Current practices of craniospinal irradiation techniques in Turkey: a comprehensive dosimetric analysis.

OBJECTIVE: This study evaluates various craniospinal irradiation (CSI) techniques used in Turkish centers to understand their advantages, disadvantages and overall effectiveness, with a focus on enhancing dose distribution. METHODS: Anonymized CT scans of adult and pediatric patients, alongside target volumes and organ-at-risk (OAR) structures, were shared with 25 local radiotherapy centers. They were tasked to develop optimal treatment plans delivering 36 Gy in 20 fractions with 95% PTV coverage, while minimizing OAR exposure. The same CT data was sent to a US proton therapy center for comparison. Various planning systems and treatment techniques (3D conformal RT, IMRT, VMAT, tomotherapy) were utilized. Elekta Proknow software was used to analyze parameters, assess dose distributions, mean doses, conformity index (CI), and homogeneity index (HI) for both target volumes and OARs. Comparisons were made against proton therapy. RESULTS: All techniques consistently achieved excellent PTV coverage (V95 > 98%) for both adult and pediatric patients. Tomotherapy closely approached ideal Dmean doses for all PTVs, while 3D-CRT had higher Dmean for PTV_brain. Tomotherapy excelled in CI and HI for PTVs. IMRT resulted in lower pediatric heart, kidney, parotid, and eye doses, while 3D-CRT achieved the lowest adult lung doses. Tomotherapy approached proton therapy doses for adult kidneys and thyroid, while IMRT excelled for adult heart, kidney, parotid, esophagus, and eyes. CONCLUSION: Modern radiotherapy techniques offer improved target coverage and OAR protection. However, 3D techniques are continued to be used for CSI. Notably, proton therapy stands out as the most efficient approach, closely followed by Tomotherapy in terms of achieving superior target coverage and OAR protection.

Gamma Knife radiosurgery for the treatment of trigeminal neuralgia: A single center-experience.

INTRODUCTION AND OBJECTIVES: We aimed to assess the outcomes of patients with trigeminal neuralgia (TGN) who underwent Gamma Knife radiosurgery (GKRS). MATERIALS AND METHODS: Fifty-three patients with typical TGN underwent GKRS from May 2012 until December 2022. Among these patients, 45 patients who were follow-up for at least 12 months were included in the study. A mean dose of 87.5 Gy (range, 80-90) was administered to the trigeminal nerve. Postoperatively, outcome was considered excellent if the patient was pain- and medication-free. RESULTS: The mean symtpom duration was 9.53 years, and the mean patient age was 59.8 years (range, 34-85). The mean follow-up period was 46.8 months (range, 12-127 months). 46.7% of patients had a history of previous surgical interventions. A single nerve division was affected in 14 patients (31.1%), and multiple divisions were affected in 31 patients (68.9%). The rate of initial pain relief was 80%. Hypoesthesia in the area of trigeminal nerve developed in 30 (66.7%). Twenty patients (44.4%) exhibited excellent results within 72.4 months. Recurrence occurred in 11 patients (24.4%) with 27.6 months. CONCLUSIONS: Our results suggest that GKRS is a safe and effective procedure. Thus, it is an attractive first- and second-line treatment choice for TGN.

Optimal Sensor Placement for Reliable Virtual Sensing Using Modal Expansion and Information Theory.

A framework for optimal sensor placement (OSP) for virtual sensing using the modal expansion technique and taking into account uncertainties is presented based on information and utility theory. The framework is developed to handle virtual sensing under output-only vibration measurements. The OSP maximizes a utility function that quantifies the expected information gained from the data for reducing the uncertainty of quantities of interest (QoI) predicted at the virtual sensing locations. The utility function is extended to make the OSP design robust to uncertainties in structural model and modeling error parameters, resulting in a multidimensional integral of the expected information gain over all possible values of the uncertain parameters and weighted by their assigned probability distributions. Approximate methods are used to compute the multidimensional integral and solve the optimization problem that arises. The Gaussian nature of the response QoI is exploited to derive useful and informative analytical expressions for the utility function. A thorough study of the effect of model, prediction and measurement errors and their uncertainties, as well as the prior uncertainties in the modal coordinates on the selection of the optimal sensor configuration is presented, highlighting the importance of accounting for robustness to errors and other uncertainties.

Replacement of the tumor bed following oncoplastic breast-conserving surgery with immediate latissimus dorsi mini-flap.

