Journal of Medical Physics
 Home | Search | Ahead of print | Current Issue | Archives | Instructions | Subscription | Login  The official journal of Association of Medical Physicists of India      
 Users online: 339  Home  EMail this page Print this page Decrease font size Default font size Increase font size 
ORIGINAL ARTICLE
Year : 2010  |  Volume : 35  |  Issue : 2  |  Page : 73-80

Dosimetry of interface region near closed air cavities for Co-60, 6 MV and 15 MV photon beams using Monte Carlo simulations


1 Cancer Centre of South Eastern Ontario at Kingston General Hospital, 25 King Street West, Kingston, ON, K7L5P9, Canada; Departments of Oncology and Physics, Queen's University, Kingston, ON, Canada; Department of Physics, University of Pune, Pune-411 007, India
2 Cancer Centre of South Eastern Ontario at Kingston General Hospital, 25 King Street West, Kingston, ON, K7L5P9, Canada; Departments of Oncology and Physics, Queen's University, Kingston, ON, Canada
3 Department of Physics, University of Pune, Pune-411 007, India

Correspondence Address:
Chandra P Joshi
Department of Medical Physics, Cancer Centre of South Eastern Ontario, Kingston General Hospital, 25 King Street West, Kingston, ON, K7L5P9, Canada

Login to access the Email id

Source of Support: Funding by the Canadian Institute of Health Research (CIHR) and the Ontario Research Development Challenge Fund: Ontario Consortium for Image Guided Therapy and Surgery, (ORDCF/OCITS), Conflict of Interest: None


DOI: 10.4103/0971-6203.62197

Rights and Permissions

Underdosing of treatment targets can occur in radiation therapy due to electronic disequilibrium around air-tissue interfaces when tumors are situated near natural air cavities. These effects have been shown to increase with the beam energy and decrease with the field size. Intensity modulated radiation therapy (IMRT) and tomotherapy techniques employ combinations of multiple small radiation beamlets of varying intensities to deliver highly conformal radiation therapy. The use of small beamlets in these techniques may therefore result in underdosing of treatment target in the air-tissue interfaces region surrounding an air cavity. This work was undertaken to investigate dose reductions near the air-water interfaces of 1x1x1 and 3x3x3 cm 3 air cavities, typically encountered in the treatment of head and neck cancer utilizing radiation therapy techniques such as IMRT and tomotherapy using small fields of Co-60, 6 MV and 15 MV photons. Additional investigations were performed for larger photon field sizes encompassing the entire air-cavity, such as encountered in conventional three dimensional conformal radiation therapy (3DCRT) techniques. The EGSnrc/DOSXYZnrc Monte Carlo code was used to calculate the dose reductions (in water) in air-water interface region for single, parallel opposed and four field irradiations with 2x2 cm 2 (beamlet), 10x2 cm 2 (fan beam), 5x5 and 7x7 cm 2 field sizes. The magnitude of dose reduction in water near air-water interface increases with photon energy; decreases with distance from the interface as well as decreases as the number of beams are increased. No dose reductions were observed for large field sizes encompassing the air cavities. The results demonstrate that Co-60 beams may provide significantly smaller interface dose reductions than 6 MV and 15 MV irradiations for small field irradiations such as used in IMRT and tomotherapy.


[FULL TEXT] [PDF]*
Print this article     Email this article
 Next article
 Previous article
 Table of Contents

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

 Article Access Statistics
    Viewed3093    
    Printed150    
    Emailed1    
    PDF Downloaded282    
    Comments [Add]    

Recommend this journal