Estimation of optimal matching position for orthogonal kV setup images and minimal setup margins in radiotherapy of whole breast and lymph node areas

Feasibility of surface guided radiotherapy for patient positioning in breast radiotherapy versus conventional tattoo-based setups- a systematic review

Background

Traditionally tattoos are used for patient setup in radiotherapy. However they may pose challenges for the radiotherapists to achieve precise patient alignment, and serve as a permanent visual reminder of the patient’s diagnosis and often challenging cancer journey. The psychological impact of tattoos has been recognized in recent years. The increasing complexity of treatment techniques and the utilization of hypofractionated regimes, requires an enhanced level of accuracy and safety. Surface guided radiotherapy (SGRT) enables improvements in the accuracy and reproducibility of patient isocentric and postural alignment, enhanced efficiency, and safety in breast radiotherapy.

Purpose

The aim of this review was to compare the accuracy and reproducibility of SGRT to conventional tattoo-based setups in free-breathing breast radiotherapy and to determine if SGRT can reduce the frequency of routine image guided radiotherapy (IGRT).

Materials and Methods

A systematic literature review was performed as per PRISMA guidelines. Papers identified through PubMed, Embase, Web of Science and Google Scholar database searches between 2010 and 2021, were critically appraised. Systematic, random, mean residual errors and 3D vector shifts as determined by IGRT verification were analysed.

Results

A review of 13 full papers suggests SGRT improves the accuracy and reproducibility of patient setup in breast radiotherapy with consistent reductions in the residual errors. There appears to be a good correlation between SGRT setups and radiographic imaging. The frequency of IGRT and the corresponding dose could potentially be reduced. Additionally, SGRT improves treatment efficiency.

Conclusion

SGRT appears to have improved the accuracy and reproducibility of patient setup and treatment efficiency of breast radiotherapy compared to conventional tattoo/laser-based method, with the potential to reduce the frequency of routine IGRT. The reliance on tattoos in breast radiotherapy are likely to become obsolete with positive implications for both patients and clinical practice.

Patient setup accuracy in DIBH radiotherapy of breast cancer with lymph node inclusion using surface tracking and image guidance

Studying setup accuracy in breast cancer patients with axillary lymph node inclusion in deep inspiration breath-hold (DIBH) after patient setup with surface-guided radiotherapy (SGRT) and image-guided radiotherapy (IGRT). Breast cancer patients (N = 51) were treated (50 Gy in 25 fractions) with axillary lymph nodes within the planning target volume (PTV). Patient setup was initiated with tattoos and lasers, and further adjusted with SGRT. The DIBH guidance was based on SGRT. Orthogonal and/or tangential imaging was analyzed for residual position errors of bony landmarks, the breath-hold level (BHL), the skin outline, and the heart; and setup margins were calculated for the PTV. The calculated PTV margins were 4.3 to 6.3 and 2.8 to 4.6 mm before and after orthogonal imaging, respectively. The residual errors of the heart were 3.6 ± 2.2 mm and 2.5 ± 2.4 mm before and 3.0 ± 2.5 and 2.9 ± 2.3 mm after orthogonal imaging in the combined anterior-posterior/lateral and the cranio-caudal directions, respectively, in tangential images. The humeral head did not benefit from daily IGRT, but SGRT guided it to the correct location. We presented a slightly complicated but highly accurate workflow for DIBH treatments. The residual position errors after both SGRT and IGRT were excellent compared to previous literature. With well-planned SGRT, IGRT brings only slight improvements to systematic accuracy. However, with the calculated PTV margins and the number of outliers, imaging cannot be omitted despite SGRT, unless the PTV margins are re-evaluated.

Comparison of three differently shaped ROIs in free breathing breast radiotherapy setup using surface guidance with AlignRT®

Background

Setup accuracy within adjuvant radiotherapy of breast cancer treated in free breathing is well studied, but a comparison of the typical regions of interest (ROI) used in surface guided radiation therapy (SGRT) does not exist. The aim of this study was to estimate the setup accuracy obtained with differently shaped ROIs in SGRT.

