A retrospective tomotherapy image‐guidance study: analysis of more than 9,000 MVCT scans for ten different tumor sites

Abstract

The purpose of this study was to quantify the systematic and random errors for various disease sites when daily MVCT scans are acquired, and to analyze alternative off‐line verification protocols (OVP) with respect to the patient setup accuracy achieved. Alignment data from 389 patients (9,418 fractions) treated at ten different anatomic sites with daily image‐guidance (IG) on a helical tomotherapy unit were analyzed. Moreover, six OVP were retrospectively evaluated. For each OVP, the frequency of the residual setup errors and additional margins required were calculated for the treatment sessions without image guidance. The magnitude of the three‐dimensional vector displacement and its frequency were evaluated for all OVP. From daily IG, the main global systematic error was in the vertical direction (4.4–9.4 mm), and all rotations were negligible (less than 0.5°) for all anatomic sites. The lowest systematic and random errors were found for H&N and brain patients. All OVP were effective in reducing the mean systematic error to less than 1 mm and 0.2° in all directions and roll corrections for almost all treatment sites. The treatment margins needed to adapt the residual errors should be increased by 2–5 mm for brain and H&N, around 8 mm in the vertical direction for the other anatomic sites, and up to 19 mm in the longitudinal direction for abdomen patients. Almost 70% of the sessions presented a setup error of 3 mm for OVPs with an imaging frequency above 50%. Only for brain patients it would be feasible to apply an OVP because the residual setup error could be compensated for with a slight margin increase. However, daily imaging should be used for anatomic sites of difficult immobilization and/or large interfraction movement.PACS numbers: 87.55.‐x, 87.56.‐v

Imaging dose of megavoltage computed tomography (MVCT) for treatment verification in the tomotherapy of breast cancer

“…The breast target volume extends from skin surface to the chest wall and lung interface. Affected by respiratory motion, it accounted to an unavoidable setup error of 3 mm 20 . To reduce the radiation dose, some studies suggested first three fractions or alternate-day imaging protocol 21 .…”

“…Affected by respiratory motion, it accounted to an unavoidable setup error of 3 mm. 20 To reduce the radiation dose, some studies suggested first three fractions or alternateday imaging protocol. 21 Nevertheless, Goddu et al observed significant dose differences of 11-mm shifts in the anterolateral and 3-mm shifts in the posteromedial directions if patient setup errors remained uncorrected in helical tomotherapy treatments, leading to dose reduction in target volume.…”

Evaluation of MVCT imaging dose levels during helical IGRT: comparison between ion chamber, TLD, and EBT3 films

“…It would be useful to compare the information provided by the images according to the various acquisition modes and to be able to choose, in a objective way, the most adapted IGRT protocol (frequency and mode) in order to limit the received doses while improving the quality of treatments (5,8,15,17) …”

“…Image‐guided radiotherapy (IGRT) allows us to take into account not only patient positioning and target localization, but also structure avoidance and morphological variations (1,2,3,4,5,6) . Different possibilities have been described to take into account patient management (7,8) . In order to have a comprehensive approach to the total delivered dose, it is important to evaluate these imaging doses during treatment procedures especially when these techniques are used frequently.…”

Chemoradiation for gastric cancer: controversies, updates and novel techniques

“…Megavoltage CT (MVCT) is used in different tumour sites as a daily IGRT technique to quantify systematic and random errors. 63 Johnson et al 64 used daily MVCT to analyse the interfraction variation of the stomach position in gastric lymphoma. Aggarwal et al 65 assessed the use of tomotherapy with MVCT to estimate the internal target volume of gastric tumours and showed that the target changes widely during the course of radiation treatment, and severe target displacements were observed.…”