Comparison of plan quality and robustness using VMAT and IMRT for breast cancer

Chuou Yin; Juan Deng; Guojian Mei; Hao Cheng; Yingying He; Jiang Liu

doi:10.1515/phys-2024-0026

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Comparison of plan quality and robustness using VMAT and IMRT for breast cancer

Chuou Yin , Juan Deng , Guojian Mei , Hao Cheng , Yingying He and Jiang Liu

Published/Copyright: May 15, 2024

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From the journal Open Physics Volume 22 Issue 1

Abstract

To evaluate the plan quality and robustness of volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) for breast cancer, 50 patients, including 25 patients who received radiotherapy after breast-conserving surgery (BCR) and 25 patients who received postmastectomy radiotherapy (PRT), were selected for this study. Nominal VMAT and IMRT plans were generated for each patient on Eclipse treatment planning system (version 15.6). The dosimetric metrics, dose distribution, gamma passing rate, and delivery time were compared. In addition, 12 uncertainty plans with plan isocenter uncertainty and CT density uncertainty were recalculated based on the nominal plans for each patient. The dose volume histogram (DVH) band width (DVHBW) was adopted to quantify the plan robustness of the nominal plans for the perturbed scenarios in this study. For BCR, the dosimetric metrics except planning target volume (PTV) conformal index (CI) and ipsilateral lung V ₅ were not statistically different for IMRT and VMAT plans. PTV CI of VMAT plans was better than that of IMRT plans (VMAT: 0.923 ± 0.024, IMRT: 0.855 ± 0.032, p = 0.003). The ipsilateral lung V ₅ of VMAT plan was higher than that of IMRT plan (VMAT: 42.4% ± 2.8%, IMRT: 40.5% ± 4.0%, p = 0.045). The VMAT plans save more than 1.20 min compared to the IMRT plans (VMAT: 0.87 min, IMRT: 2.08 min, p < 0.001). The gamma passing rates of VMAT plans were better than those of IMRT plans (3 mm/3%, VMAT: 99.7% ± 0.2%, IMRT: 99.4% ± 0.4%, p < 0.001; 2 mm/2%, VMAT: 97.2% ± 1.0%, IMRT: 96.9% ± 0.6%, p = 0.108). For PRT, the dosimetric metrics of VMAT plans, including PTV D _mean, homogeneity index (HI), CI, and D _max of spinal cord, were significantly better than those of IMRT plans. The VMAT plans save more than 45% time compared with IMRT plans (VMAT: 1.54 min, IMRT: 2.81 min, p < 0.001). The difference in gamma passing rates between VMAT plans and IMRT plans was not statistically significant. For the plan robustness, the DVHBW of VMAT plans and IMRT plans for BCR were 2.09% ± 0.23% and 2.98% ± 0.40%, respectively (p < 0.05). For PRT, the DVHBW of VMAT plans was significantly better than those of IMRT plans (VMAT: 3.05% ± 0.26%, IMRT: 3.57% ± 0.27%, p < 0.05). The results show that the dosimetric metrics of VMAT plans were comparable to those of IMRT plans. More importantly, the VMAT plans had excited dose distribution and fast execution efficiency. The plan robustness of VMAT plans were superior.

Keywords: robustness; delivery time; dosimetric metrics; breast cancer; volumetric modulated arc therapy; halcyon

1 Introduction

There were 19.3 million new cancer cases and about 9.96 million new deaths worldwide in 2020 [1], says the World Health Organization. The severity of cancer treatment has brought major challenges to global public health. In 2020, 2.3 million women worldwide were diagnosed with breast cancer, and 685,000 women died from breast cancer. Breast cancer has become one of the most important factors threatening women’s health [2].

