(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Conventional radiotherapy doses of 50-54 Gy or SBRT treatment (25-33 Gy in 5 fractions) have shown minimal impact on survival for patients with LAPC. Dose to pancreatic tumor can be escalated safely by simultaneous integrated boost (SIB) with more accurate localization using deep inspiration breath hold (DIBH) CT. We report our ablative dosing scheme with heterogeneous dose-painting approach for treatment of LAPC via daily CBCT-guided DIBH.
Methods: Five patients underwent DIBH-CT planning for dose-escalated SIB treatment with indexing on a SBRT board with Vac-Lok and knee cushions. Oral and GI-contrast were administered and 2.5 mm slice DIBH-CT scan was acquired followed with free-breathing scan. SIB dose of 70 Gy (biologically effective dose, BED10 > 90 Gy) was optimized for gross tumor volume (GTV), and 50.4 Gy (BED10 > 70 Gy) to planning target volume (PTV) for 28 fractions. One to three full co-planar VMAT arcs of 10 MV using Acuros-based dose calculation were used on Truebeam using daily CBCT-guided DIBH with a gating window of 5-7 mm.
Results: Average GTV and PTV were 61±36cc (range, 18–112cc) and 363±165 cc (range, 161–532cc), respectively. Average GTV conformity was 1.02 and homogeneity index was 1.11. Mean GTV dose was 72.4±0.2 Gy (range, 72.2–72.6 Gy) and to the PTV, 58.6±0.1.8 Gy (range, 55.9–60.4 Gy). Maximum and volumetric dose for normal tissues were: duodenum (54.5 Gy, D10cc=38.1Gy), small bowel (55.1Gy, D15cc=35 Gy), stomach (54.6 Gy, D15cc=35.1 Gy, Dmean=20 Gy), and cord (34.8 Gy). Mean dose to liver and kidneys was 12 Gy and 11 Gy, respectively. Average total treatment time was 15 min.
Conclusion: Dose escalation with SIB to LAPC with CBCT-guided DIBH is feasible. This technique has potential implications for Halcyon Linac with faster CBCT scan (<15 sec/scan, one breath-hold) which could facilitate further dose escalation to hypoxic center (> 100 Gy BED10).
Keywords
Stereotactic Radiosurgery, Image-guided Therapy, Target Localization
Taxonomy
TH- External beam- photons: extracranial stereotactic/SBRT
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