ESTRO 37 Abstract book

Purpose or Objective A knee support is part of the positioning protocol for patients with pelvic cancer in our department. Still, we found large rotational errors in some patient groups. Therefore, we decided to change our positioning protocol, in which we changed our knee support and added a feet fixation. To find out whether the new positioning device improved the patient position and reduced the rotational errors of the patient, we evaluated the rotations of the pelvic bone on both positioning devices. Material and Methods In 62 patients treated with external pelvic irradiation in both palliative and curative setting (2 to 25 fractions), we evaluated the differences in rotations. In our department we perform on-line positioning verification and correction with electronic portal images based on an anterior-posterior imaging field (0°/180°) and a lateral imaging field (90°/ 270°). In 42 patients we used the Kneefix device, figure 1A (Sinmed Radiotherapy Products) made of foam, the device was placed on the treatment table in a non-fixed or non-indexed position. In 20 patients we used the ProSTEP, figure 1B (Innovative Technologie Völp), this is a combined knee and feet positioning device made of plastic (ABS). It has a fixed and indexed position on the treatment couch for each individual patient. In both groups we included patients with rectal, gynaecological and anal cancer. The data were retrospectively analysed. Rotations were measured in each patient by one radiation therapist (RTT) making use of the Theraview software (Cablon Medical). This software allows a maximum rotation of 5°. We compared the standard deviations of the rotations, tested by an independent sample Mann-Whitney U test. P-values of ≤ 0.05 were considered significant. We also described the mean percentage of corrections exceeding 3°. Results Comparable rotations were found when using the two devices. For gantry 270°/90° we found a significantly smaller standard deviation of the rotation (p=0.01) for the ProSTEP, with a mean standard deviation of rotation of 1.15° compared to a mean standard deviation of 1.51° for Kneefix (Table). A smaller percentage of fractions with rotations exceeding 3°, for the 270°/90° imaging field, was found for the ProSTEP (15%). For the 0°/180° imaging field no differences were found (Table).

monitor. The patient is in DIBH as long as the laser line is on the caudal side of a threshold mark on the patient, placed at each fraction at 75% of the DIBH position (Figure 1, right). This threshold percentage correlated well with the 75% threshold using ABC, based on a breathing analysis of healthy volunteers.

Results Patients consider the newly devised method to be much more comfortable than the previously used ABC method (Elekta). They no longer have to do system specific training, which reduces the CT timeslot. Also no patient specific consumables are used, which saves both money and storage space and reduces infection hazards. Currently, CBCT anatomical information is used to compare the effect of the newly devised method with A new method for control of the DIBH condition for left sided breast cancer patients, using laser based SGRT was successfully developed and introduced clinically. With the set-up being vendor independent, low cost and easy to build, the method is adaptable to any radiotherapy facility. EP-2344 Evaluation of patient rotations using two positioning devices in pelvic radiation treatment M. Kouijzer 1 , J. Kuipers 1 , M. Buitelaar-Gallé 1 , J. Van Egmond 1 , H. Ceha 1 , J. Van Santvoort 1 , M. Mast 1 1 Haaglanden Medical Centre, Radiotherapy, Leidschendam, The Netherlands that of ABC. Conclusion

ProSTEP (n=20, fractions = 401); Rotations

Kneefix (n=42, fractions = 848); Rotations

Gantry 0/180

Gantry 270/90

Gantry 0/180

Gantry 270/90

Mean

of

0.14º

-0.01º -0.18

-0.08

means

Standard deviation of

0.56º

1.75º 0.59

1.56