Multi-institutional evaluation of a Pareto navigation guided automated radiotherapy planning solution for prostate cancer.

BACKGROUND: Current automated planning solutions are calibrated using trial and error or machine learning on historical datasets. Neither method allows for the intuitive exploration of differing trade-off options during calibration, which may aid in ensuring automated solutions align with clinical preference. Pareto navigation provides this functionality and offers a potential calibration alternative. The purpose of this study was to validate an automated radiotherapy planning solution with a novel multi-dimensional Pareto navigation calibration interface across two external institutions for prostate cancer. METHODS: The implemented 'Pareto Guided Automated Planning' (PGAP) methodology was developed in RayStation using scripting and consisted of a Pareto navigation calibration interface built upon a 'Protocol Based Automatic Iterative Optimisation' planning framework. 30 previous patients were randomly selected by each institution (IA and IB), 10 for calibration and 20 for validation. Utilising the Pareto navigation interface automated protocols were calibrated to the institutions' clinical preferences. A single automated plan (VMATAuto) was generated for each validation patient with plan quality compared against the previously treated clinical plan (VMATClinical) both quantitatively, using a range of DVH metrics, and qualitatively through blind review at the external institution. RESULTS: PGAP led to marked improvements across the majority of rectal dose metrics, with Dmean reduced by 3.7 Gy and 1.8 Gy for IA and IB respectively (p < 0.001). For bladder, results were mixed with low and intermediate dose metrics reduced for IB but increased for IA. Differences, whilst statistically significant (p < 0.05) were small and not considered clinically relevant. The reduction in rectum dose was not at the expense of PTV coverage (D98% was generally improved with VMATAuto), but was somewhat detrimental to PTV conformality. The prioritisation of rectum over conformality was however aligned with preferences expressed during calibration and was a key driver in both institutions demonstrating a clear preference towards VMATAuto, with 31/40 considered superior to VMATClinical upon blind review. CONCLUSIONS: PGAP enabled intuitive adaptation of automated protocols to an institution's planning aims and yielded plans more congruent with the institution's clinical preference than the locally produced manual clinical plans.

Multi-centre evaluation of variation in cumulative dose assessment in reirradiation scenarios.

BACKGROUND AND PURPOSE: Safe reirradiation relies on assessment of cumulative doses to organs at risk (OARs) across multiple treatments. Different clinical pathways can result in inconsistent estimates. Here, we quantified the consistency of cumulative dose to OARs across multi-centre clinical pathways. MATERIAL AND METHODS: We provided DICOM planning CT, structures and doses for two reirradiation cases: head & neck (HN) and lung. Participants followed their standard pathway to assess the cumulative physical and EQD2 doses (with provided α/ß values), and submitted DVH metrics and a description of their pathways. Participants could also submit physical dose distributions from Course 1 mapped onto the CT of Course 2 using their best available tools. To assess isolated impact of image registrations, a single observer accumulated each submitted spatially mapped physical dose for every participating centre. RESULTS: Cumulative dose assessment was performed by 24 participants. Pathways included rigid (n = 15), or deformable (n = 5) image registration-based 3D dose summation, visual inspection of isodose line contours (n = 1), or summation of dose metrics extracted from each course (n = 3). Largest variations were observed in near-maximum cumulative doses (25.4 - 41.8 Gy for HN, 2.4 - 33.8 Gy for lung OARs), with lower variations in volume/dose metrics to large organs. A standardised process involving spatial mapping of the first course dose to the second course CT followed by summation improved consistency for most near-maximum dose metrics in both cases. CONCLUSION: Large variations highlight the uncertainty in reporting cumulative doses in reirradiation scenarios, with implications for outcome analysis and understanding of published doses. Using a standardised workflow potentially including spatially mapped doses improves consistency in determination of accumulated dose in reirradiation scenarios.

Mitigating Respiratory Motion in Radiation Therapy: Rapid, Shallow, Non-invasive Mechanical Ventilation for Internal Thoracic Targets.

PURPOSE: Reducing respiratory motion during the delivery of radiation therapy reduces the volume of healthy tissues irradiated and may decrease radiation-induced toxicity. The purpose of this study was to assess the potential for rapid shallow non-invasive mechanical ventilation to reduce internal anatomy motion for radiation therapy purposes. METHODS AND MATERIALS: Ten healthy volunteers (mean age, 38 years; range, 22-54 years; 6 female and 4 male) were scanned using magnetic resonance imaging during normal breathing and at 2 ventilator-induced frequencies: 20 and 25 breaths per minute for 3 minutes. Sagittal and coronal cinematic data sets, centered over the right diaphragm, were used to measure internal motions across the lung-diaphragm interface. Repeated scans assessed reproducibility. Physiologic parameters and participant experiences were recorded to quantify tolerability and comfort. RESULTS: Physiologic observations and experience questionnaires demonstrated that rapid shallow non-invasive ventilation technique was tolerable and comfortable. Motion analysis of the lung-diaphragm interface demonstrated respiratory amplitudes and variations reduced in all subjects using rapid shallow non-invasive ventilation compared with spontaneous breathing: mean amplitude reductions of 56% and 62% for 20 and 25 breaths per minute, respectively. The largest mean amplitude reductions were found in the posterior of the right lung; 40.0 mm during normal breathing to 15.5 mm (P < .005) and 15.2 mm (P < .005) when ventilated with 20 and 25 breaths per minute, respectively. Motion variations also reduced with ventilation; standard deviations in the posterior lung reduced from 14.8 mm during normal respiration to 4.6 mm and 3.5 mm at 20 and 25 breaths per minute, respectively. CONCLUSIONS: To our knowledge, this study is the first to measure internal anatomic motion using rapid shallow mechanical ventilation to regularize and minimize respiratory motion over a period long enough to image and to deliver radiation therapy. Rapid frequency and shallow, non-invasive ventilation both generate large reductions in internal thoracic and abdominal motions, the clinical application of which could be profound-enabling dose escalation (increasing treatment efficacy) or high-dose ablative radiation therapy.