Irradiation du cancer du sein : incertitudes liées aux mouvements respiratoires et au repositionnement

Modeling and prediction of set‑up errors in breast cancer image‑guided radiotherapy using the Gaussian mixture model

The aim of the present study was to develop a prediction model for set-up error distribution in breast cancer image-guided radiotherapy (IGRT) using a Gaussian mixture model (GMM). To achieve this, the image-guided set-up errors data of 80 patients with breast cancer were selected, and the GMM was used to develop the set-up errors distribution prediction model. The predicted error center points, covariance and probability were calculated and compared with the planning target volume (PTV) margin formula. A total of 1,200 sets of set-up errors in IGRT for breast cancer were collected. The results of the Gaussian model parameters showed that the set-up errors were mainly in the direction of µ1-µ4 center points. All the raw errors in the lateral, longitudinal and vertical directions were -6.30-4.60, -5.40-1.47 and -2.70-1.70 mm, respectively. According to the probability of each center, the set-up error was most likely to shift in the µ1 direction, reaching 0.53. The set-up errors of the other three centers, µ2, µ3 and µ4, were 0.11, 0.34 and 0.12, respectively. According to the covariance parameters of the GMM, the maximum statistical standard deviation of the set-up errors reached 29.06. In conclusion, the results of the present study demonstrated that the GMM can be used to quantitatively describe and predict the distribution of set-up errors in IGRT for breast cancer, and these findings could be useful as a reference for set-up error control and tumor PTV expansion in breast cancer radiotherapy without routine, daily IGRT.

Geometric and Dosimetric Evaluation of Deep Learning-Based Automatic Delineation on CBCT-Synthesized CT and Planning CT for Breast Cancer Adaptive Radiotherapy: A Multi-Institutional Study

Purpose

We developed a deep learning model to achieve automatic multitarget delineation on planning CT (pCT) and synthetic CT (sCT) images generated from cone-beam CT (CBCT) images. The geometric and dosimetric impact of the model was evaluated for breast cancer adaptive radiation therapy.

Methods

We retrospectively analyzed 1,127 patients treated with radiotherapy after breast-conserving surgery from two medical institutions. The CBCT images for patient setup acquired utilizing breath-hold guided by optical surface monitoring system were used to generate sCT with a generative adversarial network. Organs at risk (OARs), clinical target volume (CTV), and tumor bed (TB) were delineated automatically with a 3D U-Net model on pCT and sCT images. The geometric accuracy of the model was evaluated with metrics, including Dice similarity coefficient (DSC) and 95% Hausdorff distance (HD95). Dosimetric evaluation was performed by quick dose recalculation on sCT images relying on gamma analysis and dose-volume histogram (DVH) parameters. The relationship between ΔD95, ΔV95 and DSC-CTV was assessed to quantify the clinical impact of the geometric changes of CTV.

Results

The ranges of DSC and HD95 were 0.73–0.97 and 2.22–9.36 mm for pCT, 0.63–0.95 and 2.30–19.57 mm for sCT from institution A, 0.70–0.97 and 2.10–11.43 mm for pCT from institution B, respectively. The quality of sCT was excellent with an average mean absolute error (MAE) of 71.58 ± 8.78 HU. The mean gamma pass rate (3%/3 mm criterion) was 91.46 ± 4.63%. DSC-CTV down to 0.65 accounted for a variation of more than 6% of V95 and 3 Gy of D95. DSC-CTV up to 0.80 accounted for a variation of less than 4% of V95 and 2 Gy of D95. The mean ΔD90/ΔD95 of CTV and TB were less than 2Gy/4Gy, 4Gy/5Gy for all the patients. The cardiac dose difference in left breast cancer cases was larger than that in right breast cancer cases.

Conclusions

The accurate multitarget delineation is achievable on pCT and sCT via deep learning. The results show that dose distribution needs to be considered to evaluate the clinical impact of geometric variations during breast cancer radiotherapy.

Target motion management in breast cancer radiation therapy

Background

Over the last two decades, breast cancer remains the main cause of cancer deaths in women. To treat this type of cancer, radiation therapy (RT) has proved to be efficient. RT for breast cancer is, however, challenged by intrafractional motion caused by respiration. The problem is more severe for the left-sided breast cancer due to the proximity to the heart as an organ-at-risk. While particle therapy results in superior dose characteristics than conventional RT, due to the physics of particle interactions in the body, particle therapy is more sensitive to target motion.