Materials and methods

A total of 573 orthogonal image pairs were analyzed from free breathing breast patients in two groups: positioning using AlignRT^® surface guidance system (Group A, n = 20), and setup using conventional laser and tattoo setup (Group L, n = 20). For SGRT, three different setup ROIs were used: a Breast-shaped, O-shaped and T-shaped (B-O and T-ROI). We evaluated the isocenter-, rotation-, pitch and arm position accuracy and residual errors for the chest wall and shoulder joint in kV orthogonal and tangential setup images with laser- or SGRT-based setup.

Results

Less isocenter variance was found in Group A than in Group L. Rotations and posture errors were larger in group L than in Group A (p ≤ 0.05). Rotation error was smaller with T-shaped ROI than with O- or B-shape (p = 0.01-0.04).

Conclusion

Setup with AlignRT^® improves reproducibility compared to laser setup. Between the different ROI shapes only small differences were found in the patient posture or the isocenter position in the images. The T-ROI is recommended to set up the chest wall bony structure and an additional B-ROI may be used to fine-tune the soft tissue accuracy.

Evaluation of setup and intrafraction motion for surface guided whole-breast cancer radiotherapy

Surface Guided Radiotherapy (SGRT) is a relatively new technique for positioning patients and for monitoring patient movement during treatment. SGRT is completely non-invasive since it uses visible light for determining the position of the patient surface. A reduction in daily imaging for patient setup is possible if the accuracy of SGRT is comparable to imaging. It allows for monitoring of intrafraction motion and the radiation beam can be held beyond a certain threshold resulting in a more accurate irradiation. The purpose of this study was to investigate setup uncertainty and the intrafraction motion in non-gated whole breast cancer radiotherapy treatment using an integrated implementation of AlignRT (OSMS) system as SGRT. In initial setup, SGRT was compared to three-point setup using tattoos on the patient and orthogonal kV imaging. For the investigation of intrafraction motion, OSMS monitored the patient with six degrees of freedom during treatment. Using three-point setup resulted in a setup root-mean-square error from the isocenter of 5.4 mm. This was improved to 4.2 mm using OSMS. For the translational directions, OSMS showed improvements in the lateral direction (P = 0.0009, Wilcoxon rank-sum), but for the longitudinal direction and rotation it was not possible to show improvements (P = 0.96 and P = 0.46, respectively). The vertical direction proved more accurate for three-point setup than OSMS (P = 0.000004). Intrafraction motion was very limited with a translational median of 1.1 mm from the isocenter. While OSMS showed marked improvements over laser and tattoo setup, the system did not prove accurate enough to replace the daily orthogonal kV images aligned to bony anatomy.

Evaluation of interfraction setup variations for postmastectomy radiation therapy using EPID-based in vivo dosimetry

Postmastectomy radiation therapy is technically difficult and can be considered one of the most complex techniques concerning patient setup reproducibility. Slight patient setup variations — particularly when high‐conformal treatment techniques are used — can adversely affect the accuracy of the delivered dose and the patient outcome. This research aims to investigate the inter‐fraction setup variations occurring in two different scenarios of clinical practice: at the reference and at the current patient setups, when an image‐guided system is used or not used, respectively. The results were used with the secondary aim of assessing the robustness of the patient setup procedure in use. Forty eight patients treated with volumetric modulated arc and intensity modulated therapies were included in this study. EPID‐based in vivo dosimetry (IVD) was performed at the reference setup concomitantly with the weekly cone beam computed tomography acquisition and during the daily current setup. Three indices were analyzed: the ratio R between the reconstructed and planned isocenter doses, γ% and the mean value of γ from a transit dosimetry based on a two‐dimensional γ‐analysis of the electronic portal images using 5% and 5 mm as dose difference and distance to agreement gamma criteria; they were considered in tolerance if R was within 5%, γ% > 90% and γmean < 0.4. One thousand and sixteen EPID‐based IVD were analyzed and 6.3% resulted out of the tolerance level. Setup errors represented the main cause of this off tolerance with an occurrence rate of 72.2%. The percentage of results out of tolerance obtained at the current setup was three times greater (9.5% vs 3.1%) than the one obtained at the reference setup, indicating weaknesses in the setup procedure. This study highlights an EPID‐based IVD system's utility in the radiotherapy routine as part of the patient’s treatment quality controls and to optimize (or confirm) the performed setup procedures’ accuracy.

