Abstract
PurposeThe aim of the study was to investigate the potential clinical benefit from both target tailoring by excluding the tumour-free proximal part of the uterus during image-guided adaptive radiotherapy (IGART) and improved dose conformity based on intensity-modulated proton therapy (IMPT).MethodsThe study included planning CTs from 11 previously treated patients with cervical cancer with a >4-cm tumour-free part of the proximal uterus on diagnostic magnetic resonance imaging (MRI). IGART and robustly optimised IMPT plans were generated for both conventional target volumes and for MRI-based target tailoring (where the non-invaded proximal part of the uterus was excluded), yielding four treatment plans per patient. For each plan, the V15Gy, V30Gy, V45Gy and Dmean for bladder, sigmoid, rectum and bowel bag were compared, and the normal tissue complication probability (NTCP) for ≥grade 2 acute small bowel toxicity was calculated.ResultsBoth IMPT and MRI-based target tailoring resulted in significant reductions in V15Gy, V30Gy, V45Gy and Dmean for bladder and small bowel. IMPT reduced the NTCP for small bowel toxicity from 25% to 18%; this was further reduced to 9% when combined with MRI-based target tailoring. In four of the 11 patients (36%), NTCP reductions of >10% were estimated by IMPT, and in six of the 11 patients (55%) when combined with MRI-based target tailoring. This >10% NTCP reduction was expected if the V45Gy for bowel bag was >275 cm3 and >200 cm3, respectively, during standard IGART alone.ConclusionsIn patients with cervical cancer, both proton therapy and MRI-based target tailoring lead to a significant reduction in the dose to surrounding organs at risk and small bowel toxicity.
Highlights
External beam radiation therapy (EBRT) with simultaneous platin-based chemotherapy (CRT) and brachytherapy is the basis for successful treatment of advanced cervical cancer
Both intensity-modulated proton therapy (IMPT) and magnetic resonance imaging (MRI)-based target tailoring resulted in significant reductions in volumes receiving 15 Gy (V15Gy), V30Gy, V45Gy and Dmean for bladder and small bowel
IMPT reduced the normal tissue complication probability (NTCP) for small bowel toxicity from 25% to 18%; this was further reduced to 9% when combined with MRI-based target tailoring
Summary
External beam radiation therapy (EBRT) with simultaneous platin-based chemotherapy (CRT) and brachytherapy is the basis for successful treatment of advanced cervical cancer. Robust proton therapy treatment planning allows a further reduction in the dose to OARs by improving dose conformity, thanks to the characteristic Bragg peak and steep dose fall-offs around the target volume [8]. This exploratory study aims to quantify the potential dosimetric advantages and the potential benefit in terms of reduction in normal tissue complication probability (NTCP) for small bowel of target tailoring and/or proton beam therapy, compared to the current standard image-guided highprecision photon beam EBRT
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