Conclusions

This review highlights current and emerging strategies for the management of intrafractional target motion in breast cancer treatment with an emphasis on particle therapy, as a modern RT technique. There are major challenges associated with transferring real-time motion monitoring technologies from photon to particles beams. Surface imaging would be the dominant imaging modality for real-time intrafractional motion monitoring for breast cancer. The magnetic resonance imaging (MRI) guidance and ultra high dose rate (FLASH)-RT seem to be state-of-the-art approaches to deal with 4D RT for breast cancer.

[Siriade 2.0: An e-learning platform for radiation oncology contouring]

PURPOSE

In 2008, the French national society of radiation oncology (SFRO) and the association for radiation oncology continued education (AFCOR) created Siriade, an e-learning website dedicated to contouring.

MATERIAL AND METHODS

Between 2015 and 2017, this platform was updated using the latest digital online tools available. Two main sections were needed: a theoretical part and another section of online workshops.

RESULTS

Teaching courses are available as online commented videos, available on demand. The practical section of the website is an online contouring workshop that automatically generates a report quantifying the quality of the user's delineation compared with the experts'.

CONCLUSION

Siriade 2.0 is an innovating digital tool for radiation oncology initial and continuous education.

Translucent poly(vinyl alcohol) cryogel dosimeters for simultaneous dose buildup and monitoring during chest wall radiation therapy

Chest wall radiation therapy treatment delivery was monitored using a 5 mm thick radiochromic poly(vinyl alcohol) cryogel that also provided buildup material. The cryogels were used to detect positioning errors and measure the impact of shifts for a chest wall treatment that was delivered to a RANDO phantom. The phantom was shifted by ± 2, ± 3, and ± 5 mm from the planned position in the anterior/posterior (A/P) direction; these shifts represent setup errors and the uncertainty associated with lung filling during breath-hold. The two-dimensional absolute dose distributions measured in the cryogel at the planned position were compared with the distributions at all shifts from this position using gamma analysis (3%/3 mm, 10% threshold). For shifts of ± 2, ± 3, and ± 5 mm the passing rates ranged from 94.3% to 95.6%, 74.0% to 78.8%, and 17.5% to 22.5%, respectively. These results are consistent with the same gamma analysis performed on dose planes calculated in the middle of the cryogel and on the phantom surface using our treatment plan-ning system, which ranged from 94.3% to 95.0%, 76.8% to 77.9%, and 23.5% to 24.3%, respectively. The Pinnacle dose planes were then scaled empirically and compared to the cryogel measurements. Using the same gamma metric, the pass rates ranged from 97.0% to 98.4%. The results of this study suggest that cryogels may be used as both a buildup material and to evaluate errors in chest wall treat-ment positioning during deep-inspiration breath-hold delivery. The cryogels are sensitive to A/P chest wall shifts of less than 3 mm, which potentially allows for the detection of clinically relevant errors.

[Respiratory synchronization and breast radiotherapy]

Adjuvant radiation therapy following breast cancer surgery continues to improve locoregional control and overall survival. But the success of highly targeted-conformal radiotherapy such as intensity-modulated techniques, can be compromised by respiratory motion. The intrafraction motion can potentially result in significant under- or overdose, and also expose organs at risk. This article summarizes the respiratory motion and its effects on imaging, dose calculation and dose delivery by radiotherapy for breast cancer. We will review the methods of respiratory synchronization available for breast radiotherapy to minimize the respiratory impact and to spare organs such as heart and lung.

Impact of breathing on post-mastectomy radiotherapy: a dosimetric comparison between intensity-modulated radiotherapy and 3D tangential radiotherapy

Purpose

To quantify the effect of breathing motion on post-mastectomy radiotherapy with three-dimensional (3D) tangents and intensity-modulated radiotherapy (IMRT)

Materials and methods

Patients trained for breath-hold underwent routine free breathing (FB) computed tomography (CT) simulation for radiotherapy as well as additional CT scans with breath held at the end of normal inspiration (NI scan) and expiration (NE scan) for study. The FB scan was used to develop both tangents and IMRT plans. To simulate breathing, each plan was copied and applied on NI and NE scans. The respiratory parameters of the patients as well as the dosimetric data with both the plans were analysed.

Results

Breathing motion resulted in mean fall in target coverage (V95) with IMRT by more than 5% when compared with tangents, and this effect significantly correlated with higher tidal volume. There was also a decrease in the mean target minimal dose by 20–25% with IMRT when compared with 10–12% with tangents, attributable to breathing motion. However, the cardiac dose crossed the limit (V25<10%) with breathing in the 3D tangents plan.

Conclusions

Dosimetric coverage of the chest wall is sensitive to breathing motion for the IMRT technique when compared with standard tangents, especially in patients with large tidal volume.

Quantifying intra- and inter-fractional motion in breast radiotherapy

Introduction

The magnitude of intra- and inter-fractional variation in the set up of breast cancer patients treated with tangential megavoltage photon beams was investigated using an electronic portal imaging device (EPID).

