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Cervix: Oral Abstract: The impact of tumour regression in locally advanced carcinoma cervix during external beam radiotherapy and the need for adaptive planning
This article was originally published by Wolters Kluwer - Medknow and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Aim:
To study the impact of tumour regression occurring during IMRT for locally advanced carcinoma cervix and study dose distribution to target volume and OARs and hence the need for any replanning.
Materials and Methods:
40 patients undergoing IM-IGRT and weekly chemotherapy were included in the study. After 36 Gy, a second planning CT-scan was done and target volume and OARs were recontoured. First plan (non-adaptive) was compared with second plan (adaptive plan) to evaluate whether it would still offer sufficient target coverage to the CTV and spare the OARs after having delivered 36 Gy. Finally new plan was created based on CT-images to investigate whether creating a new treatment plan would optimize target coverage and critical organ sparing. To measure the response of the primary tumour and pathologic nodes to EBRT, the differences in the volumes of the primary GTV and nodal GTV between the pretreatment and intratreatment CT images was calculated. Second intratreatment IMRT plans was generated, using the delineations of the intratreatment CT images. The first IMRT plan (based on the first CT-scan or non adaptive plan) was compared with second IMRT plan (based on the second CT-scan or adaptive plan).
Results:
35% patients had regression in GTV in the range of 4.1% to 5%, 20% in the range of 1.1%-2%, 15% in the range of 2.1%-3% and 20% in the range of 6%-15%. There was significant mean decrease in GTV of 4.63 cc (p=0.000). There was a significant decrease in CTV on repeat CT done after 36 Gy by 23.31 cc (p=0.000) and in PTV by 23.31 cc (p=0.000). There was a statistically significant increase in CTV D98, CTV D95, CTV D50 and CTV D2 in repeat planning CT done after 36 Gy. There was no significant alteration in OARs doses.
Conclusion:
Despite tumour regression and increased target coverage in locally advanced carcinoma cervix after a delivery of 36 Gy there was no sparing of OARs. Primary advantage of adaptive RT seems to be in greater target coverage with non-significant normal tissue sparing.
