Potential Clinical Significance of Overall Targeting Accuracy and Motion Management in the Treatment of Tumors That Move With Respiration: Lessons Learnt From a Quarter Century of Stereotactic Body Radiotherapy From Dose Response Models

Precision in Motion Management: Long-Term Local Control and Prognostic Insights in SBRT for Oligometastatic Lung and Liver Metastases

Background/Objectives: Inadequate dosing and respiratory motion contribute to local recurrence for oligometastatic disease (OMD). While short-term LC rates are well-documented, data on long-term LC remain limited. This study investigated long-term LC after stereotactic body radiotherapy (SBRT), using respiratory motion management techniques. Methods: This retrospective study took place at UZ Brussel with follow-up until Oct 2024. It analyzed oligometastatic patients treated with SBRT between Jul 2012 and Feb 2017. Treatment involved delivering 50 Gy in 10 fractions on the 80% isodose line, building on data from a prior prospective study. Lesion movement was managed using internal target volume (ITV) or dynamic tumor tracking (DTT) with marker. The primary endpoint of the study was long-term LC and identifying variables associated with it using a Cox proportional hazards model. Results: A total of 100 patients were treated for a total of 211 metastatic lesions. Lesions were predominantly in the lungs (74%) and treated using ITV (88%). LC rates at 1, 3, 5, and 10 years were 76.5%, 53.8%, 38.1%, and 36.3%, respectively. Improved LC was observed in locations other than lung and liver (HR: 0.309; p = 0.024) and with increasing age (HR: 0.975; p < 0.010). Worse LC was seen in liver lesions (HR: 1.808; p = 0.103) and systemic therapy post-radiotherapy (HR: 3.726; p < 0.001). No significant associations were found with tumor size or tumor motion, nor between the two motion management strategies used (DTT and ITV). Conclusions: Appropriate motion management is key in LC for OMD. No significant difference in LC was found between both techniques. Lesion location, patient age, and systemic therapy post-radiotherapy were prognostic factors for LC.

Quantitative evaluation of accumulated and planned dose deviations in patients undergoing gated and non-gated lung stereotactic body radiation therapy patients: a retrospective analysis

Background

Stereotactic body radiation therapy (SBRT) is crucial for treating early-stage inoperable non-small cell lung cancer (NSCLC) due to its precision and high-dose delivery. This study aimed to investigate the dosimetric deviations in gated (GR) versus non-gated radiotherapy (NGR), analyzing the impact of tumor location, target volume, and tumor motion range on dose distribution accuracy.

Methods

Sixty patients treated with either gated (n=30) or non-gated (n=30) SBRT for early-stage NSCLC were retrospectively analyzed. The planned dose distributions were determined using four-dimensional computed tomography simulations to account for breathing motion, while the actual dose delivered was determined by accumulating each fractional dose with synthetic computed tomography (sCT) methods. The deviations between the planned and actual accumulated doses were statistically analyzed for both groups. The effects of tumor location and volume on dose distribution were also assessed.

Results

Gated SBRT showed significantly higher dosimetric precision with median relative changes in the minimum dose within the ITV (ITV_Dmin), mean dose received by the ITV (ITV_Dmean), and maximum dose within the ITV (ITV_Dmax) of -0.44%, -0.33%, and -0.49%, respectively. Non-gated SBRT presented with larger median relative changes in these parameters (P<0.001 for the ITV_Dmin). In gated SBRT, the PTV_Dmin (minimum dose within the PTV) and PTV_Dmean (mean dose received over the entire PTV) differences were significantly lower favoring gated SBRT (P=0.01 and P=0.007, respectively), and for the prescribed dose volumes, the volume of PTV receiving 90% prescription dose (PTV_V90%PD) and the volume of PTV receiving 100% prescription dose (PTV_V100%PD) were more accurately delivered, also favoring gated SBRT (P=0.006 and P=0.03, respectively). The tumor location and volume analyses demonstrated that the dosimetric benefits of gated SBRT were particularly significant in the smaller internal target volumes (ITVs) and in the left lower central lung region (P<0.001 for the ITV_Dmin in small volumes).

