Image guidance and stabilization for stereotactic ablative body radiation therapy (SABR) treatment of primary kidney cancer

Treatment Time Optimization in Single Fraction Stereotactic Ablative Radiation Therapy: A 10-Year Institutional Experience

Purpose

Stereotactic ablative radiation therapy (SABR) delivered in a single fraction (SF) can be considered to have higher uncertainty given that the error probability is concentrated in a single session. This study aims to report the variation in technology and technique used and its effect on intrafraction motion based on a 10 years of experience in SF SABR.

Methods and Materials

Records of patients receiving SF SABR delivered at our instruction between 2010 and 2019 were included. Treatment parameters were extracted from the patient management database by using an in-house script. Treatment time was defined as the time difference between the first image acquisition to the last beam off of a single session. The intrafraction variation was measured from the 3-dimensional couch displacement measured after the first cone beam computed tomography (CBCT) acquired during a treatment.

Results

The number of SF SABR increased continuously from 2010 to 2019 and were mainly lung treatments. Treatment time was minimized by using volumetric modulated arc therapy, flattening filter-free dose rate, and coplanar field (24 ± 9 min). Treatment time increased as the number of CBCTs per session increased. The most common scenario involved both 2 and 3 CBCTs per session. On the average, a CBCT acquisition added 6 minutes to the treatment time. All treatments considered, the average intrafraction variation was 1.7 ± 1.6 mm.

Conclusions

SF SABR usage increased with time in our institution. The intrafraction motion was acceptable and therefore a single fraction is an efficacious treatment option when considering SABR.

Personalising treatment plan quality review with knowledge-based planning in the TROG 15.03 trial for stereotactic ablative body radiotherapy in primary kidney cancer

INTRODUCTION

Quality assurance (QA) of treatment plans in clinical trials improves protocol compliance and patient outcomes. Retrospective use of knowledge-based-planning (KBP) in clinical trials has demonstrated improved treatment plan quality and consistency. We report the results of prospective use of KBP for real-time QA of treatment plan quality in the TROG 15.03 FASTRACK II trial, which evaluates efficacy of stereotactic ablative body radiotherapy (SABR) for kidney cancer.

METHODS

A KBP model was generated based on single institution data. For each patient in the KBP phase (open to the last 31 patients in the trial), the treating centre submitted treatment plans 7 days prior to treatment. A treatment plan was created by using the KBP model, which was compared with the submitted plan for each organ-at-risk (OAR) dose constraint. A report comparing each plan for each OAR constraint was provided to the submitting centre within 24 h of receiving the plan. The centre could then modify the plan based on the KBP report, or continue with the existing plan.

RESULTS

Real-time feedback using KBP was provided in 24/31 cases. Consistent plan quality was in general achieved between KBP and the submitted plan. KBP review resulted in replan and improvement of OAR dosimetry in two patients. All centres indicated that the feedback was a useful QA check of their treatment plan.

CONCLUSION

KBP for real-time treatment plan review was feasible for 24/31 cases, and demonstrated ability to improve treatment plan quality in two cases. Challenges include integration of KBP feedback into clinical timelines, interpretation of KBP results with respect to clinical trade-offs, and determination of appropriate plan quality improvement criteria.

Reducing the impact on renal function of kidney SABR through management of respiratory motion

PURPOSE

Stereotactic ablative body radiotherapy (SABR) is as a viable treatment option to treat kidney cancer. This study quantifies dose reduction to non-tumour ipsilateral kidney and estimated renal function gain from elimination of respiratory motion.

METHODS

We reviewed 62 previously treated kidney SABR patients. The gross tumour volume (GTV) was segmented in each phase of a four-dimensional CT (4DCT). Tumour motion amplitude (TMA) was obtained from the GTV centroid on each phase. Low modulation, motion managed (MM) plans were generated on the exhale phase image. Internal target volume (ITV)-based plans were generated on the 4DCT average intensity projection. To estimate delivered kidney dose, the ITV-based plan was copied ten times to the exhale phase image, with isocentre located at the GTV centroid position in each phase. The dose was calculated and averaged to result in non-motion managed plans. Difference in ipsilateral kidney volume receiving 50% of the prescription dose (V50%) and estimated glomerular filtration rate (GFR) change were compared between ITV and MM plans.

RESULTS

The mean ± st.dev. TMA was 0.79 ± 0.49 cm. Removing respiratory motion reduced ipsilateral kidney V50% (slope of the difference = 12 cc/cm of TMA, Pearson-r = 0.69, p-value <10^-9), and estimated GFR was improved (slope = 4.4 %/cm of TMA, Pearson-r = 0.85, p-value < 10^-10).

CONCLUSIONS

We have quantified the improvement in healthy kidney dose when removing respiratory motion from kidney SABR plans, and demonstrated an expected gain in GFR of 4.4 %/cm of motion removed.

Adaptive Magnetic Resonance-Guided Stereotactic Body Radiotherapy: The Next Step in the Treatment of Renal Cell Carcinoma

Adaptive MR-guided radiotherapy (MRgRT) is a new treatment paradigm and its role as a non-invasive treatment option for renal cell carcinoma is evolving. The early clinical experience to date shows that real-time plan adaptation based on the daily MRI anatomy can lead to improved target coverage and normal tissue sparing. Continued technological innovations will further mitigate the challenges of organ motion and enable more advanced treatment adaptation, and potentially lead to enhanced oncologic outcomes and preservation of renal function. Future applications look promising to make a positive clinical impact and further the personalization of radiotherapy in the management of renal cell carcinoma.