Facility-Based Optimisation and Standardisation of Vmat Breast Cancer Treatment Planning: A Dosimetric and Quality Assurance Study

Abstract

Variations in planning protocols can compromise treatment plan quality, impacting patient outcomes. The study analyses systematic approach in improving the overall Volumetric Modulated Arc Therapy (VMAT) breast cancer treatment plan quality through a 'plan-overview' optimisation approach. The main objective of the study was to conduct confirmatory studies to evaluate current VMAT breast treatment planning, which will subsequently inform and justify the development of standardised facility-based VMAT breast treatment planning optimisation criteria. The objective was achieved through four distinct phases aimed at investigating structured approaches to enhance overall plan quality and at developing clinical tools to standardise VMAT breast treatment planning optimisation. Results from eleven respondents during the National Breast Cancer EBRT survey identified minor inter-protocol variations from adopted international guidelines and the recognition of improvements in plan quality through new techniques as vital. From the plan acceptability criteria established, acceptable plans can be developed even though plan acceptability deviations from the planning objectives were observed. The criteria for intact breast cases had a mean target volume that received 95% of the prescribed (50 Gy dose) to be 95.08 ± 1.11% and 94.95 ± 1.19% for the chest-wall cases. Significant low doses in contralateral volumes were observed with absolute doses of 7.64 Gy and 7.28 Gy recorded in the contralateral breast volumes for intact breasts and chest-wall VMAT plans, respectively. The current facility protocol tends to improve target conformity at the expense of increasing low doses of contralateral organ volumes. The proposed planning optimisation criteria were established based on results from the plan overview analysis. Comparing the analysed dosimetric parameters between the automated plans with its manual training plan cohort, the mean intact breast target volume that received the 95% of the prescribed dose were 95.81 ± 0.64% and 95.46 ± 0.40%, respectively with a percentage difference of 0.37 ± 0.79%. A mean volume of 95.11 ± 0.72% and 95.04 ± 0.61%, respectively for the chest-wall cases with a percentage difference of 0.07 ± 0.99% also evaluated. The proposed optimisation criteria, however, produced VMAT plans with significantly reduced low doses to the contralateral organ volumes for both intact breast and chest-wall cases. There were no significant differences in the gamma index analysed during intact breast (p-value = 0.962 and p-value = 0.742) and chest-wall (p-value = 0.925 and p-value = 0.779) cohort plans pretreatment QA measurements using both the Octavius 4-D phantom and EPID-based EPIbeam software respectively. There was no statistically significant difference in all dosimetric parameters evaluated between the three cohort plans and among any pair of cohort plans compared during the validation phase of the study. This is a positive demonstration of the clinical feasibility of the proposed optimisation criteria as optimal VMAT breast plans can be consistently reproduced by other treatment planners. This study undoubtedly introduces a new optimisation approach, grounded in a sufficiently extensive dosimetric, quality assurance and radiation therapy efficiency comparative study. Innovative clinical research focusing on standardising local evidence-based outcomes should be encouraged to derive maximum patient treatment benefits. The radiotherapy facility should incorporate the plan acceptability criteria into its planning protocols, and adherence to these criteria must be ensured.