Conclusions

Gated SBRT affords dosimetric accuracy compared to non-gated SBRT, and thus could improve the therapeutic outcomes of NSCLC patients. These results should advocate for the preferential use of gated SBRT in cases requiring precise dose delivery due to large respiratory motion or small target volumes.

A model that predicts a real-time tumour surface using intra-treatment skin surface and end-of-expiration and end-of-inhalation planning CT images

OBJECTIVES

To develop a mapping model between skin surface motion and internal tumour motion and deformation using end-of-exhalation (EOE) and end-of-inhalation (EOI) 3D CT images for tracking lung tumours during respiration.

METHODS

Before treatment, skin and tumour surfaces were segmented and reconstructed from the EOE and the EOI 3D CT images. A non-rigid registration algorithm was used to register the EOE skin and tumour surfaces to the EOI, resulting in a displacement vector field that was then used to construct a mapping model. During treatment, the EOE skin surface was registered to the real-time, yielding a real-time skin surface displacement vector field. Using the mapping model generated, the input of a real-time skin surface can be used to calculate the real-time tumour surface. The proposed method was validated with and without simulated noise on 4D CT images from 15 patients at Léon Bérard Cancer Center and the 4D-lung dataset.

RESULTS

The average centre position error, dice similarity coefficient (DSC), 95%-Hausdorff distance and mean distance to agreement of the tumour surfaces were 1.29 mm, 0.924, 2.76 mm, and 1.13 mm without simulated noise, respectively. With simulated noise, these values were 1.33 mm, 0.920, 2.79 mm, and 1.15 mm, respectively.

CONCLUSIONS

A patient-specific model was proposed and validated that was constructed using only EOE and EOI 3D CT images and real-time skin surface images to predict internal tumour motion and deformation during respiratory motion.

ADVANCES IN KNOWLEDGE

The proposed method achieves comparable accuracy to state-of-the-art methods with fewer pre-treatment planning CT images, which holds potential for application in precise image-guided radiation therapy.

Preoperative single fraction breast radiotherapy: Intra-fraction geometric uncertainties and dosimetric implications

PURPOSE

A preoperative breast robotic radiosurgery trial was concluded in our centre. Purposes of the present study were to evaluate retrospectively over the enrolled patients: i) respiratory patterns ii) tracking uncertainties iii) necessity of respiratory compensation iv) tracking errors dosimetric effects.

METHODS

22 patients were treated in 21 Gy single fraction using CyberKnife (CK) respiratory modelling and tracking (SynchronyResp) and data extracted from log-files. Respiratory motion and baseline drifts (BD) were analyzed. SynchronyResp uncertainties were computed and compared with errors simulated for CK fiducial tracking without respiratory compensation. Plans were perturbed by tracking errors and perturbed doses calculated on the planning CT scan in order to simulate the dosimetric consequences of intra-fraction errors.

RESULTS

After BD correction, respiratory amplitudes were below 5.5 mm except one value of 8 mm. 50% of patients showed BD above 3 mm. Standard deviations of SynchronyResp errors remained within 2.1 mm. Standard deviations of tracking errors without respiratory compensation were comparable and below 2.5 mm. Using a 3 mm PTV margin, perturbed CTV coverage was below 95% (93.7%) just for one patient. The latter case presented a large CTV-Skin interface. Perturbed OAR doses were always judged clinically acceptable.

CONCLUSION

Intra-fraction geometric uncertainties and their effects were quantified for breast neoadjuvant CK treatments. Data indicated that in the majority of cases respiratory compensation may be disabled without increasing uncertainties and reducing treatment time, provided that fiducial intra-fraction tracking is performed to account for BD. Dosimetric effects are mostly not clinically relevant.

