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| ORIGINAL ARTICLE |
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| Year : 2021 | Volume
: 7
| Issue : 1 | Page : 57-63 |
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Volumetric-modulated arc therapy versus intensity-modulated radiotherapy on the left-sided chest wall and locoregional nodes irradiation in treating postmastectomy breast cancer patients: A comparative dosimetric analysis
Mukesh Kumar Zope1, Deepali Bhaskar Patil1, Umra Fatima2, Satyendra Sinha2, Abhijeet Mandal3, Shekhar Kumar Keshri2
1 Department of Medical Physics, State Cancer Institute, Indira Gandhi Institute of Medical Sciences, Patna, Bihar, India
2 Department of Radiation Oncology, Paras HMRI Hospital, Patna, Bihar, India
3 Department of Radiotherapy and Radiation Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India
| Date of Submission | 09-Jan-2021 |
| Date of Acceptance | 15-Mar-2021 |
| Date of Web Publication | 28-Jun-2021 |
Correspondence Address:
Mukesh Kumar Zope
Department of Medical Physics, State Cancer Institute, Indira Gandhi Institute of Medical Sciences, Patna - 800 014, Bihar
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/jigims.jigims_6_21
Purpose: This study was aimed to compare the suitable treatment plan for left-sided chest wall, regional node irradiation by the intensity-modulated radiotherapy (IMRT), and volumetric-modulated arc therapy (VMAT).
Materials and Methods: Fifteen patients' computed tomography data set was import into the treatment planning system (Oncentra). Two plans were generated for each patient, the first one using the VMAT technique with two partial arcs and the second one using the IMRT technique with seven coplaner radiation portals using 3D Oncentra TPS with 6 MV photons, step and shoot treatment delivery technique with 80 leaf multileaf collimator, and 1 cm leaf width at the isocenter. The VMAT plans optimized using the collapsed cone (GPU) algorithm and IMRT plans optimized using a collapsed cone algorithm. A hypofractionated prescription dose of 40 Gy/15# was used. The VMAT and IMRT plans compared for Planning Target Volume (PTV) target coverage, homogeneity index (HI), conformity index (CI), and monitor units (MUs) were evaluated. The Organ At Risk (OAR) doses also compared.
Results: A comparable PTV coverage (V95%) and mean PTV doses were observed between VMAT and IMRT plans. The PTV maximum dose was higher within IMRT than the VMAT. We observed a better HI for VMAT plans. For conformity index (CI) both plan showed no significant difference. MU values of VMAT are higher than the IMRT treatment in this study. However, VMAT plans show significantly better right lung, heart, and larynx sparing when compared to the IMRT plans. No significant difference was observed in both groups of plan for the right breast and spinal cord. The maximum dose for the left humerus head was compared for both groups of plans.
Conclusions: VMAT is dosimetrically superior to the IMRT for irradiation of left-sided chest wall and regional nodes patients in terms of target coverage and OAR sparing.
Keywords: Conformity Index, Homogeneity Index, intensity-modulated radiotherapy, volumetric modulated arc therapy
How to cite this article:
Zope MK, Patil DB, Fatima U, Sinha S, Mandal A, Keshri SK. Volumetric-modulated arc therapy versus intensity-modulated radiotherapy on the left-sided chest wall and locoregional nodes irradiation in treating postmastectomy breast cancer patients: A comparative dosimetric analysis. J Indira Gandhi Inst Med Sci 2021;7:57-63 |
How to cite this URL:
Zope MK, Patil DB, Fatima U, Sinha S, Mandal A, Keshri SK. Volumetric-modulated arc therapy versus intensity-modulated radiotherapy on the left-sided chest wall and locoregional nodes irradiation in treating postmastectomy breast cancer patients: A comparative dosimetric analysis. J Indira Gandhi Inst Med Sci [serial online] 2021 [cited 2021 Sep 24];7:57-63. Available from: http://www.jigims.co.in/text.asp?2021/7/1/57/318927 |
| Introduction | |  |
Breast cancer is the most common cancer and is the leading cause of cancer deaths in women worldwide.[1] Most early-stage patients can be treated with breast-conserving surgery followed by systemic treatment and adjuvant radiotherapy. Few patients undergo mastectomy followed by adjuvant chemotherapy and radiotherapy as per recommendations.[2] Large prospective trials and a meta-analysis have shown that adjuvant radiotherapy of the chest wall improves local control and survival in node-positive breast cancer patients after mastectomy.[3] The adjuvant radiotherapy of the left-sided chest wall is commonly delivered by three-dimensional conformal radiotherapy with a field-in-field technique.[4] Increased cardiac morbidity and mortality have been seen in patients treated with radiotherapy for left-sided breast cancer compared to right-sided breast cancer, due to the higher cardiac dose.[5]
Volumetric-modulated arc therapy (VMAT) belongs to rotational intensity-modulated radiotherapy (IMRT), and several works of literature have shown that VMAT can produce dose distribution similar superior to IMRT. VMAT can achieve highly conformal dose distribution by simultaneously changing the position of the MLC, dose rate, and gantry speed during patient treatment. The important advantage of VMAT when compared to IMRT was a substantial reduction in treatment time. In the treatment of left-sided chest wall patients, VMAT treatment improves target coverage and homogeneity index (HI) and reduces high dose in ipsilateral lung and heart but increases low dose region for contralateral organs compared to three-dimensional conformal radiotherapy.[4]
In this study, we compared the dosimetric parameters between VMAT and IMRT in a patient with left-sided chest wall with locoregional lymph nodes irradiation.
