Raffaela Doro

Stereotactic Radiotherapy for Adrenal Gland Metastases: University of Florence Experience

PURPOSE To evaluate a retrospective single-institution outcome after hypofractionated stereotactic body radiotherapy (SBRT) for adrenal metastases. METHODS AND MATERIALS Between February 2002 and December 2009, we treated 48 patients with SBRT for adrenal metastases. The median age of the patient population was 62.7 years (range, 43-77 years). In the majority of patients, the prescription dose was 36 Gy in 3 fractions (70% isodose, 17.14 Gy per fraction at the isocenter). Eight patients were treated with single-fraction stereotactic radiosurgery and forty patients with multi-fraction stereotactic radiotherapy. RESULTS Overall, the series of patients was followed up for a median of 16.2 months (range, 3-63 months). At the time of analysis, 20 patients were alive and 28 patients were dead. The 1- and 2-year actuarial overall survival rates were 39.7% and 14.5%, respectively. We recorded 48 distant failures and 2 local failures, with a median interval to local failure of 4.9 months. The actuarial 1-year disease control rate was 9%; the actuarial 1- and 2-year local control rate was 90%. CONCLUSION Our retrospective study indicated that SBRT for the treatment of adrenal metastases represents a safe and effective option with a control rate of 90% at 2 years.

Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy

PURPOSE To evaluate the effect of plan parameters on volumetric modulated arc therapy (VMAT) dosimetric accuracy, together with the possibility of scoring plan complexity. METHODS 142 clinical VMAT plans initially optimized using a 4° control point (CP) separation were evaluated. All plans were delivered by a 6 MV Linac to a biplanar diode array for patient-specific quality assurance (QA). Local Γ index analysis (3%, 3 mm and 2%, 2 mm) enabled the comparison between delivered and calculated dose. The following parameters were considered for each plan: average leaf travel (LT), modulation complexity score applied to VMAT (MCSv), MU value, and a multiplicative combination of LT and MCSv (LTMCS). Pearsons correlation analysis was performed between Γ passing rates and each parameter. The effects of CP angular separation on VMAT dosimetric accuracy were also analyzed by focusing on plans with high LT values. Forty out of 142 plans with LT above 350 mm were further optimized using a finer angle spacing (3° or 2°) and Γ analysis was performed. The average Γ passing rates obtained at 4° and at 3°∕2° sampling were compared. A further correlation analysis between all parameters and the Γ pass-rates was performed on 142 plans, but including the newly optimized 40 plans (CP every 3° or 2°) in place of the old ones (CP every 4°). RESULTS A moderate significant (p < 0.05) correlation between each examined parameter and Γ passing rates was observed for the original 142 plans at 4° CP discretization. A negative correlation was found for LT with Pearsons r absolute values above 0.6, suggesting that a lower dosimetric accuracy may be expected for higher LT values when a 4° CP sampling is used. A positive correlation was observed for MCSv and LTMCS with r values above 0.5. In order to score plan complexity, threshold values of LTMCS were defined. The average Γ passing rates were significantly higher for the plans created using the finer CP spacing (3°∕2°) compared to the plans optimized using the standard 4° spacing (Student t-test p < 0.05). The correlation between LT and passing rates was strongly diminished when plans with finer angular separations were considered, yielding Pearsons r absolute values below 0.45. CONCLUSIONS At 4° CP sampling, LT, MCSv, and LTMCS were found to be significantly correlated with VMAT dosimetric accuracy, expressed as Γ pass-rates. These parameters were found to be possible candidates for scoring plan complexity using threshold values. A finer CP separation (3°∕2°) led to a significant increase in dosimetric accuracy for plans with high leaf travel values, and to a decrease in correlation between LT and Γ passing rates. These results indicated that the influence of LT on VMAT dosimetric accuracy can be controlled by reducing CP separation. CP spacing for all plans requiring large leaf motion should not exceed 3°. The reported data were integrated to optimize our clinical workflow for plan creation, optimization, selection among rival plans, and patient-specific QA of VMAT treatments.

