Background: Several high-precision stereotactic radiation therapy modalities are currently used in clinical settings. We aimed to evaluate whether the CyberKnife (CK) or TrueBeam (TB) radiation treatment systems were more appropriate for treating targets of various morphologies according to the physical properties of each device.  Materials and Methods: Spheres (diameter = 5–50 mm), as well as triangular prisms and cubes (length of a side = 10–50 mm), were used as virtual targets for each treatment delivery system. A phantom with dosimetry film was irradiated to evaluate the flatness and gradient of the radiation treatment from each modality. Results: The homogeneity index (HI) for the spherical targets was significantly higher (dose distribution was more homogeneous) using the TB than when using the CK (1.9 vs. 1.4; p = 0.002). There were no significant differences between treatment modalities in the HI for more complex shapes. The HI increased monotonically as the virtual target diameter increased for the CK (p = 0.048). The flatness parameter was lower for the TB than for the CK (1.4 vs. 1.1; p < 0.001). Conclusion: The CK is particularly robust for delivering therapeutic radiation to small targets, while the TB is more suitable for targets with a simple shape or when the HI is a critical treatment factor.
 

 

Purpose: This study was conducted to evaluate single collimator (SC) and double collimator (DC) plans with respect to dosimetric analysis, calculated dose delivery to OAR and treatment time in carcinoma prostate patients treated with cyberknife. Materials and Methods: A retrospective study was conducted among twenty low and intermediate risk carcinoma prostate previously treated with Cyberknife. PTV was created and OARs were delineated. The prescribed dose was set as 37.5 Gy in 5 fractions and a base plan (BP), followed by three reduction plans (time, beam and node) were generated for both single and double collimators with sequential optimization module. The SC and DC plans were compared for the above-said variables. The mean differences were compared using paired t-test. A p-value of <0.05 was taken as statistically significant. Results: The median age of the patients was 63 years. DC plans had tighter isodose lines. The means of minimum doses did not vary significantly across the plans but the mean and maximum doses, PTV D2 and V95 means were significantly higher in single collimator plan. The mean CI and HI values were better in DC plans. The doses to OAR were comparable in both single and double collimator plans in terms of maximum doses. The mean doses received by OAR’s were significantly lesser in DC plans.SC plans resulted in lesser beams, nodes, MU and treatment time.

Background: Stereotactic body radiotherapy (SBRT) is an emerging treatment option which allows for extreme hypofractionation using modern technologies, because the low α/β-ratio favors the use of high dose per fraction in prostate cancer. There is a need for more data about SBRT. We provide a long-term update of SBRT clinical outcome using CyberKnife for the treatment of localized prostate cancer. Materials and Methods: This study was based on a retrospective analysis of 43 patients treated with SBRT using CyberKnife for localized prostate cancer (23.3% in low risk, 67.4% in intermediate risk and 9.3% in high risk). The target volume included the prostate with or without the seminal vesicles depending on the risk stratification and uncertainty margins that are kept at 3-5 mm. Total dose of 36.25 Gy in 5 fractions of 7.25 Gy were administered. Results: 43 patients with a median 73.6 months (range, 14 to 119 months) follow-up were analyzed. There was three biochemical failure (BCF). Eight-year BCF free survival and overall survival were 92.0% and 73.1%, respectively. Median PSA decline rates were -0.301, -0.191 and -0.115 ng/mL/month, respectively, for durations of 1, 2 and 3 years after radiotherapy and has remained plateau. Median PSA nadir was 0.27 ng/mL at median 38 months and PSA bounce (median 0.33 ng/mL) occurred in 32.6% (n = 14) of patients at median 19 months after SBRT. There was no grade 3 acute and late toxicity. Conclusion: Our long-term experience with SBRT using CyberKnife for localized prostate cancer demonstrates favorable efficacy and toxicity.

