Abstract 3974: 18F-sodium fluoride PET/CT-guided dose escalation in stereotactic body radiotherapy for spine oligometastases from prostate cancer
Authors: Kuang Yu , Wu Lili , Kwee Sandi A. , Li Mei , Peng Xun , Xie Liangxi , Lin Zhixiong 
Published: July 2016

Purpose: Recent clinical evidence has shown that SBRT using high dose with either a single fraction or a limited number of fractions can lead to excellent pain control as well as local tumor control in patients with spine oligometastases. However, as a dose limiting factor, proximity to spinal cord often precludes SBRT delivering the full prescription dose (PD) and/or escalating dose to the planning target volume (PTV) of spine oligometastases, thus compromising the therapeutic ratio. To investigate the technical feasibility of SBRT dose painting using 18F-NaF positron emission tomography (PET) scans guidance in patients with spine oligometastases from prostate cancer.

Methods: As a proof of concept, six patients with 15 spine oligometastatic lesions from prostate cancer who had 18F-NaF PET/CT scan prior to treatment were retrospectively included. GTVreg was delineated according to the regular tumor boundary shown on PET and/or CT images; and GTVMATV was contoured based on a net metabolically active tumor volume (MATV) defined by 60% of the SUVmax values on 18F-NaF PET images. The PTVs (PTVreg and PTVMATV) were defined as respective GTVs (plus involved entire vertebral body for PTVreg) with a 3-mm isotropic expansion margin. Three 1-fraction SBRT plans using VMAT technique along with 10 MV FFF beams (Plan24Gy, Plan24-27Gy, and Plan24-30Gy) were generated for each patient. All plans included a dose of 24 Gy prescribed to PTVreg. The Plan24-27Gy and Plan24-30Gy also included a simultaneous boost dose of 27 Gy or 30 Gy prescribed to the PTVMATV, respectively. The feasibility of 18F-NaF PET-guided SBRT dose escalation was evaluated by its ability to achieve the prescription dose objectives while adhering to organ-at-risk (OAR) dose constraints. The normal tissue complication probabilities (NTCP) calculated by radiological models were also compared between the plans.

Results: In all 33 SBRT plans generated, the planning objectives and dose constraints were met without exception. Plan24-27Gy and Plan24-30Gy had a significantly higher dose in PTVMATV than Plan24Gy (p &lt; 0.05), respectively, while maintaining a similar OAR sparing profile and NTCP values.

Conclusion: The strategy of delivering differential doses using SBRT with a simultaneous integrated dose boost to MATV offers the option of irradiating host facilitating cells simultaneously with the cancer cells in the tumor ecosystem. Using VMAT with FFF beams to incorporate a simultaneous 18F-NaF PET-guided radiation boost dose up to 30 Gy into a SBRT plan is technically feasible. The relationship between local control and normal tissue toxicity in SBRT dose painting should be validated in clinical trials.

Citation Format: Yu Kuang, Lili Wu, Sandi A. Kwee, Mei Li, Xun Peng, Liangxi Xie, Zhixiong Lin. 18F-sodium fluoride PET/CT-guided dose escalation in stereotactic body radiotherapy for spine oligometastases from prostate cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3974.