Matchline dosimetry of half beam technique at .xed SSD using Co-60 and 4 MV photons in the treatment of head and neck tumors

H. Bilge1, H. Kucucuk1, M. Okutan1, A. Cakir1, S. Kucucuk2

1. Oncology Institute of Istanbul University, Medical Physics Division, Istanbul (Turkey)

2. Oncology Institute of Istanbul University, Radiation Oncology Department, Istanbul (Turkey)

Manuscript received: November 12, 2001; revised: August 19 and November 19, 2002

Accepted for publication: November 26, 2002

Abstract

The problem of beam divergence and overlapping of adjacent .elds in the conventional treatment of cancer of the head and neck is well known. The use half beam technique has been suggested as one way of solving this problem. This work reports a matchline

dosimetry of this technique using Co-60 beam and 4 MV photons beam and .xed SSD technique. The dose distributions at the junction between two adjacent .elds were measured with .lms in solid water phantoms for

both machines. The dose distributions are compared and discussed. This study shows that ± 1 mm .eld placement errors are acceptable for each machine within ± 5% dose variations. On the other hand in ± 2, 3, 5 mm .eld placement errors dose variations

exceed tolerance limits. However dose variations in Co-60 machine with half block are much less than 4 MV linear accelerator with asymmetric collimator.

KEYWORDS: Matchline dosimetry, 4 MV x-ray, Co-60, Head and neck.

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