Yu Kuang PhD, Presenter: Nothing to Disclose

Lili Wu MS, Abstract Co-Author: Nothing to Disclose

Mei Li MD, Abstract Co-Author: Nothing to Disclose

Liangxi Xie MD, PhD, Abstract Co-Author: Nothing to Disclose

Hui Wang PhD, Abstract Co-Author: Nothing to Disclose

Xia Li PhD, Abstract Co-Author: Nothing to Disclose

Higher radiotherapy (RT) doses delivered to bone metastases would result in a higher local control rate. However, such a high dose is impossible to achieve using conventional RT without an unacceptably high risk of severe toxicity. In this study, we propose, for the first time, to utilize 18F-NaF PET/CT to identify regions within the conventional bone metastasis target volumes that may have different biology and thus allowing RT dose escalation (i.e. dose painting) to attain tumor control.

Nine patients with bone metastases from prostate cancer who had 18F-NaF PET/CT scan prior to treatment were retrospectively included in this study. Two gross tumor volumes (GTV) were generated for each patient: GTVreg was delineated according to the regular tumor boundary shown in PET/CT images; GTV60% was contoured based on 60% of the maximum SUV values. The planning target volumes (PTVs) were defined as respective GTVs with a 3-mm isotropic expansion margin. Two hypofractionated Volumetric Modulated Arc Therapy (VMAT) plans with 6 MV flattened filter free (FFF) beams (1400MU/min) were generated for each patient based on PTVreg and PTV60%, respectively. The standard plan (Planreg) included a dose of 24 Gy prescribed to PTVreg. The dose escalation plan (Planreg) consisted of a dose of 24 Gy prescribed to PTVreg and a boost dose of 30Gy prescribed to the PTV60%. TCP and the NTCP were also compared between the plans.

In all 18 VMAT plans generated, the target volume objectives and the organs-at-risk (OARs) dose constraints were met. The use of pre-treatment 18F-NaF PET/CT led to a better estimate of the dominant lesion areas within routine GTV, which translated into an advantageous escalation of target dose while maintaining normal tissue sparing.

This study demonstrates the technical feasibility of 18F-NaF PET/CT-based dose painting for hypofractionated VMAT with FFF beams in patients with bone metastases from prostate cancer.

This molecular image guided VMAT approach, with exquisite tumor metabolic activity arising from 18F-NaF PET, would offer therapeutic insight impossible with the current design. Given the higher dose responsive nature in cancer and the facts that the proposed method requires only minimal protocol modification in routine care, it could have major therapeutic value for the clinical outcome in the long term patient care in the future.

Kuang, Y, Wu, L, Li, M, Xie, L, Wang, H, Li, X, First Demonstration of Hypofractionated Volumetric Modulated Arc Therapy Dose Painting with Unflattened Beams for Bone Metastases Using 18F-NaF PET/CT scan.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14016636.html