Adaptive radiation therapy for breast IMRT-simultaneously integrated boost: three-year clinical experience

SurVolT: Surface to Volume conversion Tool. A proof of concept

PURPOSE

To develop SurVolT, a conversion tool able to apply volumetric changes to DICOM Computed Tomography (CT) data using daily surface (obj) data acquired with AlignRT® (VisionRT Ltd.), primarily designed and validated for breast treatments.

MATERIALS AND METHODS

SurVolT proceeds in 4 steps: 1. AlignRT .obj files extraction, 2. Contour deformation where the surface data points are matched to the initial external contour on a Region Of Interest, ROI_match, on which the anatomy is supposed to be unchanged. Then, external contour substitution is performed on the ROI_ttt covering the treated breast area. This is validated on a female torso phantom with a tissue-equivalent bolus mimicking an edema. The Planning Treatment Volume (PTV) contour from the initial CT is also deformed according to the new external contour in the ROI_ttt. 3. Volumetric data estimation according to the new external contour, validated on an anthropomorphic pelvis phantom. 4. Import of new DICOM data into the Treatment Planning System (TPS). Finally, the workflow is applied on a first patient presenting an anatomical change during the treatment.

RESULTS

The validation of step 2 and 3 shows a bolus thickness estimation of 5.8±1.2mm (expected 5 mm) and the non-rigid deformation of initial CT images follows the new external contour at the ROI_ttt bolus site while revealing negligible deformation elsewhere.

CONCLUSION

This first proof of concept introducing a Surface Guided Radiotherapy (SGRT) tool allowing daily surface data to volume conversion is a fundamental step toward SGRT-based adaptive radiotherapy.

Adaptive radiotherapy for breast cancer

Research in the field of local and locoregional breast cancer radiotherapy aims to maintain excellent oncological outcomes while reducing treatment-related toxicity. Adaptive radiotherapy (ART) considers variations in target and organs at risk (OARs) anatomy occurring during the treatment course and integrates these in re-optimized treatment plans. Exploiting ART routinely in clinic may result in smaller target volumes and better OAR sparing, which may lead to reduction of acute as well as late toxicities. In this review MR-guided and CT-guided ART for breast cancer patients according to different clinical scenarios (neoadjuvant and adjuvant partial breast irradiation, whole breast, chest wall and regional nodal irradiation) are reviewed and their advantages as well as challenging aspects discussed.

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.

Quality assurance program and early toxicities in the phase III BONBIS randomized trial evaluating the role of a localized radiation boost in ductal carcinoma in situ

PURPOSE

To describe the quality assurance (QA) program and early toxicities in the phase III randomized trial BONBIS (NCT00907868) on the role of a localized radiation boost in ductal carcinoma in situ (DCIS).

MATERIALS AND METHODS

From November 2008 to July 2014, 2004 patients were randomized in arm A (only whole breast radiotherapy, WBRT) and arm B (WBRT + boost). The QA program involved 44 participant centers that performed the dummy run (DR). Compliance and uniformity of clinical target volume (CTV) delineations, and dose prescription and delivery according to the BONBIS trial radiotherapy guidelines were analyzed. Acute toxicities (during and up to 3 months after radiotherapy completion, NCI-CTCAE v3.0 classification) were evaluated in 1929 patients.

RESULTS

The differences in whole breast CTV (CTV1) and planning target volume (PTV1) were ≤10%, and the differences in boost CTV (CTV2) and PTV (PTV2) were ≥20% compared with the reference DR values; 95% of the prescribed dose encompassed 98.7% and 100% of the median CTV1 and CTV2. Grade ≥2 breast erythema (38.3% vs. 22.4% of grade 2 and 5.4% vs. 2.1% of grade 3, p < 0.001), grade ≥2 dermatitis (2.8% vs. 0.7%, p < 0.001), and grade 2 hyperpigmentation (6.9% vs. 3.6%, p = 0.005) were more frequent in arm B than arm A. No acute lung or cardiac toxicity was observed. Smoking history, large breast size, and large breast CTV were strong predictive factors of grade ≥2 acute skin toxicities.

CONCLUSIONS

The QA program showed deviations in breast and tumor bed delineation. The boost significantly increased acute skin toxicities.

Magnetic Resonance Imaging for Breast Tumor Bed Delineation: Computed Tomography Comparison and Sequence Variation

Purpose

Our purpose was to investigate the interobserver variability in breast tumor bed delineation using magnetic resonance (MR) compared with computed tomography (CT) at baseline and to quantify the change in tumor bed volume between pretreatment and end-of-treatment MR for patients undergoing whole breast radiation therapy.

