Towards range-guidance in proton therapy to detect organ motion-induced dose degradations.

Introduction.Internal organ motion and deformations may cause dose degradations in proton therapy (PT) that are challenging to resolve using conventional image-guidance strategies. This study aimed to investigate the potential ofrange guidanceusing water-equivalent path length (WEPL) calculations to detect dose degradations occurring in PT.Materials and methods. Proton ranges were estimated using WEPL calculations. Field-specific isodose surfaces in the planning CT (pCT), from robustly optimised five-field proton plans (opposing lateral and three posterior/posterior oblique beams) for locally advanced prostate cancer patients, were used as starting points. WEPLs to each point on the field-specific isodoses in the pCT were calculated. The corresponding range for each point was found in the repeat CTs (rCTs). The spatial agreement between the resulting surfaces in the rCTs (hereafter referred to as iso-WEPLs) and the isodoses re-calculated in rCTs was evaluated for different dose levels and Hausdorff thresholds (2-5 mm). Finally, the sensitivity and specificity of detecting target dose degradation (V95% < 95%) using spatial agreement measures between the iso-WEPLs and isodoses in the pCT was evaluated.Results. The spatial agreement between the iso-WEPLs and isodoses in the rCTs depended on the Hausdorff threshold. The agreement was 65%-88% for a 2 mm threshold, 83%-96% for 3 mm, 90%-99% for 4 mm, and 94%-99% for 5 mm, across all fields and isodose levels. Minor differences were observed between the different isodose levels investigated. Target dose degradations were detected with 82%-100% sensitivity and 75%-80% specificity using a 2 mm Hausdorff threshold for the lateral fields.Conclusion. Iso-WEPLs were comparable to isodoses re-calculated in the rCTs. The proposed strategy could detect target dose degradations occurring in the rCTs and could be an alternative to a fully-fledged dose re-calculation to detect anatomical variations severely influencing the proton range.

Individualised 3D printed vaginal template for MRI guided brachytherapy in locally advanced cervical cancer.

Intracavitary-interstitial applicators for MRI guided brachytherapy are becoming increasingly important in locally advanced cervical cancer. The 3D printing technology enables a versatile method for obtaining a high degree of individualisation of the implant. Our clinical workflow is presented and exemplified by a stage IVA cervical cancer with superior dose distribution.

A model for managing patient booking in a radiotherapy department with differentiated waiting times.

BACKGROUND: In Denmark, the waiting time from the ready-to-treat date to the first radiotherapy fraction is by national legislation guaranteed not to exceed 4 weeks. This guarantee has now been tightened for some specific diagnoses as it is required that e.g. intestinal and head and neck cancer patients have to be treated without unnecessary delays. Thus, patients with these tumour sites have to start radiotherapy treatment immediately after diagnosis, if it is their primary treatment modality. Previously, patients have been booked at the first empty time slot after their ready-to-treat date. Now, booking has to take the differentiated waiting times into account. To facilitate this, a model has been developed. It is used to manage the booking of patients, reserve accelerator capacity for patients with no waiting time and establish the waiting times for other patients. METHODS: The patients are divided into categories according to their waiting time guarantee and for each category a maximum waiting time is defined. The required daily accelerator capacity and average new starts rate for each waiting time category has been determined from the actual patient case-mix in the department. To account for variations in treatment capacity, a prospective daily accelerator capacity is set. Based on the prospective capacity, preparation times, maximum waiting times, and new starts rates, a maximum booking curve (MBC) and a lower limit curve (LLC) are derived. They show the daily maximum and minimum limits, respectively, for booking at future dates. RESULTS: The method is evaluated by a retrospective analysis of actual number of appointments booked compared to the MBC and LLC in situations of both excessive workload and ineffective use of capacity. CONCLUSION: The model represents a tool for effectively managing the capacity in a radiotherapy department with differentiated waiting times. It improves the transparency of the booking process and prospective waiting times can easily be derived on a daily basis.