Stereotactic radiosurgery (SRS) has proven itself as an effective tool in the treatment of intracranial lesions. Image-guided high dose single fraction treatments have the potential to deliver ablative doses to tumours; however, treatment times can be long. Flattening filter free (FFF) beams are available on most modern linacs and offer a higher dose rate compared to conventional flattened beams which should reduce treatment times. This study aimed to compare 6 MV FFF and 10 MV FFF to a 6 MV flattened beam for single fraction dynamic conformal arc SRS for a Varian Truebeam linac.

In total, 21 individual clinical treatment plans for 21 brain metastases treated with 6 MV were retrospectively replanned using both 6 MV FFF and 10 MV FFF. Plan quality and efficiency metrics were evaluated by analysing dose coverage, dose conformity, dose gradients, dose to normal brain, beam-on-time (BOT), treatment time and monitor units.

FFF resulted in a significant reduction in median BOT for both 6 MV FFF (57·9%; p < 0·001) and 10 MV FFF (76·3%; p < 0·001) which led to reductions in treatment times of 16·8 and 21·5% respectively. However, 6 MV FFF showed superior normal brain dose sparing (p < 0·001) and dose gradient (p < 0·001) compared to 10 MV FFF. No differences were observed for conformity.

6 MV FFF offers a significant reduction in average treatment time compared to 6 MV (3·7 minutes; p = 0·002) while maintaining plan quality.

Stereotactic body radiation therapy for lung tumours can expose patients to radiation pneumonitis (RP) (<6 months after irradiation) and lung fibrosis (beyond 6 months). The aim of this study was to describe post-irradiation radiographics appearances.

This retrospective study of 90 patients with a stage I non-small cell lung carcinoma reports a detailed description of the computed tomography (CT) or positron emission tomography/CT changes that can be observed after treatment, according to modified Kimura score for RP and Koenig’s classification for fibrosis. This evaluation was realised at 1 month and then every 3–4 months, with a median follow-up of 35 months.

The most common radiological RP pattern was diffuse consolidation. It appears in a mean time of 4 months and reaches its maximum at 9 months after radiotherapy. Seventy-three per cent of the RP evolved to fibrosis. Most of these findings were encompassed in the 35 Gy isodose.

Radiological parenchymal changes are frequent in the treatment region, which renders the tumour response monitoring by tumour size, particularly by response evaluation criteria in solid tumours, unsuitable.

Brain metastases (BM) are common in patients with HER2-positive and triple-negative breast cancer. In this study we aim to report clinical outcomes with LINAC-based stereotactic radiosurgery/radiotherapy (SRS/SRT) for BM in patients of breast cancer.

Clinical and dosimetric records of breast cancer patients treated for BM at our institute between May, 2015 and December, 2019 were retrospectively reviewed. Patients of previously treated or newly diagnosed breast cancer with at least a radiological diagnosis of BM; 1–4 in number, ≤3·5 cm in maximum dimension, with a Karnofsky Performance Score of ≥60 were taken up for treatment with SRS. SRT was generally considered if a tumour was >3·5 cm in diameter, near a critical or eloquent structure, or if the proximity of moderately sized tumours would lead to dose bridging in a single-fraction SRS plan. The median prescribed SRS dose was 15 Gy (range 7–24 Gy) and SRT dose was 27 Gy in 3 fractions.

Clinical assessment and MR imaging was done at 6 weeks post-SRS and then every 3 months thereafter. Intracranial progression-free survival (PFS) and overall survival (OS) were calculated using Kaplan–Meier method and subgroups were compared using log rank test.

Total, 40 tumours were treated in 31 patients. The median tumour diameter was 2·3 cm (range 1·0–4·6 cm). SRS and SRT were delivered in 27 and 4 patients, respectively. SRS/SRT was given as a boost to whole brain radiotherapy (WBRT) in four patients and as salvage for progression after WBRT in six patients. In general, nine patients underwent prior surgery. The median follow-up was 7·9 months (0·2–34 months). Twenty (64·5%) patients developed local recurrence, 10 (32·3%) patients developed distant intracranial relapse and 7 patients had both local and distant intracranial relapse. The estimated local control at 6 months and 1 year was 48 and 35%, respectively. Median intracranial progression free survival (PFS) was 3·73 months (range 0·2–25 months). Median intracranial PFS was 3·02 months in patients who received SRS alone or as boost after WBRT, while it was 4·27 months in those who received SRS as salvage after WBRT (p = 0·793). No difference in intracranial PFS was observed with or without prior surgery (p = 0·410). Median overall survival (OS) was 21·7 months (range 0·2–34 months) for the entire cohort. Patients who received prior WBRT had a poor OS (13·31 months) as compared to SRS alone (21·4 months; p = 0·699).

In patients with BM after breast cancer SRS alone, WBRT + SRS and surgery + SRS had comparable PFS and OS.

Induction chemotherapy (iC) followed by concurrent chemoradiation has been shown to improve overall survival (OS) for locally advanced pancreatic cancer (LAPC). However, the survival benefit of stereotactic body radiation therapy (SBRT) versus conventionally fractionated radiation therapy (CFRT) following iC remains unclear.

