Improvements in the treatment of rectal cancer patients have led to increased survival. Therefore, long-term outcome has become an increasingly important factor. Both neoadjuvant (chemo... Show moreImprovements in the treatment of rectal cancer patients have led to increased survival. Therefore, long-term outcome has become an increasingly important factor. Both neoadjuvant (chemo)radiotherapy and total mesorectal excision surgery are associated with toxicity. As a result, research for rectal cancer treatment has focused on the reduction of radiation dose to healthy tissue and less extensive surgery or omission of surgery in selected patients. The work described in this thesis can be used to reduce uncertainties related to image-guided external beam radiotherapy (EBRT) and high-dose-rate endorectal brachytherapy (HDREBT) of rectal cancer. By decreasing treatment related uncertainties, dose to surrounding healthy tissue can be reduced and/or a higher dose to the target volume can be delivered with an isotoxic effect. The MRI visibility of four types of fiducial markers as a surrogate for gross tumor volume (GTV) location was evaluated. In addition, it was found that the use of fiducial markers as a surrogate for GTV location in an EBRT GTV boost setting allows smaller treatment margins. For HDREBT, it was found that daily CT imaging should be the minimal standard to verify a correct applicator setup. In addition, we propose the use of an ultrashort echo time MRI sequence to visualize the applicator on MRI. Lastly, we determined the added value of a national study group meeting on the quality and variability of EBRT treatment plans for the introduction of a novel target volume that includes only the mesorectum. Show less
Ende, R.P.J. van den; Ercan, E.; Keesman, R.; Kerkhof, E.M.; Marijnen, C.A.M.; Heide, U.A. van der 2020
PURPOSE: The individual channels in an endorectal applicator for high-dose-rate endorectal brachytherapy are not visible on standard MRI sequences. The aim of this study was to test whether an... Show morePURPOSE: The individual channels in an endorectal applicator for high-dose-rate endorectal brachytherapy are not visible on standard MRI sequences. The aim of this study was to test whether an ultrashort echo time (UTE) MRI sequence could be used to visualize the individual channels to enable MR-only treatment planning for rectal cancer.METHODS AND MATERIALS: We used a radial three-dimensional (3D) UTE pulse sequence and acquired images of phantoms and two patients with rectal cancer. We rigidly registered a UTE image and CT scan of an applicator phantom, based on the outline of the applicator. One observer compared channel positions on the UTE image and CT scan in five slices spaced 25 mm apart. To quantify geometric distortions, we scanned a commercial 3D geometric quality assurance phantom and calculated the difference between detected marker positions on the UTE image and corresponding marker positions on two 3D T-1-weighted images with opposing readout directions.RESULTS: On the UTE images, there is sufficient contrast to discern the individual channels. The difference in channel positions on the UTE image compared with the CT was on average -0.1 +/- 0.1 mm (left-right) and 0.1 +/- 0.3 mm (anteroposterior). After rigid registration to the 3D T-1-weighted sequences, the residual 95th percentile of the geometric distortion inside a 550-mm-diameter sphere was 1.0 mm (left-right), 0.9 mm (anteroposterior), and 0.9 mm (craniocaudal).CONCLUSIONS: With a UTE sequence, the endorectal applicator and individual channels can be adequately visualized in both phantom and patients. The geometrical fidelity is within an acceptable range. (C) 2020 The Authors. Published by Elsevier Inc. on behalf of American Brachytherapy Society. Show less
Ende, R.P.J. van den; Peters, F.P.; Harderwijk, E.; Rutten, H.; Bouwmans, L.; Berbee, M.; ... ; Kerkhof, E.M. 2020
Background The STAR-TReC trial is an international multi-center, randomized, phase II study assessing the feasibility of short-course radiotherapy or long-course chemoradiotherapy as an alternative... Show moreBackground The STAR-TReC trial is an international multi-center, randomized, phase II study assessing the feasibility of short-course radiotherapy or long-course chemoradiotherapy as an alternative to total mesorectal excision surgery. A new target volume is used for both (chemo)radiotherapy arms which includes only the mesorectum. The treatment planning QA revealed substantial variation in dose to organs at risk (OAR) between centers. Therefore, the aim of this study was to determine the treatment plan variability in terms of dose to OAR and assess the effect of a national study group meeting on the quality and variability of treatment plans for mesorectum-only planning for rectal cancer. Methods Eight centers produced 25 x 2 Gy treatment plans for five cases. The OAR were the bowel cavity, bladder and femoral heads. A study group meeting for the participating centers was organized to discuss the planning results. At the meeting, the values of the treatment plan DVH parameters were distributed among centers so that results could be compared. Subsequently, the centers were invited to perform replanning if they considered this to be necessary. Results All treatment plans, both initial planning and replanning, fulfilled the target constraints. Dose to OAR varied considerably for the initial planning, especially for dose levels below 20 Gy, indicating that there was room for trade-offs between the defined OAR. Five centers performed replanning for all cases. One center did not perform replanning at all and two centers performed replanning on two and three cases, respectively. On average, replanning reduced the bowel cavity V20Gy by 12.6%, bowel cavity V10Gy by 22.0%, bladder V35Gy by 14.7% and bladder V10Gy by 10.8%. In 26/30 replanned cases the V10Gy of both the bowel cavity and bladder was lower, indicating an overall lower dose to these OAR instead of a different trade-off. In addition, the bowel cavity V10Gy and V20Gy showed more similarity between centers. Conclusions Dose to OAR varied considerably between centers, especially for dose levels below 20 Gy. The study group meeting and the distribution of the initial planning results among centers resulted in lower dose to the defined OAR and reduced variability between centers after replanning. Show less
Ende, R.P.J. van den; Kerkhof, E.M.; Rigter, L.S.; Leerdam, M.E. van; Peters, F.P.; Triest, B. van; ... ; Heide, U.A. van der 2019
