Establishing stereotactic body radiotherapy with flattening filter free techniques in the treatment of pulmonary lesions - initial experiences from a single institution

Progress and prospects of flattening filter free beam technology in radiosurgery and stereotactic body radiotherapy

The aim of this work is to summarize and evaluate the current status of knowledge on flattening filter free (FFF) beams and their applications in stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). A PubMed search was undertaken in order to identify relevant publications using FFF and stereotactic radiotherapy as keywords. On a clinical aspect, lung tumors treated with FFF SBRT show promising results in terms of local control and overall survival with acute toxicities consistent with those that occur with standard radiotherapy. Beside lung, SBRT is suitable for different anatomical sites such as liver, prostate, cervix, etc. offering similar results: reduced treatment time, good tumor control and mild acute toxicities. Regarding brain tumors, the employment of SRS with FFF beams significantly reduces treatment time and provides notable normal tissue sparing due to the sharp dose fall-off outside the tumor.

Starting the Stereotactic Radiosurgery Facility in Bangladesh: An Initial Experience

Radiotherapy is an integral part of a well-defined cancer management program. Bangladesh is a fast-growing East Asian country with 161 million population, and approximately 2 lakh cancer patients are diagnosed newly ever year. Though there are several modern treatment facilities to deliver radiotherapy, only limited facilities were available to deliver stereotactic radiotherapy (SRS) programs for needy patients. Evercare Hospitals Dhaka has recently started SRS and stereotactic therapy (SRT) with a dedicated team of trained people. The hospital is equipped with modern linear accelerator capable of delivering high dose rate mode and micro multileaf collimators with 2.45-mm thickness at isocenter to deliver larger doses of radiation precisely. This paper summarizes patient selection criteria and workflow for the SRS/SRT treatment established, including patient preparation, image data acquisition, target and organ at risk delineation on CT (computed tomography) and MRI (magnetic resonance imaging) images, treatment planning process, and quality assurance. Each stage of the process is explained in detail, with specific emphasis on certain areas to achieve a higher degree of accuracy. This article also highlights the need for dedicated timeout procedures to be followed to avoid drastic errors in treatment delivery. We also summarized demographics data of patients treated in the first 6 months, including diagnosis, sizes of lesions, and dose fraction. The dosimetric and setup uncertainties encountered during SRS/SRT treatment delivery are also described. Though, initially, we faced challenges, SRS/SRT treatment was successfully implemented and more than 35 patients were treated, with appreciable clinical outcomes.

On the use of single‐isocenter VMAT plans for SBRT treatment of synchronous multiple lung lesions: Plan quality, treatment efficiency, and early clinical outcomes

Cone‐beam computed tomography (CT)‐guided volumetric‐modulated arc therapy (VMAT) plans for stereotactic body radiotherapy (SBRT) treatment of synchronous multiple lung lesions with a flattening filter‐free (FFF) beam is a safe and highly effective treatment option for oligometastases lung cancer patients. Fourteen patients with metastatic non–small‐cell lung cancer (NSCLC) lesions (two to five) received a single‐isocenter VMAT SBRT treatment in our clinic. Four‐dimensional (4D) CT‐based treatment plans were generated using advanced AcurosXB‐based dose calculation algorithm using heterogeneity corrections with a single isocenter placed between/among the lesions. Compared to 10X‐FFF and traditional flattened 6X (6X‐FF) beams, 6X‐FFF beam produced highly conformal radiosurgical dose distribution to each target volume, reduced dose to adjacent organs at risk (OAR), and significantly reduced the lung SBRT fraction duration to < 3.5 min/fraction for 54/50 Gy treatments in 3/5 fractions — significantly improving patient convenience and clinic workflow. Early follow‐up CT imaging (mean, 9 months) results show high local control rates (100%) with no acute lung or rib toxicity. Longer clinical follow up in a larger patient cohort is ongoing to further validate the outcomes of this treatment approach.

The effect of stereotactic body radiotherapy (SBRT) using flattening filter-free beams on cardiac implantable electronic devices (CIEDs) in clinical situations

PURPOSE

This study focused on determining risks from stereotactic radiotherapy using flattening filter-free (FFF) beams for patients with cardiac implantable electronic device (CIEDs). Two strategies were employed: a) a retrospective analysis of patients with CIEDs who underwent stereotactic radiosurgery (SRS)/SBRT at the Peter MacCallum Cancer Centre between 2014 and 2018 and b) an experimental study on the impact of FFF beams on CIEDs.

