Automated hybrid volumetric modulated arc therapy (HVMAT) for whole-breast irradiation with simultaneous integrated boost to lumpectomy area : A treatment planning study

Dosimetric Evaluation of Three-dimensional Conformal Radiotherapy, RapidArc, and Hybrid RapidArc Radiotherapy Techniques for Left-sided Breast Cancer

OBJECTIVE

This study aimed to assess the irradiation techniques-three-dimensional conformal radiotherapy (3DCRT), RapidArc (RArc), and hybrid RapidArc (h-RArc)-for left-sided breast cancer patients, focusing on dose distribution in the planning target volume (PTV) and organs at risks (OARs).

MATERIALS AND METHODS

This study enrolled 20 patients diagnosed with early-stage left-sided breast cancer. All patients received a prescribed dose of 40.05 Gy in 15 fractions (2.67 Gy per fraction), optimized to achieve 95% dose coverage to 95% of the PTV. The dosimetric variations across the three treatment plans for the 20 patients were examined using a one-way ANOVA test. P <0.05 was regarded as statistically significant.

RESULTS

In the 3DRCT plan, D95% of the PTV was 37.21 ± 0.51 Gy. This value was significantly increased to 39.43 ± 0.27 Gy in the RArc plan (P = 0.001) and to 38.47 ± 0.19 Gy in the h-RArc plan (P = 0.630). The RArc plans demonstrated a superior homogeneity index of 0.12 ± 0.02 compared to both 3DCRT (0.18 ± 0.02) and h-RArc (0.13 ± 0.02). When comparing the increase in monitor units (MUs), h-RArc showed a 62.82% increase over 3D-CRT, whereas demonstrating a 38.05% decrease compared to RArc (P = 0.000).

CONCLUSIONS

h-RArc treatment plans for breast cancer may be recommended due to their superior and consistent PTV dose coverage and sparing of OARs, in comparison to both 3DRCT and RArc plans. These h-RArc plans are characterized by reduced MU and beam on time, as well as a less low volume dose when compared to RArc plans.

Automated single-isocenter stereotactic body radiotherapy for multiple metastases from breast cancer: A case study

Oligometastatic breast cancer patients can today could benefit from a multimodal approach, combining systemic therapy with metastasis-directed treatment using stereotactic body radiotherapy (SBRT). However, the possibility to synchronously treat multiple lesions is still challenging, needing the ability to generate complex dose distributions with steep dose gradients outside the lesions and major sparing of surrounding organs at risk and accurately track and reproduce the patient's position before and during radiation therapy. We report the case of an oligometastatic patient from left breast cancer, which occurred after a full course of whole breast radiotherapy, treated using the potential of modern technology including single-isocenter setup, plan automation, breath-hold technique and surface guided tracking and reproducibility of patient's position before and during radiation therapy. A 44-year-old female patient with a history of left breast cancer, specifically a luminal-B-like invasive ductal carcinoma with Her2 overexpression, was admitted to our department. The patient previously underwent a left mastectomy (pT2N0M0), 4 cycles of adjuvant chemotherapy, adjuvant radiotherapy on the chest wall and lymph nodes drainage, and 5 years of hormonal therapy. A chest wall ultrasound and positron emission tomography revealed the presence of new lesions in the area of the surgical scar from the previous mastectomy, internal mammary, axillary and retropectoral levels. The 3 lesions were simultaneously treated with a mono-isocentric VMAT plan using SBRT technique with a total dose of 30 Gy delivered in 5 fractions. Due to the technical challenges, this treatment was supported by the use of planning automation, breath-hold technique and surface-guided radiation therapy to improve the accuracy of the dose delivery. Two different plans were generated and compared to pursue the best dosimetric result, including a summed plan obtained from 3 individual SBRT plans for each lesion with a separate isocenter placed in each of them (MIP), and a single-isocenter SBRT plan able to treat multiple lesions synchronously (SIP). Because of the advantages in terms of dosimetry and dose delivery efficiency, the patient was successfully treated with the SIP plan. The treatment time was reduced to about 4.5 minutes, allowing the comfortably use of breath-hold technique. After treatment, the condition of the patient was normal, and no toxicities have been observed in follow-up. SBRT with mono isocentric VMAT planning represents the recommended approach to simultaneously treat multiple lesions in close proximity in the thoracic district.