| Materials and Methods | | |
Retrospectively, fifteen consecutive left breast cancer patients were planned for adjuvant radiotherapy to the left-sided chest wall with the inclusion of mastectomy scar and locoregional lymph nodes. All patients were immobilized while free breathing using a thermoplastic mold in supine position over a breast board fixed on the couch with both arms extended above their head onto the armrests, the patient's head turned to the right side. Radio-opaque wires were used to mark the mastectomy scar.
Planning computed tomography (CT) images were acquired from the level of the mandible to the lung base on a CT scanner (Siemens dual slice Somatom Spirit CT) with a slice thickness of 2.5 mm. All the images were exported to the 3D-Oncentra treatment planning system (version 4.3) for contouring and treatment planning.
The clinical target volume (CTV) includes the left chest wall, mastectomy scar, supraclavicular region, and other regional lymph nodes. The CTV was extended by 5 mm circumferentially to create the planning target volume (PTV) and anterior margin kept underneath the skin. The OARs such as ipsilateral and both lung, heart, left humeral head, esophagus, and opposite breast were contoured as per the Radiation Therapy Oncology Group recommendation.
Planning
The VMAT plans consisted of two coplanar partial arcs (2P-VMAT), one with clockwise direction from 315° to 175° and the other arc counter-clockwise direction from 160° to 325° used. The 2P-VMAT plans were optimized using a collapsed cone (GPU) algorithm.
For all IMRT plans generated using seven fields (312°, 307°, 315°, 150°, 135°, 125°, and 40°) and optimized using the collapsed cone algorithm using 6 MV photons with a dose rate of 600 monitor unit (MU). A hypofractionated prescription dose of 40 Gy in 15 fractions was used for all patients. We observed PTV coverage that VMAT and IMRT plan V95% (cc) PTV was 985.20 cc (781.29 cc ± 1258.37 cc) for VMAT versus 980.95 cc (774.43 ± 1260.73) for IMR T; P = 0.286 is considered as a nonsignificant difference.
Plan evaluation
The VMAT and IMRT plans were compared and evaluated for PTV Target Coverage, HI, conformity index (CI) and number of MU, doses of the left lung (V5 Gy <50%, V10 Gy <30%, V20 Gy <20%, and V30 Gy <10%), heart (V5 Gy <50%, V10 Gy <20%, V20 Gy <15%, and V30 Gy <20%), right lung (V5 Gy <10% and mean), maximum dose to the spinal cord, right breast, left humeral head, and mean dose to the larynx.
DVH parameters were studied in details.
ICRU 83 is used to evaluate target volume coverage and its conformity.
The HI was calculated according to the following formula:
HI = (D2% − D98%)/D50%,
where, D2%, D98%, and D50% = dose to 2%, 50%, and 98% of the volume, respectively.
Values of HI closer to 0 indicate greater dose homogeneity within the volume of PTV, while large
values indicate more heterogeneous dose distribution.
The conformity index (CI) was calculated according to the following formula:
CI = VRI/TV
where, VRI: Volume of the prescription reference isodose, TV: Total PTV Volume.
