1. Introduction and Objectives
Comparison of 3 Image-guided Adaptive Strategies for Bladder Radiotherapy V. Kong1, A. Taylor2, T Craig1, 3, P. Chung1, 3, T. Rosewall1, 3 1Radiation Medicine Program, Princess Margaret Cancer Centre; 2Sheffield Hallam University, 3Department of Radiation Oncology, University of Toronto
Plan of the Day (PoD)
4 PTVs:
Introduction and Objectives
Significant interfractional variation of bladder volume is observed throughout the course of bladder radiotherapy
Despite the use of image guidance, irradiated volume remains large to ensure adequate target coverage
Various adaptive strategies such as Plan of the Day (PoD)1, 2, Patient-Specific PTV (PS-PTV)3, 4 and daily Reoptimization (ReOpt)5 have been developed to improve the quality of treatment
The study compared the dosimetric differences between a population-based PTV approach and three adaptive strategies
Methods
4 Treatment Strategies
10 Pati ents (7 Mal e; 3 Fem ale)
Plan ned and treat ed with full Blad der
Planning CT & 23 CBCTs
Volume Delineation
Bladder and Pelvic Lymph Node (PLN)
Planning CT-CBCT rigid registration
Bony anatomy
4 Treatment Strategies
Standard PTV, PoD, PS-PTV, ReOpt
7-field IMRT delivering 46Gy/23
Planning CT-CBCT Deformable Image Registration
Dose computation on CBCT & Dose Accumulation
Sagittal view of pelvis showing the PTVs of the adaptive strategies. Only the PTV for the bladder was modified for each adaptive strategy. PTV for PLN remained the same (PLN + 5mm)
Standard PTV
Planning Bladder + 15 mm
Adaptive Strategy 1: Plan of the Day (PoD)
4 PTVs: Bladder, Bladder + 5mm, Bladder + 10mm, Bladder + 15mm
The distribution generated based on the smallest PTV that encompassed the bladder of the day was selected to deliver the fraction dose
Adaptive Strategy 2: Patient-Specific PTV (PS-PTV)
PS-PTV: [Planning Bladder + Fraction 1-5 CBCT Bladder] + 5mm
Population-based PTV distribution was used for Fraction 1-5 and new distribution generated based on the PS-PTV were used for Fraction
Adaptive Strategy 3: Daily Re-Optimization (ReOpt)
ReOpt PTV: Bladder of the day + 5mm
Distribution was re-optimized for each fraction based on the ReOpt PTV
V95 (volume receiving 95% prescription dose) for each strategy was calculated and compared
Results
Conclusions
All adaptive strategies significantly reduced the irradiated volume (Figure a)
ReOpt is the most superior in reducing the irradiated volume, followed by PS-PTV and PoD (Figure b)
The difference in the magnitude of reduction between ReOpt and the other 2 adaptive strategies reached statistical significance (p = )
Deformable image registration accounts for the daily motion of the bladder, enabling a better estimation of the actual delivered dose
ReOpt is the best adaptive strategy in reducing the irradiated volume, due to its frequent adaptation based on the daily geometry of the bladder
Resource burden associated with this strategy needs to be quantified to further assess the feasibility of clinical implementation a) b)
Reference
BURRIDGE, N., AMER, A., MARCHANT, T., SYKES, J., STRATFORD, J., HENRY, A., MCBAIN, C., PRICE, P. & MOORE, C Online adaptive radiotherapy of the bladder: small bowel irradiated-volume reduction. International Journal of Radiation Oncology Biology Physics, 66,
TUOMIKOSKI, L., VALLI, A., TENHUNEN, M., MUREN, L. & VESTERGAARD, A A comparison between two clinically applied plan library strategies in adaptive radiotherapy of bladder cancer. Radiotherapy Oncology, 117,
POS, F. J., HULSHOF, M., LEBESQUE, J., LOTZ, H., VAN TIENHOVEN, G., MOONEN, L. & REMEIJER, P Adaptive radiotherapy for invasive bladder cancer: a feasibility study. International Journal of Radiation Oncology* Biology Physics, 64,
TOLAN, S., KONG, V., ROSEWALL, T., CRAIG, T., BRISTOW, R., MILOSEVIC, M., GOSPODAROWICZ, M. & CHUNG, P Patient-specific PTV margins in radiotherapy for bladder cancer - a feasibility study using cone beam CT. Radiotherapy Oncology, 99,
VESTERGAARD, A., MUREN, L. P., SONDERGAARD, J., ELSTROM, U. V., HOYER, M. & PETERSEN, J. B Adaptive plan selection vs. re-optimisation in radiotherapy for bladder cancer: a dose accumulation comparison. Radiotherapy Oncology, 109,
a) Mean and range of V95 of the 10 patients for each strategy
b) Mean and range of the % decrease by each adaptive strategy from the Standard approach
Adaptive Strategies for Bladder Radiotherapy ESTRO36 PV-0460