Evaluation of combining bony anatomy and soft tissue position correction strategies for IMRT prostate cancer patients

Background: Radiotherapy treatment requires delivering high homogenous dose to target volume while sparing organs at risk. That is why accurate patient positioning is one of the most important steps during the treatment process. It reduces set-up errors which have a strong influence on the doses given to the target and surrounding tissues. Aim: The aim of this study was to investigate the efficiency of combining bony anatomy and soft tissue imaging position correction strategies for patients with prostate cancer. Materials and methods: The study based on pre-treatment position verification results determined for 10 patients using kV images and CBCT match. At the same patients' position, two orthogonal kV images and set of CT scans were acquired. Both verification methods gave the information about patients' position changes in vertical, longitudinal and lateral directions. Results: For 93 verifications, the mean values of kV shifts in vertical, longitudinal and lateral directions equaled: -0.11 +/- 0.54 cm, 0.26 +/- 0.38 cm and -0.06 +/- 0.47 cm, respectively. The same values achieved for CBCT matching equaled: 0.07 +/- 0.62 cm, 0.22 +/- 0.36 cm and -0.02 +/- 0.45 cm. Statistically significant changes between the values of shifts received during the first week of treatment and the rest time of the irradiation process were found for 2 patients in the lateral direction and 2 patients in vertical direction among kV results and for 3 patients in the longitudinal direction among CBCT results. A significant difference between kV and CBCT match results was found in the vertical direction. Conclusions: In clinical practice, CBCT combined with kV or even portal imaging improves precision and effectiveness of prostate cancer treatment accuracy. (c) 2012 Greater Poland Cancer Centre, Poland. Published by Elsevier Urban & Partner Sp. z.o.o. All rights reserved.