The closer the values of CI close to 1.0, the better the dose conformity.
Statistical analysis
A Wilcoxon signed-rank test was used to compare the VMAT and IMRT techniques in respect of dose to the target and normal structures with significance declared for a P < 0.05 [Table 1]. | Table 1: Comparison of volumetric modulated therapy and intensity-modulated radiotherapy in terms of planning target volume parameters
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| Results | | |
Dose distributions between IMRT and VMAT plans are presented in [Figure 1], and dose-volume histograms are shown in [Figure 2]. | Figure 1: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to monitor unit
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 | Figure 2: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to homogeneity index
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PTV
We observed PTV coverage that VMAT and IMRT plan V95% (cc) PTV was 985.20 cc (781.29 cc ± 1258.37 cc) for VMAT versus 980.95 cc (774.43 ± 1260.73) for IMR Our observed PTV coverage V95% (cc) was 985.20 cc (781.29 cc ± 1258.37 cc)for VMAT versus 980.95 cc (774.43 ± 1260.73) for IMRT; (P = 0.286 no significant difference) and mean PTV was 40.75 (40.53 ± 40.94) for VMAT versus 40.82 (40.42 ± 41.07) for IMRT; P = 0.286 is considered as a nonsignificant difference. Maximum dose to PTV was 45.18 Gy (44.38 ± 45.77) for VMAT versus 45.50 Gy (44.45 ± 46.34) for IMRT; P = 0.016 is considered as a significant difference. In comparison between two plans, the PTV maximum dose was higher with IMRT than in the VMAT as shown in [Table 1].
HI PTV was 0.14 (0.12 ± 0.17) for VMAT versus 0.15 (0.14 ± 0.18) for IMRT; (P = 0.021) significant difference for both techniques means that HI was better in VMAT plans as shown in [Figure 1] and [Table 1]. CI PTV was 0.97 (0.95 ± 0.99) for VMAT versus 0.97 (0.94 ± 0.98) for IMRT; P = 0.286 is considered as a nonsignificant difference for both techniques as shown in [Figure 2] and [Table 1].
MU was 962.48 (775.95 ± 1063.67) in VMAT versus 824.38 (448.90 ± 960.12) in IMRT; P = 0.010 is considered as a significant difference for both techniques. In our study, MU of VMAT is significantly higher than the IMRT techniques as shown in [Figure 3] and [Table 1]. | Figure 3: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to conformity index
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Left lung
However, the OARs sparing was better with the VMAT plans when compared to the IMRT plans. The V5 Gy (47.93 VMAT vs. 53.70 IMRT), V10 Gy (31.61 VMAT vs. 33.24 IMRT), V20 Gy (20.74 VMAT vs. 23.74 IMRT), and V30 Gy (11.17 VMAT vs. 13.93 IMRT) for the left lung were significantly higher for the IMRT plans when compared to VMAT plans (P = 0.005, P = 0.013, P = 0.009, and P = 0.005) as shown [Table 2] and [Figure 4]. | Table 2: Comparison of volumetric modulated therapy and intensity-modulated radiotherapy plans in terms of OARs (left lung and heart)
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 | Figure 4: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to left lung
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Heart
Similarly, the V5 Gy (35.66VMAT vs. 45.29 IMRT), V10 Gy (18.07 VMAT vs. 24.26 IMRT), and V20 Gy (9.724 VMAT vs. 15.71 IMRT) are higher for the IMRT plans when compared to VMAT plans (P = 0.005, P = 0.005, and P = 0.005 respectively). Whereas V30 Gy (5.41 VMAT vs. 7.90 IMRT), showed. No significant difference between two plans (P = 0.074) [Table 2] and [Figure 5]. | Figure 5: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to heart
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Right lung and larynx
For right lung, V5 Gy (8.49 VMAT vs. 9.84 IMRT), mean (2.32 VMAT vs. 2.68 IMRT) and for larynx, mean (14.04 VMAT vs. 14.49 IMRT) (P = 0.005, P = 0.022, and P = 0.028 respectively) were considered as significant difference between VMAT plans and IMRT plans [Table 3] and [Figure 6]. | Table 3: Plan comparison parameters, mean values, and range for volumetric modulated therapy and intensity-modulated radiotherapy for this study in terms of OARs
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 | Figure 6: Comparison between volumetric modulated arc therapy and intensity-modulated radiotherapy plans according to OARs
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Spinal cord and right breast
[Table 3] and [Figure 6] show the maximum dose for spinal cord (6.85 VMAT vs. 7.11 IMRT); P = 0.221 was considered as a nonsignificant difference and maximum dose for right breast (2.51 VMAT vs. 2.68 IMRT); P = 0.083 was considered as a nonsignificant difference.