Methods and Materials

Forty-eight patients with breast cancer planned for whole breast radiation therapy underwent CT and MR (T1, T1 fat-suppression [T1fs], and T2) simulation in the supine treatment position before radiation therapy and MR (T1, T1fs, and T2) at the end of treatment in the same position. Two observers delineated 50 tumor beds on the CT and all MR sequences and assigned cavity visualization scores to the images. The primary endpoint was interobserver variability, measured using the conformity index (CI).

Results

The mean cavity visualization scores at baseline were 3.14 (CT), 3.26 (T1), 3.41 (T1fs), and 3.58 (T2). The mean CIs were 0.65, 0.65, 0.72, and 0.68, respectively. T1fs significantly improved interobserver variability compared with CT, T1, or T2 (P < .001, P < .001, and P = .011, respectively). The CI for T1fs was significantly higher than T1 and T2 at the end of treatment (mean 0.72, 0.64, and 0.66, respectively; P < .001). The mean tumor bed volume on the T1fs sequence decreased from 18 cm³ at baseline to 13 cm³ at the end of treatment (P < .01).

Conclusions

T1fs reduced interobserver variability on both pre- and end-of-treatment scans and measured a reduction in tumor bed volume during whole breast radiation therapy. This rapid sequence could be easily used for adaptive boost or partial breast irradiation, especially on MR linear accelerators.

Adaptive radiation therapy of breast cancer by repeated imaging during irradiation

Breast cancer is the most frequent cancer among females and also a leading cause of cancer related mortality worldwide. A multimodality treatment approach may be utilized for optimal management of patients with combinations of surgery, radiation therapy (RT) and systemic treatment. RT composes an integral part of breast conserving treatment, and is typically used after breast conserving surgery to improve local control. Recent years have witnessed significant improvements in the discipline of radiation oncology which allow for more focused and precise treatment delivery. Adaptive radiation therapy (ART) is among the most important RT techniques which may be utilized for redesigning of treatment plans to account for dynamic changes in tumor size and anatomy during the course of irradiation. In the context of breast cancer, ART may serve as an excellent tool for patients receiving breast irradiation followed by a sequential boost to the tumor bed. Primary benefits of ART include more precise boost localization and potential for improved normal tissue sparing with adapted boost target volumes particularly in the setting of seroma reduction during the course of irradiation. Herein, we provide a concise review of ART for breast cancer in light of the literature.

Actual target coverage after setup verification using surgical clips compared with external skin markers in postoperative breast cancer radiation therapy

PURPOSE

After changing from offline setup verification to online setup verification using external skin markers in breast cancer patients, we noticed an increase in localized acute skin toxicity beneath the markers. Also, in vivo 3-dimensional dose measurements showed deviations between the delivered and the planned dose distributions; therefore, we investigated the accuracy of setup verification using surgical clips in the tumor bed, with a focus on target coverage of whole breast and tumor bed.

METHODS AND MATERIALS

Orthogonal kilovoltage images were acquired before every fraction in 35 breast cancer patients, deriving an online 3-dimensional setup error by matching on external skin markers. In retrospect, a rematch was performed using surgical clips. For 155 fractions (ie, 5-6 fractions/patient), a cone beam computed tomography (CT) scan was available. Analysis concerned: (1) visibility of the clips, (2) migration of the clips, (3) comparison of setup errors according to both match methods, and (4) comparison of target coverage by recalculating the dose on the online setup-corrected cone beam CT scan with the patient setup according to both match methods. External validation of the surgical clip-based online setup verification was performed in 23 patients by analyzing kilovoltage images of 100 fractions, obtained after treatment.

RESULTS

All types of surgical clips could be visualized. The clip to center-of-mass distance decreased on average by 2 mm (standard deviation, 1) over the course of treatment. Setup differences between match methods were on average <0.5 mm in all directions. The reconstructed dose distributions showed standard deviations of volumes receiving 95% or 107% of prescribed dose and mean dose of the breast and boost planning target volume were similar for the planning CT and the cone beam CTs, for both match procedures. An external validation in 23 patients showed reassuring setup errors <2 mm.

CONCLUSIONS

Online setup verification using surgical clips results in comparable setup corrections and target volume coverage as verification using skin markers. By omitting skin markers acute skin toxicity beneath the markers is prevented.

