Three-dimensional intrafractional internal target motions in accelerated partial breast irradiation using three-dimensional conformal external beam radiotherapy

Repeated deep-inspiration breath-hold CT scans at planning underestimate the actual motion between breath-holds at treatment for lung cancer and lymphoma patients

PURPOSE/OBJECTIVE

Deep-inspiration breath-hold (DIBH) during radiotherapy may reduce dose to the lungs and heart compared to treatment in free breathing. However, intra-fractional target shifts between several breath-holds may decrease target coverage. We compared target shifts between four DIBHs at the planning-CT session with those measured on CBCT-scans obtained pre- and post-DIBH treatments.

MATERIAL/METHODS

Twenty-nine lung cancer and nine lymphoma patients were treated in DIBH. An external gating block was used as surrogate for the DIBH-level with a window of 2 mm. Four DIBH CT-scans were acquired: one for planning (CTDIBH3) and three additional (CTDIBH1,2,4) to assess the intra-DIBH target shifts at scanning by registration to CTDIBH3. During treatment, pre-treatment (CBCTpre) and post-treatment (CBCTpost) scans were acquired. For each pair of CBCTpre/post, the target intra-DIBH shift was determined. For lung cancer, tumour (GTV-Tlung) and lymph nodes (GTV-Nlung) were analysed separately. Group mean (GM), systematic and random errors, and GM for the absolute maximum shifts (GMmax) were calculated for the shifts between CTDIBH1,2,3,4 and between CBCTpre/post.

RESULTS

For GTV-Tlung, GMmax was larger at CBCT than CT in all directions. GMmax in cranio-caudal direction was 3.3 mm (CT)and 6.1 mm (CBCT). The standard deviations of the shifts in the left-right and cranio-caudal directions were larger at CBCT than CT. For GTV-Nlung and CTVlymphoma, no difference was found in GMmax or SD.

CONCLUSION

Intra-DIBH shifts at planning-CT session are generally smaller than intra-DIBH shifts observed at CBCTpre/post and therefore underestimate the intra-fractional DIBH uncertainty during treatment. Lung tumours show larger intra-fractional variations than lymph nodes and lymphoma targets.

Difference between planned and delivered radiotherapy dose to the internal mammary nodes in high-risk breast cancer patients

Background and purpose

Chest wall movement during radiotherapy can impact the delivered dose to the internal mammary nodes (IMN) in high-risk breast cancer patients. Using portal imaging and dose reconstruction we aimed to examine the delivered IMN dose coverage.

Material and methods

Cine MV images were recorded for 39 breast cancer patients treated with daily image-guided radiotherapy (IGRT) in deep-inspiration breath-hold (DIBH). On the final frame of each cine MV recording the chest wall was matched with the Digitally Reconstructed Radiograph (DRR) from the treatment plan. The geometrical chest wall error was determined in the imager-plane perpendicular to the cranio-caudal direction, rounded to integer millimeters, and binned. For each 1 mm bin, an isocenter-shifted treatment plan was recalculated assuming that the projected error observed in the cine MV image was caused by anterior-posterior chest wall movement in the IMN region. A weighted plan sum yielded the IMN clinical target volume receiving at least 90% dose (V90_CTVn_IMN).

Results

The mean number of cine MV observations per patient was 36 (range 26-55). Most patients (67%) had on average a posterior chest wall position at treatment compared to planned. This translated into a change in the delivered median V90_CTVn_IMN of -0.7% (range, -11.9-2.9%; p < 0.001). The V90_CTVn_IMN reduction was greater than 9% in three patients. No clinically relevant differences were found for the mean lung dose or mean heart dose.

Conclusion

Using cine MV images, we found that the delivered V90_CTVn_IMN was significantly lower than planned. In 8% of the patients, the V90_CTVn_IMN reduction exceeded 9%.

Surface-guided positioning eliminates the need for skin markers in radiotherapy of right sided breast cancer: A single center randomized crossover trial

BACKGROUND AND PURPOSE

To prospectively investigate whether surface guided setup of right sided breast cancer patients can increase efficiency and accuracy compared to traditional skin marker/tattoo based setup.

