KEY POINTS
- The study included 50 prostate cancer patients treated with VMAT. Thirty cases were used to build a RapidPlan model, while 20 independent patients were used to compare standard knowledge-based plans with plans subsequently re-optimized using PlanIQ feasibility DVHs.
- Treatment consisted of 60 Gy in 20 fractions using two coplanar VMAT arcs. Re-optimization added mean-dose and upper generalized equivalent uniform dose objectives for rectum and bladder while increasing target-objective priorities.
- Target homogeneity improved. PTV-minus-rectum D2% decreased from 63.69 to 62.35 Gy (p<0.001, r=0.84), while D98% increased from 59.02 to 59.24 Gy (p=0.009, r=0.58).
- Rectal low-dose exposure also improved: V31 Gy decreased from 35.51% to 32.03% (p=0.010, r=0.58). Higher-dose rectal parameters V46, V54 and V58 did not significantly change.
- Bladder sparing did not clearly improve. V31 Gy was unchanged, while the statistically significant difference in V50 Gy actually slightly favored the original RapidPlan plans and was not considered clinically meaningful by the authors.
- The approach therefore appears most useful as a second-pass optimization tool, rather than a replacement for RapidPlan: feasibility information can expose anatomically achievable gains that a population-trained knowledge-based model may leave behind.
CLINICAL TAKEAWAY
RapidPlan can generate consistent plans, but consistency does not necessarily mean that an individual patient's anatomy has been fully exploited. FDVH-guided re-optimization modestly improved target homogeneity and rectal sparing here, although validation was limited to 20 prostate cases from one institution.