Left humeral head
[Table 3] and Graph 6 show the maximum dose for left humerus head (35.95 VMAT vs. 36.79 IMRT); P = 0.007 was a significant difference between the VMAT plans and IMRT plans.
| Discussion | | |
In the context of breast cancer, critical OAR includes contralateral breast, lungs, and heart. VMAT techniques that use full rotation arc around the patients are likely to increase radiation received by these structures, although the lower isodose. However, even this low dose can be detrimental to the heart and the normal breast in the long term. It is for this reason that in our VMAT techniques, we used only partial arc, with tight control overdose deposition to vulnerable OARS.
Literature suggests the importance of radiation therapy in controlling the locoregional disease for the overall survival of breast cancer patients.[6],[7] Simultaneously, there is literature evidence of some detriment by radiation to critical OARs such as the heart and contralateral breast.[7] It is, therefore, crucial to plan carcinoma breast patients meticulously by radiotherapy to attain good locoregional control and spare side effects.
In this study, we reported of dosimetric comparison between two techniques including two partial arc – VMAT and IMRT of ten consecutive breast cancer patients. It can shape the dose to the concave target on the left-sided chest wall including locoregional lymph node. An example of the dose distribution and cumulative dose-volume histogram of volumetric modulated arc therapy and intensity-modulated radiotherapy plans are shown in [Figure 7] and [Figure 8] for left-sided chest wall adjuvant radiation. | Figure 7: An example of dose distribution between intensity-modulated radiotherapy and volumetric modulated arc therapy left-sided chest wall treatment plans
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 | Figure 8: An example of the cumulative dose-volume histogram of volumetric modulated arc therapy and intensity-modulated radiotherapy plans for left-sided chest wall
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In the present study, statistically significant improvement was noted inhomogeneity index with VMAT plans compared to IMRT plans. However, no significant difference was noted in the conformity index. The results of our study demonstrate that VMAT techniques have lower doses to mention OARs as compared to IMRT. VMAT plans consistently scored significantly lower values for all the evaluated parameters for the left lung in terms of V5 Gy (P = 0.005), V10 Gy (P = 0.013), V20 Gy (P = 0.009), and V30 Gy (P = 0.005) and for the heart V5 Gy (P = 0.005), V10 Gy (P = 0.005), and V20 Gy (P = 0.005) except for V30 Gy (P = 0.07).
VMAT has been revealed to deliver lower doses to the ipsilateral breast and lung and offer better dose coverage. VMAT plans consistently scored significantly lower values for all the evaluated parameters for the left lung conformity than a 3D-CRT technique for partial breast irradiation patients.[8] In our study, VMAT plans as compared to IMRT showed lower values in all parameters of left lung dose.
Significantly lower values of mean doses with VMAT also have been observed for right lung larynx and maximum dose for the left humeral head.
Previous studies showed that there was high long-term risk of developing the secondary malignancy of contralateral breast, and the mean dose to the contralateral breast was 3.2 Gy with RapidArc. In our study, a slightly the lower mean dose of 2.5 Gy was observed with VMAT, which may be the results of different dose calculation algorithms or inhomogeneity correction in the two treatment planning systems.[9],[10],[11]
In this study, nonsignificant difference was found between two groups of the plan for the maximum dose of the contralateral breast (P = 0.08) and spinal cord (P = 0.2).
| Conclusions | | |
VMAT is dosimetrically superior to the IMRT for left-sided chest wall and regional nodes patie nts owing to its comparable PTV coverage and better sparing of heart, lung, left humerus head, and larynx.
Acknowledgment
The author would like to thank Prof. (Dr.) Rajesh Kumar Singh, Head Radiation Oncology Department of State Cancer Institute, IGIMS, Patna, India, and extend gratitude to the department at Paras HMRI Hospital, Patna.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
[Table 1], [Table 2], [Table 3]
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