Journal of Medical Physics
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Year : 2002  |  Volume : 27  |  Issue : 1  |  Page : 1-8

Stereotactic Radiotherapy Of Intracranial Lesions With Micro Multileaf Collimator Mounted On Linear Accelerator

Correspondence Address:
D D Deshpande

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Source of Support: None, Conflict of Interest: None

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Stereotactic Radiotherapy (SRT) is advancement on three-dimensional conformal radiotherapy (3DCRT) which aims not only to conform the therapeutic dose volume to the shape of the tumor, but also ensures low dose to the other normal tissues. As the therapeutic dose volume tightly covers the tumor, small variation between intended plan and executed plan parameters may lead to significant under-dose of tumor or over-dose of normal tissue, which may result in the failure of the treatment. Therefore, SRT should be carried out through a well-laid out systematic procedure in order to achieve its goal. This paper highlights the systematic procedure and comprehensive Quality Assurance (QA) involved at various steps of intra cranial SRT followed in our hospital and our preliminary experience with Brain Lab Stereotactic System. Of the 18 patients treated so far with SRT, we have analyzed the SRT treatment plans for the first 11 brain tumor patients to highlight the volume of tumor covered by the therapeutic dose and integral dose to other normal tissues. The average Gross Target Volume (GTV) and Planning Target Volume (PTV) treated are 14.07 cc and 43.72 cc, respectively. Out of the 11 patients treated, 100% volume of PTV is covered by 95% isodose volume in 4 patients, 99% of PTV in another 4 patients and 98% of PTV in the remaining 3 patients. But in all the cases, a minimum volume of 96% of the GTV is adequately covered by 100% dose. The conformity index of PTV varies from 1.27 to 1.56, with a mean value of 1.42. As the target volume decreases from 76 cc to 20 cc, the mean dose within the target volume increases from 1.7 Gy to 1.76 Gy. The average volume of normal brain treated with 80%, 50% and 33% dose are 6.53 cc, 73 cc and 298 cc, respectively. Stereotactic radiotherapy with static beams and micro-Multileaf Collimator (mMLC) shaped fields gives the flexibility to tailor the irregular shaped target volume, thereby ensuring better dose conformity and homogeneous dose distribution. Precise delivery of the therapeutic dose to the tumor needs comprehensive quality assurance, both at machine and patient levels.

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