Improvement of dose distribution in breast radiotherapy using a reversible transverse magnetic field Linac-MR unit

Abstract

Applying a reversible magnetic field during breast radiotherapy, not only reduces the dose to the lung and heart but also produces a sharp drop dose volume histogram for planning target volume, because of bending of the path of secondary charged particles toward the chest wall by the Lorentz force. The simulations have shown that use of the magnetic field at 1.5 T is not feasible for clinical applications due to the increase of ipsilateral chest wall skin dose in comparison to the conventional planning while 0.25 T is suitable for all patients due to dose reduction to the chest wall skin.

Dose enhancement in radiotherapy of small lung tumors using inline magnetic fields: A Monte Carlo based planning study

“…5 In particular, these include interface, entry and exit dose changes, [6][7][8][9] and dose perturbation in breast treatments. [10][11][12] There have also been various effects studied in IMRT planning in the presence of perpendicular magnetic fields. [13][14][15][16] For an inline MRI-Linac system, such as the inline orientation of the 0.56 T Alberta system, or the inline orientation of the split-bore 1 T Australian design under construction, the dose perturbation effects are mostly limited to entry dose changes due to electron contamination being focused by the MRI field.…”

Breast dosimetry in transverse and longitudinal field MRI‐Linac radiotherapy systems

“…Therefore, the energy of returning electrons from the air was more than those returning from the lung, which made a margin of high-dose distribution at the breast-air boundaries. 11 In the longitudinal geometry, the central axis depth dose response to a broad beam in the presence of a longitudinally oriented magnetic field is not different from the zero field case, 22,23 with the possible exception of surface dose changes due to confinement of contaminant electrons. 24 In this geometry, at the chest wall-lung interface and on the exit surface, the ERE increases the absorbed dose in the chest wall skin, lung, and PTV.…”

“…In this work, similar patients and treatment plans were examined as discussed for breast cases in our previous studies. 11,12 One patient had intact breast while the other was mastectomized. The patients had left-sided cancer.…”

“…Delivery of too high a dose in the breast radiotherapy will cause complications to normal tissues, including radiation-induced pneumonitis, cardiac toxicity, and adverse skin reactions, 1 and can induce secondary cancers in nearby organs. [2][3][4] It has been demonstrated that a static magnetic field can alter the dose deposition characteristics of a 6 MV photon beam, both in homogeneous [5][6][7][8] and inhomogeneous [9][10][11][12] media, through the deflection of secondary charged particles. 6,[10][11][12][13] There is considerable interest in the medical physics community on the influence of magnetic fields for both online imaging for margin reduction and, thereby, improvement of treatment, and on the dose distribution within patients in order to optimize the treatment plan by maximizing the dose to the planning target volume while minimizing the dose to normal tissues.…”

“…[2][3][4] It has been demonstrated that a static magnetic field can alter the dose deposition characteristics of a 6 MV photon beam, both in homogeneous [5][6][7][8] and inhomogeneous [9][10][11][12] media, through the deflection of secondary charged particles. 6,[10][11][12][13] There is considerable interest in the medical physics community on the influence of magnetic fields for both online imaging for margin reduction and, thereby, improvement of treatment, and on the dose distribution within patients in order to optimize the treatment plan by maximizing the dose to the planning target volume while minimizing the dose to normal tissues. To achieve this goal, multiple groups have proposed designs for merging a megavoltage radiation therapy linear accelerator (Linac) or a 60Co teletherapy unit with a magnetic resonance imaging system that can be grouped into two basic geometries: a solenoidal and stationary MRI, 14 and rotating biplanar (RBP) geometries.…”