Relations between dose cumulated in organs at risk and treatment based on different image-guidance strategies of cervical cancer

Abstract

Purpose: In this study, relations between dose cumulated in organs at risk and treatment based on different image guidance strategies (IG) of cervical cancer were analyzed.

Material/methods: Thirty patients with cervical cancer were subjected to analysis. The first phase of the study involved analysis of shifts resulting from the registration process and calculations of margins based on shifts data. The margin was calculated for two imaging scenarios - based on the analysis of bones and soft tissues. The margins thus obtained were used in the second phase of the study where the VMAT and IMRT treatment plans were prepared and, in consequence, analyzed in the light of the dose distribution.

Results: Using different IG implicates different margins for specified parts of the CTV. IG based on bones allows to establish margins for lymph nodes (CTV2) that are smaller than margins for the vagina/paravaginal tissues (CTV1). The opposite applies to the IG based on soft tissues, for which margins for CTV1 are smaller than for CTV2. While decreasing the margins for CTV1 reduces the doses in the bladder and rectum, doses cumulated in the bone marrow are independent of the size of the margin resulting from the type of IG used. Nevertheless, the average doses and the values of normal tissue complication probability in the bone marrow were smaller for VMAT than for IMRT.

Conclusion: The VMAT plan and image guidance based on soft tissue registration for the vagina/paravaginal tissues are recommended for radiotherapy of cervical cancer patients.

Keywords: Bone marrow; Cervical cancer; IMRT; Image guidance; NTCP modeling; VMAT.