Dosimetric comparison of the simultaneous integrated boost in whole-breast irradiation after breast-conserving surgery: IMRT, IMRT plus an electron boost and VMAT

Off-isocentric VMAT technique for breast cancer: Effective dose reduction to organs at risk and its applicability based on patient anatomy

PURPOSE

This study aims to explore the off-isocentric volumetric modulated arc therapy (offVMAT) technique for breast cancer and determine its applicability based on patient anatomical parameters.

METHODS

We retrospectively analyzed 44 breast cancer patients with varied lymph node involvement using different arc designs. Off-isocentric techniques were benchmarked against previously published arc techniques: classic arcs (clVMAT), tangential arcs (tVMAT), and split arcs (spVMAT). During optimization, target coverage was made for all plans as close as possible to the criteria D99% > 95% and Dmax < 110% of the prescribed dose. A novel patient categorization, based on anatomical parameters (auxiliary structures) rather than lymph node involvement, is introduced. This categorization considers the volume of ipsilateral organs at risk (OARs) adjacent to the target. A binary regression model was developed on these anatomical parameters. It predicts the likelihood of offVMAT (P[offVMAT]) achieving better criteria.

RESULTS

Using the regression model, patients were divided into two groups: P(offVMAT) > 0.5 and P(offVMAT) < 0.5. For the P(offVMAT) > 0.5 group, most tVMAT plans are unable to achieve the clinical objectives. Comparing offVMAT with spVMAT, offVMAT exhibited better dose parameters for the heart (V20, V10, and D2 are 7.1, 2.4, and 1.5 times lower respectively), ipsilateral lung (V20, V10, V5 and the mean dose are 1.4, 1.3, 1.2, and 1.2 times lower respectively). The average doses to the contralateral side are consistent. In the P(offVMAT) < 0.5 group, the tVMAT technique showed increased doses at medium and high levels, yet reduced doses in contralateral OARs compared to spVMAT and offVMAT. spVMAT showed lower doses in the contralateral lung relative to the offVMAT technique, while clVMAT trailed in both groups. Validation of the model yielded a 90% accuracy rate.

CONCLUSIONS

The new off-isocentric breast planning technique effectively reduces doses to ipsilateral OARs, maintaining acceptable contralateral mean doses. This technique has an advantage over other techniques for patients with intricate anatomies. It is evaluated using anatomical parameters, which are also used to build binary regression model, which shows the dependence of anatomical parameters on whether offVMAT is preferred for individual patients. Also, such anatomical parameters provide a more objective and precise comparison between different planning techniques.

Comparison of helical and TomoDirect techniques with simultaneous integrated boost in early breast cancer patients

Background

The aim of the study was to perform dosimetric comparisons of helical (H) and TomoDirect (TD) plans for whole-breast irradiation (WBI) with simultaneous integrated boost (SIB) in early-stage breast cancer patients undergoing breast conserving surgery.

Materials and methods

Fifty patients, 25 with left-side and 25 with right-side tumors, were determined for a treatment planning system for a total dose of 50.4Gy in 1.8Gy per fraction to WBI, with a SIB of 2.3Gy per fraction delivered to the tumor bed. The planning target volume (PTV) doses and the conformity (CI) and homogeneity indices (HI) for PTVbreast and PTVboost, as well as organ-at-risk (OAR) doses and treatment times, were compared between the H and TD plans.

Results

All plans met the PTV coverage criteria for the H plan, except for mean V107 of PTVbreast for TD plan. The H plan yielded better homogeneity and conformity of dose distribution compared to the TD plan. The ipsilateral mean lung doses were not significantly different between the two plans. The TD plans is advantageous for mean doses to the heart, contralateral breast and lung, spinal cord, and esophagus than the H plans. In both the H and TD plans, the right-sided breast patients had lower heart dose parameters than the left-sided breast patients. The TD plan is superior to the H plan in sparing the contralateral breast and lung by decreasing low-dose volumes.

Conclusions

While the OAR dose advantages of TD are appealing, shorter treatment times or improved dose homogeneity and conformity for target volume may be advantageous for H plan.

Comparative analysis of dosimetry and predictive somatotype parameters of prone and supine whole-breast irradiation among Chinese women after breast-conserving surgery

Purpose

Finding a better treatment position (prone or supine) for whole-breast irradiation for Chinese female patients diagnosed with breast cancer by identify the associations between predictive somatotype parameters and dosimetric gains.

