University Hospital Department of Radiation Oncology is pleased to be able to offer the most technologically advanced treatment available in external beam radiation therapy with the installation of the Clinac 21EX by Varian. Intensity Modulated Radiation Therapy or IMRT is the latest in precision external beam radiotherapy treatments. Rather than having a single large radiation beam pass through the body, with IMRT the radiation is effectively broken up into thousands of tiny pencil-thin radiation beams by utilizing the integrated Millennium™ Multileaf Collimator system. With millimeter accuracy, these “beamlets” enter the body from many directions and intersect on the tumor. This results in a highest possible dosage to the tumor while resulting in the lowest possible dose to the surrounding healthy tissues.
What is the difference between the Clinac 21 EX and other IMRT Systems?
 The MillenniumTM Multileaf Collimator system is the difference. There are some radiation therapy offices in Central New York that have purchased expensive secondary collimation units (see table) that can be used to perform IMRT like treatments. However, they are limited by the size and number of leafs in the collimator there by limiting the type and size of tumors that can be treated and their ability to spare healthy tissue. In contrast the MillenniumTM Multileaf Collimator provides the highest resolution IMRT by delivering beamlets of 2.5 mm x 5 mm. Such fine resolution enables clinicians to achieve levels of dose sculpting never before attained in radiotherapy. In addition, unlike other IMRT systems the Millennium Multileaf Collimator system allows for the largest IMRT field size (40cm x34cm) thusly allowing more flexibility in the types of tumors treated. All of this provides for greater precision for treating small targets and protecting normal tissue.
| Model |
No. Leaves |
Field Size |
Leaf Widths @ Isocenter |
| Varian Millennium Multileaf Collimator |
120 |
40 x 40 cm2 |
Central 20 cm
of field: 0.5 cm
Outer 20 cm
of field: 1.0 cm
|
| NOMOS MIMiC |
40 |
10 x 10 |
1 or 2 cm |
| 3DLINE DMLC |
40 |
10 x 10 |
1 cm |
Another feature of the Clinac 21 EX is its Portal Imaging capability which gives the therapist immediate on-line visual confirmation of the patients positioning.
Some Cancers being treated today using IMRT
- Lung cancer
- Prostate cancer
- Metastatic brain tumors
- Primary brain tumors
- Liver tumors
- Pancreatic tumors
- Head & neck cancer
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