Seroma change during magnetic resonance imaging-guided partial breast irradiation and its clinical implications

Background

To investigate the patterns of post-lumpectomy seroma volume (SV) change and related clinical factors to determine the benefits of adaptive planning in magnetic resonance imaging (MRI)-guided partial breast irradiation (PBI).

Methods

MRI data obtained from 37 women with early breast cancer acquired at simulation and at the 1st, 6th, and 10th fractions were analyzed. The planning target volume (PTV) was defined as unequal margins of 10–15 mm added according to the directional surgical margin status of each seroma. Treatment was performed using a 0.35 T MRI-guided radiotherapy system. Univariate analysis was performed to assess the correlations between SV change rate and clinical factors. Seroma and PTV for adaptive planning were based on the images obtained at the 6th fraction.

Results

The average time intervals between surgery-simulation, simulation-1st, 1st-6th, and 6th-10th fractions were 23.1, 8.5, 7.2, and 5.9 days, respectively. Of the 37 patients, 33 exhibited decreased SV over the treatment period. The mean SV of these 33 patients decreased from 100% at simulation to 60, 48, and 40% at each MRI scan. In most cases (26/33), the logarithm of SV was inversely proportional to the elapsed time from surgery (R² > 0.90, Pearson’s correlation test). The volume of spared normal tissue from adaptive radiotherapy was proportional to the absolute change in SV (R² = 0.89, Pearson’s correlation test).

Conclusion

Seromas exhibit exponential shrinkage over the course of PBI. In patients receiving PBI, frequent monitoring of SV could be helpful in decision-making regarding adaptive planning, especially those with a large seroma.

Dosimetric Effects of the Interfraction Variations during Whole Breast Radiotherapy: A Prospective Study

Introduction

The aim of this work was to assess the dosimetric impact of the interfraction variations during breast radiotherapy.

Materials and methods

Daily portal imaging measurements were prospectively performed in 10 patients treated with adjuvant whole breast irradiation (50 Gy/25 fractions). Margins between the clinical target volume and the planning target volume (PTV) were 5 mm in the three dimensions. Parameters of interest were the central lung distance (CLD) and the inferior central margin (ICM). Daily movements were applied to the baseline treatment planning (TP1) to design a further TP (TP2). The PTV coverage and organ at risk exposure were measured on both TP1 and TP2, before being compared.

Results

A total of 241 portal images were analyzed. The random and systematic errors were 2.6 and 3.7 mm for the CLD, 4.3 and 6.9 mm for the ICM, respectively. No significant consequence on the PTV treatments was observed (mean variations: +0.1%, p = 0.56 and −1.8%, p = 0.08 for the breast and the tumor bed, respectively). The ipsilateral lung and heart exposure was not significantly modified.

Conclusion

In our series, the daily interfraction variations had no significant effect on the PTV coverage or healthy tissue exposure during breast radiotherapy.

Automated planning of breast radiotherapy using cone beam CT imaging

PURPOSE

Develop and clinically validate a methodology for using cone beam computed tomography (CBCT) imaging in an automated treatment planning framework for breast IMRT.

METHODS

A technique for intensity correction of CBCT images was developed and evaluated. The technique is based on histogram matching of CBCT image sets, using information from "similar" planning CT image sets from a database of paired CBCT and CT image sets (n = 38). Automated treatment plans were generated for a testing subset (n = 15) on the planning CT and the corrected CBCT. The plans generated on the corrected CBCT were compared to the CT-based plans in terms of beam parameters, dosimetric indices, and dose distributions.

RESULTS

The corrected CBCT images showed considerable similarity to their corresponding planning CTs (average mutual information 1.0±0.1, average sum of absolute differences 185 ± 38). The automated CBCT-based plans were clinically acceptable, as well as equivalent to the CT-based plans with average gantry angle difference of 0.99°±1.1°, target volume overlap index (Dice) of 0.89±0.04 although with slightly higher maximum target doses (4482±90 vs 4560±84, P < 0.05). Gamma index analysis (3%, 3 mm) showed that the CBCT-based plans had the same dose distribution as plans calculated with the same beams on the registered planning CTs (average gamma index 0.12±0.04, gamma <1 in 99.4%±0.3%).

CONCLUSIONS

The proposed method demonstrates the potential for a clinically feasible and efficient online adaptive breast IMRT planning method based on CBCT imaging, integrating automation.

