Magnetic field dose effects on different radiation beam geometries for hypofractionated partial breast irradiation

Abstract

PurposeHypofractionated partial breast irradiation (HPBI) involves treatment to the breast tumor using high doses per fraction. Recent advances in MRI‐Linac solutions have potential in being applied to HPBI due to gains in the soft tissue contrast of MRI; however, there are potentially deleterious effects of the magnetic field on the dose distribution. The purpose of this work is to determine the effects of the magnetic field on the dose distribution for HPBI tumors using a tangential beam arrangement (TAN), 5‐beam intensity‐modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT).MethodsFive patients who have received HPBI were selected with two patients having bilateral disease resulting in a total of two tumors in this study. Six planning configurations were created using a treatment planning system capable of modeling magnetic field dose effects: TAN, IMRT and VMAT beam geometries, each of these optimized with and without a transverse magnetic field of 1.5 T.ResultsThe heart and lung doses were not statistically significant when comparing plan configurations. The magnetic field had a demonstrated effect on skin dose: for VMAT plans, the skin (defined to a depth of 3 mm) D1cc was elevated by +11% and the V30 by +146%; for IMRT plans, the skin D1cc was increased by +18% and the V30 by +149%. Increasing the number of beam angles (e.g., going from IMRT to VMAT) with the magnetic field on reduced the skin dose.ConclusionThe impact of a magnetic field on HPBI dose distributions was analyzed. The heart and lung doses had clinically negligible effects caused by the magnetic field. The magnetic field increases the skin dose; however, this can be mitigated by increasing the number of beam angles.

Single dose partial breast irradiation using an MRI linear accelerator in the supine and prone treatment position

“…Two previous studies have focused on magnetic field dose effects for postoperative RT in the supine position [26] , [27] . Van Heijst et al investigated the magnetic-field impact on skin dose with WBI (42.56 Gy in 16 fractions, 2-field forward IMRT) and APBI (38.5 Gy in 10 fractions, 7-field IMRT) at 0T, 0.35T and 1.5T [26] .…”

“…Other OARs were not adversely influenced by the magnetic field. Kim et al analyzed the 1.5T magnetic field dose effects using a tangential beam arrangement, 5-beam IMRT, and VMAT for APBI delivered in 8 fractions of 5 Gy [27] . Heart and lung doses were minimally impacted by the magnetic field.…”

Optimizing MR-Guided Radiotherapy for Breast Cancer Patients

“…Therefore, the increase in skin dose for PBI in a magnetic field would be highly unlikely to translate into a higher risk of radiation dermatitis. Furthermore, it has been reported that increasing the number of beam angles helps in decreasing the skin dose (60,62). Therefore, although PBI is a good indication for breast RT on a hybrid machine, one should remain aware of the risk of increased skin dose and use more rather than fewer beams.…”

“…Therefore, although PBI is a good indication for breast RT on a hybrid machine, one should remain aware of the risk of increased skin dose and use more rather than fewer beams. Because the ERE effect is also present at the lung-tissue interface, it is also important to check the maximum lung and chest wall dose (57,62). Previous planning studies concluded that the effects of the magnetic field on OARs, other than the skin, are generally negligible, and doses were within clinical constraints (60,62,63).…”

Use of magnetic resonance imaging-guided radiotherapy for breast cancer: a scoping review protocol

“…The MR linac is also considerably different to the conventional linac, with mechanical limitations on the collimator, couch, treatment field size and delivery techniques, which change the treatment planning and delivery process for breast radiotherapy. The radiofrequency coils required for MR imaging, associated geometric accuracy and isotropic resolution, and the very presence of a magnetic field during treatment delivery with the effects upon secondary electrons [27][28][29][30], are important factors for dose calculations and affect the dosimetry in the breast. Given longer fraction durations on the MR linac, especially with high dose per fraction prescriptions and the adaptive nature of treatments, intrafraction motion must also be considered.…”