The National Cancer Database (NCDB) was queried for primary stage III, cT4N0-1M0 LAPC (2004–15). Kaplan–Meier analysis, Cox proportional hazards method and propensity score matching were used.

Among 872 patients, 738 patients underwent CFRT and 134 patients received SBRT. Median follow-up was 24·3 and 22·9 months for the CFRT and SBRT cohorts, respectively. The use of SBRT showed improved survival in both the multivariate analysis (hazards ratio 0·78, p = 0·025) and 120 propensity-matched pairs (median OS 18·1 versus 15·9 months, p = 0·004) compared to the CFRT.

This NCDB analysis suggests survival benefit with the use of SBRT versus CFRT following iC for the LAPC.

Partial breast irradiation (PBI) can reduce the volume of treatment and number of treatment sessions in low-risk breast cancer patients. Stereotactic body radiotherapy (SBRT) allows the administration of high doses per fraction thereby reducing the number of fractions and reducing the dose to the surrounding tissues. The objective of this study is to review the literature on the use of SBRT in PBI using the Cyberknife® (CK) unit.

In this review, we analysed the literature in PubMed and MEDLINE with articles published in the last 10 years. All citations were evaluated for relevant content and validity.

We include articles in the English language with information about PBI, SBRT in PBI, the use of the CK unit in PBI and other applications of SBRT in breast carcinoma. A total of 68 articles were found and 28 articles were selected for inclusion in this review.

The treatment of PBI using the CK unit has clear advantages in reducing the treatment volume, and therefore theoretically reducing side effects and good cosmetic results with adequate tumour control. However, the placement of fiducial markers is necessary, requiring an adequate learning curve for the placement of the markers and longer treatment times.

The aim of this study was to investigate the extent to which lung stereotactic body radiotherapy (SBRT) treatment plans can be improved by replacing conventional flattening filter (FF) beams with flattening filter-free (FFF) beams.

We selected 15 patients who had received SBRT with conventional 6-MV photon beams for early-stage lung cancer. We imported the patients’ treatment plans into the Eclipse 13·6 treatment planning system, in which we configured the AAA dose calculation model using representative beam data for a TrueBeam accelerator operated in 6-MV FFF mode. We then created new treatment plans by replacing the conventional FF beams in the original plans with FFF beams.

The FFF plans had better target coverage than the original FF plans did. For the planning target volume, FFF plans significantly improved the D98, D95, D90, homogeneity index and uncomplicated tumour control probability. In most cases, the doses to organs at risk were lower in FFF plans. FFF plans significantly reduced the mean lung dose, V10, V20, V30, and normal tissue complication probability for the total lung and improved the dosimetric indices for the ipsilateral lung. For most patients, FFF beams achieved lower maximum doses to the oesophagus, heart and the spinal cord, and a lower chest wall V30.

Compared with FF beams, FFF beams achieved lower doses to organs at risk, especially the lung, without compromising tumour coverage; in fact, FFF beams improved coverage in most cases. Thus, replacing FF beams with FFF beams can achieve a better therapeutic ratio.

Vestibular schwannomas (VS) are benign slow-growing tumours treated either with microsurgery or stereotactic radiosurgery (SRS) or both. The aim of this study was to correlate the outcome factors—tumour control and adverse factors—facial nerve function and hearing loss with patient and treatment factors.

A retrospective review of the records of 98 patients with 99 VS treated from June 2007 to June 2014, all patients receiving Linear Accelerator (LINAC)-based SRS.

Median follow-up period was 5·6 years (range: 1–12 years). The response to treatment was stable disease in 37 (37·4%), regression in 46 (46·5%), asymptomatic minimal progression in 9 (9·1%) and symptomatic progression in 5 (5%) and unknown in 2 (2%) patients. There was no evidence of SRS induced tissue damage on magnetic resonance scans for any. Hearing preservation rate after SRS was 92%. The patients who developed worsening of facial function were predominantly in the cohort that had prior surgery.

SRS is an effective modality to treat VS lesser than 3 cm in size. Tumour control rate was 95% with a median follow-up period of 5·6 years. The complication rates were 8% each for facial function worsening and worsening of hearing. Prior surgery was a statistically significant factor that affected facial nerve function deterioration.

Fractionated stereotactic radiotherapy (FSRT) is an alternative treatment for large vestibular schwannomas (VS), if patients are not fit for or refuse surgery. In this study, we compared long-term clinical and radiological outcome in both small–medium sized and larger tumours.

A retrospective study was performed of patients with sporadic VS who underwent primarily conventional FSRT. In total, 50 consecutive patients were divided into two groups by volume. Clinical and volumetric parameters were analysed.