Materials and methods

Two volumetric-modulated arc therapy (VMAT) plans were deployed for whole-breast irradiation in supine and prone position with a total dose of 50 Gy in 25 fractions. Dose-volume parameters were compared and analysed both in the target volume and organs at risk, and equivalent uniform dose-based figure-of-merit (fEUD) models were further used to quantitatively evaluate the overall merits of the two plans. Body shape parameters, including body mass index (BMI), body surface area (BSA), breast shape, cup size, bust size and chest size, were collected. Anatomic features such as the central heart distance (CHD) were measured on supine CT. Spearman’s correlation analysis, receiver operating characteristic (ROC) curve analysis, and the linear regression models were conducted.

Results

Doses to the heart and left anterior descending coronary artery (LADCA) are greater in left-sided breast cancer (BC) patients in the prone position than in the supine position, and the opposite was true for right-sided BC patients (p&lt;0.001). 19 of 63 patients (5 left-sided and 14 right-sided BC) achieved greater benefit from the prone position according to the fEUD score. Right-sided BC patients with a bust size ≥92.25 cm, drop-type breasts and cup size ≥B are very likely to benefit from prone-position radiotherapy. The CHD is significantly positively associated with △fEUD among right-sided BC patients (rho=0.506, p=0.004). Using a cut-off point of 2.215, the CHD had 71.4% sensitivity and 81.2% specificity in predicting a successful prone plan.

Conclusions

Right-sided BC patients had better dosimetric gain in the prone position than left-sided BC patients. The CHD is an especially good and novel predictor that could help to select prone-benefitting right-sided BC patients.

Quality of life after simultaneously integrated boost with intensity-modulated versus conventional radiotherapy with sequential boost for adjuvant treatment of breast cancer: 2-year results of the multicenter randomized IMRT-MC2 trial

BACKGROUND

We recently published 2-year results of the prospective, randomized IMRT-MC2 trial, showing non-inferior local control and cosmesis in breast cancer patients after conventionally fractionated intensity-modulated radiotherapy with simultaneously integrated boost (IMRT-SIB), compared to 3D-conformal radiotherapy with sequential boost (3D-CRT-seqB). Here, we report on 2-year quality of life results.

PATIENTS AND METHODS

502 patients were enrolled and randomized to IMRT-SIB (50.4 Gy in 1.8 Gy fractions with a 64.4 Gy SIB to the tumor bed) or to 3D-CRT-seqB (50.4 Gy in 1.8 Gy fractions, followed by a sequential boost of 16 Gy in 2 Gy fractions). For quality of life (QoL) assessment, patients completed the QLQ-C30 and QLQ-BR23 questionnaires at baseline, 6 weeks and 2 years after radiotherapy.

RESULTS

Significant differences between treatment arms were seen 6 weeks after radiotherapy for pain (22.3 points for IMRT vs. 27.0 points for 3D-CRT-seqB; p = 0.033) and arm symptoms (18.1 points for IMRT vs. 23.6 points for 3D-CRT-seqB; p = 0.013), both favoring IMRT-SIB. Compared to baseline values, both arms showed significant improvement in global score (IMRT: p = 0.009; 3D-CRT: p = 0.001) after 2 years, with slight deterioration on the role (IMRT: p = 0.008; 3-D-CRT: p = 0.001) and social functioning (IMRT: p = 0.013, 3D-CRT: p = 0.001) as well as the future perspectives scale (IMRT: p = 0.003; 3D-CRT: p = 0.0034).

CONCLUSION

This is the first randomized phase III trial demonstrating that IMRT-SIB was associated with slightly superior QoL compared to 3-D-CRT-seqB. These findings further support the clinical implementation of SIB in adjuvant breast cancer treatment.

Dosimetric Comparison of Sequential Versus Simultaneous-integrated Boost in Early-stage Breast Cancer Patients Treated With Breast-conserving Surgery

BACKGROUND/AIM

To compare simultaneous-integrated boost (SIB) versus sequential-boost (SB) delivered in the context of whole-breast irradiation (WBI) via volumetric-modulated arc therapy (VMAT) and helical-tomotherapy (HT).

