RESUMO
Purpose: To implement an in-house developed position monitoring software, SeedTracker, for conventional fractionation prostate radiotherapy, and study the effect on dosimetric impact and intrafraction motion. Methods: Thirty definitive prostate radiotherapy patients with implanted fiducial markers were included in the study. All patients were treated with VMAT technique and plans were generated using the Pinnacle planning system using the 6MV beam model for Elekta linear accelerator. The target dose of 60 Gy in 20 fractions was prescribed for 29 of 30 patients, and one patient was treated with the target dose of 78 Gy in 39 fractions. The SeedTracker position monitoring system, which uses the x-ray images acquired during treatment delivery in the Elekta linear accelerator and associated XVI system, was used for online prostate position monitoring. The position tolerance for online verification was progressively reduced from 5 mm, 4 mm, and to 3 mm in 10 patient cohorts to effectively manage the treatment interruptions resulting from intrafraction motion in routine clinical practice. The delivered dose to target volumes and organs at risk in each of the treatment fractions was assessed by incorporating the observed target positions into the original treatment plan. Results: In 27 of 30 patients, at least one gating event was observed, with a total of 177 occurrences of position deviation detected in 146 of 619 treatment fractions. In 5 mm, 4 mm, and 3 mm position tolerance cohorts, the position deviations were observed in 13%, 24%, and 33% of treatment fractions, respectively. Overall, the mean (range) deviation of -0.4 (-7.2 to 5.3) mm, -0.9 (-6.1 to 15.6) mm, and -1.7 (-7.0 to 6.1) mm was observed in Left-Right, Anterior-Posterior, and Superior-Inferior directions, respectively. The prostate CTV D99 would have been reduced by a maximum value of 1.3 Gy compared to the planned dose if position deviations were uncorrected, but with corrections, it was 0.3 Gy. Similarly, PTV D98 would have been reduced by a maximum value of 7.6 Gy uncorrected, with this difference reduced to 2.2 Gy with correction. The V60 to the rectum increased by a maximum of 1.0% uncorrected, which was reduced to 0.5%. Conclusion: Online target position monitoring for conventional fractionation prostate radiotherapy was successfully implemented on a standard Linear accelerator using an in-house developed position monitoring software, with an improvement in resultant dose to prostate target volume.
RESUMO
To perform implanted fiducial based real-time target position monitoring in pancreas stereotactic body radiotherapy (SBRT) using the x-ray imaging system available in a Elekta linear accelerator. An in-house system was developed and clinically utilised for real-time target position monitoring of pancreas SBRT delivery. The developed system was used for the target position monitoring of a pancreas cancer patient treated in free breathing treatment within the study entitled 'Mfolfirinox And STEreotactic Radiotherapy for Patients with Locally Advanced paNcreas cancer (MASTERPLAN): a feasibility study' (ACTRN 12617001642370) consisting of five treatment fractions. The clinical efficacy of the system was studied by performing a retrospective cumulative dose assessment of delivered dose using observed position deviations. The developed system identified two events of baseline shifts in target position that exceeded the accepted tolerance level of ± 3 mm from reference planned position. The retrospective dose assessment study showed that if the position deviations were not detected and corrected for, the maximum dose to duodenum would have increased from 34.6 to 38.8 Gy. The first real-time position monitoring in pancreas SBRT on an Elekta linear accelerator was successfully performed. The developed system was shown to improve the safety and accuracy of SBRT delivery.