Multi-centre real-world validation of automated treatment planning for breast radiotherapy

PURPOSE

To present the results of the first multi-centre real-world validation of autoplanning for whole breast irradiation after breast-sparing surgery, encompassing high complexity cases (e.g. with a boost or regional lymph nodes) and a wide range of clinical practices.

METHODS

The 24 participating centers each included 10 IMRT/VMAT/Tomotherapy patients, previously treated with a manually generated plan ('manplan'). There were no restrictions regarding case complexity, planning aims, plan evaluation parameters and criteria, fractionation, treatment planning system or treatment machine/technique. In addition to dosimetric comparisons of autoplans with manplans, blinded plan scoring/ranking was conducted by a clinician from the treating center. Autoplanning was performed using a single configuration for all patients in all centres. Deliverability was verified through measurements at delivery units.

RESULTS

Target dosimetry showed comparability, while reductions in OAR dose parameters were 21.4 % for heart Dmean, 16.7 % for ipsilateral lung Dmean, and 101.9 %, 45.5 %, and 35.7 % for contralateral breast D0.03cc, D5% and Dmean, respectively (all p < 0.001). Among the 240 patients included, the clinicians preferred the autoplan for 119 patients, with manplans preferred for 96 cases (p = 0.01). Per centre there were on average 5.0 ± 2.9 (1SD) patients with a preferred autoplan (range [0-10]), compared to 4.0 ± 2.7 with a preferred manplan ([0,9]). No differences were observed regarding deliverability.

CONCLUSION

The automation significantly reduced the hands-on planning workload compared to manual planning, while also achieving an overall superiority. However, fine-tuning of the autoplanning configuration prior to clinical implementation may be necessary in some centres to enhance clinicians' satisfaction with the generated autoplans.

Hybrid Treatment Planning for Chest Wall Irradiation Utilizing Three-Dimensional Conformal Radiotherapy (3DCRT), Intensity-Modulated Radiation Therapy (IMRT), and Volumetric Modulated Arc Therapy (VMAT): A Systematic Review

Novel hybrid approaches for chest wall irradiation show promising outcomes regarding target coverage and sparing organs at risk (OARs). In this systematic review, we compared hybrid volumetric modulated arc therapy (H-VMAT) or hybrid intensity-modulated radiotherapy (H-IMRT) techniques with non-hybrid techniques, such as three-dimensional conformal radiation therapy (3DCRT), field-in-field (FIF), intensity-modulated arc therapy (IMRT), and volumetric modulated arc therapy (VMAT), for breast cancer patients with mastectomy. Our focus was the plan quality and dose distribution to the OARs. Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) checklist, we performed a systematic review and quality appraisal of primary studies evaluating hybrid therapy to the chest wall and the OARs. An extensive online search of PubMed and Scopus databases was conducted using appropriate keywords. The dose to the OARs (lung, heart, and contralateral breast), planning target volume (PTV), homogeneity index (HI), and conformity index (CI) were extracted. The data were then tabulated and compared for the outcomes between modalities among the studies. Nine studies that met the search criteria were selected to evaluate the PTV coverage and dosimetric results of hybrid and non-hybrid techniques. In terms of 95% PTV coverage, among nine reviewed studies, the largest difference between the two techniques was between VMAT (47.6 Gy) and H-VMAT (48.4 Gy); for the conformity index, the largest difference was noted between 3DCRT (0.58) and H-VMAT (0.79). In both cases, differences were statistically significant (P < 0.005). Two studies showed dose homogeneity improvement within the treatment target in H-VMAT (0.15 and 0.07) compared with 3DCRT (0.41 and 0.12), with a P value of <0.001. Two studies did not report on the homogeneity index, and three others observed no statistical difference. Regarding OARs, in the comparison of H-VMAT and VMAT, the largest significant change was in the volume receiving 5 Gy (V5Gy) of the ipsilateral lung and the V10Gy of the contralateral lung. For the ipsilateral lung, V5Gy was 90.7% with VMAT versus 51.45% with H-VMAT. For the contralateral lung, V10Gy was 54.9% with VMAT versus 50.5% with H-VMAT. In six studies, the mean dose of the contralateral breast was lower in hybrid techniques than in single modalities: VMAT (4.2%, 6.0%, 1.9%, 7.1%, 4.57%) versus H-VMAT (1.4%, 3.4%, 1.8%, 3.5%, 2.34%) and IMRT (9.1%) versus H-IMRT (4.69%). Although most studies did not report on monitor units and treatment time, those that included them showed that hybrids had lower monitor units and shorter treatment times. Hybrid techniques in radiotherapy, such as combining two modalities, can indeed facilitate lower doses to OARs for patients with a high risk of toxicities. Prospective clinical studies are needed to determine the outcomes of breast cancer treated with hybrid techniques.

