Restricted bowel loop contouring: Improving efficiency in radiotherapy contouring for abdomino-pelvic Stereotactic Ablative Radiotherapy (SABR)

We present a time-saving alternative to individual bowel loop delineation for abdomino-pelvic Stereotactic Ablative Radiotherapy. Here, individual bowel loop contouring is only performed within a 3 cm circumferential and 2 cm superio-inferior expansion of the PTV. A bowel bag structure represents distal bowel. No relevant doses are ‘missed’ with this time-saving strategy

ADAPTIVE MR-GUIDED RADIOTHERAPY: FROM CONCEPT TO ROUTINE PRACTICE

Radiotherapy is an established curative treatment for cancer and is also widely used in the treatment of metastatic disease. Magnetic resonance guided radiotherapy (MRgRT) represents a major treatment advance as it permits precise soft tissue setup and the continuous visualization of tumors and surrounding organs, thereby improving the safety and effectiveness of radiotherapy delivery. MRgRT was first introduced clinically in 2014, and in 2016, the Amsterdam UMC became the first Dutch adopters, focusing on treating patients using stereotactic ablative radiotherapy (SABR). The work performed in this thesis describes a number of approaches developed in order to ensure a practical and feasible workflow for MRgRT delivery of SABR using daily on-couch adaptive treatment plan delivery whenever possible. A key development was the strategy for plan adaptation using only a single treatment optimization step that only requires clinicians to review and adjust organ contours located within 2-3 cm from the target. This novel and fast approach resulted in treatment plans meeting all clinical constraints, and contributed to the feasibility of using daily adaptive MRgRT, as plan adaptation added only about 15 minutes to the total workflow. Use of this strategy has led to more than 1200 patients undergoing 6000 treatment fractions to tumor in the prostate, pancreas, high-risk lung cancer, renal- and adrenal lesions, and liver metastases. Almost all fractions have been delivered using the adapted plan. The delivery of daily adapted MRgRT requires time slots of approximately 45 to 60 minutes for SABR delivery. To reduce treatment times further, it is essential to identify patients groups that are less likely to benefit from having a new daily radiotherapy plan, and our studies identified patients with abdominal tumors who could be treated faster without plan adaptation. This will permit a more efficient use of resources. Organs in the body can move during treatment, leading to a need for intrafractional adapted radiotherapy plans. To approach this problem, we used fraction partitioning with successive re-optimization, and showed that plan adaptation benefits both tumor coverage and healthy organ sparing. Similarly, plan adaptation during treatment was also shown to be useful in some instances, although it can prolong the treatment duration to 90 minutes. The continuous visualization of anatomical changes during MRgRT allows for a more accurate reconstruction of delivered doses to tumors and organs. Our study of accumulated radiation doses revealed that the accumulated bladder dose in 100 patients with prostate cancer better predicted acute radiation-related urinary toxicity, than was possible using the baseline radiotherapy plans. This finding opens the door for personalized radiation delivery approaches using prospective dose accumulation for each subsequent fraction. In summary, the work performed for this thesis has allowed for fast and accurate delivery of MRgRT, and it has identified a number of areas for further improvements in treatment efficiency

ADAPTIVE MR-GUIDED RADIOTHERAPY: FROM CONCEPT TO ROUTINE PRACTICE

Radiotherapy is an established curative treatment for cancer and is also widely used in the treatment of metastatic disease. Magnetic resonance guided radiotherapy (MRgRT) represents a major treatment advance as it permits precise soft tissue setup and the continuous visualization of tumors and surrounding organs, thereby improving the safety and effectiveness of radiotherapy delivery. MRgRT was first introduced clinically in 2014, and in 2016, the Amsterdam UMC became the first Dutch adopters, focusing on treating patients using stereotactic ablative radiotherapy (SABR). The work performed in this thesis describes a number of approaches developed in order to ensure a practical and feasible workflow for MRgRT delivery of SABR using daily on-couch adaptive treatment plan delivery whenever possible. A key development was the strategy for plan adaptation using only a single treatment optimization step that only requires clinicians to review and adjust organ contours located within 2-3 cm from the target. This novel and fast approach resulted in treatment plans meeting all clinical constraints, and contributed to the feasibility of using daily adaptive MRgRT, as plan adaptation added only about 15 minutes to the total workflow. Use of this strategy has led to more than 1200 patients undergoing 6000 treatment fractions to tumor in the prostate, pancreas, high-risk lung cancer, renal- and adrenal lesions, and liver metastases. Almost all fractions have been delivered using the adapted plan. The delivery of daily adapted MRgRT requires time slots of approximately 45 to 60 minutes for SABR delivery. To reduce treatment times further, it is essential to identify patients groups that are less likely to benefit from having a new daily radiotherapy plan, and our studies identified patients with abdominal tumors who could be treated faster without plan adaptation. This will permit a more efficient use of resources. Organs in the body can move during treatment, leading to a need for intrafractional adapted radiotherapy plans. To approach this problem, we used fraction partitioning with successive re-optimization, and showed that plan adaptation benefits both tumor coverage and healthy organ sparing. Similarly, plan adaptation during treatment was also shown to be useful in some instances, although it can prolong the treatment duration to 90 minutes. The continuous visualization of anatomical changes during MRgRT allows for a more accurate reconstruction of delivered doses to tumors and organs. Our study of accumulated radiation doses revealed that the accumulated bladder dose in 100 patients with prostate cancer better predicted acute radiation-related urinary toxicity, than was possible using the baseline radiotherapy plans. This finding opens the door for personalized radiation delivery approaches using prospective dose accumulation for each subsequent fraction. In summary, the work performed for this thesis has allowed for fast and accurate delivery of MRgRT, and it has identified a number of areas for further improvements in treatment efficiency

