Abstract
Purpose: Bulky tumor is a challenge to surgery, chemotherapy, and conventional radiation therapy. In this study, we propose a novel therapeutic paradigm using the strategy of Stereotactic Core Ablative Radiation Therapy (SCART), which delivers an ablative dose to a large core of the bulky tumor and a relative low dose at tumor periphery.
Methods and Materials: We pre-defined SCART-treatment volume (STV) at the core of bulky gross tumor volume (GTV) and irradiated with ablative dose. The remaining GTV surrounding STV was defined as Transitional Treatment Volume (TTV). SCART planning process was standardized. Linac-based VMAT, Cyberknife technique, and 6MV photon were adopted. Numerous radiation fields passed TTV, intersected within STV, and generated an ultra-heterogeneous dose distribution, including an ablative dose at STV. The dose quickly fell off at TTV and reached a low and safe level at the edge of GTV, sparing the surrounding tissue.
Results:
In Phase 1 trial, 19 patients with 21 biopsy-proven recurrent or metastatic bulky tumors were enrolled. The five dose levels were 15Gy X1, 15Gy X3, 18GyX3, 21GyX3, and 24GyX3; the GTV’s peripheral dose was limited at 5Gy per fraction. All patients completed treatment with average beam-on time of 8.9min and average treatment time of 18.5min. Mean follow-up time is 15.4 month. No grade-III or higher toxicity was observed. 7/19 patients still survive, with the overall survival of 40% at 30 months. Mean tumor volume shrinks by 60% between initial 301cc and post-SCART volumes of 118cc. Long follow-up showed that 14/21 tumors achieved PR, 2/21 CR, 3/21 SD, and 1/21 PD, leading to an encouraging local control of 95%.
Conclusion:
SCART emerges as a safe and effective strategy for treating bulky malignant tumors, demonstrating excellent local control and overall survival. Multiple treatment courses were feasible. The results from phase-1 study suggest that SCART could revolutionize the treatment landscape for bulky tumors, offering a promising avenue for further exploration and application in clinical practice.