Radiation and Cancer Biology

SS 03 - Biology 1 - Innovative Biologic Approaches to Improve Risk Stratification and Treatment Outcomes

26 - Partial Tumor Irradiation Exploiting the Bystander and Abscopal Effects

Sunday, October 21
1:55 PM - 2:05 PM
Location: Room 008

Partial Tumor Irradiation Exploiting the Bystander and Abscopal Effects
S. Tubin; KABEG Klinikum Klagenfurt, Institute für Strahlentherapie und Radioonkologie, Klagenfurt, Austria

Purpose/Objective(s): We have previously proved for the first time that high-single-dose irradiation of hypoxic tumor cells results in significant radiation-hypoxia-induced bystander (R-H-IBE) and abscopal effects (R-H-IAE). Our preclinical findings were recently translated to clinic leading to development of a novel radiotherapy technique for partial tumor irradiation (PTI) that exploits R-H-IBE and R-H-IAE. We hypothesized that irradiating exclusively the hypoxic tumor segment with high-single dose will generate a strong abscopal tumor-signaling leading to significant regression of partially targeted tumor (bystander effects) and non-targeted (metastatic) tumor sites (abscopal effect). The aims of this study were to assess the safety and feasibility of PTI and analyze its impact on induction of R-H-IBE and R-H-IAE. Our novel technique has been applied to hard to treat large (bulky) tumors. The primary endpoint was to assess a neoadjuvant potential of PTI to downsize bulky tumors by inducing a strong R-H-IBE converting in that way a palliative into a potentially curative treatment.

Materials/Methods: 20 oligometastatic patients with hypoxic bulky tumors were included in a presenting study. The targeted hypoxic tumor segment, a so-called “bystander tumor volume (BTV)”, was defined by using PET/CT (SUVmax cut-off value of 3). Exclusively the BTV (no additional margins were added to the BTV) was irradiated with 10 or 12Gy SBRT in a single fraction to the 70% isodose line (Dmax: 14.5 or 18 Gy, respectively). Treatment was delivered by 6MV flattening filter free photon beams. SBRT plan was calculated on Monaco treatment planning system. Before each treatment was performed, a kilovoltage cone-beam CT was carried out. No patient received chemotherapy or immunotherapy.

Results: Among 20 patients treated with PTI, in 95% a significant R-H-IBE (bulky shrinkage) and in 55% also R-H-IAE (regression of un-treated distant metastases) was observed. On an average, BTV corresponded to about 30% of bulky tumor mass (mean bulky volume 215 cc, mean diameter 9.1 cm). After a mean time of 3 weeks, average bulky shrinkage induced by the bystander effect was 60% (range: 40-100%) and mean reduction of the metastases was 50% (range: 50-100%). Disease-specific survival was 85%. None of the patients experienced acute or late toxicity of any grade. Median follow-up was 8 months (range: 4-20).

Conclusion: PTI of bulky tumors was feasible, effective and without any toxicity. The results confirmed our hypothesis since in almost all cases unresectable partially irradiated bulky tumors were significantly down-sized and converted to radically treatable lesions. In addition, in a majority of cases regression of un-treated metastases was also induced. This 1-day neoadjuvant approach can improve therapeutic ratio and cost-effectiveness profile offering a very safe basis for further (re-)irradiation.

Author Disclosure: S. Tubin: None.

Slavisa Tubin, MD

Disclosure:
No relationships to disclose.

Presentation(s):

Send Email for Slavisa Tubin


Assets

26 - Partial Tumor Irradiation Exploiting the Bystander and Abscopal Effects



Attendees who have favorited this

Please enter your access key

The asset you are trying to access is locked. Please enter your access key to unlock.

Send Email for Partial Tumor Irradiation Exploiting the Bystander and Abscopal Effects