Quality assurance of volumetric modulated arc therapy: Evaluation and comparison of different dosimetric systems

PURPOSE To compare and evaluate different dosimetric techniques and devices for the QA of VMAT plans created by two treatment planning systems (TPSs). METHODS A total of 50 VMAT plans were optimized for treatment of anatomical sites of various complexities by two TPSs which use rather different approaches to VMAT optimization. Dosimetric plan verifications were performed both as part of commissioning and as patient specific QA of clinical treatments. Absolute point doses were measured for all plans by a micro ion chamber inserted in a dedicated water-filled cylindrical phantom. Delivered dose distributions were verified by four techniques based on different detectors: radiographic and gafchromic films, two systems based on 2D diode arrays and an ion chamber array. Gamma index analysis with various tolerance levels (3%, 3 mm and 3%, 2 mm) was used to analyze differences between calculated and delivered doses. Sensitivity to possible delivery errors was also evaluated for three of the considered devices introducing +/-3 mm shifts along the three directions and a 3 degrees gantry offset. RESULTS Ion chamber measured point doses were within 3% of calculated ones for 48 out of 50 values. For delivered dose distribution, the average fraction of passed gamma values using 3% and 3 mm criteria was above 95% for both TPSs and all detectors except gafchromic film which yielded on average of 91.4%. For 49 out of 50 plans, a pass-rate above 94% was obtained by at least one of the four techniques. Shrinking the tolerance to 3% and 2 mm, the average pass-rate by all detectors (except film) was still above 95% for one of the two TPSs, but lower for the other one. The detector sensitivity to 3 mm shifts and to gantry angle offset was strongly plan and partially detector dependent: the obtained pass-rate reduction ranged from 2% to 30%. CONCLUSIONS The presented results for VMAT plans QA assess the reliability of the delivered doses for both TPSs. The slightly lower pass-rate obtained for one of the considered TPS can be attributed to a higher level of complexity of the optimized plans. The results by different dosimetric techniques are coherent, apart from a few measurements by gafchromic films. The detector sensitivity to delivery errors, being strongly plan dependent, is not easy to evaluate.

On-line image guidance for frameless stereotactic radiotherapy of lung malignancies by cone beam CT: comparison between target localization and alignment on bony anatomy.

Introduction. Free-breathing stereotactic radiotherapy for lung malignancies requires reliable prediction of respiratory motion and accurate target localization. A protocol was adopted for reproducibility and reduction of respiratory motion and for target localization by CBCT image guidance. Tumor respiratory displacements and tumor positioning errors relative to bony anatomy alignment are analyzed. Materials and method. Image guided SRT was performed for 99 lung malignancies. Two groups of patients were considered: group A did not perform any breathing control; group B controlled visually their respiratory cycle and volumes on an Active Breathing Coordinator (ABC) monitor during the acquisition of simulation CT and CBCT, and treatment delivery. GTV on end inhale and exhale CT data sets were fused in an ITV and the extent of tumor motion evaluated between these 2 phases. A pre-treatment CBCT was acquired and aligned to the reference CT using bony anatomy; for tumor positioning the ITV contour on the reference CT was matched to the visible tumor on CBCT. Interobserver variability of tumor positioning was evaluated. ITV and CBCT tumor dimensions were compared. Results. 3D tumor breathing displacement (mean±SD) was significantly higher for group A (14.7±9.9 mm) than for group B (4.7±3.1 mm). The detected differences between tumor and bony structure alignment below 3 mm were 68% for group B and 45% for group A, reaching statistical significance. Interobserver variability was 1.7±1.1 mm (mean±SD). Dimensions of tumor image on CBCT were consistent with ITV dimensions for group B (max difference 14%). Conclusions. The adopted protocol seems effective in reducing respiratory internal movements and margin. Tumor positioning errors relative to bony anatomy are also reduced. However bony anatomy as a surrogate of the target may still lead to some relevant positioning errors. Target visualization on CBCT is essential for an accurate localization in lung SRT.