Comparison of breast simultaneous integrated boost (SIB) radiotherapy techniques

Purpose

To dosimetrically evaluate different breast SIB techniques with respect to target coverage and organs at risk (OARs) doses.

Methods

Four IMRT techniques were compared in 12 patients. Three techniques employ tangential whole breast irradiation with either two coplanar fields (T-2F), or four non-coplanar fields (T-NC), or one Volumetric Modulated Arc Therapy (T-VMAT) for the boost volume. The fourth technique is a fully-modulated VMAT technique (f-VMAT). Dosimetric parameters were compared for the boost and breast target volumes as well as OARs. Delivery efficiency was analysed based on number of monitor units (MUs) and estimated delivery time.

Results

T-VMAT and f-VMAT ranked highest with respect to integral assessment of boost and breast treatment quality measures. T-VMAT significantly outperformed f-VMAT with respect to ipsi-lateral lung and left-sided patients’ heart volumes ≥ 5 Gy (35 % ± 5 % vs. 52 % ± 6 % and 11 % ± 5 % vs. 22 % ± 6 %, respectively). f-VMAT significantly outperformed T-VMAT with respect to ipsi-lateral lung volume ≥ 20 Gy (13 % ± 2 % vs. 15 % ± 3 %) and heart volume ≥ 30 Gy in left breast cancer (0 % ± 0 % vs. 1 % ± 1 %). T-VMAT and f-VMAT needed 442 ± 58 and 1016 ± 152 MUs, respectively.

Conclusions

The hybrid T-VMAT is considered the technique of choice due to its balance of quality, efficiency and dose to OARs.

A clip-based protocol for breast boost radiotherapy provides clear target visualisation and demonstrates significant volume reduction over time

Introduction

The clinical target volume (CTV) for early stage breast cancer is difficult to clearly identify on planning computed tomography (CT) scans. Surgical clips inserted around the tumour bed should help to identify the CTV, particularly if the seroma has been reabsorbed, and enable tracking of CTV changes over time.

Methods

A surgical clip-based CTV delineation protocol was introduced. CTV visibility and its post-operative shrinkage pattern were assessed. The subjects were 27 early stage breast cancer patients receiving post-operative radiotherapy alone and 15 receiving post-operative chemotherapy followed by radiotherapy. The radiotherapy alone (RT/alone) group received a CT scan at median 25 days post-operatively (CT1rt) and another at 40 Gy, median 68 days (CT2rt). The chemotherapy/RT group (chemo/RT) received a CT scan at median 18 days post-operatively (CT1ch), a planning CT scan at median 126 days (CT2ch), and another at 40 Gy (CT3ch).

Results

There was no significant difference (P = 0.08) between the initial mean CTV for each cohort. The RT/alone cohort showed significant CTV volume reduction of 38.4% (P = 0.01) at 40 Gy. The Chemo/RT cohort had significantly reduced volumes between CT1ch: median 54 cm³ (4–118) and CT2ch: median 16 cm³, (2–99), (P = 0.01), but no significant volume reduction thereafter.

Conclusion

Surgical clips enable localisation of the post-surgical seroma for radiotherapy targeting. Most seroma shrinkage occurs early, enabling CT treatment planning to take place at 7 weeks, which is within the 9 weeks recommended to limit disease recurrence.

Adaptive replanning to account for lumpectomy cavity change in sequential boost after whole-breast irradiation

PURPOSE

To evaluate the efficiency of standard image-guided radiation therapy (IGRT) to account for lumpectomy cavity (LC) variation during whole-breast irradiation (WBI) and propose an adaptive strategy to improve dosimetry if IGRT fails to address the interfraction LC variations.

METHODS AND MATERIALS

Daily diagnostic-quality CT data acquired during IGRT in the boost stage using an in-room CT for 19 breast cancer patients treated with sequential boost after WBI in the prone position were retrospectively analyzed. Contours of the LC, treated breast, ipsilateral lung, and heart were generated by populating contours from planning CTs to boost fraction CTs using an auto-segmentation tool with manual editing. Three plans were generated on each fraction CT: (1) a repositioning plan by applying the original boost plan with the shift determined by IGRT; (2) an adaptive plan by modifying the original plan according to a fraction CT; and (3) a reoptimization plan by a full-scale optimization.

RESULTS

Significant variations were observed in LC. The change in LC volume at the first boost fraction ranged from a 70% decrease to a 50% increase of that on the planning CT. The adaptive and reoptimization plans were comparable. Compared with the repositioning plans, the adaptive plans led to an improvement in target coverage for an increased LC case (1 of 19, 7.5% increase in planning target volume evaluation volume V95%), and breast tissue sparing for an LC decrease larger than 35% (3 of 19, 7.5% decrease in breast evaluation volume V50%; P=.008).