CArdiac and REspiratory adaptive Computed Tomography (CARE-CT): a proof-of-concept digital phantom study

Current respiratory 4DCT imaging for high-dose rate thoracic radiotherapy treatments are negatively affected by the complex interaction of cardiac and respiratory motion. We propose an imaging method to reduce artifacts caused by thoracic motion, CArdiac and REspiratory adaptive CT (CARE-CT), that monitors respiratory motion and ECG signals in real-time, triggering CT acquisition during combined cardiac and respiratory bins. Using a digital phantom, conventional 4DCT and CARE-CT acquisitions for nineteen patient-measured physiological traces were simulated. Ten respiratory bins were acquired for conventional 4DCT scans and ten respiratory bins during cardiac diastole were acquired for CARE-CT scans. Image artifacts were quantified for 10 common thoracic organs at risk (OAR) substructures using the differential normalized cross correlation between axial slices (ΔNCC), mean squared error (MSE) and sensitivity. For all images, on average, CARE-CT improved the ΔNCC for 18/19 and the MSE and sensitivity for all patient traces. The ΔNCC was reduced for all cardiac OARs (mean reduction 21%). The MSE was reduced for all OARs (mean reduction 36%). In the digital phantom study, the average scan time was increased from 1.8 ± 0.4 min to 7.5 ± 2.2 min with a reduction in average beam on time from 98 ± 28 s to 45 s using CARE-CT compared to conventional 4DCT. The proof-of-concept study indicates the potential for CARE-CT to image the thorax in real-time during the cardiac and respiratory cycle simultaneously, to reduce image artifacts for common thoracic OARs.

Experience With Normal Breathhold Planning Scans for Radiosurgery of Moving Targets With Live Tracking

PURPOSE

Utilization of breathhold scans with live tracking has a long track record of good published outcomes for stereotactic body radiation therapy (SBRT) and is recommended by the manufacturer of the Synchrony tracking system. However, the popularity of four-dimensional computed tomography (4DCT) scans challenges the validity of the breathhold scan with live tracking technique. Although this study is not intended to prove the superiority of either method, we demonstrate the feasibility of using the breathhold scans with a phantom test and clinical examples.

METHODS

A 4DCT of a perfect sphere was scanned at 20 breaths per minute and compared to a 4DCT of a small lung tumor in one patient and a 4DCT of a larger renal tumor in another patient, as well as to fiducial matching in a patient with pancreatic cancer. Normal exhale and normal inhale breathhold CT scans were performed for the pancreatic cancer patient, combined with Synchrony tracking on CyberKnife (Sunnyvale, CA: Accuray) for treatment.

RESULTS

The 4DCT scan of the phantom exhibited considerable apparent deformation, which must be entirely due to imaging artifact since the perfect sphere in the phantom is known to be completely rigid. The 4DCT of the lung and renal tumors in patients had similar apparent deformation. Usually in patients, from 4DCT alone, it is difficult to determine how much was due to deformation and how much was due to artifact. Fiducial positions in the final normal exhale and normal inhale breathhold scans for Synchrony matched each other within 1mm for the pancreatic cancer patient.

CONCLUSION

We demonstrated the feasibility of breathhold scans with Synchrony live tracking, as recommended by the manufacturer. More studies will be needed to determine whether this method is better than using a 4DCT.

Adoption of respiratory motion management in radiation therapy

Background and Purpose

A survey on the patterns of practice of respiratory motion management (MM) was distributed to 111 radiation therapy facilities to inform the development of an end-to-end dosimetry audit including respiratory motion.

Materials and methods

The survey (distributed via REDCap) asked facilities to provide information specific to the combinations of MM techniques (breath-hold gating – BHG, internal target volume – ITV, free-breathing gating – FBG, mid-ventilation – MidV, tumour tracking – TT), sites treated (thorax, upper abdomen, lower abdomen), and fractionation regimes (conventional, stereotactic ablative body radiation therapy – SABR) used in their clinic.

Results

The survey was completed by 78% of facilities, with 98% of respondents indicating that they used at least one form of MM. The ITV approach was common to all MM-users, used for thoracic treatments by 89% of respondents, and upper and lower abdominal treatments by 38%. BHG was the next most prevalent (41% of MM users), with applications in upper abdominal and thoracic treatment sites (28% vs 25% respectively), but minimal use in the lower abdomen (9%). FBG and TT were utilised sparingly (17%, 7% respectively), and MidV was not selected at all.

Conclusions

Two distinct treatment workflows (including use of motion limitation, imaging used for motion assessment, dose calculation, and image guidance procedures) were identified for the ITV and BHG MM techniques, to form the basis of the initial audit. Thoracic SABR with the ITV approach was common to nearly all respondents, while upper abdominal SABR using BHG stood out as more technically challenging. Other MM techniques were sparsely used, but may be considered for future audit development.