Radiation therapy (RT) plays a very important role in the treatment of breast cancer. For early-stage breast cancer, RT can prevent women from having to undergo mastectomy. For late-stage cancer, RT can reduce the risk of cancer recurrence, even if a mastectomy has been performed. For advanced breast cancer, RT can reduce the likelihood of dying from the disease in some cases [3]. Both intensity modulated radiation therapy (IMRT) [4,5] and volumetric modulated arc therapy (VMAT) [6,7,8] are the main radiotherapy techniques for breast cancer. Different radiation techniques have a great impact on the dose distribution of the target volume and the organs at risk (OARs). There are also some differences in treatment time due to different radiation techniques. Whether using IMRT or VMAT technology, the ultimate goal is to give the target as high a dose as possible and protect the adjacent OARs as much as possible.

Previous studies have demonstrated that IMRT is beneficial in reducing the volume of the affected lung that is irradiated at low dose, which can reduce the chance of radiation pneumonitis caused by RT [9,10]. In addition, the mean dose of the heart is reduced. VMAT is conducive in improving the uniformity and dose conformity of the target volume [6], reducing the number of monitor units (MUs) in the radiotherapy plan, and shortening the treatment time of patients.

The Halcyon accelerator is a new generation of smart radiotherapy system of Varian, equipped with a double-layer multi-leaf collimator (MLC) that greatly improves radiation leakage and has a high level of safety [11,12]. The misaligned design of the double-layer MLC can better conform the target and provide better protection of the OARs. In addition, the dose rate of Halcyon accelerator reaches 800 MU/min, which can greatly improve the efficiency of treatment.

The present study will explore the clinical application of IMRT and VMAT in breast cancer radiotherapy based on the Eclipse treatment planning system and the Halcyon V2.0 linear accelerator. Several tools will be introduced to assess the plan quality and plan robustness for breast cancer.

2 Materials and methods

2.1 Patients selection

This retrospective study included 50 patients with breast cancer who have undergone radiotherapy. 25 of them were treated with radiotherapy after breast-conserving surgery (BCR), named as group BCR, and the other 25 were treated with postmastectomy radiation therapy (PRT), named as group PRT.

2.2 CT scanning

CT scans were performed using Somatom Confidence CT (Siemens, Germany). The upper boundary was the mandible, lower boundary was the lower border of the liver, and the slice thickness was 3 mm. The scanning current and voltage were 400 mAs and 120 kV, respectively. Field of View was 300 mm.

2.3 Contouring

Clinical target volume (CTV) and OARs were defined according to the Guideline of target delineation and treatment planning of adjuvant radiotherapy for breast cancer issued by the National Cancer Center & National Cancer Quality Control Center, where the prescription dose has been standardized [13]. CTV included breast/chest wall, supraclavicular, internal mammary, and axillary lymph nodes (CTV of group BCR only included breast/chest wall). Planning target volume (PTV) included CTV and a 5 mm margin based on CTV. OARs, including ipsilateral lung, heart, spinal cord, and contralateral lung, were delineated.

2.4 Treatment planning

Plans based on IMRT or VMAT were created for all patients using the Eclipse treatment planning system (Version 15.6). The calculation algorithm is anisotropic analytical algorithm (AAA) and the calculation grid is 2.5 mm. The IMRT plans used six fields with the gantry angle of 300°, 315°, 330°, 100°, 115°,and 130° for the left-sided BCR and 215°, 230°, 245°, 45°, 60°, and 75° for the right-sided BCR. For the group PRT based on IMRT, seven fields were used with the gantry angle of 300°, 315°, 330°, 10°, 100°, 115°, and 130° for the left-sided PRT and 215°, 230°, 245°, 350°, 45°, 60°, and 75° for the right-sided PRT. All the VMAT plans used two semi-arcs for all patients. For the left-sided BCR or PRT, the gantry was rotated from 300° to 130° clockwise and then from 130° to 300° counterclockwise. For the right-sided BCR or PRT, the gantry was rotated from 215° to 75° clockwise and then from 75° to 215° counterclockwise. The total prescribed dose was 50 Gy in 25 fractions for all patients.

