Dosimetric Impact of Image-Guided Radiotherapy in Liver Stereotactic Radiotherapy

A systematic review of tumour position reproducibility and stability in breath-hold for radiation therapy of the upper abdomen

Background and purpose

Upper abdominal malignancies are relatively rare, and although surgery is considered the primary treatment option, radiation therapy has an emerging role in the management of liver, pancreas, kidney and adrenal gland tumours. Furthermore, stereotactic radiation therapy for the management of upper abdominal metastases is an expanding clinical indication. Breath-hold is one respiratory motion management strategy used in upper abdominal radiation therapy, and the reproducibility, and stability of breath-hold is critical for overall treatment accuracy.

Materials and methods

A systematic review of the literature was conducted in Medline, Embase and Cochrane databases with keyword and vocabulary terms related to radiation therapy, breath-hold and upper abdominal tumours.

Results

Following screening against the selection criteria, 41 studies were included. Breath-hold reproducibility was the most commonly reported outcome and exhale breath-hold was the most common type. Studies were either prospective or retrospective cohort studies, and the mean sample size was 19 participants. The risk of bias of each included study was assessed, and the mean quality assessment score for included studies was 90 % (77-100 %). Median exhale breath-hold cranio-caudal inter-fraction reproducibility was 0.6 mm, (IQR 0.3-1.6 mm), compared to inspiratory breath-hold 0.0 mm (IQR -0.6-2.97 mm). Stability measurements were ≤3 mm in 71 % of studies, irrespective of breath-hold type.

Discussion

Formulating institutional protocols for best clinical practice regarding breath-hold for upper abdominal tumours is challenging, given the significant variation in practices, interventions and definitions observed in the literature. Further investigation to individualise breath-hold strategies and safety margins is warranted.

Liver SBRT with active motion-compensation results in excellent local control for liver oligometastases: An outcome analysis of a pooled multi-platform patient cohort

BACKGROUND

Local treatment of metastases in combination with systemic therapy can prolong survival of oligo-metastasized patients. To fully exploit this potential, safe and effective treatments are needed to ensure long-term metastases control. Stereotactic body radiotherapy (SBRT) is one means, however, for moving liver tumors correct delivery of high doses is challenging. After validating equal in-vivo treatment accuracy, we analyzed a pooled multi-platform liver-SBRT-database for clinical outcome.

METHODS

Local control (LC), progression-free interval (PFI), overall survival (OS), predictive factors and toxicity was evaluated in 135 patients with 227 metastases treated by gantry-based SBRT (deep-inspiratory breath-hold-gating; n = 71) and robotic-based SBRT (fiducial-tracking, n = 156) with mean gross tumor volume biological effective dose (GTV-BED_α/β=10Gy) of 146.6 Gy₁₀.

RESULTS

One-, and five-year LC was 90% and 68.7%, respectively. On multivariate analysis, LC was significantly predicted by colorectal histology (p = 0.006). Median OS was 20 months with one- and two-year OS of 67% and 37%. On multivariate analysis, ECOG-status (p = 0.003), simultaneous chemotherapy (p = 0.003), time from metastasis detection to SBRT-treatment (≥2months; p = 0.021) and LC of the treated metastases (≥12 months, p < 0.009) were significant predictors for OS. One- and two-year PFI were 30.5% and 14%. Acute toxicity was mild and rare (14.4% grade I, 2.3% grade II, 0.6% grade III). Chronic °III/IV toxicities occurred in 1.1%.

CONCLUSIONS

Patient selection, time to treatment and sufficient doses are essential to achieve optimal outcome for SBRT with active motion compensation. Local control appears favorable compared to historical control. Long-term LC of the treated lesions was associated with longer overall survival.

The Dosimetric Impact of Interfractional Organ-at-Risk Movement During Liver Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiation therapy (SBRT) is an effective therapy for treating liver malignancies. However, little is known about interfractional dose variations to adjacent organs at risk (OARs). We examine the effects of interfractional organ movement and setup variation on dose delivered to OARs in patients receiving liver SBRT.

METHODS AND MATERIALS

Thirty patients treated with liver SBRT were analyzed. Daily image guidance with diagnostic quality computed tomography-on-rails imaging was performed before each fraction. In phase 1, these daily images were used to delineate all OARs including the liver, heart, right kidney, esophagus, stomach, duodenum, and large bowel in 10 patients. In phase 2, only OARS in close proximity to the target were contoured in 20 additional patients. Dose distribution on each daily computed tomography was generated, and daily doses to each OAR were recorded and compared with clinical thresholds to determine whether a daily dose excess (DDE) occurred.

RESULTS

In phase 1, significant interfractional dose differences between planned and delivered dose to OARs were observed, but differences were rarely clinically significant, with just 1 DDE. In phase 2, multiple DDEs were recorded for OARs close to the target, mainly involving the stomach, heart, and esophagus. Tumors in the hilum and liver segments I, IV, and VIII were the most common locations for DDEs. On root cause analysis, 3 etiologies of DDE emerged: craniocaudal shift (69.2%), anatomic changes (28.2%), and anteroposterior shifts (2.6%).

CONCLUSIONS

OARs close to liver lesions may receive higher doses than expected during SBRT owing to interfractional variations in OARs relative to the target. These differences in planned versus expected dose can lead to toxicity. Efforts to better evaluate OARs with daily image guidance may help reduce risks. Application of adaptive replanning and improved and real-time image guidance could mitigate risks of toxicity, and further study into their applications is warranted.