On-line and off-line correction strategies using megavoltage computed tomography in prostate cancer helical tomotherapy

S. Broggi

Research output: Contribution to journalArticlepeer-review


At our Institution around 200 patients were treated for prostate cancer with helical tomotherapy (HT) in the last two years. MVCT was routinely used to correct patient/tumour positioning. For adjuvant treatments the study reports our experience in the application of on- and off-line set-up correction strategies in order to modelling and to assess the optimal off-line strategies to reduce set-up errors: data on 36 patients were analyzed. For radically treated patients, daily on-line correction with "prostate" matching is routinely performed and the data of 21 patients concerning daily correction taking both organ motion and set-up into account were analyzed. Before assessing the organ motion component, an investigation about inter-observer variability in tracking the prostate through direct MVCT visualization was also considered. In summary, using MVCT during the first week of the treatment with an action level equal to 3 mm was found to be effective in significantly reducing systematic set-up error for adjuvant prostate treatment; the estimate of the residual error from the on-line correction strategy analysis suggests that the application of an off-line protocol with systematic set-up correction after the first 4 sessions without any action level may further reduce the residual systematic error below or around 1.5 mm (1 SD). Compared to such off-line approach, the additional improvement of on-line correction does not seem to be clinically relevant; off-line correction strategies for set-up correction with HT may reasonably replace on-line correction with a large sparing of time and resources. Concerning "prostate" registration, a small inter-user variability registration was found probably due to a relatively small impact of organ motion depending on the rectal emptying procedures routinely performed. The same result was confirmed by the small difference estimated between planning and therapy position through an automatic bone matching and then by the manually adjustment of the physician trough direct visualization of prostate.

Original languageEnglish
Pages (from-to)43-48
Number of pages6
JournalRivista Medica
Issue number3
Publication statusPublished - Sep 2007


  • Helical tomotherapy
  • Prostate cancer
  • Set-up and organ motion modelling

ASJC Scopus subject areas

  • Medicine(all)


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