During the planning design process, in order to limit the range of motion of the MLC and protect the affected lung and heart, an auxiliary structure will be delineated. The range of the auxiliary structure is shown in Figure 1, the left-right directions and the head-feet directions of the auxiliary structure do not exceed the range of the affected lung, the anterior and posterior directions are bounded by 3 cm from the target volume, and the posterior boundary does not exceed the range of the affected lung. OARs around the target volume are protected by limiting the beam fluence through auxiliary structure. In addition, for the BCR patients, the target volume is located on the chest wall, close to the heart. The target volume will move with breathing during the treatment process. In order to avoid missed radiation in the target caused by breathing, the out-diffusion of the fluence along the chest wall will be carried out, and the range of the external expansion is 1 cm. The out-diffusion of the fluence is shown in Figure 2.

Figure 1

Schematic diagram of the auxiliary structure.

Figure 2

Out-diffusion of fluence.

All treatment plans should meet the following optimization objectives: the volume that PTV received the prescription dose more than 95% of PTV (PTV V _50Gy ≥ 95%) and at most 5% of PTV received a maximum of 107% of the prescription dose (PTV V _53.5Gy ≤ 5%). For the OARs, the specific optimization objectives are shown in Table 1. The maximum dose rate of Halcyon accelerator is 800 MUs per minute.

Table 1

Optimization objectives of OARs in the plans

Optimization objectives	Group BCR	Group PRT
Ipsilateral lung
V _5Gy	≤45%	≤50–55%
V _20Gy	≤20%	≤25%
D _mean	≤900 cGy	≤1,200 cGy
Heart
V _5Gy	≤20%(R) ≤30%(L)	≤25%(R) ≤35%(L)
D _mean	≤400 cGy(R) ≤600 cGy(L)	≤500 cGy(R) ≤800 cGy(L)
Spinal cord
D _max	≤1,500 cGy	≤3,000 cGy
Contralateral lung
V _5Gy	≤20%	≤25%

Abbreviation: BCR: radiotherapy after breast-conserving surgery; PRT: postmastectomy RT; V _xGy: the volume that a structure received xGy as a percentage of the volume of the structure; D _mean: mean dose; *R: right-sided breast cancer; *L: left-sided breast cancer.

2.5 Evaluation

2.5.1 Dose volume histogram (DVH) curves

DVH curves for all regions of interest were calculated on the same coordinate. The nominal doses and perturbed doses are displayed in this study.

2.5.2 Dosimetric parameters

The comparison between IMRT and VMAT plans on dosimetric parameters was performed when the endpoint in this study was plan quality. The primary evaluation indices are shown in Table 2. In addition to the parameters mentioned in Table 2, the PTV conformal index (CI) and homogeneity index (HI) recommended by ICRU report 83 [14] was introduced in this study.

Table 2

Details of the evaluation indices in the plans

Structure	Evaluation metrics
PTV	V _50Gy/D _98%/D _50%/D _2%/D _mean
Ipsilateral lung	V _5Gy/V _20Gy/D _mean
Heart	D _mean/V _5Gy
Spinal cord	D _max
Contralateral lung	V _5Gy

The PTV CI is defined as formula (1).

(1) CI = V PT V,ref 2 V PTV × V ref ,

where V PTV is the volume of the PTV; V ref is the volume of the reference isodose, namely, the prescription dose curve; V PTV , ref means the volume of PTV covered by the reference isodose. The value of CI is usually less than 1. The closer the CI is to 1, the better the overlap between PTV and the reference isodose.

The PTV HI is defined as formula (2).

(2) HI = D 2 % − D 98 % D 50 % ,

where D _2%, D _98%, and D _50% is the dose received by 2, 98, and 50% volume of PTV, respectively. The lower HI means the better uniformity for PTV.

2.5.3 Delivery time

The quality assurance mode based on the Halcyon accelerator was used to simulate the irradiation of two plans for each case to obtain the delivery time of the patient during radiotherapy when the end point of the study was the delivery time.

2.5.4 Gamma passing rate

All plans were tested with the gamma passing rate using the ArcCheck 3D matrix verification system based on the SNC Patient gamma passing rate analysis software of SUN NUCLEAR corporation. The evaluation metrics were gamma passing rate under the conditions of 3 mm/3% and 2 mm/2%, respectively.