In all, 41 patients (82%) had large tumours affecting the 4th ventricle (modified Koos stage 4). Definitive expansion of VS occurred in eight out of 50 patients (16%). After 7·2 years (median) the overall freedom from clinical failure was 100% in smaller and 92% in larger schwannomas (arbitrarily sized >7·4 cc). Useful hearing was preserved in only 35% of the patients. The facial nerve remained intact in all cases, while new deficit of the trigeminal nerve occurred in 20% of the cases. Of the larger tumours 20% needed a cerebrospinal fluid (CSF) shunt.

FSRT is a treatment in its own right as it is highly effective in both smaller and larger VS without causing permanent disabling complications. The outcome is beneficial also in larger tumours that affect the 4th ventricle.

Stereotactic ablative body radiotherapy (SABR) for spine metastases is associated with a risk of vertebral compression fracture (VCF). The aim of this study was to determine the rate of VCF at one UK institution and evaluate the use of the Spinal Instability Neoplastic Score (SINS) to predict these.

A retrospective analysis of all patients who underwent SABR for spinal metastases between 2014 and 2018 at one UK institution was performed. Basic demographic data were collected, and SINS prior to SABR was calculated. The primary outcome was VCF rate. Secondary outcomes included time to VCF and need for surgical intervention following VCF.

A total of 48 oligometastases were treated with a median follow-up of 20·5 months. A maximum of two vertebral bodies were treated. The median baseline SINS was calculated as 3. The median dose was 26 Gy in three fractions. Two patients were reported to have VCF and both were successfully conservatively managed.

SABR for spine oligometastases is being performed safely with low VCF rates which are comparable with those in international publications. This may be as a result of strict adherence to criteria for delivery of SABR with low pre-treatment SINS.

The complexity associated with the treatment planning and delivery of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) volumetric modulated arc therapy (VMAT) plans which employs continuous dynamic modulation of dose rate, field aperture and gantry speed necessitates diligent pre-treatment patient-specific quality assurance (QA). Numerous techniques for pre-treatment VMAT treatment plans QA are currently available with the aid of several different devices including the electronic portal imager (EPID). Although several studies have provided recommendations for gamma criteria for VMAT pre-treatment QA, there are no specifics for SRS/SRT VMAT QA. Thus, we conducted a study to evaluate intracranial SRS/SRT VMAT QA to determine clinical action levels for gamma criteria based on the institutional estimated means and standard deviations.

We conducted a retrospective analysis of 118 EPID patient-specific pre-treatment QA dosimetric measurements of 47 brain SRS/SRT VMAT treatment plans using the integrated Varian solution (RapidArcTM planning, EPID and Portal dosimetry system) for planning, delivery and EPID QA analysis. We evaluated the maximum gamma (γmax), average gamma (γave) and percentage gamma passing rate (%GP) for different distance-to-agreement/dose difference (DTA/DD) criteria and low-dose thresholds.

The gamma index analysis shows that for patient-specific SRS/SRT VMAT QA with the portal dosimetry, the mean %GP is ≥98% for 2–3 mm/1–3% and Field+0%, +5% and +10% low-dose thresholds. When applying stricter spatial criteria of 1 mm, the mean %GP is >90% for DD of 2–3% and ≥88% for DD of 1%. The mean γmax ranges: 1·32 ± 1·33–2·63 ± 2·35 for 3 mm/1–3%, 1·57 ± 1·36–2·87 ± 2·29 for 2 mm/1–3% and 2·36 ± 1·83–3·58 ± 2·23 for 1 mm/1–3%. Similarly the mean γave ranges: 0·16 ± 0·06–0·19 ± 0·07 for 3 mm/1–3%, 0·21 ± 0·08–0·27 ± 0·10 for 2 mm/1–3% and 0·34 ± 0·14–0·49 ± 0·17 for 1 mm/1–3%. The mean γmax and mean γave increase with increased DTA and increased DD for all low-dose thresholds.

The establishment of gamma criteria local action levels for SRS/SRT VMAT pre-treatment QA based on institutional resources is imperative as a useful tool for standardising the evaluation of EPID-based patient-specific SRS/SRT VMAT QA. Our data suggest that for intracranial SRS/SRT VMAT QA measured with the EPID, a stricter gamma criterion of 1 mm/2% or 1 mm/3% with ≥90% %GP could be used while still maintaining an in-control QA process with no extra burden on resources and time constraints.

Vaginal cancer is a rare malignancy that poses a challenge to treat and cure, as surgical excision requires life-changing procedures because of the proximity and involvement of rectum, bladder and anus. We report in this case study the successful delivery of stereotactic ablative radiotherapy (SABR) for a patient with vaginal cancer after previous radiotherapy.

A 71-year-old white female who presented with dyspareunia and irritative urinary symptoms proven by biopsy was our candidate patient. Subsequent PET/CT revealed a hypermetabolic 3 cm lesion at the 12–1 o’clock position in the distal vagina involving the clitoris. The patient was initially treated with volumetric-modulated arc therapy (VMAT) with simultaneous integrated boost technique to the involved nodes, and later upon recurrence treated with SABR using 30 Gy in six fractions.

To our knowledge, this is the first report of a vaginal cylinder used to physically distance organs at risk from the treatment target and also as a localising device with image guidance for the delivery of SABR using an external beam.