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The dosimetric impact of manual adjustments following automated registration in prostate image-guided radiotherapy

Published online by Cambridge University Press:  19 September 2017

Mohamed Nazmy ElBeltagi ,
Dean Harper  and
Lisa Coleman
Mohamed Nazmy ElBeltagi*
Affiliation:
St Luke’s Radiation Oncology Network, Dublin, Ireland NCI Cairo University, Egypt
Dean Harper
Affiliation:
St Luke’s Radiation Oncology Network, Dublin, Ireland
Lisa Coleman
Affiliation:
St Luke’s Radiation Oncology Network, Dublin, Ireland
*
Correspondence to: Mohamed Nazmy ElBeltagi, MBBCh, MSc, PhD, FRCR, Consultant Radiation Oncology, St Luke’s Radiation Oncology Network, Rathgar, Dublin 6, Ireland. Tel: 0035 389 460 8541. E-mail: mnazmy@hotmail.com; nazmy.elbeltagi@slh.ie
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Abstract

Aim

Although manual adjustment of automatic cone beam computed tomography (CBCT) matching may improve the target coverage in certain points of interest, concerns exist that this may lead to dosimetric uncertainties which would negate the theoretical benefit of this approach. The objective of this study is to evaluate the dosimetric impact of manual adjustments made after automatic bony registration on CBCT in prostate patients.

Methods

A total of 50 CBCT datasets of ten high-risk prostate cancer patients were randomly chosen. Each CBCT dataset was registered three times. Method (A): Automatic registration, Method (M1): Manual adjustment carried out by two experienced radiation therapists, Method (M2): Manual adjustment carried out by different radiation therapists with varying levels of experience. The clinical target volume (CTV), planning target volume (PTV), the bladder and the rectum were subsequently contoured on each CBCT dataset by a radiation oncologist blinded to the registration methods. The absolute difference of various dosimetric parameters were then analysed and compared with the original planning doses. A comparison of the three matching methods employed was also carried out.

Results

There was a statistically significant difference in the magnitude of move taken in the inferior superior direction between M1 and M2 method. There were no significant differences observed in any of the dosimetric parameters examined in relation to the rectum, bladder or CTV. The only significant difference observed was the volume of PTV covered by the prescription isodose (95%) which was statistically significant lower in method A compared with both M1 and M2. There was no difference observed between M1 and M2 methods. The mean duration of the automated registration and subsequent analysis was 64 seconds compared with 91 seconds for automated registrations which included the additional manual adjustment.

Findings

CBCT-based manual adjustments of automated bony-based registrations during the image-guided radiotherapy verification of prostate cancer patients can improve PTV coverage without impacting negatively on the doses received by the organs at risk. This strategy is associated with a small increase in overall treatment time.

Keywords

cone beam computed tomographyimage-guided radiotherapyimage registrationprostate cancer
Type
Original Articles
Information
Journal of Radiotherapy in Practice , Volume 17 , Issue 1 , March 2018 , pp. 29 - 36
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Copyright
© Cambridge University Press 2017 

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