2.6 Plan robustness

According to the previous study, the crucial factors causing the difference between the actual dose distribution and the planned dose distribution are plan isocenter shift and CT density uncertainty [15,16,17]. Paganetti [18] suggested setting a plan isocenter shift of 5 mm and CT density uncertainties of ±2% to calculate the perturbed dose. Liu et al. [19] set a value of 3 mm isocenter uncertainty and ±3% CT density uncertainty for the treatment of distal esophageal carcinoma.

114 patients who had finished radiotherapy for breast cancer in our center were retrospectively selected; the data about plan isocenter shift of 2,352 treatments for these patients are shown in Figure 3. 95% confidence interval for the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) directions are (−0.09, 0.31), (−0.11, 0.44), and (−0.10, 0.43), respectively. Thus, the plan isocenter shifts were set to 0.31 cm for AP direction, 0.44 cm for SI direction, and 0.43 cm for LR direction in this study. Finally, all perturbed doses were calculated with 12 scenarios. The details of these 12 scenarios taken into account are shown in Table 3.

Figure 3

Plan isocenter shift distances in the anterior-posterior, superior-inferior, and left-right directions of 2,352 treatments of the 114 breast cancer patients.

Table 3

Plan isocenter uncertainty and CT density uncertainty with 12 scenarios

	1	2	3	4	5	6	7	8	9	10	11	12
AP, cm	0.31	0.31	−0.31	−0.31	0	0	0	0	0	0	0	0
SI, cm	0	0	0	0	0.44	0.44	−0.44	−0.44	0	0	0	0
LR, cm	0	0	0	0	0	0	0	0	0.43	0.43	−0.43	−0.43
CT, %	2	−2	2	−2	2	−2	2	−2	2	−2	2	−2

DVH band width (DVHBW) was adopted to quantify the plan robustness in this study, the difference between the perturbed scenario and nominal scenario were calculated. The DVHBW can be defined as formula (3) [20,21].

(3) λ = D 95 % best − D 95 % worst D P × 100 % ,

where λ is the quantification parameter for plan robustness, D 95 % best , and D 95 % worst represent the best PTV coverage and worst PTV coverage in the scenario, respectively. D P is the prescription dose of PTV, namely, 50 Gy.

2.7 Statistical analysis

The paired t test was performed using SPSS Statistics version 21 software. The p value of less than 0.05 (p < 0.05) was considered statistically significant.

3 Results

3.1 DVH curves

Figure 4 shows the results obtained using two typical cases. As can be seen in Figure 4a (BCR), the V _50Gy of PTV for both IMRT and VMAT are 98%, but the homogeneity of the VMAT plan is better than that of the IMRT plan. For the ipsilateral lung, V _20Gy, V _30Gy, and mean dose of VMAT plan are better than those of IMRT plan, and V _5Gy is slightly higher. The doses to heart and contralateral lung of the VMAT plan are higher than those of the IMRT plan, but they are far less than the dose limitation. As can be seen in Figure 4b (PRT), the V _50Gy of PTV for VMAT plan and IMRT plan are 99.1 and 99.0%, respectively. The homogeneity of the VMAT plan is better than that of the IMRT plan. For the ipsilateral lung, the volume of VMAT plan is higher than that of IMRT plan when the dose is less than 1,000 cGy. However, the opposite result is found when the dose is between 1,000 and 3,000 cGy. In the high-dose region (>3,000 cGy), the DVH curves of the two plans almost overlapped. The doses to heart, contralateral lung, and spinal cord in VMAT plan are higher than those in IMRT plan, but they are lower than their dose limitations.

Figure 4

Dose Volume histogram curves for (a) BCR plan and (b) PRT plan. (Note: * is VMAT plan, Ip is the abbreviation of ipsilateral, and Co is the abbreviation of contralateral).

