Implementing Simultaneous Integrated Boost (SIB) GRID Radiation Therapy for Spatially Fractionated Radiotherapy (SFRT)
Abstract
Purpose
This study explored the clinical feasibility of implementing simultaneous integrated boost (SIB) GRID therapy planning technique for Spatially Fractionated Radiotherapy (SFRT).
Methods
The GRID SFRT SIB plan was generated by delivering 10Gy for the whole target (PTV: 248 cc) and then a boosted dose to 15Gy for the centrally-located high-risk target (PTV_boost: 26cc). A Truebeam STX linac with HD-MLC (multileaf collimator) and brass GRID block were used to generate a conformal GRID therapy plan. The plan was generated with Eclipse treatment planning system v15.6. The plan used two GRID beams “Fld_PTV” (13x12 cm2) and “Fld_PTV_boost” (6x5 cm2). The MLC of "Fld_PTV" and "Fld_PTV_boost" were set to fit shape of PTV and PTV_boost in Beam's Eye View. The dose was prescribed at dmax of a standard GRID beam along the central axis of the central hole. The output factors (OF) of GRID beams were verified with the CC04 ion chamber and solid water phantom using clinical plan set up (at dmax). Treatment plan QA was performed with ArcCheck.
Results
The dose of the central peak in "PTV_boost" was 15Gy while the peak dose of the "PTV" (excluding PTV_boost) was 10Gy.The peak-valley dose ratio (PVDR) for PTV_boost was 4.7. The PVDR of Fld_PTV and Fld_PTV_boost were 4.5 and 4.8, respectively. D10/D90 of PTV (including PTV_boost) and PTV_boost were 5.4 and 4.9, respectively. The difference in OF between the measurement and treatment planning system (TPS) calculation was within 3%. The gamma passing rate was 91% (3% and 3mm).
Conclusion
This study demonstrated the feasibility of target dose escalation in GRID therapy. The overall target volume will achieve the typical GRID pattern for SFRT while the boosted area can achieve a higher PVDR from this novel GRID SFRT plan.