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Session Item

Monday
April 06
00:00 - 00:00
Brachytherapy: Breast
Poster
00:00 - 00:00
MR-based adaptive IGRT of prostate cancer: feasibility, plan adaptation and acute toxicity
PO-1194

Abstract

MR-based adaptive IGRT of prostate cancer: feasibility, plan adaptation and acute toxicity
Authors: Wegener|, Daniel(1)*[daniel.wegener@med.uni-tuebingen.de];Paulsen|, Frank(1);De Colle|, Chiara(1);Thorwart|, Daniela(2);Grosse|, Ulrich(3);Othman|, Ahmed (3);Afat|, Saif(3);Bedke|, Jens(4);Stenzl|, Arnulf(4);Nikolaou|, Konstantin(3);Zips|, Daniel(5);Müller|, Arndt-Christian(5);
(1)University Hospital Tübingen, Department of Radiation Oncology, Tübingen, Germany;(2)University Hospital Tübingen, Department of Radiation Oncology- Section Medical Physics- German Cancer Consortium DKTK- partner site Tübingen- and German Cancer Research Center DKFZ- Heidelberg- Germany, Tübingen, Germany;(3)University Hospital Tübingen, Department of Radiology, Tübingen, Germany;(4)University Hospital Tübingen, Department of Urology, Tübingen, Germany;(5)University Hospital Tübingen, Department of Radiation Oncology- German Cancer Consortium DKTK- partner site Tübingen- and German Cancer Research Center DKFZ- Heidelberg- Germany, Tübingen, Germany;
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Purpose or Objective

Conventional fractionated dose-escalated radiotherapy (RT) up to 80 Gy +/- androgen deprivation therapy (ADT) is a standard treatment option for prostate cancer (PC). Since ADT reduces prostate volume by ~10% per month a significant decrease of the target volume and increased overlap with organs at risk at the end of IGRT might be expected. Therefore, we studied whether multiparametric MRI-based treatment planning and threshold-/constraint-based adaption of the radiation treatment plan using a weekly MRI is able to reduce G2+ gastrointestinal (GI) and genitourinary (GU) side effects within a prospective phase II study (M-base Pro 1.0).

Material and Methods

Patients with MRI-staged PC (cT1-3b N0 M0) were included in this prospective study (ClinicalTrials.gov Identifier: NCT02724670). Treatment consisted of 78 Gy (39 frx) to prostate and seminal vesicles (low/intermediate/high risk or cT3b: 0/1/2cm or complete SV). ADT was given according to national guidelines. Diagnostic 3T MRI was performed at diagnosis, after neoadjuvant ADT (treatment planning), at week 2 and 7 of RT. 1.5 T MRIs without gadolinium (T2w, DWI) were performed before and weekly during RT. Daily Image-guided RT (IGRT, gold fiducials, cone-beam CT) was planned with a PTV margin of 6 mm, dorsally 5 mm. The need for plan adaption was weekly checked by MRI. In case of prostate volume changes ≥25% / ≥20ml or unmet predefined OAR-constraints the radiation treatment plan was adapted. Acute toxicity (RTOG, CTC) was scored before RT start, weekly during RT and 3 months post RT in the predefined exploratory cohort (n=25).

Results

All 25 patients of the exploratory cohort were able to follow the study protocol. Plan adaptions were performed in 28% of patients (n=7). CTC urinary frequency decreased from baseline with 12% (G1) to 4% (G1) after neo-ADT, increased during IGRT (climax at week 8: G1=75%; G2=8%) and decreased three months after IGRT to 26% of G1. Acute RTOG bladder toxicity (Fig. 1) increased from 4% (G1) at baseline to week 8 (G1= 80%, G2=8%) and decreased again three months later (G1=8%). CTC proctitis was absent at baseline and reached 40% (G1) and 16% (G2) at week 8 and decreased to 18% of G1 3 months post RT. Acute RTOG rectum toxicity (Fig. 2) increased from baseline (0%) to 60% of G1 at week 8 and decreased to 8% of G1 three months after IGRT. No grade 3+ acute toxicity occurred in any scored item.

Conclusion

In this single-arm prospective study we were able to demonstrate feasibility of an ambitious imaging protocol with MR-based adaptive IGRT. In addition, the extent of acute toxicity of this weekly adaptive IGRT in PC was very encouraging.