Dosimetric Evaluation of a Conformal Seven-field Coplanar Technique for Planning Lung Stereotactic Body Radiotherapy

Long-term Overall Survival Outcomes in Patients with Early Stage, Peripherally Located, Non-small Cell Lung Cancer Treated with Stereotactic Ablative Radiotherapy in a Non-academic Cancer Centre

AIMS

To report long-term outcomes of patients treated with stereotactic ablative radiotherapy (SABR) for early stage, peripherally located non-small cell lung cancer.

MATERIALS AND METHODS

Data were collected retrospectively between September 2009 and May 2019. Electronic medical records were reviewed for baseline characteristics, treatment details and outcomes. All patients were treated according to local protocol based on the national UK SABR Consortium guidelines. Risk-adapted treatment schedules were used depending on the size and the location of the tumour (54 Gy in three fractions, 55 Gy in five fractions, 60 Gy in eight fractions or 50 Gy in 10 fractions). Overall survival outcomes were evaluated using the Kaplan-Meier method.

RESULTS

In total, 412 patients were included in the analysis. The median age was 76 years (range 48-93 years). Histological confirmation was obtained in 233 cases (56.6%). The median overall survival for all patients was 42.3 months (95% confidence interval 37.3-47.3 months), with 3- and 5-year overall survival of 52.8% and 37.3%, respectively. For biopsy-proven patients (56.6%), 3- and 5-year overall survival was 57.3% and 40.1%, respectively. With respect to overall survival, univariate and multivariate analysis revealed no significant difference in survival by technique (volume-modulated arc therapy versus conformal; three-dimensional computed tomography versus four-dimensional computed tomography), tumour location, smoking status at first contact, pre-treatment tumour stage or pre-treatment standardised uptake value. Survival was poorer for patients who received the 50 Gy in 10 fractions schedule. Treatment was very well tolerated with very low rates of grade 3-4 toxicity (1%).

CONCLUSIONS

SABR for peripherally located, medically inoperable non-small cell lung cancer can be safely and effectively implemented in a non-academic institution with appropriate equipment and training. Overall survival outcomes and toxicity rates are comparable with internationally published studies. Patients treated with 50 Gy in 10 fractions had a poorer survival outcome.

A Comparison of Non-coplanar Three-dimensional Conformal Radiation Therapy, Intensity Modulated Radiation Therapy, and Volumetric Modulated Radiation Therapy for the Delivery of Stereotactic Ablative Radiation Therapy to Peripheral Lung Cancer

AIM

The objective of the study was to compare three noncoplanar delivery techniques (three-dimensional conformal radiation therapy [3DCRT], intensity-modulated radiation therapy [IMRT], and volumetric-modulated arc therapy [VMAT]) for the delivery of lung stereotactic ablative radiation therapy to peripheral lung tumours.

METHODS AND MATERIALS

The plans were compared by assessing the planning target volume coverage, doses to organs at risk, high and intermediate dose constraints (D_2cm and R_50%) and delivery times using analysis of variance for repeated measurements or Friedman's test when appropriate.

RESULTS

Mean PTV54 Gy coverage was found to be 95.6%, 95.7%, and 95.6% for the 3DCRT, IMRT, and VMAT techniques, respectively. No deviations to the intermediate dose constraints were found in 65%, 65%, and 85% of the patients for the 3DCRT, IMRT, and VMAT plans, respectively. Mean treatment times (excluding setup and imaging) were 20.0 minutes (±1.67), 25.2 minutes (±2.15), and 11.7 (±2.0) minutes respectively for 3DCRT, IMRT, and VMAT.

CONCLUSION

A noncoplanar VMAT technique was found to provide superior intermediate dose sparing with comparable prescription dose coverage when compared with noncoplanar 3DCRT or IMRT. In addition, VMAT was found to reduce the treatment times of stereotactic ablative radiation therapy delivery for peripheral lung tumours.

The effect of beam arrangements and the impact of non-coplanar beams on the treatment planning of stereotactic ablative radiation therapy for early stage lung cancer

INTRODUCTION

The aim of this study was to compare various coplanar and non-coplanar 3-dimensional conformal radiation therapy (3DCRT) beam arrangements for the delivery of stereotactic ablative radiation therapy (SABR) to patients with early stage lung cancer, based on the dosimetric criteria from the Radiation Therapy Oncology Group (RTOG) 1021 protocol.

METHODS

Ten medically inoperable lung cancer patients eligible for SABR were re-planned using three different coplanar and three different non-coplanar beam arrangements. The plans were compared by assessing planning target volume (PTV) coverage, doses to normal tissues, the high-dose conformity (conformity index) and intermediate dose spillage as defined by the D2cm, (the dose at any point 2 cm away from the PTV), and the R50% (the ratio of the volume of half the prescription dose to the volume of the PTV).

RESULTS

Sixty plans in total were assessed. Mean PTV coverage with the prescription isodose was similar between coplanar (95.14%) and non-coplanar (95.26%) techniques (P = 0.47). There was significant difference between all coplanar and all non-coplanar fields for the R50% (P < 0.0001) but none for the D2cm (P = 0.19). The seven and nine field beam arrangements with two non-coplanar fields had less unacceptable protocol deviations (10 and 7) than the seven and nine field plans with only coplanar fields (13 and 8). The 13 field coplanar fields did not improve protocol compliance with eight unacceptable deviations. The 10 field non-coplanar beam arrangement achieved best compliance with the RTOG 1021 dose criteria with only one unacceptable deviation (maximum rib dose).

CONCLUSION

A 3DCRT planning technique using 10 fields with ≥6 non-coplanar beams best satisfied high and intermediate dose constraints stipulated in the RTOG 1021 trial. Further investigations are required to determine if minor protocol deviations should be balanced against efficiency with the extended treatment times required to deliver non-coplanar fields and if treatment times can be improved using novel intensity modulated techniques.