Online

ESTRO 2020

Session Item

Sunday
August 29
08:00 - 08:40
Room 1
How to tailor your cervical cancer treatment based on evidence-based dose-effect relationships
Ina Jürgenliemk-Schulz, The Netherlands
0570
Teaching lecture
Clinical
23:00 - 23:00
Do 2DKV images add value in online position verification of breast ca patients treated with protons?
PO-1898

Abstract

Do 2DKV images add value in online position verification of breast ca patients treated with protons?
Authors: Estelle Batin.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands), Anne Crijns.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands), Martin Kuijpers.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands), J. a. Langendijk.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands), Arturs Meijers.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands), Tirza van Faassen.(University Medical Center Groningen, Department of Radiation Oncology / GPTC, Groningen, The Netherlands)
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Purpose or Objective

At our institution the initial positioning workflow for breast cancer patients treated with proton therapy consisted of surface imaging, followed by two dimensional kilovoltage (2DkV) images and cone beam computed tomography (CBCT).  Tolerances of 3mm/1.5° were used for CBCT and it was assumed that surface imaging and 2DkV images would prevent a need for a second CBCT acquisition, resulting in reduction of the X-ray dose and shorter positioning time. In order to estimate the added value of 2DkV images, a second workflow was introduced using only surface images followed by CBCT.

Material and Methods

Nineteen breast cancer patients treated with protons were initially positioned using surface imaging (AlignRTTN). 2DkV images were then acquired for ten patients and the resulting translations and pitch applied before CBCT acquisition. The other 9 patients were imaged with CBCT directly after positioning based on surface imaging only. The 2DkV-based corrections were analyzed as well as the CBCT-based 6 degrees of freedom corrections obtained with or without prior 2DkV-based corrections. A particular attention was paid for correction values out of our tolerances of 3mm/1.5°.

Results

2DkV-based translation corrections in lateral direction were 0.55 mm on average (± 1.75 mm SD), longitudinal corrections: 0.51 (± 1.91 mm SD), vertical corrections: 0.67 (± 1.56 mm SD). These corrections exceeded the tolerances of +/- 3 mm in 9.6% of all fractions for lateral, 13.0% for longitudinal and 8.5% for vertical directions. 2/3rd of these corrections were in only one direction. 2DkV pitch corrections were less than 1° for 91.5% of all fractions. CBCT translation corrections after 2DkV corrections were on average less than 0.8 mm compared to less than 1.3 mm without 2DkV corrections. Standard deviations were similar for both workflows: and between 1.7 mm and 2.2 mm. With 2DkV corrections, CBCT translation corrections exceeded +/- 3 mm in 15.3% of all fractions laterally, 13.6% longitudinally, 15.3% vertically and respectively 14.4%, 16.1% and 14.4% without 2DkV corrections (figure 1). Corrections found with CBCT were in 49.2% in the opposite direction from corrections with 2DkV for lateral direction. In 22.6% there was > 3mm difference between 2DkV and CBCT. For longitudinal direction 37.9 % of corrections were in opposite direction and resulted in > 3 mm difference in 21.5% of all fractions. While for vertical direction 48.0% of corrections were in opposite direction and exceeded 3mm difference in 25.4 % of the cases (figure 2).For rotation corrections, the number of CBCT corrections superior or equal to 1.5° after 2DkV were 11.4% of all fractions for yaw, 4.5% for pitch and 8.5% for roll and 6.8% for yaw, 5.9% for pitch and 16.9% for roll without 2DkV corrections.


Conclusion

Excluding 2DkV-based corrections from proton breast positioning workflow did not impact CBCT based corrections with a similar proportion of translations corrections superior to 3 mm/1.5°.