CONCLUSION

Significant changes in LC shape and volume at the time of boost that deviate from the original plan for WBI with sequential boost can be addressed by adaptive replanning at the first boost fraction.

Image-guided radiotherapy for cardiac sparing in patients with left-sided breast cancer

Patients with left-sided breast cancer are at risk of cardiac toxicity because of cardiac irradiation during radiotherapy with the conventional 3-dimensional conformal radiotherapy technique. In addition, many patients may receive chemotherapy prior to radiation, which may damage the myocardium and may increase the potential for late cardiac complications. New radiotherapy techniques such as intensity-modulated radiotherapy (IMRT) may decrease the risk of cardiac toxicity because of the steep dose gradient limiting the volume of the heart irradiated to a high dose. Image-guided radiotherapy (IGRT) is a new technique of IMRT delivery with daily imaging, which may further reduce excessive cardiac irradiation. Preliminary results of IGRT for cardiac sparing in patients with left-sided breast cancer are promising and need to be investigated in future prospective clinical studies.

Making the right software choice for clinically used equipment in radiation oncology

The customer of a new system for clinical use in radiation oncology must consider many options in order to find the optimal combination of software tools. Many commercial systems are available and each system has a large number of technical features. However an appraisal of the technical capabilities, especially the options for clinical implementations, is hardly assessable at first view.

The intention of this article was to generate an assessment of the necessary functionalities for high precision radiotherapy and their integration in ROKIS (Radiation oncology clinic information system) for future customers, especially with regard to clinical applicability. Therefore we analysed the clinically required software functionalities and divided them into three categories: minimal, enhanced and optimal requirements for high conformal radiation treatment.

Normal tissue complication probability (NTCP) parameters for breast fibrosis: pooled results from two randomised trials

INTRODUCTION

The dose-volume effect of radiation therapy on breast tissue is poorly understood. We estimate NTCP parameters for breast fibrosis after external beam radiotherapy.

MATERIALS AND METHODS

We pooled individual patient data of 5856 patients from 2 trials including whole breast irradiation followed with or without a boost. A two-compartment dose volume histogram model was used with boost volume as the first compartment and the remaining breast volume as second compartment. Results from START-pilot trial (n=1410) were used to test the predicted models.

RESULTS

26.8% patients in the Cambridge trial (5 years) and 20.7% patients in the EORTC trial (10 years) developed moderate-severe breast fibrosis. The best fit NTCP parameters were BEUD3(50)=136.4 Gy, γ50=0.9 and n=0.011 for the Niemierko model and BEUD3(50)=132 Gy, m=0.35 and n=0.012 for the Lyman Kutcher Burman model. The observed rates of fibrosis in the START-pilot trial agreed well with the predicted rates.

CONCLUSIONS

This large multi-centre pooled study suggests that the effect of volume parameter is small and the maximum RT dose is the most important parameter to influence breast fibrosis. A small value of volume parameter 'n' does not fit with the hypothesis that breast tissue is a parallel organ. However, this may reflect limitations in our current scoring system of fibrosis.

Probing early tumor response to radiation therapy using hyperpolarized [1-¹³C]pyruvate in MDA-MB-231 xenografts

Following radiation therapy (RT), tumor morphology may remain unchanged for days and sometimes weeks, rendering anatomical imaging methods inadequate for early detection of therapeutic response. Changes in the hyperpolarized [1-¹³C]lactate signals observed in vivo following injection of pre-polarized [1-¹³C]pyruvate has recently been shown to be a marker for tumor progression or early treatment response. In this study, the feasibility of using ¹³C metabolic imaging with [1-¹³C]pyruvate to detect early radiation treatment response in a breast cancer xenograft model was demonstrated in vivo and in vitro. Significant decreases in hyperpolarized [1-¹³C]lactate relative to [1-¹³C]pyruvate were observed in MDA-MB-231 tumors 96 hrs following a single dose of ionizing radiation. Histopathologic data from the treated tumors showed higher cellular apoptosis and senescence; and changes in the expression of membrane monocarboxylate transporters and lactate dehydrogenase B were also observed. Hyperpolarized ¹³C metabolic imaging may be a promising new tool to develop novel and adaptive therapeutic regimens for patients undergoing RT.