value of dosimetric parameters extracted for the DIBH plans is shown in Table 1. The absolute volume of 20 Gy, 10 Gy and 5 Gy irradiated left lung was 307cc + 156 cc, 411.9±186.3, and 671.1±261.7 respectively. The absolute volume of ipsilateral lungs covered by 10 Gy was about 35 percent higher than that covered by 20 Gy in these DIBH plans, whereas that of 5 Gy was almost 120 percent higher than that covered by 20 Gy.
The Conclusion:
The dosimetry of tailored plans consistently decreases cardiac exposure to radiation with DIBH, but inevitably increases absolute ipsilateral lung volume at low dose exposure. In these cases, the clinical importance of possible increased low dose lung exposure is uncertain and understudied. Further research into clinical results is required to quantify the merits of the low radiation dose trade-off to save the heart and improve exposure to lung volume.