Background: Accurate dosimetry in CyberKnife® is challenging because of the unavailability of suitable detectors to satisfy all the criteria of small-field dosimetry. In this work, eight different small-field detectors from PTW and IBA Dosimetry were used to determine the dosimetric parameters for twelve fixed collimators in the CyberKnife® radiosurgery system. The scope of this work was to assist medical physicists in detector selection in small-field dosimetry. Materials and Methods: Dosimetric parameters such as the surface dose (D_s), dose buildup (D_B), percentage dose at 100 mm (D₁₀₀), percentage dose at 200 mm (D₂₀₀), depth of dose maximum (D_max), and total scatter factor (S_cp) were compared and analyzed from the acquired Percentage Depth Dose(PDD). Results: Large variations in D_s were observed with different detectors for smaller collimator sizes. On analyzing the dose buildup, considerable differences were observed with all detectors from the surface to  6 mm depth for the smallest cone of 5 mm diameter. The D₁₀₀ and D₂₀₀ values obtained using ion chambers were higher than those using diodes, likely due to the volume averaging effect. The depth of dose maximum was found to increase with increase in the field size for most of the detectors. Considerable variation in S_cp was noticed with all detectors in smaller field ranges. Conclusion: For small fields, the selection of detector is crucial, and awareness of the advantages, disadvantages and limitations of the detectors used is crucial. As in absolute dosimetry, the relative dosimetry in small fields is challenging and requires further studies and recommendations.

Background: Pineal parenchymal tumor (PPT) is extremely rare and histologically heterogeneous, and the optimal treatment strategy is controversial. This study examined clinical outcomes of patients with PPT treated with cyberknife radiosurgery (CKRS) as a primary treatment modality after tumor biopsy. Materials and Methods: Between 2009 and 2018, there were six patients diagnosed with PPT who were treated with single or hypofractionated cyberknife radiosurgery (CKRS) after undergoing endoscopic third ventriculostomy (ETV) and tumor biopsy. Two tumors were pineocytoma (PC) and four were pineal parenchymal tumor of intermediate differentiation (PPTID). The marginal dose was 18 Gy, and the median target volume was 3.05 (range 1.4-7.4) cc. The median follow-up period was 55 (range 18 -141) months. Results: Five patients were alive, and all of their tumors were locally controlled during follow-up periods. Two tumors disappeared completely, two other tumors partially regressed, and another tumor showed no interval change after CKRS. One patient with PPTID showed local progression 14 months after CKRS and died 21 months after CKRS. There were no acute or late complications related to CKRS. Conclusion: This study suggested that CKRS can be used as a primary treatment modality after ETV and tumor biopsy for PPT with favorable clinical outcomes. However, alternative treatment modalities need to be considered for higher risk groups of patients with PPTID.

Background: We report our long-term outcomes with Cyberknife to deliver hypofractionated SBRT boost combined with EBRT to patients with intermediate to high risk prostate cancer. Materials And Methods: From March 2008 to July 2014, 42 patients with newly diagnosed, intermediate (73.8%, 31) and high risk (26.2%, 11) localized prostate cancer were treated with EBRT and SBRT boost. The whole pelvis dose was 45 Gy (25 fractions of 1.8 Gy) and the SBRT boost dose was 21 Gy (3 fractions of 7 Gy). Results: With a median follow-up duration of 84.2 months (range, 20-139.6), the median PSA decline rates were -0.605, -0.229, -0.166 and -0.094 ng/mL/month, respectively, for durations of 1, 2, 3 and 4 years after radiotherapy and has remained near plateau. Four BCFs were observed only in high risk group. The actuarial 8 year BCF free survival and overall survival were 90.3 % and 83.7 %, respectively. BCF-free survival at 8 years were 100 % and 77.8 % for intermediate and high risk group, respectively (p=0.014). No grade 3 or 4 acute and late genitourinary (GU) and gastrointestinal (GI) toxicities were observed. Acute grade 2 GU toxicities were seen in 23.8 % (n = 10) and acute grade 2 GI toxicities in 21.4 % (n = 9). Late grade 2 GU toxicities were observed in 11.9 % (n = 5) and grade 2 GI toxicities in 14.2 % (n = 6). Conclusions: We demonstrated that SBRT boost after EBRT in intermediate- and high-risk prostate cancer had favorable outcomes with tolerable toxicities.