Limits...
Commissioning experience and quality assurance of helical tomotherapy machines.

Sen A, West MK - J Med Phys (2009)

Bottom Line: The linac can be operated at a lower voltage (3.5 MV) and dose rate to produce megavoltage CT images, which are used for image-guided patient setup.We have installed two such units since 2004 and treated more than 2000 patients.Our experience with commissioning the machines and periodic quality assurance with tolerance limits for optimal performance are described.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Cancer Treatment Centers of America, Tulsa, OK 74133, USA.

ABSTRACT
A helical tomotherapy machine combines a straight 6 MV linear accelerator mounted on a ring gantry with CT technology for image-guided intensity-modulated radiation therapy (IMRT) treatment. A fan beam created by the collimator and jaws produces a maximum of 40 x 5 cm(2) field size at the isocenter. The gantry and hence the fan beam rotates at a constant speed while the couch moves linearly into the gantry bore, thus producing a helical delivery. The beam is modulated by a 64-leaf binary multileaf collimator (MLC), which enables IMRT treatment. The linac can be operated at a lower voltage (3.5 MV) and dose rate to produce megavoltage CT images, which are used for image-guided patient setup. We have installed two such units since 2004 and treated more than 2000 patients. The machine comes "precommissioned" from the manufacturer, and the beam characteristics and IMRT plans on phantom are measured and compared with manufacturer's data after acceptance tests are performed on site. Our experience with commissioning the machines and periodic quality assurance with tolerance limits for optimal performance are described.

No MeSH data available.


Cylindrical on-axis and off-axis targets and cheese phantom setup for measurement. The CT image of the cheese phantom (left) shows an on-axis and two off-axis target structures. The cheese phantom has multiple holes in which A1SL ion chambers can be inserted for simultaneous dose measurement at multiple points as shown on the right
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Figure 0002: Cylindrical on-axis and off-axis targets and cheese phantom setup for measurement. The CT image of the cheese phantom (left) shows an on-axis and two off-axis target structures. The cheese phantom has multiple holes in which A1SL ion chambers can be inserted for simultaneous dose measurement at multiple points as shown on the right

Mentions: IMRT plan verification: IMRT plans are generated for cylindrical targets on a “cheese” phantom for “on-axis” and “off-axis” locations for each beam [Figure 2]. Point dose is measured at several points at high-dose and low-gradient, and low-dose high-gradient locations using multiple ion chambers and multichannel tomoelectrometer. Dose distributions are measured by putting an extended dose range film in a selected plane in the cheese phantom, and dose profiles are generated in transverse and longitudinal directions for comparison. The model is adjusted till the calculated and measured data match and IMRT plan measurements are repeated as needed.


Commissioning experience and quality assurance of helical tomotherapy machines.

Sen A, West MK - J Med Phys (2009)

Cylindrical on-axis and off-axis targets and cheese phantom setup for measurement. The CT image of the cheese phantom (left) shows an on-axis and two off-axis target structures. The cheese phantom has multiple holes in which A1SL ion chambers can be inserted for simultaneous dose measurement at multiple points as shown on the right
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2807140&req=5

Figure 0002: Cylindrical on-axis and off-axis targets and cheese phantom setup for measurement. The CT image of the cheese phantom (left) shows an on-axis and two off-axis target structures. The cheese phantom has multiple holes in which A1SL ion chambers can be inserted for simultaneous dose measurement at multiple points as shown on the right
Mentions: IMRT plan verification: IMRT plans are generated for cylindrical targets on a “cheese” phantom for “on-axis” and “off-axis” locations for each beam [Figure 2]. Point dose is measured at several points at high-dose and low-gradient, and low-dose high-gradient locations using multiple ion chambers and multichannel tomoelectrometer. Dose distributions are measured by putting an extended dose range film in a selected plane in the cheese phantom, and dose profiles are generated in transverse and longitudinal directions for comparison. The model is adjusted till the calculated and measured data match and IMRT plan measurements are repeated as needed.

Bottom Line: The linac can be operated at a lower voltage (3.5 MV) and dose rate to produce megavoltage CT images, which are used for image-guided patient setup.We have installed two such units since 2004 and treated more than 2000 patients.Our experience with commissioning the machines and periodic quality assurance with tolerance limits for optimal performance are described.

View Article: PubMed Central - PubMed

Affiliation: Department of Radiation Oncology, Cancer Treatment Centers of America, Tulsa, OK 74133, USA.

ABSTRACT
A helical tomotherapy machine combines a straight 6 MV linear accelerator mounted on a ring gantry with CT technology for image-guided intensity-modulated radiation therapy (IMRT) treatment. A fan beam created by the collimator and jaws produces a maximum of 40 x 5 cm(2) field size at the isocenter. The gantry and hence the fan beam rotates at a constant speed while the couch moves linearly into the gantry bore, thus producing a helical delivery. The beam is modulated by a 64-leaf binary multileaf collimator (MLC), which enables IMRT treatment. The linac can be operated at a lower voltage (3.5 MV) and dose rate to produce megavoltage CT images, which are used for image-guided patient setup. We have installed two such units since 2004 and treated more than 2000 patients. The machine comes "precommissioned" from the manufacturer, and the beam characteristics and IMRT plans on phantom are measured and compared with manufacturer's data after acceptance tests are performed on site. Our experience with commissioning the machines and periodic quality assurance with tolerance limits for optimal performance are described.

No MeSH data available.