Fast and robust online adaptive planning in stereotactic MR-guided adaptive radiation therapy (SMART) for pancreatic cancer

doi:10.1016/j.radonc.2017.07.028

Radiotherapy and Oncology

Volume 125, Issue 3, December 2017, Pages 439-444

https://doi.org/10.1016/j.radonc.2017.07.028 Get rights and content

Abstract

Background and purpose

To implement a robust and fast stereotactic MR-guided adaptive radiation therapy (SMART) online strategy in locally advanced pancreatic cancer (LAPC).

Material and methods

SMART strategy for plan adaptation was implemented with the MRIdian system (ViewRay Inc.). At each fraction, OAR (re-)contouring is done within a distance of 3 cm from the PTV surface. Online plan re-optimization is based on robust prediction of OAR dose and optimization objectives, obtained by building an artificial neural network (ANN). Proposed limited re-contouring strategy for plan adaptation (SMART_3CM) is evaluated by comparing 50 previously delivered fractions against a standard (re-)planning method using full-scale OAR (re-)contouring (FULLOAR). Plan quality was assessed using PTV coverage (V_95%, D_mean, D_1cc) and institutional OAR constraints (e.g. V_33Gy).

Results

SMART_3CM required a significant lower number of optimizations than FULLOAR (4 vs 18 on average) to generate a plan meeting all objectives and institutional OAR constraints. PTV coverage with both strategies was identical (mean V_95% = 89%). Adaptive plans with SMART_3CM exhibited significant lower intermediate and high doses to all OARs than FULLOAR, which also failed in 36% of the cases to adhere to the V_33Gy dose constraint.

Conclusions

SMART_3CM approach for LAPC allows good OAR sparing and adequate target coverage while requiring only limited online (re-)contouring from clinicians.

Section snippets

General SMART workflow for LAPC

The online SMART procedure for LAPC consists of three steps: 1) MR simulation during breath-hold, 2) deformation and adjustment of OAR contours and 3) online plan re-optimization. MR acquisition is performed during a 17 s breath-hold in shallow inspiration, using a FOV of 45 cm and 1.6 mm × 1.6 mm × 3 mm resolution. MR protocol for delineation is based on a true FISP sequence (Siemens) with a TR/TE of 3.83/1.62 ms and Flip Angle of 60°. The contours of the OAR, i.e. the duodenum, stomach, bowel and

Results

An overview of PTV and OAR volumes up to a distance of 3 cm from the PTV of the 10 patients included in the study is shown in Table 1. PTV size at baseline ranged from 16 to 99 cc and, because of non-adapting the GTV, there was little inter-fraction variation in PTV size. The small inter-fraction variations in PTV size that were seen were caused by the variation in OAR volumes at the proximity of the GTV that are excluded during the generation of PTV’s from the GTV’s. Inter-fractional changes in

Discussion

We describe an ART strategy for daily online plan (re-)optimization that is currently in clinical use at our institution. The strategy consistently resulted in high quality plans, which complied with all institutional OAR constraints for LAPC. The methodology used relies on robust prediction of optimization objectives, deformation and physician’s review of OARs within a distance of 3 cm from the PTV, and partitioning OAR contours in separate portions to allow for spatial control of the dose

Conclusion

In this manuscript a new adaptive strategy is proposed for plan (re-)optimization which produces robust and fast treatment plans meeting all clinical constraints and achieving good OAR sparing. This approach requires clinicians to only review and adjust OARs located within 3 cm from the PTV. This methodology has been analysed for pancreatic tumours but it can also be implemented for other treatment sites which benefit from daily plan adaptation, such as prostate or adrenal gland.

Conflict of interest

Mr. Bohoudi has nothing to disclose.

Dr. Lagerwaard has nothing to disclose.

Dr. Senan reports grants from Varian medical systems outside the submitted work.

Dr. Cuijpers has nothing to disclose.

Dr. Slotman reports grants and personal fees from Varian medical systems, grants and personal fees from BrainLab AG, outside the submitted work.

Dr. Bruynzeel has nothing to disclose.

Dr. Palacios has nothing to disclose.

Acknowledgments

We thank A. Bohoudi and G. Ybeles Smit from FUTURE FACTS Amsterdam for their advice and knowledge regarding the ANN model.

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MRI-guided radiotherapyFast and robust online adaptive planning in stereotactic MR-guided adaptive radiation therapy (SMART) for pancreatic cancer

Abstract

Background and purpose

Material and methods

Results

Conclusions

Section snippets

General SMART workflow for LAPC

Results

Discussion

Conclusion

Conflict of interest

Acknowledgments

Phys Medica

Med Dosim

Int J Radiat Oncol Biol Phys

Radiother Oncol

Radiother Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Semin Radiat Oncol

Int J Radiat Oncol Biol Phys

Int J Radiat Oncol Biol Phys

Radiother Oncol

Int J Radiat Oncol Biol Phys

Semin Radiat Oncol

MRI-guided radiotherapy
Fast and robust online adaptive planning in stereotactic MR-guided adaptive radiation therapy (SMART) for pancreatic cancer