J. Wloch

Outcomes After Stereotactic Lung Radiotherapy or Wedge Resection for Stage I Non–Small-Cell Lung Cancer

PURPOSE To compare outcomes between lung stereotactic radiotherapy (SBRT) and wedge resection for stage I non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS One hundred twenty-four patients with T1-2N0 NSCLC underwent wedge resection (n = 69) or image-guided lung SBRT (n = 58) from February 2003 through August 2008. All were ineligible for anatomic lobectomy; of those receiving SBRT, 95% were medically inoperable, with 5% refusing surgery. Mean forced expiratory volume in 1 second and diffusing capacity of lung for carbon monoxide were 1.39 L and 12.0 mL/min/mmHg for wedge versus 1.31 L and 10.14 mL/min/mmHg for SBRT (P = not significant). Mean Charlson comorbidity index and median age were 3 and 74 years for wedge versus 4 and 78 years for SBRT (P < .01, P = .04). SBRT was volumetrically prescribed as 48 (T1) or 60 (T2) Gy in four to five fractions. Results Median potential follow-up is 2.5 years. At 30 months, no significant differences were identified in regional recurrence (RR), locoregional recurrence (LRR), distant metastasis (DM), or freedom from any failure (FFF) between the two groups (P > .16). SBRT reduced the risk of local recurrence (LR), 4% versus 20% for wedge (P = .07). Overall survival (OS) was higher with wedge but cause-specific survival (CSS) was identical. Results excluding synchronous primaries, nonbiopsied tumors, or pathologic T4 disease (wedge satellite lesion) showed reduced LR (5% v 24%, P = .05), RR (0% v 18%, P = .07), and LRR (5% v 29%, P = .03) with SBRT. There were no differences in DM, FFF, or CSS, but OS was higher with wedge. CONCLUSION Both lung SBRT and wedge resection are reasonable treatment options for stage I NSCLC patients ineligible for anatomic lobectomy. SBRT reduced LR, RR, and LRR. In this nonrandomized population of patients selected for surgery versus SBRT (medically inoperable) at physician discretion, OS was higher in surgical patients. SBRT and surgery, however, had identical CSS.

Comparison of Planned Versus Actual Dose Delivered for External Beam Accelerated Partial Breast Irradiation Using Cone-Beam CT and Deformable Registration

PURPOSE To assess the adequacy of dose delivery to the clinical target volume (CTV) using external beam (EB) accelerated partial breast irradiation (APBI). METHODS AND MATERIALS Sixteen patients treated with EB APBI underwent cone beam CT (CBCT) before each fraction and daily helical CT (HCT) scans to determine setup errors and calculate the dose per fraction. For 12 patients, an in-house image-intensity-based deformable registration program was used to register the HCTs to the planning CT and generate the cumulative dose. Treatment was 38.5 Gy in 10 fractions. EB APBI constraints from the National Surgical Adjuvant Breast and Bowel Project B39/Radiation Therapy Oncology Group 0413 Phase III protocol were used. RESULTS The mean setup error per CBCT registration was 9 ± 5 mm. Dose-volume histogram analysis showed only one patient (8%) with a decrease in the CTV V90 (8% underdosage). All other patients demonstrated adequate target coverage. PTV_EVAL V90 was on average 3% (range, 0%-16%) less than planned. For the ipsilateral breast, four patients had an increase in V50 (≤ 1% increase) and three patients had an increase in V100 (≤ 9% increase). Only one patient showed an increase >5%. Four patients had an increase in ipsilateral lung V30 (maximum 3%), and one had an increase in heart V5 (1%). Four patients had an increase in MaxDose (maximum 89 cGy). CONCLUSIONS The current CTV-to-PTV margin of 10 mm appears sufficient for ∼92% of patients treated with EB APBI. Although expansion of the population PTV margin to 14 mm would provide ∼97% confidence level for CTV coverage, online image guidance should be considered.

MO‐F‐144‐02: Real‐Time 4D Ultrasound Prostate Gland Motion Tracking During Radiotherapy Fraction Delivery

PURPOSE The intra-fraction variability of target position during the prostate cancer radiotherapy may cause dose discrepancy between planned and delivered dose, especially with longer hypo-fractionated treatments. We report our clinical experience with real-time 4D ultrasound imaging (4D-US) to monitor intrafraction prostate motion. METHODS Three prostate patients were treated on an IRB-approved protocol delivering 51 Gy in 10 fractions using single arc volumetric modulated arc therapy (VMAT). Each patient had three gold markers implanted and had simultaneous CT and 4D-US simulation, followed by an MRI scan. Target and normal organs were delineated on MR images. During setup simultaneous cone-beam CT (CBCT) and continuous 4D-US were acquired, and during VMAT delivery (about 2 min) 4D-US was acquired. The prostate 4D-US position was compared to the CBCT average position, and movement during treatment was characterized. RESULTS The median (range) of mean intra-fraction prostatic motion in the right-left(RL), anterior-posterior(AP) and superior-inferior(SI) directions were 0.1 mm (-1.6 to 0.8 mm), 0 mm (-1.8 to 1.3 mm), and -0.1 mm (-2.2 to 1.4 mm), with respective median (range) of standard deviation were 0.2 mm (0 to 0.8 mm), 0.2 mm (0 to 1.2 mm), and 0.2 mm (0 to 0.7mm). There were 9/27 fractions with shifts >=2 mm in any direction, with an average duration of 23% of treatment time, with a single fraction having a shift greater than 3mm. The discrepancy between 4D-US and CBCT shifts were 0.6±1.6 mm, -0.2±1.4 mm and -0.4±0.7 mm in the RL, AP and SI directions. There was one instance of flatulence during treatment setup where vertical shifts >=3 mm (up to 6.1 mm) persisted for 108 sec. CONCLUSION Real-time imaging is essential for tracking hypo-fractionated prostate motion to reduce dosimetric uncertainty. 4D ultrasound imaging during treatment improves accuracy of dose delivery, and may allow a reduction of treatment margins.