CyberKnife beam output factor measurements: A multi-site and multi-detector study.

PURPOSE New promising detectors are available for measuring small field size output factors (OFs). This study focused on a multicenter evaluation of two new generation detectors for OF measurements on CyberKnife systems. METHODS PTW-60019 microDiamond and W1 plastic scintillation detector (PSD) were used to measure OFs on eight CyberKnife units of various generations for 5-60mm fixed cones. MicroDiamond and PSD OF were compared to routinely used silicon diodes data corrected applying published Monte Carlo (MC) factors. PSD data were corrected for Čerenkov Light Ratio (CLR). The uncertainties related to CLR determination were estimated. RESULTS Considering OF values averaged over all centers, the differences between MC corrected diode and the other two detectors were within 1.5%. MicroDiamond exhibited an over-response of 1.3% at 7.5mm and a trend inversion at 5mm with a difference of 0.2%. This behavior was consistent among the different units. OFs measured by PSD slightly under-responded compared to MC corrected diode for the smaller cones and the differences were within 1%. The observed CLR variability was 2.5% and the related variation in OF values was 1.9%. CONCLUSION This study indicates that CyberKnife microDiamond OF require corrections below 2%. The results are enhanced by the consistency observed among different units. Scintillator shows a good agreement to MC corrected diode but CLR determination remains critical requiring further investigations. The results emphasized the value of a multi-center validation over a single center approach.

Clinical outcome of stereotactic body radiotherapy for abdominal lymph node metastases.

Aims and background. To report the clinical outcome of linac-based or robotic, image-guided stereotactic body radiotherapy in patients affected by abdominal lymph node metastases from different primary cancers. Methods and methods. Twenty-six patients with 32 abdominal lymph node metastases were consecutively treated at the University of Florence between April 2011 and May 2012. The mean follow-up was 4.6 months (SD, 3.9; range, 0.3-13). The dose prescription ranged between 24 Gy and 36 Gy delivered in 1-5 fractions. Results. In terms of local control, complete response to stereotactic body radiotherapy was obtained in 18 cases (66.7%), partial response in 7 (25.9%), and stable disease in 2 (7.4%). At the Cox univariate regression analysis, an increased risk of partial response or absence of local response to radiotherapy was found for subjects of the female sex (P = 0.036), age less than 50 years (P = 0.022), primary tumor of the genital tract (P = 0.007), and previous chemotherapy (P = 0.057). An excellent local control rate (90.9%) was obtained in patients affected by abdominal lymph node metastases of prostatic origin. Conclusions. Stereotactic body radiotherapy for abdominal lymph node metastases is a safe and effective treatment in terms of high rates of local control, especially in a subset of patients affected by prostate cancer.

Salvage stereotactic re-irradiation with CyberKnife for locally recurrent head and neck cancer: a single center experience.

Aims and Background We report the toxicity and preliminary clinical outcome in patients affected by locally recurrent head and neck cancer treated with stereotactic reirradiation. Methods Between February 2012 and August 2013, 17 patients were treated with CyberKnife as stereotactic re-irradiation for locally recurrent head and neck cancer. All patients had previously received a full dose radiation treatment with radical intent, with a median total dose of 66 Gy (range, 50–70) delivered with standard fractionation. The median interval between the primary radiotherapy and re-irradiation was 24 months (range, 10–168). Results All patients completed the prescribed treatment, which was delivered in 5 fractions. The median tumor dose administered was 30 Gy (range, 25–35) prescribed to the 80% isodose line. Treatment sites were as follows: neck lymph nodes in 5 patients, paranasal sinuses in 5, oropharynx in 2, nasopharynx, and larynx, oral cavity, nasal fossa and parotid gland each in 1 patient. The median target volume treated was 58.7 cm3 (range, 8.5–211.3). Sixteen patients (94%) were evaluated for response. At a median follow-up of 7.5 months (range, 2–17), 4 patients achieved complete response (25%), 5 had partial response (31%) and 7 showed stable disease (44%). No patient showed in-field progression after re-irradiation. Grade 3 acute toxicity was noted in one patient only; no late side effect was observed during the follow-up. Conclusions Stereotactic re-irradiation with CyberKnife is an appealing non-surgical salvage treatment for selected patients with local-regionally recurrent head and neck cancer.