Risk evaluation of secondary malignancies after radiotherapy of breast cancer in light of the continuous development of planning techniques

Secondary cancer risk is a significant concern for women treated with breast radiation therapy due to improved long-term survival rates. We evaluated the potential of new advanced automated planning algorithms together with hybrid techniques to minimize the excess absolute risk (EAR) for secondary cancer in various organs after radiation treatment for early staged breast cancer. Using CT data set of 25 patients, we generated 4 different radiation treatment plans of different complexity, including 3-dimensional conformal radiotherapy (3D-CRT), field-in-field (FinF), hybrid-IMRT (HMRT) and automated hybrid-VMAT (HVMAT) techniques. The organ-equivalent dose (OED) was calculated from differential dose-volume histograms on the basis of the "linear-exponential," "plateau," and "full mechanistic" dose-response models and was used to evaluate the EAR for secondary cancer in the contralateral breast (CB), contralateral lung (CL), and ipsilateral lung (IL). Statistical comparisons of data were performed by a Kruskal-Wallis analysis of variance. The planning objectives were fulfilled with all the planning techniques for both target coverage and organs-at-risk sparing. The differences in EAR for CB, CL and IL secondary tumor induction were not significant among the 4 techniques. For the CB and CL, the mean absolute difference did not reach 1 case of 10000 patient-years. For the IL, the mean absolute difference was up to 5 cases of 10,000 patient-years. In conclusion, the automated HVMAT technique allows an EAR reduction at the level of well-consolidated tangential 3D-CRT or FinF techniques, keeping all the HVMAT dosimetric improvements unchanged. On the basis of this analysis, the adoption of the HVMAT technique poses no increase in EAR and could be considered safe also for younger patients.

Knowledge-based DVH estimation and optimization for breast VMAT plans with and without avoidance sectors

BACKGROUND

To analyze RapidPlan knowledge-based models for DVH estimation of organs at risk from breast cancer VMAT plans presenting arc sectors en-face to the breast with zero dose rate, feature imposed during the optimization phase (avoidance sectors AS).

METHODS

CT datasets of twenty left breast patients in deep-inspiration breath-hold were selected. Two VMAT plans, PartArc and AvoidArc, were manually generated with double arcs from ~ 300 to ~ 160°, with the second having an AS en-face to the breast to avoid contralateral breast and lung direct irradiation. Two RapidPlan models were generated from the two plan sets. The two models were evaluated in a closed loop to assess the model performance on plans where the AS were selected or not in the optimization.

RESULTS

The PartArc plans model estimated DVHs comparable with the original plans. The AvoidArc plans model estimated a DVH pattern with two steps for the contralateral structures when the plan does not contain the AS selected in the optimization phase. This feature produced mean doses of the contralateral breast, averaged over all patients, of 0.4 ± 0.1 Gy, 0.6 ± 0.2 Gy, and 1.1 ± 0.2 Gy for the AvoidArc plan, AvoidArc model estimation, RapidPlan generated plan, respectively. The same figures for the contralateral lung were 0.3 ± 0.1 Gy, 1.6 ± 0.6 Gy, and 1.2 ± 0.5 Gy. The reason was found in the possible incorrect information extracted from the model training plans due to the lack of knowledge about the AS. Conversely, in the case of plans with AS set in the optimization generated with the same AvoidArc model, the estimated and resulting DVHs were comparable. Whenever the AvoidArc model was used to generate DVH estimation for a plan with AS, while the optimization was made on the plan without the AS, the optimizer evidentiated the limitation of a minimum dose rate of 0.2 MU/°, resulting in an increased dose to the contralateral structures respect to the estimation.

CONCLUSIONS

The RapidPlan models for breast planning with VMAT can properly estimate organ at risk DVH. Attention has to be paid to the plan selection and usage for model training in the presence of avoidance sectors.