MATERIAL AND METHODS

Twenty-five patients were included in this study. Each patient was positioned using skin marks and tattoos (procedure A) for half of the fractions and surface guidance using AlignRT (procedure B) for the other half of the fractions. The order of the two procedures was randomized. Pretreatment CBCT was acquired at every fraction for both setup procedures. A total of ten time points were recorded during every treatment session. Applied couch shifts after CBCT match were recorded and used for potential error calculations if no CBCT had been used.

RESULTS

In the vertical direction procedure B showed significant smaller population based systematic (Ʃ) and random (σ) errors. However, a significant larger systematic error on the individual patient level (M) was also shown. This was found to be due to patient relaxation between setup and CBCT matching. Procedure B also showed a significant smaller random error in the lateral direction, while no significant differences were seen in the longitudinal direction. No significant difference in setup time was found between the two procedures.

CONCLUSION

Setup of right sided breast cancer patients using surface guidance yields higher accuracy than setup using skin marks/tattoos and lasers with the same setup time. Patient alignment for this patient group can safely be done without the use of permanent tattoos and skin marks when utilizing surface-guided patient positioning. However, CBCT should still be used as final setup verification.

Factors impacting on patient setup analysis and error management during breast cancer radiotherapy

Radiotherapy is required to deliver an accurate dose to the tumor while protecting surrounding normal tissues. Breast cancer radiotherapy involves a number of factors that can influence patient setup and error management, including the immobilization device used, the verification system and the patient's treatment position. The aim of this review is to compile and discuss the setup errors that occur due to the above-mentioned factors. In view of this, a systematic search of the scientific literature in the Medline/PubMed databases was performed over the 1990-2021 time period, with 93 articles found to be relevant for the study. To be accessible to all, this study not only aims to identify factors impacting on patient setup analysis, but also seeks to evaluate the role of each verification device, board immobilization and position in influencing these errors.

Intra-fraction motion monitoring during fast modulated radiotherapy delivery in a closed-bore gantry linac

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Surface scanning allows for continuous intra fraction monitoring in a closed-bore gantry.

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Patient baseline drift during fast cone-beam computed tomography imaging is non-negligible.

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Peak-to-peak breathing amplitude is smaller than baseline drift in 69% of fractions.

Background and purpose

New closed-bore linacs allow for highly streamlined workflows and fast treatment delivery resulting in brief treatment sessions. Motion management technology has only recently been integrated inside the bore, yet is required in future online adaptive workflows. We measured patient motion during every step of the workflow: image acquisition, evaluation and treatment delivery using surface scanning.

Materials and methods

Nineteen patients treated for breast, lung or esophageal cancer were prospectively monitored from the end of setup to the end of treatment delivery in the Halcyon linac (Varian Medical Systems). Motion of the chest was tracked by way of 6 degrees-of-freedom surface tracking. Baseline drift and rate of drift were determined. The influence of fraction number, patient and fraction duration were analyzed with multi-way ANOVA.

Results

Median fraction duration was 4 min 48 s including the IGRT procedure (kV-CBCT acquisition and evaluation) (N = 221). Baseline drift at the end of the fraction was −1.8 ± 1.5 mm in the anterior-posterior, −0.0 ± 1.7 mm in the cranio-caudal direction and 0.1 ± 1.8 mm in the medio-lateral direction of which 75% occurred during the IGRT procedure. The highest rate of baseline drift was observed between 1 and 2 min after the end of patient setup (-0.62 mm/min). Baseline drift was patient and fraction duration dependent (p < 0.001), but fraction number was not significant (p = 0.33).

Conclusion

Even during short treatment sessions, patient baseline drift is not negligible. Drift is largest during the initial minutes after completion of patient setup, during verification imaging and evaluation. Patients will need to be monitored during extended contouring and re-planning procedures in online adaptive workflows.

Does the protocol-required uniform margin around the CTV adequately account for setup inaccuracies in whole breast irradiation?

Purpose

To use cone-beam computed tomography (CBCT) imaging to determine the impacts of patient characteristics on the magnitude of geometric setup errors and obtain patient-specific planning target volume (PTV) margins from the correlated patient characteristics in whole breast irradiation (WBI).

