open access
The effect of beam shape on physical parameters of head and neck simultaneous-integrated boost intensity-modulated radiation therapy
open access
Abstract
Aim
To evaluate the influence of the beam shape created by X-rays with “flat beams” and without “flattening-filter-free [FFF] beams” a flattening filter, and the isocenter locations for FFF beams on the treatment of a large irradiated volume for tumours.
Background
The increase of dose rate and the decrease of out-of-field dose can be expected for FFF beams and lead to effective and safety radiotherapy. On the other hand, the bell-shaped dose profile is thought to be a factor of negating these advantages.
Materials and methods
Treatment plans for 15 patients with head and neck cancer were created using XiO (Elekta, Stockholm AB, Sweden) in fixed-gantry step-and-shoot delivery under the same dose constraints. Seven fields of FFF beams with 7 MV and flat beams with 6 MV were used with the technique of intensity-modulated radiation therapy (IMRT). We compared the dose homogeneity and conformity of targets and dose constraints for organs as the plan quality and evaluated physical parameters: monitor unit (MU) values, number of segments and their locations from the isocenter in beam's-eye-view.
Results
No significant differences were found in the plan quality. The isocenter locations do not affect the physical parameters for FFF beams. It has been confirmed that the number of segments and MU values were 40% higher with FFF beams than with flat beams (p < 0.05).
Conclusion
This study demonstrates flat dose distribution is more suitable for IMRT with large and complex targets.
Abstract
Aim
To evaluate the influence of the beam shape created by X-rays with “flat beams” and without “flattening-filter-free [FFF] beams” a flattening filter, and the isocenter locations for FFF beams on the treatment of a large irradiated volume for tumours.
Background
The increase of dose rate and the decrease of out-of-field dose can be expected for FFF beams and lead to effective and safety radiotherapy. On the other hand, the bell-shaped dose profile is thought to be a factor of negating these advantages.
Materials and methods
Treatment plans for 15 patients with head and neck cancer were created using XiO (Elekta, Stockholm AB, Sweden) in fixed-gantry step-and-shoot delivery under the same dose constraints. Seven fields of FFF beams with 7 MV and flat beams with 6 MV were used with the technique of intensity-modulated radiation therapy (IMRT). We compared the dose homogeneity and conformity of targets and dose constraints for organs as the plan quality and evaluated physical parameters: monitor unit (MU) values, number of segments and their locations from the isocenter in beam's-eye-view.
Results
No significant differences were found in the plan quality. The isocenter locations do not affect the physical parameters for FFF beams. It has been confirmed that the number of segments and MU values were 40% higher with FFF beams than with flat beams (p < 0.05).
Conclusion
This study demonstrates flat dose distribution is more suitable for IMRT with large and complex targets.
Keywords
Flat beams; Flattening-filter-free (FFF) beams; Treatment plans; Beam profile
About this articleTitle
The effect of beam shape on physical parameters of head and neck simultaneous-integrated boost intensity-modulated radiation therapy
Journal
Reports of Practical Oncology and Radiotherapy
Issue
Pages
425-432
Published online
2018-09-01
DOI
10.1016/j.rpor.2018.08.008
Bibliographic record
Rep Pract Oncol Radiother 2018;23(5):425-432.
Keywords
Flat beams
Flattening-filter-free (FFF) beams
Treatment plans
Beam profile
Authors
Toshiro Tsubouchi
Masashi Yagi
Iori Sumida
Keisuke Tamari
Yuji Seo
Kazuhiko Ogawa