A comparative dosimetric study on tangential photon beams, intensity-modulated radiation therapy (IMRT) and modulated electron radiotherapy (MERT) for breast cancer treatment

Abstract

Recently, energy- and intensity-modulated electron radiotherapy (MERT) has garnered a growing interest for the treatment of superficial targets. In this work. we carried out a comparative dosimetry study to evaluate MERT, photon beam intensity-modulated radiation therapy (IMRT) and conventional tangential photon beams for the treatment of breast cancer. A Monte Carlo based treatment planning system has been investigated, which consists of a set of software tools to perform accurate dose calculation, treatment optimization, leaf sequencing and plan analysis. We have compared breast treatment plans generated using this home-grown treatment optimization and dose calculation software forthese treatment techniques. The MERT plans were planned with up to two gantry angles and four nominal energies (6, 9, 12 and 16 MeV). The tangential photon treatment plans were planned with 6 MV wedged photon beams. The IMRT plans were planned using both multiple-gantry 6 MV photon beams or two 6 MV tangential beams. Our results show that tangential IMRT can reduce the dose to the lung, heart and contralateral breast compared to conventional tangential wedged beams (up to 50% reduction in high dose volume or 5 Gy in the maximum dose). MERT can reduce the maximum dose to the lung by up to 20 Gy and to the heart by up to 35 Gy compared to conventional tangential wedged beams. Multiple beam angle IMRT can significantly reduce the maximum dose to the lung and heart (up to 20 Gy) but it induces low and medium doses to a large volume of normal tissues including lung, heart and contralateral breast. It is concluded that MERT has superior capabilities to achieve dose conformity both laterally and in the depth direction, which will be well suited for treating superficial targets such as breast cancer.

Can Photon IMRT be improved by combination with mixed electron and photon techniques?

“…This property has been used in the treatment of breast cancer with segmented electron beams (9,10), a 3-D bolus technique (11), and intensity modulated electron beams (12,13). However, the depth dependent penumbra, the small effective field size, and the high skin dose limit the use of pure electron therapy in many other clinical situations.…”

Accounting for the fringe magnetic field from the bending magnet in a Monte Carlo accelerator treatment head simulation

“…The electron source incident on the exit window was characterized by six parameters: (1) mean energy, E, (2) Gaussian energy spread, '( E), (3) Gaussian (spot) spatial distribution, r S , '(E) of ± 7.1%, ± 4.9%, ± 6.2%, ± 6.0%, ± 4.8% and ± 3.3%, respectively, consistent with the approximate ± 7% transmission bandwidth of the vacuum envelope. R= mv eB (1) where is the Lorentz factor, m is the electron mass = 9.10938188 × 10 -31 kg, v is velocity of the particle perpendicular to the magnetic field, e is the electron charge = 1.60217646 × 10 The EMF macros treat scattering and magnetic field deflections as independent processes. Velocity changes resulting from magnetic field deflection are added at the end of each conventional charged particle transport step.…”

“…Monte Carlo treatment head and patient simulation is a preferred method of accurate electron dose calculation in conformal electron and mixed beam therapy techniques 1,2 and also has potential to improve beam models employed in commercial treatment planning software. , Elekta 8 and Siemens.…”

Minimizing toxicity in breast irradiation

“…Clinical and dosimetric data have demonstrated not only the feasibility of the technique but also its ability to reduce dose to heart [17,18]. Alternative cardiacsparing techniques exist including IMRT, prone positioning, as well as techniques limiting the target volume such as APBI [19,20]. Clinicians can use the cardiac-sparing technique that fits best with their patient and tumor characteristics; for example, a large-breasted patient may benefit from IMRT or prone positioning to reduce skin and cardiac toxicity.…”