Methods

Between January 2019 and December 2019, a total of 97 patients who underwent breast-conserving surgery, followed by intensity-modulated radiation therapy in WBI, were scanned with pre-treatment CBCT for the first three treatment fractions and weekly for the subsequent fractions. Setup errors in the left–right (LR), superior–inferior (SI) and anterior–posterior (AP) directions were recorded and analyzed with patient characteristics—including age, tumor location, body mass index (BMI), chest circumference (CC) and breast volume (BV)—to examine the predictors for setup errors and obtain specific PTV margins.

Results

A total of 679 CBCT images from 97 patients were acquired for analysis. The mean setup errors for the whole group were 2.32 ± 1.21 mm, 3.71 ± 2.21 mm and 2.75 ± 1.56 mm in the LR, SI and AP directions, respectively. Patients’ BMI, CC and BV were moderately associated with setup errors, especially in the SI directions (R = 0.40, 0.43 and 0.22, respectively). Setup errors in the SI directions for patients with BMI > 23.8 kg/m², CC > 89 cm and BV > 657 cm³ were 4.56 ± 2.59 mm, 4.77 ± 2.42 mm and 4.30 ± 2.43 mm, respectively, which were significantly greater than those of patients with BMI ≤ 23.8 kg/m², CC ≤ 89 cm and BV ≤ 657 cm³ (P < 0.05). Correspondingly, the calculated PTV margins in patients with BMI > 23.8 kg/m², CC > 89 cm and BV > 657 cm³ were 4.25/7.95/4.93 mm, 4.37/7.66/5.24 mm and 4.22/7.54/5.29 mm in the LR/SI/AP directions, respectively, compared with 3.64/4.64/5.09 mm, 3.31/4.50/4.82 mm and 3.29/5.74/4.73 mm for BMI ≤ 23.8 kg/m², CC ≤ 89 cm and BV ≤ 657 cm³, respectively.

Conclusions

The magnitude of geometric setup errors was moderately correlated with BMI, CC and BV. It was recommended to set patient-specific PTV margins according to patient characteristics in the absence of daily image-guided treatment setup.

Image-guided study of inter-fraction and intra-fraction set-up variability and margins in reverse semi-decubitus breast radiotherapy

BACKGROUND

This study aimed to evaluate the inter-fraction set-up error and intra-fraction motion during reverse semi-decubitus (RSD) breast radiotherapy, and to determine a planning target volume (PTV) margin.

MATERIAL AND METHODS

Pre- and post-treatment cone-beam computed tomography (CBCT) scans were prospectively acquired at fractions 1, 4, 7, 8, 11, and 14 for 30 patients who underwent RSD breast radiotherapy. Online correction for initial set-up error greater than 5 mm or 2° was performed and post-correction CBCT was acquired. An off-line analysis was performed to quantify initial and residual inter-fraction set-up errors and intra-fraction motion in three-dimensions. Patient inter-fraction errors were analysed for time trends during the course of radiotherapy. PTV margins were calculated from the systematic and random errors.

RESULTS

The initial inter-fraction population systematic errors were 1.8-3.3 mm (translation) and 0.5° (rotation); random errors were 1.8-2.1 mm (translation) and 0.3-0.5° (rotation). After online correction, the residual inter-fraction population systematic errors were 1.2-1.8 mm (translation) and 0.3-0.4° (rotation); random errors were 1.4-1.6 mm (translation) and 0.3-0.4° (rotation). Intra-fraction population systematic and random errors were ≤ 1.3 mm (translation) and ≤ 0.2° (rotation). The magnitude of inter-fraction set-up errors in the anterior-posterior direction, roll, and yaw were significantly correlated with higher body weight and body mass index (BMI). The inter-fraction set-up error did not change significantly as a function of time during the course of radiotherapy. The magnitude of intra-fraction motion was not correlated with patient characteristics and treatment time. The total PTV margins accounting for pre-correction and intra-fraction errors were 6.5-10.2 mm; those accounting for post-correction and intra-fraction errors were 4.7-6.3 mm.

CONCLUSIONS

CBCT is an effective modality to evaluate and improve the inter-fraction set-up reproducibility in RSD breast radiotherapy, particularly for patients with higher BMI. Intra-fraction motion was minimal during RSD breast radiotherapy.

