Stereotactic radiotherapy (SRT) for patients with intracranial tumours are delivered using a dedicated platform or a conventional linear accelerator with a flattening filter-free beam.

This study compares treatment plans with intracranial tumours. A total of 29 patients were treated on CyberKnife and planned using the Accuray Precision. The same structure sets ws then exported to Varian Eclipse, and plans were made using a 6 MV FFF beam. Both plans were compared for parameters of target coverage, homogeneity index (HI), new conformity index (nCI), gradient index, selectivity index (SI), volumetric and OAR doses.

The treatment plans made for CyberKnife exhibit better results in terms of nCI (1·168 ± 0·08 versus 1·173 ± 0·077), SI (0·885 ± 0·05 versus 0·877 ± 0·05) and GI (3·64 ± 0·5 versus 4·45 ± 1·25), while HI values are better for TrueBeam. For OAR doses, in 65·5% and 72% of treatment plans, brainstem and optic pathways received lower doses on CyberKnife, respectively. In terms of dose spillage, Truebeam plans are better for very low doses (V5%), while for V10%, V20% and V50% CyberKnife plans are better.

CyberKnife is a better modality for the delivery of SRS/SRT to intracranial tumours except for dose homogeneity where TrueBeam offered better results.

The objective of this article is to evaluate the dosimetric efficacy of volumetric modulated arc therapy (VMAT) in comparison to dynamic conformal arc therapy (DCAT) and 3D conformal radiotherapy (3DCRT) for very small volume (≤1 cc) and small volume (≤3 cc) tumours for flattened (FF) and unflattened (FFF) 6 MV beams.

A total of 21 patients who were treated with single-fraction stereotactic radiosurgery, using either VMAT, DCAT or 3DCRT, were included in this study. The volume categorisation was seven patients each in <1, 1–2 and 2–3 cc volume. The treatment was planned with 6 MV FF and FFF beams using three different techniques: VMAT/Rapid Arc (RA) (RA_FF and RA_FFF), dynamic conformal arc therapy (DCA_FF and DCA_FFF) and 3DCRT (Static_FF and Static_FFF). Plans were evaluated for target coverage (V100%), conformity index, homogeneity index, dose gradient for 50% dose fall-off, total MU and MU/dose ratio [intensity-modulated radiotherapy (IMRT) factor], normal brain receiving >12 Gy dose, dose to the organ at risk (OAR), beam ON time and dose received by 12 cc of the brain.

The average target coverage for all plans, all tumour volumes (TVs) and delivery techniques is 96·4 ± 4·5 (range 95·7 ± 6·1–97·5 ± 2·9%). The conformity index averaged over all volume ranges <1, 2, 3 cc> varies between 0·55 ± 0·08 and 0·68 ± 0·04 with minimum and maximum being exhibited by DCA_FFF for 1 cc and Static_FFF/RA_FFF for 3 cc tumours, respectively. Mean IMRT factor averaged over all volume ranges for RA_FF, DCA_FF and Static_FF are 3·5 ± 0·8, 2·0 ± 0·2 and 2·0 ± 0·2, respectively; 50% dose fall-off gradient varies in the range of 0·33–0·42, 0·35–0·40 and 0·38–0·45 for 1, 2 and 3 cc tumours, respectively.

This study establishes the equivalence between the FF and FFF beam models and different delivery techniques for stereotactic radiosurgery in small TVs in the range of ≤1 to ≤3 cc. Dose conformity, heterogeneity, dose fall-off characteristics and OAR doses show no or very little variation. FFF could offer only limited time advantage due to excess dose rate over an FF beam.

Treatment of metachronous second primary non-small cell lung cancer (NSCLC) in patients already treated with definitive radiotherapy is a matter of debate, since most patients are excluded from surgical treatment, which remains a therapeutic standard for patients with isolated lung masses. Salvage chemotherapy or immunotherapy alone offers a low probability of disease control. The option of re-irradiation often remains the only viable, but the risks of severe acute or late toxicities affecting the surrounding normal tissues make this a real clinical challenge.

From January 2015 to April 2018, five patients (male/female: 4/1; age 54–81 years, median 68) with previously irradiated NSCLC presented with a second primary lung tumour.

A partial response was seen in four patients, one complete responses in the fifth. The toxicity was low: two patients experienced a grade 2 asymptomatic radiation pneumonitis after 6 and 12 months from the end of stereotactic body radiation therapy, resolved with cortisone therapy. No acute or late oesophageal or cardiac toxicity was found.

In this work, we present our initial experience about the use of stereotactic radiotherapy technique in already irradiated patients. We reported a local disease control in all cases with an acceptable toxicity.