ADAPTIVE MR-GUIDED RADIOTHERAPY: FROM CONCEPT TO ROUTINE PRACTICE

Radiotherapy is an established curative treatment for cancer and is also widely used in the treatment of metastatic disease. Magnetic resonance guided radiotherapy (MRgRT) represents a major treatment advance as it permits precise soft tissue setup and the continuous visualization of tumors and surrounding organs, thereby improving the safety and effectiveness of radiotherapy delivery. MRgRT was first introduced clinically in 2014, and in 2016, the Amsterdam UMC became the first Dutch adopters, focusing on treating patients using stereotactic ablative radiotherapy (SABR). The work performed in this thesis describes a number of approaches developed in order to ensure a practical and feasible workflow for MRgRT delivery of SABR using daily on-couch adaptive treatment plan delivery whenever possible. A key development was the strategy for plan adaptation using only a single treatment optimization step that only requires clinicians to review and adjust organ contours located within 2-3 cm from the target. This novel and fast approach resulted in treatment plans meeting all clinical constraints, and contributed to the feasibility of using daily adaptive MRgRT, as plan adaptation added only about 15 minutes to the total workflow. Use of this strategy has led to more than 1200 patients undergoing 6000 treatment fractions to tumor in the prostate, pancreas, high-risk lung cancer, renal- and adrenal lesions, and liver metastases. Almost all fractions have been delivered using the adapted plan. The delivery of daily adapted MRgRT requires time slots of approximately 45 to 60 minutes for SABR delivery. To reduce treatment times further, it is essential to identify patients groups that are less likely to benefit from having a new daily radiotherapy plan, and our studies identified patients with abdominal tumors who could be treated faster without plan adaptation. This will permit a more efficient use of resources. Organs in the body can move during treatment, leading to a need for intrafractional adapted radiotherapy plans. To approach this problem, we used fraction partitioning with successive re-optimization, and showed that plan adaptation benefits both tumor coverage and healthy organ sparing. Similarly, plan adaptation during treatment was also shown to be useful in some instances, although it can prolong the treatment duration to 90 minutes. The continuous visualization of anatomical changes during MRgRT allows for a more accurate reconstruction of delivered doses to tumors and organs. Our study of accumulated radiation doses revealed that the accumulated bladder dose in 100 patients with prostate cancer better predicted acute radiation-related urinary toxicity, than was possible using the baseline radiotherapy plans. This finding opens the door for personalized radiation delivery approaches using prospective dose accumulation for each subsequent fraction. In summary, the work performed for this thesis has allowed for fast and accurate delivery of MRgRT, and it has identified a number of areas for further improvements in treatment efficiency

Pitfalls of Ovarian Ablative Magnetic Resonance-guided Radiation Therapy for Refractory Endometriosis.

Contains fulltext : 200752.pdf (publisher's version ) (Open Access

An end-to-end test for MR-guided online adaptive radiotherapy

In the evolving field of adaptive MR guided radiotherapy, the need for dedicated procedures for acceptance and quality assurance is increasing. Research has been devoted to MR compatible dosimeters and phantoms, but to date no end-to-end test has been presented that covers an MRgRT workflow. Such an end-to-end test should comprise each step of the workflow and include all associated uncertainties. The purpose of this study was to investigate the usability of an anthropomorphic deformable and multimodal pelvis (ADAM-pelvis) phantom in combination with film dosimetry for end-to-end testing of an MRgRT adaptive workflow. The ADAM-pelvis phantom included surrogates for muscle tissue, adipose and bone, as well as deformable silicone organs mimicking a prostate patient. At the interfaces of the critical structures (bladder and rectum), small pieces of GafChromic EBT3 films were placed to measure delivered dose. Pre-treatment MR imaging of the phantom was used to delineate the prostate, rectum and bladder and to generate a treatment plan to deliver 2 Gy to the prostate. Electron density (ED) map from CT imaging was used for dose calculation after deformable image registration (DIR) to the pre-treatment MR scan. At each fraction, bladder- and rectum filling was varied and a new adapted plan was generated. Dose calculation was performed using both a DIR-based ED map and a CT-based ED map after acquisition of a new CT scan of the phantom at each fraction. All dose calculations were performed taking into account the magnetic field. A good agreement between measured and calculated dose was found using both, the CT-derived and the DIR-based ED map (2.0% and 2.8% dose difference, respectively). The gamma index pass-rate (3%/2 mm) varied from 96.4% to 100%.The ADAM-pelvis phantom was suitable for end-to-end testing in MR-guided radiotherapy and a very good agreement with the calculated dose was achieved