Beam spot position measurement using corotational penumbra modulation and image center shift methods

Rofikoh, A. Rafliansyah, Sugiyantari, D. S. Soejoko

Research output: Contribution to journalConference articlepeer-review


Image and treatment quality of radiotherapy are influenced by the position of beam spot, therefore it is important to know the position of the beam spot. Beam spot position measured by the corotational penumbra modulation (CPM) and the image center shift (ICS). The CPM method uses a cylindrical ion chamber that rotate with collimator angle. The position of ion chamber, jaws, central axis are fixed to collimator angle. The signal measured to half blocked field 10x20 cm2 for every 30° collimator angle. The beam spot calculated from signal measurement results. The ICS method uses two radiopaque rings with 8.5 cm diameter. Both of rings are placed at different heights of 64.5 cm and 150 cm SSD. Image acquired by varying both collimator and couch angle for every 30° and the beam spot position calculated by measuring the shift of rings centre. Measurement also performed using ball bearing test. Beam spot shift values from the CAOR using CPM and ICS measurements are closely similar, in the range of 0.05-0.65 mm and 0-0.53 mm respectively. The measurement using CPM and ICS methods can be used for routine quality assurance (QA) to ensure that the beam spot position still in tolerance.

Original languageEnglish
Article number012022
JournalJournal of Physics: Conference Series
Issue number1
Publication statusPublished - 15 Jun 2020
Event3rd Annual Scientific Meeting on Medical Physics and Biophysics, PIT-FMB in conjunction with the 17th South-East Asia Congress of Medical Physics, SEACOMP 2019 - Bali, Indonesia
Duration: 8 Aug 201910 Aug 2019


Dive into the research topics of 'Beam spot position measurement using corotational penumbra modulation and image center shift methods'. Together they form a unique fingerprint.

Cite this