The aim of the present study was to evaluate the geographic variability of the tumor bed following oncoplastic breast-conserving surgery (OP-BCS), and to assess its relevance for radiotherapy planning. In this prospective study, pre- and postoperative computerized tomography (CT) scans of 22 patients with early-stage breast cancer were fused. The preoperative gross tumor volume or excisional biopsy cavity were contoured under the guidance of preoperative radiological images. Postoperative lumpectomy cavities were contoured under the guidance of surgical clips. The conformity index (CI) was calculated and defined on a scale between 0 and 1, where 0 indicated no overlap and 1 indicated 100% concordance. Associations between CI and the number of clips, time interval between surgery and CT scans, pathological tumor size and age were assessed using independent sample testing. The median CI was 0.07 (in five cases, 1, and in eight cases, 0). The lumpectomy cavity shifted from the primary location in 36.4% of the cases. Median shifts between the isocenters of pre- and postoperative volumes were measured as 1.02 cm (range, 0.4-4.43 cm) in the x, 1.07 cm (range, 0.05-5.67 cm) in the y, and 1.12 cm (range, 0-3.75 cm) in the z directions. Only the clip number was determined to be significantly associated with CI (P=0.017). Pre- and postoperative tumor bed volumes were fully superposed in five of the 22 cases. The present study has shown that the tumor bed is markedly replaced following OP-BCS with latissimus dorsi mini-flap (LDMF) reconstruction. Special care should therefore be taken when defining the lumpectomy cavity following OP-BCS with LDMF reconstruction.

The effect of bladder contrast on dose calculation in volumetric modulated arc therapy planning in patients treated for postoperative prostate cancer.

PURPOSE: The aim of this study was to evaluate the effect of contrast agent on dose calculation in volumetric modulated arc therapy (VMAT) in the post-prostatectomy setting. METHODS AND MATERIAL: Ten patients were studied. Each patient received planning computed tomography (CT) images with contrast agent. All of the plans were done on virtually simulated contrast-free CT scans. The plan approved by the radiation oncologist was replicated to the contrast CT series. In both of the plans the same monitor unit was used. The doses calculated from the two plans were compared in regard to target volumes and organs at risk. A paired sample t-test was used to evaluate the differences in cumulative dose volume histogram between the two plans. RESULTS: We showed that the use of contrast agent may cause significant differences in dose distribution. There was a significant decrease in doses received by planning target volume (PTV70), rectum V65 Gy, rectum V40 Gy, bladder V65 Gy, penile bulb V40 Gy in plans with contrast-enhanced CT sets. The decrease in mean, maximum and minimum doses received by PTV70 also contributed to the significant decrease in conformity index. CONCLUSIONS: Using a contrast agent at the time of CT simulation may cause significant differences in dose distribution. For this reason, the plan should always be carried out on non-contrast CT data sets to avoid additional errors in the treatment planning process.

Dosimetric comparison of field in field intensity-modulated radiotherapy technique with conformal radiotherapy techniques in breast cancer.

PURPOSE: The aim of this study was to be able to implement the field-in-field intensity-modulated radiotherapy (FiF) technique in our daily practice for breast radiotherapy. To do this, we performed a dosimetric comparison. MATERIALS AND METHODS: Treatment plans were produced for 20 consecutive patients. FiF plans and conformal radiotherapy (CRT) plans were compared for doses in the planning target volume (PTV), the dose homogeneity index (DHI), doses in irradiated soft tissue outside the target volume (SST), ipsilateral lung and heart doses for left breast irradiation, and the monitor unit counts (MU) required for treatment. Averaged values were compared using Student's t-test. RESULTS: With FiF, the DHI is improved 7.0% and 5.7%, respectively (P < 0.0001) over the bilateral and lateral wedge CRT techniques. When the targeted volumes received 105% and 110% of the prescribed dose in the PTV were compared, significant decreases are found with the FiF technique. With the 105% dose, the SST, heart, and ipsilateral lung doses and the MU counts were also significantly lower with the FiF technique. CONCLUSION: The FiF technique, compared to CRT, for breast radiotherapy enables significantly better dose distribution in the PTV. Significant differences are also found for soft tissue volume, the ipsilateral lung dose, and the heart dose. Considering the decreased MUs needed for treatment, the FiF technique is preferred over tangential CRT.

Insufficiency fractures after pelvic radiotherapy in patients with prostate cancer.

PURPOSE: To assess the incidence, predisposing factors, and clinical characteristics of insufficiency fractures (IF) in patients with prostate cancer, who received pelvic radiotherapy as part of their definitive treatment. METHODS AND MATERIALS: The charts of 134 prostate cancer patients, who were treated with pelvic radiotherapy between 1998 and 2007 were retrospectively reviewed. IF was diagnosed by bone scan and/or CT and/or MRI. The cumulative incidence of symptomatic IF was estimated by actuarial methods. RESULTS: Eight patients were identified with symptomatic IF after a median follow-up period of 68 months (range, 12-116 months). The 5-year cumulative incidence of symptomatic IF was 6.8%. All patients presented with lower back pain. Insufficiency fracture developed at a median time of 20 months after the end of radiotherapy and was managed conservatively without any need for hospitalization. Three patients were thought to have metastatic disease because of increased uptake in their bone scans. However, subsequent CT and MR imaging revealed characteristic changes of IF, avoiding any further intervention. No predisposing factors for development of IF could be identified. CONCLUSIONS: Pelvic IF is a rare complication of pelvic radiotherapy in prostate cancer. Knowledge of pelvic IF is essential to rule out metastatic disease and prevent unnecessary treatment, especially in a patient cohort with high-risk features for distant spread.