Methods

Daily cine-EPID images were captured during delivery of the tangential fields for ten breast cancer patients treated in the supine position. Measurements collected from each image included the central lung distance (CLD), central flash distance (CFD), superior axial measurement (SAM) and the inferior axial measurement (IAM). The variation of motion within a fraction (intra-fraction) and the variation between fractions (inter-fraction) was analysed to quantify set up variation and motion due to respiration.

Results

Altogether 3775 EPID images were collected from 10 patients. The effect of respiratory motion during treatment was <0.1 cm standard deviation (SD) in the anterior–posterior (AP) direction. The inter-fraction movement caused by variations in daily set up was larger at 0.28 cm SD in the AP direction. Superior–inferior (SI) variation was more difficult to summarise and proved unreliable as the measurements were taken to an ambiguous point on the images. It was difficult to discern true SI movement from that implicated by AP movement.

Conclusion

There is minimal intra-fractional chest wall motion due to respiration during treatment. Inter-fractional variation was larger, however, on average it remained within departmental tolerance (0.5 cm) for set up variations. This review of our current breast technique provides confidence in the feasibility of utilising advanced treatment techniques (field-in-field, intensity modulated radiotherapy or volumetric modulated arc therapy) following a review of the current imaging protocol.

Set-up uncertainty during breast radiotherapy. Image-guided radiotherapy for patients with initial extensive variation

PURPOSE

The aim of this work was to establish a customized strategy for image-guided radiotherapy during whole breast irradiation. Risk factors associated with extensive errors were assessed.

METHODS AND MATERIALS

A series of 176 consecutive breasts in 174 patients were retrospectively assessed. Electronic portal images from 914 medial and 807 lateral directions were reviewed. On the basis of the chest wall, the deviations between the simulation and each treatment were measured. The systematic (Σ) and random error (σ) of population, and the planning target volume (PTV) margin (2 Σ + 0.7σ) were calculated for each direction. Extensive set-up errors were defined as the fraction over the PTV margins in any direction. For extensive set-up errors, χ(2) tests and logistic regression analyses were conducted.

RESULTS

The medial and lateral PTV margins for the right-left, superior-inferior, and anterior-posterior axes and the rotation of collimator were 2.6 and 2.4 mm, 4.6 and 4.6 mm, and 3.1 and 3.3 mm and 2.8 and 2.9 ° and cut-off values for extensive errors were 3, 5, and 4 mm and 3 °, respectively. In χ(2) tests, tumor in upper outer quadrant (p = 0.012) and chest wall thickness ≥ 2.0 cm (p = 0.003) for medial portals and age group (p = 0.036) for lateral portals were associated with extensive errors. In multivariate tests, the extensive error on the initial fraction had a high probability of extensive set-up errors in both medial (OR = 4.26, p < 0.001) and lateral portals (OR = 3.07, p < 0.001).

CONCLUSION

In terms of the set-up uncertainty during breast irradiation, patients with extensive error in the initial treatment should be closely observed with serial image-guided radiotherapy.

[Gated radiotherapy in breast cancer]

Postoperative radiotherapy is a cornerstone of the local treatment in breast cancer. It has been proved with high level of evidence that it decreases local relapse and improves survival of patients. However, radiotherapy comes with healthy tissue toxicity, heart and lung in particular. With constant improvement of radiation techniques, several methods have been developed to decrease the dose to the heart and the lungs. Sometimes, respiratory maneuvers can help, due to patient's anatomy: the radiotherapy is gated with patient's breath. The Deep Inspiration Breath Hold technique is the most popular and there are several ways to perform it. This note will describe the different systems with published data in order to help the radiation oncologist in the daily practice.

[Organs at risk and target volumes: definition for conformal radiation therapy in breast cancer]

Adjuvant radiotherapy is a standard component of breast cancer treatment. The addition of radiotherapy after breast conserving surgery has been shown to reduce local recurrence rate and improve long-term survival. Accurate delineation of target volumes and organs at risk is crucial to the quality of treatment planning and delivered accomplished with innovate technologies in radiation therapy. This allows the radiation beam to be shaped specifically to each individual patient's anatomy. Target volumes include the mammary gland and surgical bed in case of breast conserving surgery, the chest wall in case of mastectomy, and if indicated, regional lymph nodes (axillary, supra- and infraclavicular and internal mammary). Organs at risk include lungs, thyroid, brachial plexus, heart, spinal cord and oesophagus. The aim of this article is to encourage the use of conformal treatment and delineation of target volumes and organs at risk and to describe specifically the definition of these volumes.