Breast deformation during the course of radiotherapy: The need for an additional outer margin

PURPOSE

The aim of this retrospective study was to investigate and quantify the extent of breast deformation during the course of breast cancer (BC) radiotherapy (RT). The magnitude of breast deformation determines the additional outer margin needed for treatment planning to deliver a full dose to the target volume. This is especially important when using inverse planning techniques.

METHODS

A total of 93 BC patients treated with RT and with daily CBCT image guidance were selected for this study. Patients underwent either only breast-conserving surgery (BCS) (n = 5), BCS with sentinel node biopsy (n = 57) or BCS with radical axillary node dissection (n = 31). The treatment area included the whole breast and chest wall (54%) or also the axillary lymph nodes (46%). 3D-registration was conducted between 1731 CBCT images and the respective planning CT images to assess the difference in breast surface.

RESULTS

The largest maximum breast surface expansion (MBSE) was 15 mm; the average was 2.4 ± 2.1 mm. In 294 fractions (17%), the MBSE was ≥5 mm. An outer margin of 8 mm would have been required to cover the whole breast in 95% of the treated fractions. There was a statistically significant correlation between the MBSE and body mass index (r = 0.38, p = 0.001).

CONCLUSIONS

Significant changes in the breast surface occur during the course of BC RT which should be considered in treatment planning. An additional margin outside the breast surface of at least 8 mm is required to take into account the anatomical changes occurring during BC RT.

AlignRT® and Catalyst™ in whole-breast radiotherapy with DIBH: Is IGRT still needed?

Purpose

Surface guided radiotherapy (SGRT) is reported as a feasible setup technique for whole‐breast radiotherapy in deep inspiration breath hold (DIBH), but position errors of bony structures related to deeper parts of the target are not fully known. The aim of this study was to estimate patient setup accuracy and margins obtained with two different SGRT workflows with and without daily kV‐ and/or MV‐based image guidance (IGRT).

Methods

A total of 50 breast cancer patients were treated in DIBH, using SGRT for the patient setup, and IGRT for isocenter corrections. The patients were treated at two different departments, one using AlignRT^® (25 patients) and the other using Catalyst™ (25 patients). Inter‐fractional position errors were analyzed retrospectively in orthogonal and tangential setup images, and analyzed with and without IGRT.

Results

In the orthogonal kV‐kV images, the systematic residual errors of the bony structures were ≤ 3 mm in both groups with SGRT‐only. When fine‐adjusted by daily IGRT, the errors decreased to ≤ 2 mm; except for the shoulder joint. The residual errors of the ribs in tangential images were between 1 and 2 mm with both workflows. The heart planning margins were between 3 and 7 mm.

Conclusions

The frequency of IGRT may be considerably reduced with a well‐planned SGRT‐workflow for whole‐breast DIBH with residual errors ≤ 3 mm. This accuracy can be further improved with an IGRT scheme.

Dosimetric effects of anatomical deformations and positioning errors in VMAT breast radiotherapy

AIM

Traditional radiotherapy treatment techniques of the breast are insensitive for deformations and swelling of the soft tissue. The purpose of this study was to evaluate the dose changes seen with tissue deformations using different image matching methods when VMAT technique was used, and compare these with tangential technique.

METHODS

The study included 24 patients with breast or chest wall irradiations, nine of whom were bilateral. In addition to planar kV setup imaging, patients underwent weekly cone-beam computed tomography (CBCT) imaging to evaluate soft tissue deformations. The effect of the deformations was evaluated on VMAT plans optimized with 5-mm virtual bolus to create skin flash, and compared to standard tangential plans with 2.5 cm skin flash. Isocenter positioning using 2D imaging and CBCT were compared.

RESULTS

With postural changes and soft tissue deformations, the target coverage decreased more in the VMAT plans than in the tangential plans. The planned V90% coverage was 98.3% and 99.0% in the tangential and VMAT plans, respectively. When tattoo-based setup and online 2D match were used, the coverage decreased to 97.9% in tangential and 96.5% in VMAT plans (P < 0.001). With automatic CBCT-based image match the respective coverages were 98.3% and 98.8%. In the cases of large soft tissue deformations, the replanning was needed for the VMAT plan, whereas the tangential plan still covered the whole target volume.

CONCLUSIONS

The skin flash created using an optimization bolus for VMAT plans was in most cases enough to take into account the soft tissue deformations seen in breast VMAT treatments. However, in some cases larger skin flash or replanning were needed. The use of 2D match decreased the target coverage for VMAT plans but not for FinF plans when compared to 3D match. The use of CBCT match is recommended when treating breast/chest wall patients with VMAT technique.

