Room: Exhibit Hall
Purpose: To study the feasibility of predictive treatment planning (PTP), i.e., integrating geometric and biological predictions of tumor response into dose escalation from the beginning of lung radiotherapy for maximal therapeutic ratio and reduced workload.
Methods: Six non-small cell lung cancer patients were recruited in this retrospective planning study. Potential residual tumor in response to conventional 2Gy/fraction lung radiotherapy was first predicted using a geometrical atlas for an anatomical target within the original GTV (gpGTV), and using a PET based biological model for a metabolic target (bpGTV). Four boost PTVs (PTVboost) were generated with 5 mm and 10 mm margins from the union and intersection of gpGTV and bpGTV (UbPTV-5mm, UbPTV-10mm, IbPTV-5mm, and IbPTV-10mm). Five IMRT plans were generated using the Eclipse treatment planning system for each scenario. 60 Gy was given to the original PTV (PTVorig) serving as a reference. 74 Gy was simultaneously boosted to each PTVboost on the other 4 plans while ensuring 60Gy to PTVorig. Dosimetric end points including D95 to PTVboost, and volume of original and boost PTVs; maximum spinal cord dose; V20Gy and mean lung dose of total lungs; mean esophagus dose; and V30Gy of heart were tabulated and analyzed.
Results: The ratio of boost over original PTV volume ranged 0.17-0.28,0.30-0.47, 0.02-0.13 and 0.04-0.25 for UbPTV-5mm, UbPTV-10mm, IbPTV-5mm, and IbPTV-10mm, respectively. gpGTV and bpGTV volume range were 29.5-306.5 c.c. and 3.1-49.2 c.c. All plans can achieve the goal of escalating dose to 74Gy except one case where overlap between GTV and cord limited escalating dose to 66Gy. No significant differences were found in OAR doses.
Conclusion: It is feasible to escalate dose to subvolumes of tumor where are predicted as geometrically or biologically resistant while meeting all clinical critical organsâ€™ dose guidelines. Clinical implementation of PTP is merited and ongoing.