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.


Tomotherapy HI ART II machine
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC2807140&req=5

Figure 0001: Tomotherapy HI ART II machine

Mentions: The concept of a helical tomotherapy machine for radiation therapy was originally proposed by Mackie et al.[1] in 1993, and the first commercial machine was installed 10 years later. It combines the conventional linac technology with CT technology for image-guided intensity-modulated radiation therapy (IMRT) treatment. An in-line straight 6-megavoltage (MV) linac mounted on a ring gantry and powered by a magnetron rotates continuously while the horizontal couch carrying the patient moves linearly in to the gantry bore [Figure 1], thus producing a helical beam delivery. The beam is fan-shaped, produced by a set of collimating jaws with maximum transverse length of 40 cm and a selectable width up to 5 cm in the longitudinal direction at the isocenter. There is no flattening filter and the beam is cone shaped in the transverse direction. This produces an increased dose rate of about 850 cGy/min at the isocenter. The fan beam passes through a 64-leaf binary multileaf collimator (MLC) driven pneumatically, thus producing 64 beamlets for beam modulation. The fan beam is intercepted by a set of 640 xenon detectors mounted on the ring gantry opposite to the x-ray source similar to those used in a CT scanner. These detectors are used for reconstruction of the MVCT images, dose delivery verification, performance checks and quality assurance of the machine. A 13-cm-thick lead beam stopper is mounted behind the xenon detectors on the ring gantry for beam attenuation. Unlike a conventional radiotherapy linac there is no light field for patient setup. Instead, the patient is set up with the help of two fixed green lasers and five red movable lasers intersecting at a virtual isocenter on the axis of gantry rotation, 70 cm away from the real isocenter. Therefore, the alignment of the lasers is critical to treatment planning and delivery. The isocenter is 85 cm from the source (SAD), which is also the bore diameter. A shorter SAD also helps increase the dose rate. A comparison between the tomotherapy machine and a conventional linac is given in Table 1.


Commissioning experience and quality assurance of helical tomotherapy machines.

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

Tomotherapy HI ART II machine
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 0001: Tomotherapy HI ART II machine
Mentions: The concept of a helical tomotherapy machine for radiation therapy was originally proposed by Mackie et al.[1] in 1993, and the first commercial machine was installed 10 years later. It combines the conventional linac technology with CT technology for image-guided intensity-modulated radiation therapy (IMRT) treatment. An in-line straight 6-megavoltage (MV) linac mounted on a ring gantry and powered by a magnetron rotates continuously while the horizontal couch carrying the patient moves linearly in to the gantry bore [Figure 1], thus producing a helical beam delivery. The beam is fan-shaped, produced by a set of collimating jaws with maximum transverse length of 40 cm and a selectable width up to 5 cm in the longitudinal direction at the isocenter. There is no flattening filter and the beam is cone shaped in the transverse direction. This produces an increased dose rate of about 850 cGy/min at the isocenter. The fan beam passes through a 64-leaf binary multileaf collimator (MLC) driven pneumatically, thus producing 64 beamlets for beam modulation. The fan beam is intercepted by a set of 640 xenon detectors mounted on the ring gantry opposite to the x-ray source similar to those used in a CT scanner. These detectors are used for reconstruction of the MVCT images, dose delivery verification, performance checks and quality assurance of the machine. A 13-cm-thick lead beam stopper is mounted behind the xenon detectors on the ring gantry for beam attenuation. Unlike a conventional radiotherapy linac there is no light field for patient setup. Instead, the patient is set up with the help of two fixed green lasers and five red movable lasers intersecting at a virtual isocenter on the axis of gantry rotation, 70 cm away from the real isocenter. Therefore, the alignment of the lasers is critical to treatment planning and delivery. The isocenter is 85 cm from the source (SAD), which is also the bore diameter. A shorter SAD also helps increase the dose rate. A comparison between the tomotherapy machine and a conventional linac is given in Table 1.

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.