TU-C-ValB-09: Setup Error Analysis of HN-IMRT Patients Using Electronic Portal Images and Cone-Beam CTs

Purpose: It is important to monitor and correct patient setup during treatment course for head and neck IMRT because highly conformal dose distribution is sensitive to setup uncertainties. Setup for HN region is unstable because patient is usually uncomfortable under the mask and the flexible bony structures in the neck region. The purpose of this study is to analyze the setup errors during entire treatment course. These findings will help make appropriate corrective decisions. Method and Materials: Patients enrolled in our IMRT protocol are immobilized with a large thermoplastic mask attached to the MedTec IPPS. 2D analysis is accomplished by comparing electronic portal images to DRRs using in‐house software. Systematic setup error exceeding 3mm is corrected. 3D analysis is performed by registering cone‐beam CT to planning CT. Data from 21 patients with total 185 sessions were used. Correlation between 2D and 3D were analyzed. Time trend was analyzed for patients with daily CBCTs (4 patients with 131 scans total). Results: Good correlations were observed between 2D and 3D analyses with mean difference less than 1mm. Both methods showed that the mean of setup errors is under 1mm in all directions. The systematic and random errors were about 2mm. Margin of 5mm used in the planning seemed to be adequate based on empirical recipes. Time trend analysis shows that changes occurring during treatment course are significant for 3 (out of 4) patients. Conclusion: 2D and 3D analyses agree with each other, but 3D should be used whenever possible because it has the advantage of better image quality, lower imaging dose, and better software to interpret information. The difference is caused mainly from image quality and non‐rigid bony motion. It may be necessary to redo the mask in the middle of treatment course to reduce overall setup error.

SU-E-T-408: Dosimetric Effect of Intrafraction Motion in Spine SRS: A Retrospective Study

PURPOSE To investigate the dosimetric consequence of intrafraction motion in stereotactic radiosurgery (SRS) to the spine. METHODS Post-treatment CBCT registration results from 103 spine SRS cases were used as surrogates to analyze the scale of intrafraction motion. For only those cases with motion vectors greater than the 2 mm planning margin (subgroup, n=20), dose was re-calculated in the TPS assuming a worst case scenario where the entire treatment was delivered in the post-treatment position. Dosimetric data was evaluated only for subgroup patients. DVH parameters, including PTV V100%, V90%, D99%, D80%, and maximum cord dose in equivalent dose of 2 Gy (EQD2_cord, α/β=2 Gy) were compared with those in the original plans. The correlations between DVH differences, treatment time, and motion distance were calculated. RESULTS The intrafraction motions for all cases and the subgroup were 1.3±1.2 mm and 3.1±1.4 mm, respectively, with a max of 6.5 mm. In the subgroup, the re-calculated PTV V100%, V90%, D99% and D80% values were significantly less than in the original plan: 78.6%, 90.6%, 60.2%, and 99.6% vs. 83.2%, 92.8%, 66.3%, and 102.2%, respectively (paired t-tests, p<0.01). The corresponding differences were significantly correlated to motion distances, with V100% the best correlated parameter (R=0.834 and R2=0.695, p<0.01). The subgroup maximum EQD2_cord dose in the re-calculated vs. original plans was 11.7±5.3 Gy vs. 10.4±4.4 Gy (p=0.14), with one case violating in-house criteria. For all patients, the mean treatment time was 31.8±12.9 minutes, and no significant correlation was found between total treatment time and motion distance (R=-0.12, p=0.23). CONCLUSION Intrafraction motion in spine SRS patients can cause significant deviations from planned tumor dose proportional to the motion magnitude. Since local failure is significantly correlated to PTV coverage, and intrafraction motion may exceed the 2mm PTV margin, intrafraction imaging and motion management could improve spine SRS local failure rates.

SU‐FF‐J‐73: Non‐Rigid Setup Errors in HN‐IMRT Patients and Their Dosimetric Effect

Purpose: Dose distribution in head and neck IMRT plan is highly conformal and therefore sensitive to setup error. Rigid setup error measurements and its dosimetric effects have been reported previously. In this study, we investigate the non‐rigid component caused by the flexible bony structures in the neck region. The purposes are to define and measure the non‐rigid setup errors throughout the treatment course and to study its dosimetric effect and margin implications. Method and Materials: Daily cone beam CT(CBCT) was acquired for patients receiving HN‐IMRT treatment. For each CBCT three regions (head, neck and shoulder) were rigidly registered to their corresponding part in planning CT individually. We define the non‐rigid setup error as the difference between the maximum and minimum of the translation/rotation variables among three registrations. A zero value indicates a non‐existent non‐rigid setup error. To model the dosimetric effect, we mathematically transformed helical planning CT by keeping shoulder still, rigidly rotating head by ±10 degrees in three directions and deforming neck regions to match head and shoulder. The original plan was applied to these deforming CTs. Results: The non‐rigid setup error is larger in last week than first week, also larger in second half than first half of treatment course, probably due to the weight loss and the mask getting loose. The rotations in L‐R axis (4°) and translations in S‐I direction (5 mm) are larger than others. Margins of 5 mm used in treatment planning are adequate for most organs to account for the non‐rigid setup errors. Conclusion: We have measured non‐rigid setup errors in HN‐IMRT patients using daily CBCTs. We found that rotations in L‐R axis and translations in S‐I direction are dominant and they increase during the treatment course. We also developed a technique to study its dosimetric effect by transforming/deforming planning CTimage.