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Dosimetric variations for high-risk prostate cancer by VMAT plans due to patient’s weight changes

Published online by Cambridge University Press:  21 May 2019

David Miguel Open the ORCID record for David Miguel [Opens in a new window] ,
Victor de la Llana ,
Daniel Martinez ,
Angel del Castillo ,
Delfín Alonso ,
Jesús-María de Frutos ,
Carlos Andrés ,
Manuel Agulla ,
Ricardo Torres  and
Francisco López-Lara
David Miguel*
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Victor de la Llana
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Daniel Martinez
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Angel del Castillo
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Delfín Alonso
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Jesús-María de Frutos
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Carlos Andrés
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Manuel Agulla
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Ricardo Torres
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
Francisco López-Lara
Affiliation:
Hospital Clinico Universitario de Valladolid, Valladolid, Valladolid, Spain
*
Author for correspondence: David Miguel, Hospital Clinico Universitario de Valladolid, Valladolid 47014, Spain. E-mail: [email protected]
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Abstract

Purpose:

The aim of this study is to investigate the impact of anatomical changes in prostate cancer patients on the target coverage when using 6 MV beams-VMAT therapy and to propose strategies that allow us to evaluate the dose or correct it by normalization without having to perform a new simulation.

Methods and materials:

Ten patients of high-risk prostate cancer were chosen for the study. All test plans were delivered using the same isocenter and monitor units as the original plan and compared against the original unedited plan. The expansion and contraction of body contours due to size changes was mimicked by increasing and decreasing the body contour with depths of −2, −1·5, …, 1·5, 2 cm, in the anterior, and both lateral directions of the patient. A total of 90 plans were evaluated, 9 for each patient. Dose-volume histogram statistics were extracted from each plan and normalized to prescription dose.

Results:

Weight changes resulted in considerable dose modifications to the target and critical structures. Plans were found to be varied with 2·9% ± 0·3% per cm SSD change for VMAT treatment with a correlation index close to one. Therefore, doses variations were linear to the changes of depth. Gamma index evaluation was performed for the 10 renormalized plans. All of them passed criteria of 3%/3 mm in at least 98.2% of points. Eight of them passed criteria in 99% points. Gamma index 4%/4 mm passed 100% points in all patients for the chosen region of interest.

Conclusions:

The dosimetry estimation presented in this study shows important data for the radiation oncology staff to justify whether a CT rescan is necessary or not when a patient experiences weight changes during treatment. Based on the results of our study, discrepancies between real dose and planned dose were >5% for 1·7 cm of difference in external contour in the anterior and both lateral directions of the patient.

Keywords

dosevolume pointspatient’s weight changesprostatetreatment planning evaluationVMAT
Type
Original Article
Information
Journal of Radiotherapy in Practice , Volume 18 , Issue 4 , December 2019 , pp. 336 - 342
Copyright
© Cambridge University Press 2019 

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