Stereotactic body radiotherapy with CyberKnife for cardiac malignancies

Aims and Background Radiobiological and technical considerations have traditionally limited the role of radiation therapy in the context of primary and secondary cardiac malignancies. Stereotactic body radiotherapy (SBRT) is a promising modality for the delivery of focused high-dose radiation with ablative potential to complex targets such as small, deep-seated, moving lesions, allowing also for re-irradiation. Methods Between January 2013 and October 2013, 3 patients underwent SBRT for cardiac lesions: 2 patients had recurrent, previously irradiated cardiac angiosarcomas (PCA) and 1 patient had a cardiac metastasis from melanoma. They were treated with fiducial-guided robotic radiotherapy with CyberKnife. As for dose prescription, 24 Gy in 3 fractions (80% isodose) and 30 Gy in 5 fractions (80% isodose) were administered to the recurrent PCAs and cardiac metastasis, respectively. Results At 2 months after SBRT, cardiac MRI showed a partial response in the patients treated for recurrent PCA while the cardiac metastasis remained stable. In all cases, absence of local progression was subsequently confirmed by contrast-enhanced cardiac MRI after 6 months, without any evidence of treatment-related side effects. Conclusions Fiducial-guided SBRT proved to be feasible and effective in preventing local disease progression in selected patients with cardiac malignancies.

SU‐GG‐T‐236: Quality Assurance of VMAT Treatment Delivery: Comparison of Four Different Dosimetric Equipments for the Verification of Plans Created by Two Treatment Planning Systems

Purpose: To compare four dosimetric techniques for the QA of VMAT plans created by two TPS. Method and Materials: 46 VMAT plans for treatment of anatomical sites of various complexity were created using ERGO++TPS (Elekta) (35 plans) and Oncentra VMAT module (Nucletron) (11 plans) for a 6 MV Elekta Synergy. Gamma analysis was used to compare calculated dose distributions with doses measured by 4 equipments: films (EDR2 and EBT2) in a solid water phantom, a 2D diode array (Mapcheck and Mapphan phantom), 2 crossing diode arrays in a cylindrical phantom (Delta4 system), an ion chamber array (PTW seven29 and Octavius). Mapcheck, delta4 and seven29 sensitivity to possible delivery errors was evaluated introducing +−3mm shifts along the 3 directions and a 3° gantry offset. Results: The average fraction of passed gamma values with a 3% and 3 mm criteria was above 95% for both TPS and all detectors except EBT2 which yielded an average of 91.0%. For 45 out of 46 plans a pass‐rate above 93% was obtained by at least one of the 4 equipments. Shrinking the tolerance to 3% and 2mm the average pass rate by Mapcheck, delta4 and seven29 was still above 95% for ERGO, but lower for Oncentra. The detectors sensitivity to 3 mm shifts and to gantry angle offset was strongly plan and partially detector dependent: the obtained pass‐rate reduction ranged from 2% to 30%. Conclusion: The presented results for VMAT plans QA assess the reliability of the delivered doses for both TPS. The slightly lower pass rate obtained for Oncentra can be attributed to a higher complexity of some of the created plans. The results by different dosimetric techniques are coherent, apart from a few measurements by EBT2. The detectors sensitivity to delivery errors, being strongly plan dependent, is not easy to evaluate.