Monitor Unit verification for irregular fields in radiotherapy based on Clarkson method combined with in-house MLC shaper software

Document Type : Original Paper


1 Radiological Physics, Assistant Professor, S.P.Medical College,Bikaner, Rajasthan-334003

2 Assistant professor,department of radiological physics,SP Medical college

3 Department of Radiological Physics, CMC Ludhiana, Punjab, India


5 Department of Radiotherapy, SP Medical College, Bikaner, Rajasthan, India.

6 Sr.Demonstrator



Introduction: Radiotherapy is a form of treatment in which the ionizing radiations are directed toward the tumor that eradicates the cancer cells. Approximately 60% of all cancer patients will receive radiation therapy during their course of illness with an estimation that radiation therapy alone contributes to around 40% of curative treatment. In Linear accelerators, the dose delivery is achieved by delivering a proper monitor unit (MU). The accurate calculation of MU is very much essential for accurate and safe dose delivery to cancer patients performed in treatment planning systems (TPS). This TPS calculated MU has to be verified periodically using manual calculations (independent methods) to ensure the unbiased functioning of In this study we have used in-house shaper software and the well-established Clarkson method to verify the calculated MUs with the TPS generated MUs.

Materials and Methods:

In this study, 30 patients were selected from Head & Neck, thorax, and pelvic sites containing different field sizes. A single field from each clinically approved plan was randomly chosen for analysis. All the irregular fields were shaped using Multileaf collimators (1 cm leaves, 80 pairs) from Clinac 2100 CD. MLC log files were exported and fed into the in-house shaper software to get crucial inputs for Clarkson-based manual calculation. Mean deviation and t-test were evaluated to compare calculated MUs with TPS MUs. The method of MU calculation based on the Clarkson method was compared with the TPS calculation method. For the Clarkson method of calculation SMR and TMR parameters were used.


The Clarkson method based calculated MU was always higher in all the clinical sites but however under the tolerance.

Conclusion: The necessary parameter average radius of shaped fields was estimated from the in house shaper software.The compared MU was within the acceptable deviation with the TPS.


Main Subjects

Articles in Press, Accepted Manuscript
Available Online from 26 April 2023
  • Receive Date: 09 February 2022
  • Revise Date: 11 April 2023
  • Accept Date: 26 April 2023
  • First Publish Date: 26 April 2023