MATERIALS AND METHODS

Planning target-volume (PTV) dosimetric parameters and organs at risk (OAR) were analyzed for SB plan (50 Gy plus 16 Gy boost) and SIB plan (50.4 Gy WBI and 64.4 Gy tumor bed boost) in VMAT and HT techniques.

RESULTS

Conformity and homogeneity for target-volume doses were better in HT plans compared to VMAT plans. There were no significant differences in ipsilateral lung doses between VMAT and HT plans for SB/SIB techniques, except for a significantly higher lung V5 value with VMAT-SB, and lung V13 value with HT-SIB technique. HT provided a statistically significant decrease in contralateral lung mean V5.

CONCLUSION

The SIB technique showed better target-volume dose distribution in both HT and VMAT plans, and better sparing heart in HT compared to the SB technique.

Which technique of positioning and immobilization is better for breast cancer patients in postmastectomy IMRT, single-pole or double-pole immobilization?

Purpose

Our purpose was to explore which immobilization is more suitable for clinical practice in postmastectomy intensity modulation radiotherapy, the single‐pole position or the double‐pole position?

Methods

Patients treated with postmastectomy intensity modulation radiotherapy were eligible. They were selected randomly for single‐pole position or double‐pole position. Dose–volume histogram (DVH) was used to evaluate plans. After their first radiotherapy, the physicians asked a question about the comfort level of their position. The dosimetric parameters, comfort levels, and reproducibility of the two immobilization techniques were collected and analyzed after all patients had finished the whole radiotherapy.

Results

Totally, 94 patients were enrolled. Of these, 54 patients were treated with the single‐pole position, 28 (51.9%)had left‐sided lesions. While 40 patients were treated with the double‐pole position, 20 (50%) had left‐sided lesions. Patients’ characteristics in two groups were comparable. The single‐pole and double‐pole immobilizations had similar conformity (0.60 ± 0.05 vs 0.60 ± 0.06, P = 0.887) and homogeneity index (0.14 ± 0.03 vs 0.13 ± 0.03, P = 0.407). Compared to single‐pole position, double‐pole position typically increased the mean dose, V₂₀, and V₃₀ of heart (P < 0.05). Moreover, patients in the single‐pole group felt more comfortable than another group (P < 0.05). There was no difference in reproducibility between the two groups (P > 0.05).

Conclusions

Single‐pole position seems to be more comfortable and can reduce dose coverage to heart. Both devices allow for reproducible setup and acceptable dosimetry.

Chair Heterogeneity Index: Describing the dose heterogeneity inside the tumor volume where there is a boost volume

In this report, Chair Heterogeneity Index (CHI) was introduced to assess the dose heterogeneity inside the target with a boost volume. CHI was defined by dividing (V_Rx − V_Dl) by (V_Dm − V_Dh): V_Rx, V_Dl, V_Dm and V_Dh were four points selected from the target cumulative dose volume histogram curve. The effectiveness of CHI was validated by assessing the treatment plans for nasopharyngeal cancer (NPC, 12 cases), breast cancer after breast-conserving-surgery (BC, 10 cases), and stereotactic radiosurgery after whole brain irradiation (SRS, 9 cases). Our results indicate that both CHI and HI of the target can distinguish Volumetric Modulated Arc Therapy (VMAT) from Intensity Modulated Radiation Therapy (IMRT, p < 0.05) while the mean differences in CHI (NPC 1.16, BC 1.19 and SRS 3.3) were larger than those in HI (NPC 0.03, BC 0.02 and SRS 0.02). In addition, CHI of the combination volume (the target minus the boost) were statistically higher in VMAT than IMRT in all three kinds of cancer. In conclusion, CHI was effective in assessing the dose heterogeneity inside a target containing a boost volume.

Critical appraisal of the role of volumetric modulated arc therapy in the radiation therapy management of breast cancer

Background

The aim of this review is the critical appraisal of the current use of volumetric modulated arc therapy for the radiation therapy management of breast cancer. Both clinical and treatment planning studies were investigated.

Material and methods

A Pubmed/MEDLINE search of the National Library of Medicine was performed to identify VMAT and breast related articles. After a first order rejection of the irrelevant findings, the remaining articles were grouped according to two main categories: clinical vs. planning studies and to some sub-categories (pointing to significant technical features). Main areas of application, dosimetric and clinical findings as well as areas of innovations were defined.