[Cyberknife robotic stereotactic radiotherapy: technical aspects and recent developments]

Cyberknife (Accuray Inc. Sunnyvale, USA) stereotactic body radiation therapy (SBRT) involves the delivery of a small number of large doses of radiation to a target volume using continuously evolving advanced technology. It has emerged as a novel treatment modality for cancer and modified some concepts of cancer treatment. It is indicated in early-stage primary cancer, sometimes as an alternative to surgery. It is also indicated for patients with oligometastatic disease who have relatively long survival with the aim to optimize disease control with a good quality of life. Although there remain some uncertainties regarding the radiobiology of hypofractionation, local control and tolerance have been promising. Indications are increasing under strict quality assurance programs worldwide and prospective clinical evaluation.

Examination of geometric and dosimetric accuracies of gated step-and-shoot intensity modulated radiation therapy

Due to the complicated technical nature of gated radiation therapy, electronic and mechanical limitations may affect the precision of delivery. The purpose of this study is to investigate the geometric and dosimetric accuracies of gated step-and-shoot intensity modulated radiation treatments (SS-IMRT). Unique segmental MLC plans are designed, which allow quantitative testing of the gating process. Both ungated and gated deliveries are investigated for different dose sizes, dose rates, and gating window times using a commercial treatment system (Varian Trilogy) together with a respiratory gating system [Varian Real-Time Position Management system]. Radiographic film measurements are used to study the geometric accuracy, where it is found that with both ungated and gated SS-IMRT deliveries the MLC leaf divergence away from planned is less than or equal to the MLC specified leaf tolerance value for all leafs (leaf tolerance being settable from 0.5-5 mm). Nevertheless, due to the MLC controller design, failure to define a specific leaf tolerance value suitable to the SS-IMRT plan can lead to undesired geometric effects, such as leaf motion of up to the maximum 5 mm leaf tolerance value occurring after the beam is turned on. In this case, gating may be advantageous over the ungated case, as it allows more time for the MLC to reach the intended leaf configuration. The dosimetric precision of gated SS-IMRT is investigated using ionization chamber methods. Compared with the ungated case, it is found that gating generally leads to increased dosimetric errors due to the interruption of the "overshoot phenomena." With gating the average timing deviation for intermediate segments is found to be 27 ms, compared to 18 ms for the ungated case. For a plan delivered at 600 MU/min this would correspond to an average segment dose error of approximately 0.27 MU and approximately 0.18 MU for gated and ungated deliveries, respectively. The maximum dosimetric errors for individual intermediate segments are found to deviate by up to approximately 0.64 MU from their planned value when delivered at 600 MU/min using gating, this compares to only approximately 0.32 MU for the ungated case.

Bénéfice et risques potentiels de l'association du trastuzumab à la chimiothérapie et à la radiothérapie dans le cancer du sein non métastatique

Trastuzumab (Herceptin) is the first humanised monoclonal antibody targeting the HER2 antigen in breast cancer. HER2 receptor has been individualised 20 years ago. During the past 10 years, trastuzumab administration has radically modified the prognosis of the patients that are treated for HER2 positive breast cancer. Its efficacy has been demonstrated in the metastatic and adjuvant settings. While, trastuzumab based-regimens became the standard of care in the treatment of HER2/neu positive breast cancer, the optimal combination (concurrently or sequentially) to chemotherapy and radiation therapy is still unknown. Indeed, while the concurrent administration of trastuzumab and anthracyclines is not recommended because of a high risk of cardiac toxicity, there is no published data on the best sequence of trastuzumab and radiation therapy administration, particularly when internal mammary chain is involved. The benefit/risk ratio of the concurrent and sequential administration of trastuzumab with chemotherapy and radiation therapy will be discussed in this review.

Bonnes pratiques pour la radiothérapie asservie à la respiration

Respiration-gated radiotherapy offers a significant potential for improvement in the irradiation of tumor sites affected by respiratory motion such as lung, breast and liver tumors. An increased conformality of irradiation fields leading to decreased complications rates of organs at risk (lung, heart...) is expected. Respiratory gating is in line with the need for improved precision required by radiotherapy techniques such as 3D conformal radiotherapy or intensity modulated radiotherapy. Reduction of respiratory motion can be achieved by using either breath-hold techniques or respiration synchronized gating techniques. Breath-hold techniques can be achieved with active techniques, in which airflow of the patient is temporarily blocked by a valve, or passive techniques, in which the patient voluntarily holds his/her breath. Synchronized gating techniques use external devices to predict the phase of the respiration cycle while the patient breaths freely. This work summarizes the different experiences of the centers of the STIC 2003 project. It describes the different techniques, gives an overview of the literature and proposes a practice based on our experience.