Modulated electron radiotherapy treatment planning using a photon multileaf collimator for post-mastectomized chest walls
Received 12 February 2009; received in revised form 13 August 2009; accepted 13 August 2009. published online 16 September 2009.
Abstract
Background and purpose
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.
Materials and 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 70cm 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).
Conclusion
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.
cServicio de Radiofísica-ERESA, Hospital General Universitario de Valencia, Spain
Corresponding author. Address: Departamento de Fisiología Médica y Biofísica, Universidad de Sevilla, Hospital Universitario Virgen Macarena, Sevilla, Spain.
ABSTRACT