Results

A total of 131 articles were identified and of these, 67 passed a first order selection. Six studies reported clinical results while 61 treatment dealed with treatment planning investigations. Among the innovation lines, the use of high intensity photon beams (flattening filter free), altered fractionation schemes (simultaneous integrated boost, accelerated partial breast irradiation, single fraction), prone positioning and modification of standard VMAT (use of dynamic trajectories or hybrid VMAT methods) resulted among the main relevant fields of interest. Approximately 10% of the publications reported upon respiratory gating in conjunction with VMAT.

Conclusions

The role of VMAT in the radiation treatment of breast cancer seems to be consolidated in the in-silico arena while still limited evidence and only one phase II trial appeared in literature from the clinical viewpoint. More clinical reports are needed to fully proove the expected dosimetric benefits demonstrated in the planning investigations.

Static beam tomotherapy as an optimisation method in whole-breast radiation therapy (WBRT)

INTRODUCTION

TomoTherapy (Accuray, Sunnyvale, CA) has recently introduced a static form of tomotherapy: TomoDirect™ (TD). This study aimed to evaluate TD against a contemporary intensity modulated radiation therapy (IMRT) alternative through comparison of target and organ at risk (OAR) doses in breast cancer cases. A secondary objective was to evaluate planning efficiency by measuring optimisation times.

METHODS

Treatment plans of 27 whole-breast radiation therapy (WBRT) patients optimised with a tangential hybrid IMRT technique were replanned using TD. Parameters included a dynamic field width of 2.5 cm, a pitch of 0.251 and a modulation factor of 2.000; 50 Gy in 25 fractions was prescribed and planning time recorded. The planning metrics used in analysis were ICRU based, with the mean PTV minimum (D99 ) used as the point of comparison.

RESULTS

Both modalities met ICRU50 target heterogeneity objectives (TD D99 = 48.0 Gy vs. IMRT = 48.1 Gy, P = 0.26; TD D1 = 53.5 Gy vs. IMRT = 53.0 Gy, P = 0.02; Homogeneity index TD = 0.11 vs. IMRT = 0.10, P = 0.03), with TD plans generating higher median doses (TD D50 = 51.1 Gy vs. IMRT = 50.9 Gy, P = 0.03). No significant difference was found in prescription dose coverage (TD V50 = 85.5% vs. IMRT = 82.0%, P = 0.09). TD plans produced a statistically significant reduction in V5 ipsilateral lung doses (TD V5 = 23.2% vs. IMRT = 27.2%, P = 0.04), while other queried OARs remained comparable (TD ipsilateral lung V20 = 13.2% vs. IMRT = 14.6%, P = 0.30; TD heart V5 = 2.7% vs. IMRT = 2.8%, P = 0.47; TD heart V10 = 1.7% vs. IMRT = 1.8%, P = 0.44). TD reduced planning time considerably (TD = 9.8 m vs. IMRT = 27.6 m, P < 0.01), saving an average planning time of 17.8 min per patient.

CONCLUSIONS

TD represents a suitable WBRT treatment approach both in terms of plan quality metrics and planning efficiency.

Advantages of a technique using two 50 degree arcs in simultaneous integrated boost radiotherapy for left-sidebreast cancer

This study evaluated radiotherapy techniques with 15 cases for simultaneous integrated boost to treat whole left breast and tumor bed following breast conserving surgery. Treatment plans were generated using three techniques: volumetric modulated arc therapy (VMAT) with a partial arc of 190° (1ARC), VMAT with two tangential mini-arcs of 50° each (2TARC) and intensity modulated radiation therapy with four fixed angle fields (4IMRT). Dosimetric parameters for the whole breast (Target), the boost tumor bed (Boost), and surrounding normal organs were compared. Chair Index (CHI) was introduced to evaluate the dose homogeneity in Target given the two levels of prescription dose. The dose coverage in Target was better in 1ARC and 2TARC than that in 4IMRT. The mean CHI in 1ARC (2.47) and 2TARC (2.62) were higher than that in 4IMRT (1.71, p < 0.05), and this indicated the dose homogeneity of Target was better in 1ARC and 2TARC than that in 4IMRT. The mean doses to right lung, and contralateral breast in 4IMRT were lower than those in 2TARC but the differences between them were small. 2TARC was better than 4IMRT with respect to the dose to ipsilateral lung and heart. Overall, 2TARC was optimal among three techniques.

