SU-F-J-101: Stereotactic Body Radiation Therapy Planning for Primary Prostate Cancer with Selective Intraprostatic Boost Determined by 18F-Choline PET/CT

Purpose: To investigate the utility of 18F-choline positron emission tomography (PET) scans guidance for SBRT dose painting in patients with prostate cancer and its impact on tumor control probability (TCP) and normal tissue complication probability (NTCP). Methods: Twenty seven patients with localized prostate cancer who had 18F-choline PET/CT scan prior to treatment were included. A pair of nested intraprostatic dominant lesion (IDL) contours (IDLsuv60% and IDLsuv70%) were generated for each patient based on 60% and 70% of maximum prostate uptake on the 18F-choline PET images. GTVreg was delineated on prostate according to the gland boundary seen on CT images. The PTVs (PTVsuv60% and PTVsuv70%) were defined as respective IDLs with a 3-mm margin posteriorly and 5 mm in all other dimensions. Two 5-fraction SBRT plans using VMAT technique along with 10 MV FFF beams, plan36Gy and plan50–55Gy, were generated for each patient. All plans included a dose of 36.25 Gy prescribed to PTVreg. The Plan50–55Gy also included a simultaneous boost dose of 50 Gy and 55 Gy prescribed to the PTVsuv60% and PTVsuv70%, respectively. The utility of 18F-Choline 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 TCP and NTCP calculated by radiological models were also compared between two plans for each patient. Results: In all 54 SBRT plans generated, the planning objectives and dose constraints were met without exception. Plan50–55Gy had a significantly higher dose in PTVsuv60% and PTVsuv70% than those in Plan36Gy (p < 0.05), respectively, while still maintaining a safe OAR sparing profile. In addition, plan50–55Gy had significantly higher TCP than plan36Gy. Conclusion: Using VMAT with FFF beams to incorporate a simultaneous 18F-choline PET-guided radiation boost dose up to 55 Gy into a SBRT plan is technically feasible. This work was supported in part by Congressionally Directed Medical Research Programs Prostate Cancer Research Program grant PC04130, National Institutes of Health/National Cancer Institute grant R41CA110121, and the UNLV Lincy Endowed Assistant Professorship.