C. Arilli

Gamma Knife Radiosurgery in the management of single and multiple brain metastases.

OBJECTIVES To evaluate the efficacy and safety of Gamma Knife Radiosurgery (GKRS) in the treatment of single and multiple brain metastases. PATIENTS AND METHODS From October 2012 to June 2014 106 patients were treated with Radiosurgery (RS) for brain metastases at University of Florence. 77 out of 106 patients had a radiological follow up and their data were analyzed. The target was defined as the enhancing lesion. The prescription dose was defined depending on tumor volume and tumor location. Each patient performed an MRI one month after GKRS for the first three months and every 3 months thereafter. Overall survival was calculated from the day of RS until death. Local recurrence (LR) was defined as radiologic growth of the irradiated lesion, while distant brain recurrence (DBR) was the evidence of brain lesion outside the previous irradiated field. Both the LR and DBR were calculated from the RS till the day of radiological evidence of relapse. The correlations within patient and disease characteristics and the outcomes of survival and disease control were analyzed. RESULTS Mean follow up was 7.2 ± 4.8 months (range: 2.4-22.8 months). At the time of analysis 21 patients (27.3%) were dead. The overall survival (OS) at 1 year was 74%. On univariate Cox Regression analysis female gender (p=0.043, HR: 0.391, 95% CI: 0.157-0.972) and age >65 years (p=0.003 HR: 4.623, 95% CI: 1.687-12.663) were predictive for survival. On multivariate analysis, age older than 65 years (p=0.005HR: 4.254, 95% CI: 1.544-11.721) was confirmed as associated with worsened overall survival. 19 patients (24.7%) had recurrence in the radiosurgery field. The median time to local failure was 4.8 ± 2.0 months (range: 1.8-9.4 months) from GKRS. On Cox Regression univariate analysis, the only factor associated with higher risk of local failure was a number of treated lesions more than 4 (p=0.015, HR: 3.813, 95% CI: 1.298-11.202), no significant parameters were found at the multivariate analysis. The median time to develop distant brain failure was 6 ± 4.32 months (range: 1.08-21.6 months). Median distant brain control was 74% at 1 year. None of the factors analyzed was statistically significant for the distant brain relapse. The radiosurgery treatment was well tolerated. One patient treated for seven metastases developed seizures 8h after GKRS, he was treated with steroids and anticonvulsants. One patient had radiologic evidence of radionecrosis without any neurological symptoms. CONCLUSIONS In well-performing patients with stable systemic disease radiosurgery can be performed as an exclusive treatment for brain metastases. Younger patients could have a greater benefit from the RS, on the other hand our finding confirm no correlation between the survival outcome and the number of lesions treated.

γTools: A modular multifunction phantom for quality assurance in GammaKnife treatments

PURPOSE We present the γTools, a new phantom designed to assess geometric and dosimetric accuracy in Gamma Knife treatments, together with first tests and results of applications. METHODS The phantom is composed of two modules: the imaging module, a regular grid of 1660 control points to evaluate image distortions and image registration result and the dosimetry module for delivered dose distribution measurements. The phantom is accompanied by a MatLab routine for image distortions quantification. Dose measurement are performed with Gafchromic films fixed between two inserts and placed in various positions and orientations inside the dosimetry module thus covering a volume comparable to the full volume of a head. RESULTS Tests performed to assess the accuracy and precision of the imaging module demonstrated sub-millimetric values. As an example of possible applications, the phantom was employed to measure image distortions of two MRI scanners and to perform dosimetric studies of single shots delivered to homogeneous and heterogeneous materials. Due to the phantom material, the measured absolute dose do not correspond to the planned dose; doses comparisons are thus carried out between normalized dose distributions. Finally, an end-to-end test was carried out in the treatment of a neuroma-like target which resulted in a 100% gamma passing rate (2% local, 2 mm) and a distance between the real target perimeter and the prescription isodose centroids of about 1 mm. CONCLUSIONS The tests demonstrate that the proposed phantom is suitable to assess both the geometrical and relative dosimetric accuracy of Gamma Knife radiosurgery treatments.

OC-0458: Delivery errors detectability with IQM, a system for real-time monitoring of radiotherapy treatments

S215 ______________________________________________________________________________________________________ technology. Imaging using MRI shows advantages compared to CT or CBCT offering superior soft tissue contrast without additional dose. Also in particle beam therapy integrated MR guided treatment units have great potential. A complete understanding of the particle beam characteristics in the presence of magnetic fields is required. So far, studies in this area are limited.

EP-1793: Analysis of setup error in patients affected by oropharyngeal cancer treated with tomotherapy

Purpose or Objective: In head and neck cancer radiotherapy, it is still unresolved whether the use of daily image guidance (IG) allows the safe adoption of reduced PTV margins. Moreover, the extended time required for IG on a daily basis unavoidably represents a limiting factor for patients throughput in centers with busy workload. The purpose of our analysis is: 1) evaluating the interfraction error of patients undergoing tomotherapy for oropharyngeal cancer (OPC) with the aim of margins reduction and 2) investigating whether the mean error calculated on the first 5 fractions may avoid the need of performing IG on a daily basis.

EP-1665: Scalp-Sparing focal radiotherapy for gliomas using VMAT or Helical Tomotherapy: a feasibility study

Purpose or Objective: Both transient and permanent alopecia have a huge psychological impact on patient’s quality of life. Sparing the scalp during focal cranial RT for gliomas is a challenging issue during the treatment planning process due to the fact that the scalp is often strictly adjacent to the cortical or subcortical target. In addition, clear constraints for this structure to be used during the inverse planning are not available in literature, most of them being very strict. We report our preliminary experience with scalp sparing technique for patients with high grade gliomas.

EP-1514: γTools: a new multipurpose phantom for end-to-end tests in Gamma Knife SRS treatments

ESTRO 35 2016 _____________________________________________________________________________________________________ At 5 minutes after irradiation, the line profiles on the R2 map across the penumbra region showed the fall-off of the radiation field in both dosimeters while the penumbra region on the right field edge appeared steeper compared to the slope of the penumbra region on the left. The R2 color maps indicated a narrower transition from outside to fully inside the radiation field on the right compared to the transition on the left. 20 hours after irradiation the polymerization of the gel was presumably completed. The overall signal was both higher on the R2 gray scale maps and more pronounced on the R2 color maps. The line profiles across the penumbra regions exhibited a similar trend for both field edges compared to the profiles at 5 minutes post-irradiation. Over the time frame tested, the dosimeter appears stable.

Reproducibility and sensitivity of IQM: A real-time monitoring device for complex radiotherapy treatments

Global and local intra and interfraction detector repeatability results demonstrate the optimal detector performances SENSITIVITY IN DETECTING SMALL DELIVERY ERRORS was checked by inducing 7 types of ERRORS in the IMRT clinical plans for Head & Neck, prostate and the index quadrant by modifying the number of delivered MU (between 1 and 3 per beam) and by introducing deviations in linac leaf positions mimicking an MLC bank error as closing and opening one or both banks.

In-vivo and pre-treatment quality assurance software validation and verification

The aim of this study is to test the accuracy of the dose calculation algorithm available in DosimetryCheck (DC, MathResolution®), a patient QA software for both pretreatment QA and in vivo dose verification, that uses the EPID measured fluence of the treatment fields to reconstruct the dose distribution in the CT planning model of the patient.