3.2 Dosimetric parameters

As can be seen from Table 4, the major parameters of PTV, including PTV, D_95%, D _mean, and HI, are not statistically different for IMRT plan and VMAT plan (p > 0.05). PTV CI of VMAT plan is better than that of IMRT plan, and the difference is statistically significant (p < 0.05). For OARs, the ipsilateral lung V ₂₀ and D _mean, and heart D _mean and V ₅ of VMAT plan are slightly higher than those of IMRT plan, the difference is not statistically significant (p > 0.05). The V ₅ of ipsilateral lung and contralateral lung in IMRT plan are about 1.9 and 4.9% lower than those in VMAT plan, respectively (p < 0.05).

Table 4

Parameter statistics of the radiotherapy plan after BCR

Group	Structure	Parameter/unit	IMRT	VMAT	p-value
BCR	PTV	D_95%/cGy	5054.7 ± 19.3	5051.5 ± 19.5	0.704
		D _mean/cGy	5187.7 ± 17.7	5187.9 ± 24.2	0.979
		HI/–	0.062 ± 0.010	0.058 ± 0.009	0.280
		CI/–	0.855 ± 0.032	0.923 ± 0.024	0.003
	Ipsilateral lung	V ₂₀/%	15.0 ± 2.9%	15.6 ± 2.6%	0.208
		V ₅/%	40.5 ± 4.0%	42.4 ± 2.8%	0.045
		D _mean/cGy	922.6 ± 110.7	934.5 ± 93.6	0.453
	Heart	D _mean/cGy	224.3 ± 117.8	252.8 ± 102.7	0.349
		V ₅/%	9.1 ± 8.4%	10.1 ± 4.8%	0.597
	Contralateral lung	V ₅/%	2.5 ± 4.6%	7.4 ± 5.6%	0.015

As can be seen from Table 5, PTV D_95% is not statistically different for IMRT plan and VMAT plan (p = 0.151). However, PTV CI and PTV HI of VMAT plan are better than those of IMRT plan, and the difference is statistically significant (p < 0.001). For OARs, the ipsilateral lung V ₂₀, V ₅, and D _mean and heart D _mean and V ₅ are not statistically different. The D _max of spinal cord of VMAT plan is lower than that of IMRT plan (p < 0.05).

Table 5

Parameter statistics of the PRT plan

Group	Structure	Parameter/unit	IMRT	VMAT	p-value
PRT	PTV	D_95%/cGy	5029.4 ± 20.6	5034.1 ± 21.0	0.151
		D _mean/cGy	5190.4 ± 15.3	5204.0 ± 25.3	<0.001
		HI/–	0.072 ± 0.010	0.067 ± 0.010	<0.001
		CI/–	0.763 ± 0.046	0.799 ± 0.055	<0.001
	Ipsilateral lung	V ₂₀/%	18.5% ± 2.4%	18.3% ± 2.1%	0.327
		V ₅/%	49.5% ± 3.7%	49.6% ± 4.3%	0.606
		D _mean/cGy	1107.6 ± 108.8	1115.6 ± 109.6	0.052
	Heart	D _mean/cGy	371.5 ± 161.9	374.7 ± 153.3	0.523
		V ₅/%	15.0% ± 6.8%	14.2% ± 5.4%	0.263
	Spinal cord	D _max	2580.9 ± 829.5	2502.2 ± 804.4	0.047
	Contralateral lung	V ₅/%	3.5% ± 3.3%	4.0% ± 3.5%	0.130

3.3 Delivery time

As can be seen in Figure 5, the average delivery time of all VMAT plans is obviously lower than that of IMRT plans, the difference is statistically significant (VMAT: 1.20 min, IMRT: 2.45 min, p < 0.001). For the BCR plans, 1.15 min are saved using VMAT compared with using IMRT, and the difference is statistically significant (VMAT: 0.87 min, IMRT: 2.08 min, p < 0.001). For the PRT plans, the VMAT plans save more than 45% time compared with IMRT plans (VMAT: 1.54 min, IMRT: 2.81 min, p < 0.001).

