David P. Stewart

18F-FDG PET-CT SIMULATION FOR NON-SMALL-CELL LUNG CANCER: EFFECT IN PATIENTS ALREADY STAGED BY PET-CT

PURPOSE Positron emission tomography (PET), in addition to computed tomography (CT), has an effect in target volume definition for radical radiotherapy (RT) for non-small-cell lung cancer (NSCLC). In previously PET-CT staged patients with NSCLC, we assessed the effect of using an additional planning PET-CT scan for gross tumor volume (GTV) definition. METHODS AND MATERIALS A total of 28 patients with Stage IA-IIIB NSCLC were enrolled. All patients had undergone staging PET-CT to ensure suitability for radical RT. Of the 28 patients, 14 received induction chemotherapy. In place of a RT planning CT scan, patients underwent scanning on a PET-CT scanner. In a virtual planning study, four oncologists independently delineated the GTV on the CT scan alone and then on the PET-CT scan. Intraobserver and interobserver variability were assessed using the concordance index (CI), and the results were compared using the Wilcoxon signed ranks test. RESULTS PET-CT improved the CI between observers when defining the GTV using the PET-CT images compared with using CT alone for matched cases (median CI, 0.57 for CT and 0.64 for PET-CT, p = .032). The median of the mean percentage of volume change from GTV(CT) to GTV(FUSED) was -5.21% for the induction chemotherapy group and 18.88% for the RT-alone group. Using the Mann-Whitney U test, this was significantly different (p = .001). CONCLUSION PET-CT RT planning scan, in addition to a staging PET-CT scan, reduces interobserver variability in GTV definition for NSCLC. The GTV size with PET-CT compared with CT in the RT-alone group increased and was reduced in the induction chemotherapy group.

18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography–Based Radiotherapy Target Volume Definition in Non–Small-Cell Lung Cancer: Delineation by Radiation Oncologists vs. Joint Outlining With a PET Radiologist?

PURPOSE (18)F-Fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) has benefits in target volume (TV) definition in radiotherapy treatment planning (RTP) for non-small-cell lung cancer (NSCLC); however, an optimal protocol for TV delineation has not been determined. We investigate volumetric and positional variation in gross tumor volume (GTV) delineation using a planning PET/CT among three radiation oncologists and a PET radiologist. METHODS AND MATERIALS RTP PET/CT scans were performed on 28 NSCLC patients (Stage IA-IIIB) of which 14 patients received prior induction chemotherapy. Three radiation oncologists and one PET radiologist working with a fourth radiation oncologist independently delineated the GTV on CT alone (GTV(CT)) and on fused PET/CT images (GTV(PETCT)). The mean percentage volume change (PVC) between GTV(CT) and GTV(PETCT) for the radiation oncologists and the PVC between GTV(CT) and GTV(PETCT) for the PET radiologist were compared using the Wilcoxon signed-rank test. Concordance index (CI) was used to assess both positional and volume change between GTV(CT) and GTV(PETCT) in a single measurement. RESULTS For all patients, a significant difference in PVC from GTV(CT) to GTV(PETCT) exists between the radiation oncologist (median, 5.9%), and the PET radiologist (median, -0.4%, p = 0.001). However, no significant difference in median concordance index (comparing GTV(CT) and GTV(FUSED) for individual cases) was observed (PET radiologist = 0.73; radiation oncologists = 0.66; p = 0.088). CONCLUSIONS Percentage volume changes from GTV(CT) to GTV(PETCT) were lower for the PET radiologist than for the radiation oncologists, suggesting a lower impact of PET/CT in TV delineation for the PET radiologist than for the oncologists. Guidelines are needed to standardize the use of PET/CT for TV delineation in RTP.

Single institution, retrospective comparison of toxicity and outcome for static 5-field IMRT versus VMAT in the delivery of prostate and pelvic nodal irradiation in high-risk prostate cancer.

147 Background: There is emerging evidence for the role of pelvic nodal irradiation in high-risk prostate cancer. We have assessed the toxicity rates and outcomes with 2 different radiotherapy techniques. Methods: The baseline disease metrics, toxicity and outcome data for men treated at our institution with prostate and pelvic nodal irradiation during a 2 year period were retrospectively collected. The radiotherapy technique, either 5-field IMRT or VMAT was recorded along with a single dose-level to indicate normal tissue exposure (V50 to bowel and rectum, that is the percentage of total organ receiving ≥ 50Gy). Results: 67 men with a median age of 64 years were identified; 83.6% were Gleason ≥ 8, 82.1% were ≥ T3a, 50.7% were N1, 4.5% were M1a/M1b. All had neoadjuvant and concurrent hormone therapy. All received 74Gy to prostate; 70.1% received 60Gy to pelvic nodes, 28.4% received 55Gy to pelvic nodes (1 patient received 56Gy). 55.2% were treated with static IMRT and 44.8% with VMAT with no significant d...