Dual partial arc volumetric-modulated arc therapy: The game changer for accelerated hypofractionated whole-breast radiotherapy with simultaneous integrated tumor cavity boost in early breast cancer - A comparative dosimetric study with single partial arc volumetric-modulated arc therapy.

INTRODUCTION: In a previous study, we demonstrated clinical and dosimetric feasibility of single partial arc volumetric modulated arc therapy (VMAT) for accelerated hypofractionated whole breast radiotherapy with simultaneous integrated boost (SIB) to lumpectomy cavity for early breast cancer. In this dosimetric study, we compared dual partial arcs versus single arc. PATIENTS AND METHODS: Fifteen consecutive patients for treatment with hypofractionated accelerated radiotherapy with SIB using VMAT were planned with single partial arc in an earlier study, initial result of which is published elsewhere. The comparative dosimetric plan was created using two partial arcs. Skewness and kurtosis test, Paired Student's t-test, and Wilcoxon signed-rank test were applied for statistical analysis. P < 0.05 was considered statistically significant. RESULTS: Most planning targets are better achieved with dual arc technique. Coverage of planning target volume (PTV) whole breast (PTVWB) and PTV lumpectomy cavity (PTVBOOST) was significantly improved with dual partial arc without significant difference in conformity index and homogeneity index. Dual arc improved dosimetric parameter significantly. Mean dose (Dmean) and maximum dose (Dmax) of whole breast PTV as well as Dmax of PTVBOOST; ipsilateral and contralateral lung Dmean, Dmax, 5 Gy volume (V5); contralateral lung Dmean, Dmax, V5; Heart V25 and V18; Dmean of 5 mm thickness skin; Dmean and Dmax of ribs; and Dmean and Dmax of contralateral breast were improved with dual arc. CONCLUSION: This is first of its kind study establishing the advantage of dual partial arcs in the current context. Dual partial arcs improved dosimetry over single partial arc. Significant dose reduction can be achieved for multiple crucial organs at risk.

Accelerated hypofractionated adjuvant whole breast radiation with simultaneous integrated boost using volumetric modulated arc therapy for early breast cancer: A phase I/II dosimetric and clinical feasibility study from a tertiary cancer care centre of India.

BACKGROUND: Hypofractionation has become standard of care after Breast Conserving Therapy (BCT) in many European and few others western countries. Though still debatable, tumor cavity boost is routinely practised in our centre. Hypofractionation is not yet the current standard of practice in Asian countries. Employing hypofractionation and simultaneous integrated boost to lumpectomy cavity with conformal technique is not the current practice in this region. Hence the study was performed to see whether accelerated hypofractionation and simultaneous boost can be combined using volumetric modulated arc therapy (VMAT) in treating early breast cancer (EBC) patients. PATIENTS AND METHODS: Female patients with EBC treated by whole breast radiation and boost were treated simultaneously to a dose of 40.5Gy and 48Gy in fifteen fractions over three weeks to entire breast and tumor cavity respectively with VMAT. Dosimetry including target coverage, OAR (organ at risk) sparing and acute radiation toxicity were evaluated. RESULTS: Ten consecutive patients were treated. Planning target volume (PTV) coverage and OAR sparing were mostly satisfactory. Mean volume of PTVWB and PTVBoost were 786.18cm3 and 228.9cm3 respectively. Mean Dmean to PTVWB and PTVBOOST were 41.9Gy and 49.1Gy respectively. Dmax to PTVWB and PTVBOOST were 127.56% and 110.67% respectively. Ipsilateral lung mean dose and V20 were 13.92Gy and 21.53% respectively. V40 and V25 of heart were 0.17% and 2.25% respectively. All patients are disease free after a median follow up of two years. Most acute toxicities were Grade1. Only two patients out of ten developed Grade 2 skin reaction during radiation. Early cosmesis using Harvard cosmesis scale is good to excellent. CONCLUSIONS: Accelerated hypofractionated RT using SIB-VMAT is a clinically feasible technique with acceptable initial result. Initial results are encouraging. MINI ABSTRACT: Simultaneous integrated boost with accelerated hypofractionated whole breast radiotherapy using Volumetric Modulated Arc Therapy is a novel approach. Patient selection and technical considerations are of paramount importance. The present study describes successful implementation of this approach.