A new split arc VMAT technique for lymph node positive breast cancer

PURPOSE

To investigate different volumetric modulated arc therapy (VMAT) field designs for lymph node positive breast cancer patients when compared to conventional static fields and standard VMAT designs.

METHODS

Nineteen breast cancer patients with lymph node involvement (eleven left and eight right sided) were retrospectively analyzed with different arc designs. Proposed split arc designs with total rotations of 2×190° and 2×240° were compared to conventional field in field (FinF) and previously published non-split arc techniques with the same amount of total rotations.

RESULTS

All VMAT plans were superior in dose conformity, when compared to the FinF plans. Split arc design decreased significantly ipsilateral lung dose and heart V5Gy for both left and right sided cases, when compared to non-split VMAT designs. For left sided cases no significant differences were seen in contralateral lung mean dose or V5Gy between different VMAT designs. For right sided cases the contralateral lung dose V5Gy was significantly higher in split VMAT group, when compared to non-split VMAT designs. The contralateral breast dose V5Gy increased significantly for split VMAT plans for both sides, when compared to non-split VMAT designs or FinF plans.

CONCLUSIONS

The proposed split VMAT technique was shown to be superior to previously published non-split VMAT and conventional FinF techniques significantly reducing dose to the ipsilateral lung and heart. However, this came with the expense of an increase in the dose to the contralateral breast and for right-sided cases to the contralateral lung.

Evaluation of mechanical and geometric accuracy of two different image guidance systems in radiotherapy

AIM

To assess the mechanical and the geometric accuracy of two different clinically used image guidance systems in radiotherapy for a period of 6 months.

BACKGROUND

With the image guidance procedures being routine in the clinical radiotherapy department, the quality assurance tests for these systems become essential. The mechanical and geometric accuracy of these systems are crucial since it directly affects patient treatment set-up and delivery.

MATERIALS AND METHODS

We have assessed the mechanical and the geometric accuracy of two different image guidance systems (MV and kV based), being used clinically for a period of 6 months. The quality assurance tests such as imager positioning/repositioning, imaging and treatment beam isocentre coincidence, imager mechanical alignment, image scaling, geometric accuracy of cone beam computed tomography system, automatic image registration and offset calculation accuracy were assessed in this period.

RESULTS

It was found that both systems were mechanically and geometrically accurate within ±2 mm in this period.

CONCLUSION

The quality assurance tests for MV based image guidance system were simple compared to kV based systems. We recommend performing periodic quality assurance tests to verify the integrity of both image guidance systems.

Dosimetric feasibility of an "off-breast isocenter" technique for whole-breast cancer radiotherapy

AIM

To investigate the viability of placing the treatment isocenter at the patient midline for breast cancer radiotherapy in order to avoid the risk of collisions during image-guided setup and treatment delivery.

BACKGROUND

The use of kilovoltage orthogonal setup images has spread in last years in breast radiotherapy. There is a potential risk of an imaging system-patient collision when the isocenter is laterally placed.

MATERIALS AND METHODS

Twenty IMRT plans designed by placing the isocenter within the breast volume ("plan_ref"), were retrospectively replanned by shifting the isocenter at the patient's midline ("plan_off-breast"). An integrated simultaneous boost (SIB) technique was used. Multiple metrics for the planning target volumes (PTVs) and organs at risk (OARs) were compared for both approaches using a paired t test.

RESULTS

Comparing plan_ref vs. plan_off-breast, no significant differences in PTV coverage (V95%) were found (96.5% vs. 96.2%; p = 0.361 to PTVbreast; 97.0% vs. 97.0%; p = 0.977 to PTVtumor_bed). With regard to OARs, no substantial differences were observed in any analyzed metric: V5Gy (30.3% vs. 31.4%; p = 0.486), V20Gy (10.3% vs. 10.3%; p = 0.903) and mean dose (7.1 Gy vs. 7.1 Gy; p = 0.924) to the ipsilateral lung; V5Gy (11.2% vs. 10.0%; p = 0.459), V30Gy (0.7% vs. 0.6%; p = 0.251) and mean dose (2.3 Gy vs. 2.2 Gy; p = 0.400) to the heart; and average dose to the contralateral breast (0.4 Gy vs. 0.5 Gy; p = 0.107).

