Modulated electron radiotherapy treatment planning using a photon multileaf collimator for post-mastectomized chest walls.
OBJECTIVE
To evaluate the feasibility of using a photon MLC (xMLC) for modulated electron radiotherapy treatment (MERT) as an alternative to conventional post-mastectomy chest wall (CW) irradiation. A Monte Carlo (MC) based planning system was developed to overcome the inaccuracy of the 'pencil beam' algorithm. MC techniques are known to accurately calculate the dose distributions of electron beams, allowing the explicit simulation of electron interactions within the MLC.


METHODS
Four real clinical CW cases were planned using MERT which were compared with the conventional electron treatments based on blocks and by a straightforward approach using the MLC, and not the blocks (as an intermediate step to MERT) to shape the same segments with SSD between 60 and 70 cm depending on PTV size. MC calculations were verified with an array of ionization chambers and radiochromic films in a solid water phantom.


RESULTS
Tests based on gamma analysis between MC dose distributions and radiochromic film measurements showed an excellent agreement. Differences in the absolute dose measured with a plane-parallel chamber at a reference point were below 3% for all cases. MERT solution showed a better PTV coverage and a significant reduction of the doses to the organs at risk (OARs).


CONCLUSIONS
MERT can effectively improve the current electron treatments by obtaining a better PTV coverage and sparing healthy tissues. More directly, block-shaped treatments could be replaced by MLC-shaped non-modulated segments providing similar results.
Salguero
Francisco Javier
FJ
Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla, Spain.
Palma
Bianey
B
Arrans
Rafael
R
Rosello
Joan
J
Leal
Antonio
A
D001943:Breast Neoplasms / Q000532:radiotherapy* / Q000601:surgery; D004583:Electrons; D005260:Female; D006801:Humans; D008408:Mastectomy; D009010:Monte Carlo Method; D017785:Photons; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation*; D035441:Thoracic Wall / Q000528:radiation effects*