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Dosimetric comparison of incidental axillary irradiation between three-dimensional conformal and volumetric modulated arc techniques for breast cancer.

ABSTRACT: Radiotherapy techniques for breast cancer have evolved with efforts to reduce treatment-related side effects. In the present study, we conducted dosimetric analysis of incidental axillary irradiation between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3D-CRT). A total of 20 patients with early stage left breast cancer who underwent breast-conserving surgery followed by postoperative radiotherapy were analyzed. For VMAT plans, dose-volume constraints were not imposed on the axilla, as with 3D-CRT. We compared the dosimetric parameters of the planning target volumes, organs at risk and axillary level I-III of the two plans. VMAT showed better target coverage and a normal organ-sparing effect compared with 3D-CRT. The incidental axillary irradiation of VMAT was lower; the mean dose and the V40Gy were significantly reduced at all axillary levels, with the exception of no difference in the maximum dose to axillary level I. In conclusion, VMAT decreased incidental axillary irradiation, even in the absence of a dose-volume constraint on the axilla, and can, therefore, decrease the risk of radiotherapy-related lymphedema. However, caution is also required because it is unclear whether this incidental axillary irradiation is beneficial for reducing recurrence on the axilla.

SUBMITTER: Jo IY

PROVIDER: S-EPMC7179387 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Dosimetric comparison of incidental axillary irradiation between three-dimensional conformal and volumetric modulated arc techniques for breast cancer.

Jo In Young IY Kim Eun Seog ES Kim Woo Chul WC Min Chul Kee CK Yeo Seung-Gu SG

Molecular and clinical oncology 20200330 6

Radiotherapy techniques for breast cancer have evolved with efforts to reduce treatment-related side effects. In the present study, we conducted dosimetric analysis of incidental axillary irradiation between volumetric modulated arc therapy (VMAT) and three-dimensional conformal radiotherapy (3D-CRT). A total of 20 patients with early stage left breast cancer who underwent breast-conserving surgery followed by postoperative radiotherapy were analyzed. For VMAT plans, dose-volume constraints were ...[more]

PMID: 32337037

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Project description:PurposeTo assess the impact of the planner's experience and optimization algorithm on the plan quality and complexity of total marrow and lymphoid irradiation (TMLI) delivered by means of volumetric modulated arc therapy (VMAT) over 2010-2022 at our institute.MethodsEighty-two consecutive TMLI plans were considered. Three complexity indices were computed to characterize the plans in terms of leaf gap size, irregularity of beam apertures, and modulation complexity. Dosimetric points of the target volume (D2%) and organs at risk (OAR) (Dmean) were automatically extracted to combine them with plan complexity and obtain a global quality score (GQS). The analysis was stratified based on the different optimization algorithms used over the years, including a knowledge-based (KB) model. Patient-specific quality assurance (QA) using Portal Dosimetry was performed retrospectively, and the gamma agreement index (GAI) was investigated in conjunction with plan complexity.ResultsPlan complexity significantly reduced over the years (r = -0.50, p < 0.01). Significant differences in plan complexity and plan dosimetric quality among the different algorithms were observed. Moreover, the KB model allowed to achieve significantly better dosimetric results to the OARs. The plan quality remained similar or even improved during the years and when moving to a newer algorithm, with GQS increasing from 0.019 ± 0.002 to 0.025 ± 0.003 (p < 0.01). The significant correlation between GQS and time (r = 0.33, p = 0.01) indicated that the planner's experience was relevant to improve the plan quality of TMLI plans. Significant correlations between the GAI and the complexity metrics (r = -0.71, p < 0.01) were also found.ConclusionBoth the planner's experience and algorithm version are crucial to achieve an optimal plan quality in TMLI plans. Thus, the impact of the optimization algorithm should be carefully evaluated when a new algorithm is introduced and in system upgrades. Knowledge-based strategies can be useful to increase standardization and improve plan quality of TMLI treatments.

Project description:This study evaluates the volumetric modulated arc therapy (VMAT) dosimetric comparison between Halcyon ring gantry and TrueBeam c-arm linear accelerators for craniospinal irradiation (CSI) of the neuro-axis. 25 patients, who received treatment for medulloblastoma and primitive neuro-ectodermal tumors between 2018 and 2021, were planned for VMAT in True Beam (TB), and Halcyon (HAL) linear accelerators using 6 MV unflattened (FFF) photon beams (HALFFF and TBFFF). Dose-volume statistics for the target and organs at risk (OARs) and the total number of monitoring units (MUs) in the treatment plans were compared which included dose received by 95% PTV volume (V95%), volume receiving ≥ 107% dose, homogeneity index (HI), conformity index (PI), MU and dose spillage (D10%, D30%, D50%, D70%, D90%). In all 26 OARs were considered of which five were serial and the remaining were parallel structures. For the former, the dose received by 0.2 cm3, volume = D0.2 cm3) were evaluated and for the latter mean dose were evaluated. Both arms were statistically compared with paired sample t-test with a significant value of ≤ 0.05. 11 patients received treatment with the Halcyon and the rest 14 in the TrueBeam C-arm linear accelerator. Patients in the low- and intermediate-risk category (n = 13) received 23.4 Gy in 13 fractions. The remaining patients were in the high-risk category and received 35 Gy in 21 fractions or 36 Gy in 20 fractions. For HALFFF and TBFFF, PTVV95% were 97.5 ± 0.8% and 97.4 ± 0.9% respectively (p = 0.371) while the V107% were 0.6 ± 0.4% and 0.5 ± 0.5 respectively (p = 0.504). However, the number of monitoring units showed statistical significance (p < 0.001) with values of 1331.9 ± 243.4 MU and 1089 ± 206.7 MU respectively for the HAL and TB plans. The differences in spillage dose were also statistically significant, favouring HAL plans at D30% (p = 0.002), D50% (p < 0.001), D70% (p = 0.039), and D90% (p = 0.01) level except for D10% (p = 0.090). Conformity index also showed statistical significance with PI_HAL = 0.9 ± 0.02 and PI_TB = 0.89 ± 0.03 (p = 0.029). For 10 of the 21 parallel structures, the mean dose differences were statistically significant in favouring of HAL plans. Halcyon based VMAT CSI plans are dosimetrically superior in terms of organ dose, especially for the large organs, and offer lower spillage doses than the TrueBeam plans. Plans generated by both linear accelerators are suitable for the patients' treatments.

Dataset Information

Dosimetric comparison of incidental axillary irradiation between three-dimensional conformal and volumetric modulated arc techniques for breast cancer.

Publications

Dosimetric comparison of incidental axillary irradiation between three-dimensional conformal and volumetric modulated arc techniques for breast cancer.

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