Parotid sparing adaptive radiotherapy in head and neck cancer patients: A study evaluating resource intensiveness and impact on quality of life.

e24037 Background: Anatomical changes during the course of parotid sparing IMRT for head and neck cancer can lead to an increase in the actual dose absorbed by the parotid glands, which may be controlled with the use of interval adaptive replanning. In this prospective assessment of adaptive replanning for parotid dose changes, we explored the feasibility of carrying out adaptive replanning based on predefined objective dosimetric criteria at specified time points. We sought to assess the impact of this measure using a clinically meaningful endpoint of patient reported quality of life outcomes. Methods: 90 patients with head and neck radiotherapy indicated for definitive management or adjuvant therapy who had at least one parotid gland receiving a mean dose (MD) of between 25-30Gy were accrued in the study. The index parotid was delineated on the images acquired on 14th and 19th day and the MD was determined by overlaying the verification image on the planned CT. If the MD had increased by 2% of the initial intended dose, an adaptive plan was attempted with an aim to reduce MD by 2% without compromising PTV coverage; this plan was then used to deliver the remaining treatment. Patients were invited to complete QoL questionnaires: EORTC-QLQC30 with HN35 module, and XeQoL score at baseline, at 3 and 9 months after completion of treatment. Results: 46 out of 90 patients met the threshold for adaptive replanning and were switched to the new plan during treatment. Adaptive replanning was triggered at D14 for 31 patients and D19 for the remaining 15. Need for adaptive replanning was associated with receipt of concurrent chemotherapy and weight loss in the first two weeks of RT. QoL was evaluable for 50 patients at 3 months post treatment. In patients who required adaptive replanning per protocol, Mean XeQoL scores at 3 months showed significantly worse scores for overall scores (1.1 vs 2.3, p 0.001) and for the component individual physical, pain, psychological, and social domains. EORTC QLQ-C30 and HN35 questionnaires at 3 months also demonstrated significantly worse mean symptom scores of the relevant domains of mouth dryness (39 vs 60), stickiness (32 vs 54) and swallowing (39 vs 60) in patients who required adaptive replanning versus those who did not. No significant QoL trends were observable in the 31 patients who were evaluable at 9 months post treatment. The average time required for each step in the planning process was comparable for both the initial planning workflow and adaptive replanning process. Conclusions: The trigger criteria for replanning identified a population of patients who have significantly worsened quality of life due to radiation induced xerostomia. The benefits of adaptive replanning strategies based on weekly evaluation, binary thresholds and standard planning procedures is doubtful Clinical trial information: CTRI/2017/11/010683.

Knowledge-Based Statistical Inference Method for Plan Quality Quantification

Aim: The aim of the study is to develop a geometrically adaptive and statistically robust plan quality inference method. Methods and Materials: We propose a knowledge-based plan quality inference method that references to similar plans in the historical database for patient-specific plan quality evaluation. First, a novel plan similarity metric with high-dimension geometrical difference quantification is utilized to retrieve similar plans. Subsequently, dosimetric statistical inferences are obtained from the selected similar plans. Two plan quality metrics—dosimetric result probability and dose deviation index—are proposed to quantify plan quality among prior similar plans. To evaluate the performance of the proposed method, we exported 927 clinically approved head and neck treatment plans. Eight organs at risk, including brain stem, cord, larynx, mandible, pharynx, oral cavity, left parotid and right parotid, were analyzed. Twelve suboptimal plans identified by dosimetric result probability were replanned to validate the capability of the proposed methods in identifying inferior plans. Results: After replanning, left and right parotid median doses are reduced by 31.7% and 18.2%, respectively; 83% of these cases would not be identified as suboptimal without the proposed similarity plan selection. Analysis of population plan quality reveals that average parotid sparing has been improving significantly over time (21.7% dosimetric result probability reduction from year 2006-2007 to year 2016-2017). Notably, the increasing dose sparing over time in retrospective plan quality analysis is strongly correlated with the increasing dose prescription ratios to the 2 planning targets, revealing the collective trend in planning conventions. Conclusions: The proposed similar plan retrieval and analysis methodology has been proven to be predictive of the current plan quality. Therefore, the proposed workflow can potentially be applied in the clinics as a real-time plan quality assurance tool. The proposed metrics can also serve the purpose of plan quality analytics in finding connections and historical trends in the clinical treatment planning workflow.