METHODS

A retrospective review was performed. Subsequently, a phantom study was performed using 30 fully functional explanted CIEDs from two different manufacturers. Irradiation was carried out in a slab phantom with 6-MV and 10-MV FFF beams. First, a repetition-rate test (RRT) with a range of beam pulse frequencies was conducted. Then, multifraction SBRT (48 Gy/4 Fx) and single-fraction SBRT (28 Gy/1 Fx) treatment plans were used for lung tumors delivered to the phantom.

RESULTS

Between 2014 and 2018, 13 cases were treated with an FFF beam (6 MV, 1400 MU/min or 10 MV, 2400 MU/min), and 15 cases were treated with a flattening filter (FF) beam (6 MV, 600 MU/min). All the devices were positioned outside the treatment field at a distance of more than 5 cm, except for one case, and no failures were reported due to SBRT/SRS. In the phantom rep-rate tests, inappropriate sensing occurred, starting at a rep-rate of 1200 MU/min. Cardiac implantable electronic device anomalies during and after delivering VMAT-SBRT with a 10-MV FFF beam were observed.

CONCLUSIONS

The study showed that caution should be paid to managing CIED patients when they undergo SBRT using FFF beams, as it is recommended by AAPM TG-203. Correspondingly, it was found that for FFF beams although there is small risk from dose-rate effects, delivering high dose of radiation with beam energy greater than 6 MV and high-dose rate to CIEDs positioned in close vicinity of the PTV may present issues.

Flattening filter-free technique in volumetric modulated arc therapy for lung stereotactic body radiotherapy: A clinical comparison with the flattening filter technique

The present study sought to evaluate the impact of the flattening filter-free (FFF) technique in volumetric modulated arc therapy for lung stereotactic body radiotherapy. Its clinical safety and availability were compared with the flattening filter (FF) method. The cases of 65 patients who underwent lung volumetric modulated arc therapy-stereotactic body radiotherapy (VMAT-SBRT) using FF or FFF techniques were reviewed. A total of 55 Gy/4 fractions (fr) was prescribed for peripheral lesions or 56 Gy/7 fr for central lesions. The total monitor units (MU), treatment time, dose to tumors, dose to organs at risk, tumor control (local control rate, overall survival, progression-free survival) and adverse events between cases treated with FF and cases treated with the FFF technique were compared. A total of 35 patients were treated with conventional FF techniques prior to November 2014 and 30 patients were treated with FFF techniques after this date. It was revealed that the beam-on time was significantly shortened by the FFF technique (P<0.01). Other factors were similar for FFF and FF plans in respect to conformity (P=0.95), homogeneity (P=0.20) and other dosimetric values, including total MU and planning target volume/internal target volume coverage. The median follow-up period was 18 months (range, 2-35). One-year local control rates were 97.1 and 90.0% in the FF group and FFF groups, respectively (P=0.33). Grade 3 pneumonitis was observed in 5.8% of FF patients and 3.4% of FFF patients (P=1.00). No other adverse events ≥grade 3 were observed. The results of the study suggest that VMAT-SBRT using the FFF technique shortens the treatment time for lung SBRT while maintaining a high local control rate with low toxicity.

Parenchymal and Functional Lung Changes after Stereotactic Body Radiotherapy for Early-Stage Non-Small Cell Lung Cancer-Experiences from a Single Institution

Introduction

This study aimed to evaluate parenchymal and functional lung changes following stereotactic body radiotherapy (SBRT) for early-stage non-small cell lung cancer (NSCLC) patients and to correlate radiological and functional findings with patient and treatment characteristics as well as survival.

Materials and methods

Seventy patients with early-stage NSCLC treated with SBRT from 2004 to 2015 with more than 1 year of CT follow-up scans were analyzed. Incidence, morphology, severity of acute and late lung abnormalities as well as pulmonary function changes were evaluated and correlated with outcome.

Results

Median follow-up time was 32.2 months with 2-year overall survival (OS) of 83% and local progression-free survival of 88%, respectively. Regarding parenchymal changes, most patients only developed mild to moderate CT abnormalities. Mean ipsilateral lung dose (MLD) in biological effective dose and planning target volume size were significantly associated with maximum severity score of parenchymal changes (p = 0.014, p < 0.001). Furthermore, both maximum severity score and MLD were significantly connected with OS in univariate analysis (p = 0.043, p = 0.025). For functional lung changes, we detected significantly reduced total lung capacity, forced expiratory volume in 1 s, and forced vital capacity (FVC) parameters after SBRT (p ≤ 0.001). Multivariate analyses revealed SBRT with an MLD ≥ 9.72 Gy and FVC reduction ≥0.54 L as independent prognostic factors for inferior OS (p = 0.029, p = 0.004).

Conclusion

SBRT was generally tolerated well with only mild toxicity. For evaluating the possible prognostic impact of MLD and FVC reduction on survival detected in this analysis, larger prospective studies are truly needed.