Journal of Medical Physics
 Home | Search | Ahead of print | Current Issue | Archives | Instructions | Subscription | Login  The official journal of AMPI, IOMP and AFOMP      
 Users online: 616  Home  EMail this page Print this page Decrease font size Default font size Increase font size 
Year : 1994  |  Volume : 19  |  Issue : 3  |  Page : 98-103

Specifications For Photon Beam Quality From Linacs

Correspondence Address:
Anil Kumar Sharma

Login to access the Email id

Source of Support: None, Conflict of Interest: None

Rights and PermissionsRights and Permissions

The photon beam quality is normally determined along the central axis of a symmetrical beam of a defined field size. Today when there are at least three different methods for field flattening, giving significantly different energy distributions over the field area, it would certainly be important to have some more detailed information about the off-axis photon energy. The treatment techniques are further becoming more and more complex. Irregular and heavily off-centered beams, dynamic wedges etc. are often used in clinical practice today. Another drawback with the commonly used methods for beam quality specifications, TPR20/10and D20 / D10, is the large change in stopping power ratio relative to TPR20/10 when used for ionization chamber dosimetry. Further, it was recently shown that high energy electrons may affect these ratios in high energy photon beams. To obtain more detailed information about the energy distribution over the whole field, a method based on narrow beam penetration of water (HVL in water) was used to study the beam quality of a dual photon energy linac (Clinac - -1800) employing a simple and reliable device specially constructed for these measurements. Both the photon beams (6 and 18 MV) showed marked softening away from the beam central axis. It is very important to apply corrections for the observed beam quality change in the cross-section of the beam, otherwise it may result in erroneous patient dose while using large or off-centered fields.

Print this article     Email this article
 Next article
 Previous article
 Table of Contents

 Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Citation Manager
 Access Statistics
 Reader Comments
 Email Alert *
 Add to My List *
 * Requires registration (Free)

 Article Access Statistics
    PDF Downloaded176    
    Comments [Add]    

Recommend this journal