Figure 5

The delivery time of all plans on Halcyon accelerator.

3.4 Gamma passing rate

Figure 6 illustrates the gamma passing rate using ArcCheck three-dimensional verification system and SNC Patient gamma analysis software under the condition of 3 mm/3% or 2 mm/2%. On the whole, all gamma passing rates are better than 95.4%, the lowest data of 3 mm/3% is 97.9 in PRT plans using IMRT. Under the condition of 3 mm/3%, gamma passing rate for all plans is 99.5 ± 0.4%, ranging from 97.9% to 100%. Under the condition of 2 mm/2%, gamma passing rate for all plans is 97.2 ± 0.9%, ranging from 95.4 to 99.2%. Specifically, for BCR plans, gamma passing rate of VMAT plans is 99.7 ± 0.2 and 99.4 ± 0.4% for IMRT plans with the condition of 3 mm/3%, the difference between VMAT and IMRT is statistically significant (p < 0.001). 97.2 ± 1.0 and 96.9 ± 0.6% are the data for VMAT plans and IMRT plans under the condition of 2 mm/2%, respectively (p = 0.108). For PRT plans, VMAT plans and IMRT plans with 3 mm/3% are 99.6 ± 0.3 and 99.4 ± 0.6%, respectively, the difference is not statistically significant (p = 0.287). 97.3 ± 1.0 and 97.2 ± 0.8% are the data for VMAT plans and IMRT plans under the condition of 2 mm/2%, respectively. The difference is not statistically significant (p = 0.704).

Figure 6

Statistics of gamma passing rate for all plans.

3.5 Plan robustness

Previous study had demonstrated that the plan isocenter shift and CT density uncertainty will cause the difference between the actual dose distribution and the planned dose distribution [14,15,16,17,18]. In this study, plan robustness was evaluated in both IMRT plans and VMAT plans with 12 scenarios. The plan robustness quantification parameter λ was applied, and λ is displayed in Figures 7 and 8.

Figure 7

DVHBW (λ) of IMRT and VMAT plans for BCR.

Figure 8

DVHBW (λ) of IMRT and VMAT plans for PRT.

As shown in Figure 7, the λ of VMAT plans is significantly better than those of IMRT plans in BCR group (p < 0.05). Specifically, the λ of VMAT plans is 2.09 ± 0.23%, ranging from 1.67 to 2.56%. And the λ of IMRT plans is 2.98 ± 0.40%, ranging from 2.18 to 3.98%.

As shown in Figure 8, the λ of VMAT plans is significantly better than those of IMRT plans in BCR group (p < 0.05). Specifically, the λ of VMAT plans is 3.05 ± 0.26%, ranging from 2.63 to 3.66%. And the λ of IMRT plans is 3.57 ± 0.27%, ranging from 3.08 to 4.13%.

4 Discussion

Radiotherapy is one of the important methods of tumor treatment, about 70% of tumor patients receive radiotherapy during the treatment process, about 40% of malignant tumors can be cured by radiotherapy [22,23,24]. According to the statistics, breast cancer has become the first major cancer disease, and it is the main factor that threatens women’s health in the world [1,2]. In order to compare the plan robustness, plan quality, delivery time, and 3-Dimensional gamma passing rate between VMAT plans and IMRT plans for breast cancer, 25 patients, who received BCR, and another 25 patients, who received PRT, were selected for this study.

The same patient setup uncertainties and CT density uncertainty were applied for both VMAT and IMRT in this study. DVHBW was used to compare the plan robustness of VMAT plans and IMRT plans. The DVHBW of VMAT plans are 2.09% for BCR and 3.05% for PRT, which are statistically better than those of IMRT plans (BCR: 2.09% for VMAT vs 2.98% for IMRT, p < 0.05; PRT: 3.05% for VMAT vs 3.57% for IMRT, p < 0.05). Our results provide compelling evidence that VMAT is more capable of dealing with uncertainties. The perturbed dose distribution is closer to the nominal dose distribution.