Real-time intra-fraction motion management in breast cancer radiotherapy: analysis of 2028 treatment sessions

BACKGROUND

Intra-fraction motion represents a crucial issue in the era of precise radiotherapy in several settings, including breast irradiation. To date, only few data exist on real-time measured intra-fraction motion in breast cancer patients. Continuous surface imaging using visible light offers the capability to monitor patient movements in three-dimensional space without any additional radiation exposure. The aim of the present study was to quantify the uncertainties of possible intra-fractional motion during breast radiotherapy.

MATERIAL AND METHODS

One hundred and four consecutive patients that underwent postoperative radiotherapy following breast conserving surgery or mastectomy were prospectively evaluated during 2028 treatment sessions. During each treatment session the patients' motion was continuously measured using the Catalyst™ optical surface scanner (C-RAD AB, Sweden) and compared to a reference scan acquired at the beginning of each session. The Catalyst system works through an optical surface imaging with light emitting diode (LED) light and reprojection captured by a charge coupled device (CCD) camera, which provide target position control during treatment delivery with a motion detection accuracy of 0.5 mm. For 3D surface reconstruction, the system uses a non-rigid body algorithm to calculate the distance between the surface and the isocentre and using the principle of optical triangulation. Three-dimensional deviations and relative position differences during the whole treatment fraction were calculated by the system and analyzed statistically.

RESULTS

Overall, the maximum magnitude of the deviation vector showed a mean change of 1.93 mm ± 1.14 mm (standard deviation [SD]) (95%-confidence interval: [0.48-4.65] mm) and a median change of 1.63 mm during dose application (beam-on time only). Along the lateral and longitudinal axis changes were quite similar (0.18 mm ± 1.06 mm vs. 0.17 mm ± 1.32 mm), on the vertical axis the mean change was 0.68 mm ± 1.53 mm. The mean treatment session time was 154 ± 53 (SD) seconds and the mean beam-on time only was 55 ± 16 s. According to Friedman's test differences in the distributions of the three possible directions (lateral, longitudinal and vertical) were significant (p < 0.01), in post-hoc analysis there were no similarities between any two of the three directions.

CONCLUSION

The optical surface imaging system is an accurate and easy tool for real-time motion management in breast cancer radiotherapy. Intra-fraction motion was reported within five millimeters in all directions. Thus, intra-fraction motion in our series of 2028 treatment sessions seems to be of minor clinical relevance in postoperative radiotherapy of breast cancer.

Dosimetric advantages afforded by a new irradiation technique, Dynamic WaveArc, used for accelerated partial breast irradiation

PURPOSE

To identify dosimetric advantages of the novel Dynamic WaveArc (DWA) technique for accelerated partial breast irradiation (APBI), compared with non-coplanar three-dimensional conformal radiotherapy (nc3D-CRT) and coplanar tangential volumetric modulated arc therapy (tVMAT) with dual arcs of 45-65°.

METHODS

Vero4DRT enables DWA by continuous gantry rotation and O-ring skewing with movement of the multi-leaf collimator. We compared the dose distributions of DWA, nc3D-CRT and tVMAT in 24 consecutive left-sided breast cancer patients treated with APBI (38.5 Gy in 10 fractions). The average doses and volumes to the planning target volume (PTV) and organs at risk, especially heart and left anterior descending artery (LAD) were compared among DWA, nc3D-CRT and tVMAT.

RESULTS

The doses and volumes to the PTVs did not differ significantly among the three plans. For the DWA plans, the mean dose to the heart was 0.2 ± 0.1 Gy, less than those of the nc3D-CRT and tVMAT plans. The D_2% values of the planning organ at risk volume of the LAD were 9.3 ± 10.9%, 28.2 ± 31.9% and 20.3 ± 25.7% for DWA, nc3D-CRT and tVMAT, respectively. The V_20Gy and V_10Gy of the ipsilateral lung for the DWA plans were also significantly lower.

CONCLUSIONS

DWA allowed to find a better compromise for OAR which overlapped with the PTV. Use of the DWA for APBI improved the dose distributions compared with those of nc3D-CRT and tVMAT.