A study of the dosimetric characteristics between different fixed-field IMRT and VMAT in early-stage primary mediastinal B-cell lymphoma

This analysis was designed to compare dosimetric parameters among different fixed-field intensity-modulated radiation therapy (IMRT) solutions and volumetric-modulated arc therapy (VMAT) to identify which can achieve the lowest risk of organs at risk (OARs) and treatment delivery efficiently. A total of 16 patients (8 male and 8 female) with early-stage primary mediastinal large B-cell lymphoma (PMBCL) were enrolled with planned gross tumor volume (PGTV) 45 Gy and planning target volume (PTV) 40 Gy. Four different plans were generated: 5-, 7, 9-field IMRT, and VMAT. The dose distributions for PGTV and PTV OARs (lungs, left ventricle, heart, thyroid gland, and breasts) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. Mean conformity index (CI) and homogeneity index (HI) for PGTV in 5F-, 7F-, 9F-IMRT, and VMAT were 1.01 and 1.10, 1.01 and 1.10, 1.01 and 1.10, and 1.01 and 1.11 (p = 0.963 and 0.843), whereas these 2 indices for PTV were 1.04 and 1.22, 1.03 and 1.19, 1.03 and 1.17, and 1.08 and 1.14 (p = 0.964 and 0.969), respectively. D_mean (Gy), V4 (%), D50 (Gy), and D80 (Gy) to the left and right breasts increased by 0.7 Gy and 0.1 Gy, 6.8% and 7.7%, 0.9 Gy and 1.7 Gy, and 1.0 Gy and 1.5 Gy in VMAT, respectively. The 9-beam IMRT plan had the highest MUs (25,762.4 MUs) and the longest treatment delivery time (10.7 minutes); whereas, the VMAT had the lowest MUs (13,345.0) and the shortest treatment delivery time (5.9 minutes). Seven- and 9-field IMRT and VMAT provide improved tumor coverage compared with 5F-IMRT, whereas VMAT shows higher treatment delivery efficiency than IMRT technique. Seven- and 9-field IMRT slightly reduce the low dose radiation exposure of breasts compared with VMAT technique. The 7- and 9-field IMRT and VMAT techniques both can be safely and efficiently delivered to patients with PMBCL.

Which simultaneous-integrated boost (SIB) intensity-modulated radiotherapy (IMRT) technique is dosimetrically superior in the treatment of breast cancer; volumetric-modulated arc therapy (VMAT) or fixed field (ff) IMRT?

Background and purpose

To determine which concomitant boost technique is dosimetrically superior in the treatment of breast cancer; volumetric-modulated arc therapy (VMAT) or fixed field intensity-modulated radiotherapy (ff-IMRT).

Materials and methods

In total, 30 breast patients were re-planned with both VMAT and fixed field concomitant boost intensity-modulated radiotherapy techniques. A hybrid technique was used delivering 80% of the dose through tangential beams and 20% through an integrated boost. A two-tailed t-test sample for means was used to compare the dosimetric differences between the techniques.

Results

Maximum dose was statistically lower for VMAT; 103·2 versus 103·7% for ff-IMRT along with statistically lower V2 Gy doses to the contralateral lung (0·7 versus 1·6%) and heart for both left- (19·0%/22·6%), and right- (5·5%/8·8%) sided patients, respectively. ff-IMRT boasted significantly lower ipsilateral lung V20, V18 and V10 Gy (7·9/8·6/13·1 versus 8·1/8·8/13·4%) than VMAT, respectively. No differences were found with minimum coverage, mean dose and V5 Gy to all organs at risk (OARs).

Conclusion

VMAT and ff-IMRT techniques demonstrate excellent target coverage and OAR sparing facilitated by the hybrid planning technique and deep inspiration breath hold. There is no obvious dosimetrically superior option between the two techniques. Reduced treatment times with VMAT make it more desirable to implement clinically.

Dosimetric comparison of simultaneous integrated boost with whole-breast irradiation for early breast cancer

Purpose

The purpose of this study was to identify a more suitable boost plan for simultaneously integrated boost scheme in patients with breast cancer by comparing among 3 types of whole-breast irradiation plus tumor bed boost plans.

Methods

Twenty patients who received radiotherapy following breast-conserving surgery for early breast cancer were enrolled in this study. We performed 1 type of electron plan (E1P plan) and 2 types of 3-dimensional conformal plans using a photon (P3P and P5P plans). The dosimetric parameters for the heart, total lung and the target volume between the 3 treatment types were compared.