CONCLUSIONS

The off-breast isocenter solution resulted in dosimetrically comparable plans as the reference technique, avoiding the collision risk during the treatment session.

Comparison of set-up errors by breast size on wing board by portal imaging

AIM

To quantify and compare setup errors between small and large breast patients undergoing intact breast radiotherapy.

METHODS

20 patients were inducted. 10 small/moderate size breast in arm I and 10 large breast in arm II. Two orthogonal and one lateral tangent portal images (PIs) were obtained and analyzed for systematic (Σ) and random (σ) errors. Effect of no action level (NAL) was also evaluated retrospectively.

RESULTS

142 PIs were analyzed. Σ(mm) was 3.2 versus 6.7 (p = 0.41) in the mediolateral (ML) direction, 2.1 versus 2.9 (p = 0.06) in the craniocaudal (CC) and 2.2 versus 3.6 (p = 0.08) in the anteroposterior (AP) direction in small and large breast, respectively. σ(mm) was 3.0, 3.3 and 3.3 for small breast and 4.1, 3.7 and 3.2 for large breast in the ML, CC and AP direction (p = 0.07, 0.86, 0.37), respectively. 3 D Σ(mm) was 2.7 versus 4.2 (p = 0.01) and σ(mm) was 2.5 versus 3.2 (p = 0.14) in arm I and II, respectively. The standard deviation (SD) of variations (mm) in breast contour depicted by central lung distance (CLD) was 5.9 versus 7.4 (p < 0.001), central flash distance (CFD) 6.6 versus 10.5 (p = 0.002), inferior central margin (ICM) 4 versus 4.9 (p < 0.001) in arm I and II, respectively. NAL showed a significant reduction of systematic error in large breast in the mediolateral direction only.

CONCLUSION

Wing board can be used in a busy radiotherapy department for setting up breast patients with a margin of 1.1 cm, 0.76 cm and 0.71 cm for small breasts and 1.96 cm, 1.12 cm and 0.98 cm for large breast in the ML, AP and CC directions, respectively. The large PTV margin in the mediolateral direction in large breast can be reduced using NAL. Further research is needed to optimize positioning of large breasted women.

Determination of the optimal matching position for setup images and minimal setup margins in adjuvant radiotherapy of breast and lymph nodes treated in voluntary deep inhalation breath-hold

BACKGROUND

Adjuvant radiotherapy (RT) of left-sided breast cancer is increasingly performed in voluntary deep inspiration breath-hold (vDIBH). The aim of this study was to estimate the reproducibility of breath-hold level (BHL) and to find optimal bony landmarks for matching of orthogonal setup images to minimise setup margins.

METHODS

1067 sets of images with an orthogonal setup and tangential field from 67 patients were retrospectively analysed. Residual position errors were determined in the tangential treatment field images for different matches of the setup images. Variation of patient posture and BHL were analysed for position errors of the vertebrae, clavicula, ribs and sternum in the setup and tangential field images. The BHL was controlled with a Varian RPM® system. Setup margins were calculated using the van Herk's formula. Patients who underwent lymph node irradiation were also investigated.

RESULTS

For the breast alone, the midway compromise of the ribs and sternum was the best general choice for matching of the setup images. The required margins were 6.5 mm and 5.3 mm in superior-inferior (SI) and lateral/anterior-posterior (LAT/AP) directions, respectively. With the individually optimised image matching position also including the vertebrae, slightly smaller margins of 6.0 mm and 4.8 mm were achieved, respectively. With the individually optimised match, margins of 7.5 mm and 10.8 mm should be used in LAT and SI directions, respectively, for the lymph node regions. These margins were considered too large. The reproducibility of the BHL was within 5 mm in the AP direction for 75% of patients.

CONCLUSIONS

The smallest setup margins were obtained when the matching position of the setup images was individually optimised for each patient. Optimal match for the breast alone is not optimal for the lymph node region, and, therefore, a threshold of 5 mm was introduced for residual position errors of the sternum, upper vertebrae, clavicula and chest wall to retain minimal setup margins of 5 mm. Because random interfraction variation in patient posture was large, we recommend daily online image guidance. The BHL should be verified with image guidance.