When focusing on the plan quality, the traditional DVH metric methods is a convenient method for quantitatively evaluating the plan quality. Our results show that the PTV coverage differences between IMRT and VMAT are negligible. The CI is more elevated in VMAT plans than in IMRT plans (BCR: 0.923 vs 0.855, p < 0.05; PRT: 0.799 vs 0.763, p < 0.05). Most notably, there are no significant dose differences for most OARs between two beam delivery modalities. VMAT plans are more elevated than IMRT plans for both BCR and PRT when the plan quality is the endpoint of this study. Previous studies have demonstrated that effective protection of the heart and both lungs is beneficial to reduce the side effects such as ischemic heart disease and radiation pneumonitis caused by radiotherapy [25,26,27,28].

In terms of treatment efficiency, the VMAT plans provide more quick treatment than IMRT plans (VMAT: 1.20 min, IMRT: 2.45 min, p < 0.001). The gamma passing rates under the condition of 3 mm/3% or 2 mm/2% were introduced to evaluate the difference between the planned dose distribution and the actual dose distribution. On the whole, the gamma passing rates of all plans is 97.2 ± 0.9% with 2 mm/2% criteria and 99.5 ± 0.4% with 3 mm/3% criteria. The gamma passing rates of all plans are better than the recommended value of AAPM TG-119 report [29] and AAPM TG-218 report [30]. VMAT plans have a higher gamma passing rates than IMRT plans (VMAT: 98.4 ± 1.4%, IMRT: 98.2 ± 1.3%, p = 0.015).

Some limitations are worth focusing, the positional variation and anatomical variation caused by breathing are needed to be considered. In addition, the CT density uncertainty and plan isocenter shift data used in this study were based on the clinical data from our department. In the following study, further research is needed for optimizing the plan robustness to improve the robustness in the scenarios of the CT density uncertainty and plan isocenter shift. Another point to note is that the dose calculation inaccuracy of the target volume was around 3%, and the dose calculation error of the OARs was mostly within 5% when using the AAA algorithm in other published studies [31,32]. In clinical work, the deviation of AAA algorithm in dose calculation in inhomogeneous media should be fully considered to provide a more realistic and reasonable treatment plan.

5 Conclusion

In our study, the robustness, the plan quality, the treatment time, and the gamma passing rate were investigated by comparing VMAT and IMRT for breast cancer. Our results showed that VMAT generated a more robust plan in target volume. Furthermore, VMAT provides a more efficient and more accurate plan without compromising the plan quality. In the following work, the robustness optimization of the treatment plan is our focus direction. The robust optimization considers the range deviation, setup error, and CT value uncertainty. Theoretically, robust optimization will improve the robustness of the plan to better cope with setup errors and CT value uncertainty. In addition, robust optimization would reduce the dose to normal tissues and improve the HI of the target volume.

Acknowledgments

The authors sincerely thank all teachers who helped in the process of this article.

Funding information: This research was supported by the Special Support for Postdoctoral Research Projects in Sichuan Province, No TB2022072; and Special project of Chengdu University of Traditional Chinese Medicine, No XJ2023000101.
Author contributions: Chuou Yin: conceptualization, methodology, validation, data curation, data analysis, visualization, writing – original draft, and writing – review and editing; Juan Deng: design treatment plans; Guojian Mei: review treatment plans; Hao Cheng: delineation and review treatment plans; Yingying He: delineation and review treat-ment plans; and Jiang Liu: supervision. All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Conflict of interest: The authors state no conflict of interest.
Ethical approval: The research related to human use has been complied with all the relevant national regulations, institutional policies and in accordance the tenets of the Helsinki Declaration, and has been approved by the authors' institutional review board or equivalent committee.
Data availability statement: The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Received: 2023-11-27

Revised: 2024-04-03

Accepted: 2024-04-23

Published Online: 2024-05-15

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/phys-2024-0026

Keywords for this article

robustness; delivery time; dosimetric metrics; breast cancer; volumetric modulated arc therapy; halcyon

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