Results

For the tumor bed, the difference in the mean dose between the 3 plans was maximally 0.1 Gy. For normal breast parenchyma, the difference in the mean dose between the 3 plans was maximally 1.1 Gy. In the dose range over the prescribed dose of 51 Gy, V₅₅ and V₆₀ in the E1P plan were lower than those in the P3P and P5P plans, which indicated that the E1P plan was more suitable than the P3P and P5P plans. In case of the heart and total lung, the values of clinically important parameters were slightly higher in the E1P plan than in the P3P and P5P plans. However, these differences were less than 2%.

Conclusion

We observed that a simple electron plan for tumor bed boost is preferable over multi-field photon plans in terms of the target volume coverage and normal tissue sparing.

Intensity modulated radiation therapy for breast cancer: current perspectives

Background

Owing to highly conformed dose distribution, intensity modulated radiation therapy (IMRT) has the potential to improve treatment results of radiotherapy (RT). Postoperative RT is a standard adjuvant treatment in conservative treatment of breast cancer (BC). The aim of this review is to analyze available evidence from randomized controlled trials (RCTs) on IMRT in BC, particularly in terms of reduction of side effects.

Methods

A literature search of the bibliographic database PubMed, from January 1990 through November 2016, was performed. Only RCTs published in English were included.

Results

Ten articles reporting data from 5 RCTs fulfilled the selection criteria and were included in our review. Three out of 5 studies enrolled only selected patients in terms of increased risk of toxicity. Three studies compared IMRT with standard tangential RT. One study compared the results of IMRT in the supine versus the prone position, and one study compared standard treatment with accelerated partial breast IMRT. Three studies reported reduced acute and/or late toxicity using IMRT compared with standard RT. No study reported improved quality of life.

Conclusion

IMRT seems able to reduce toxicity in selected patients treated with postoperative RT for BC. Further analyses are needed to better define patients who are candidates for this treatment modality.

Small-arc volumetric-modulated arc therapy: A new approach that is superior to fixed-field IMRT in optimizing dosimetric and treatment-relevant parameters for patients undergoing whole-breast irradiation following breast-conserving surgery

Volumetric-modulated arc therapy (VMAT) is considered to deliver a better dose distribution and to shorten treatment time. There is a lack of research regarding breast irradiation after breast-conserving surgery (BCS) using VMAT with prone positioning. We developed a new small-arc VMAT methodology and compared it to conventional (fixed-field) intensity-modulated radiation therapy (IMRT) in the dosimetric and treatment relevant parameters for breast cancer patients in the prone position.Ten early-stage breast cancer patients were included in this exploratory study. All patients underwent computed tomography (CT) simulation scan in the prone position and for each patient, IMRT and VMAT plans were generated using the Monaco planning system. Two symmetrical partial arcs were applied in the VMAT plans. The angle ranges of the 2 arcs were set to approximately 60° to 100° and 220° to 260°, with small adjustments to maximize target coverage, while minimizing lung and heart exposure. The IMRT plans used 4 fixed fields. Prescribed doses were 50 Gy in 25 fractions. The target coverage, homogeneity, conformity, dose to organs at risk (OAR), treatment time, and monitor units (MU) were evaluated.Higher median conformal index (CI) and lower homogeneity index (HI) of the planning target volume (PTV) were respectively observed in VMAT and plans group (CI, 95% vs 91%; HI, 0.09 vs 0.12; P < 0.001). The volumes of ipsilateral lung receiving 30, 20, 10, and 5 Gy were lower for VMAT (P < 0.01), being 10%, 14.9%, 25.9%, and 44.9%, respectively, compared to 11.79%, 17.32%, 30.27%, and 50.58% for the IMRT plans. The mean lung dose was also reduced from 10.6 ± 1.8 to 9.6 ± 1.4 Gy (P = 0.001). The volumes of the heart receiving 30 and 40 Gy were similar for the 2 methods. In addition, the median treatment time (161 vs 412 seconds; P < 0.001) and the mean MU (713 vs 878; P < 0.001) were lower for VMAT.Small-arc VMAT plan improved CI and HI for the target, spared the dose of lung, and reduced treatment time and MU, compared to IMRT. It is a more promising irradiation technique for post-BCS radiotherapy.