CyberKnife radiosurgery for prostate cancer

Assessment of HDR brachytherapy-replicating prostate radiotherapy planning for tomotherapy, cyberknife and VMAT

A dosimetric study was undertaken to assess the ability of Cyberknife (CK), Volumetric Modulated Arc Therapy (VMAT), and TomoTherapy (Tomo) to generate treatment plans that mimic the dosimetry of high dose-rate brachytherapy (HDR BT) for prostate cancer. The project aimed to assess the potential of using stereotactic body radiotherapy (SBRT) for boost treatment of high-risk prostate cancer patients where HDR BT in combination with conformal external beam radiotherapy (EBRT) is the standard of care. The datasets of 6 prostate patients previously treated with HDR BT were collated. VMAT, CK, and TomoTherapy treatment plans were generated for each dataset using the target and organ-at-risk structures as defined by the Radiation Oncologist during the HDR BT treatment process. The HDR BT plan isodoses were also converted into planning structures to assist the other modalities to achieve a HDR BT-like dose distribution. CK plans were created using both the iris collimator (IC) and a multileaf collimator (MLC). Comparison of the techniques was made based on dose-volume indices. Each plan was created at centres experienced using the respective treatment planning systems (TPS). Planning target volume (PTV V100%), i.e., the volume of the planning target volume (PTV) receiving 100% of the relative dose, in VMAT and TomoTherapy SBRT plans was higher than HDR BT plans. PTV V150% and V200%, i.e., volume of the PTV receiving 150% and 200% of the relative dose, were approached on all the CK MLC and TomoTherapy SBRT plans. However, it is not presently achievable for "virtual brachytherapy" SBRT to replicate the same high intraprostatic doses as HDR BT while meeting the constraints on the organs-at-risk (OARs). Half of the CK IC plans achieved PTV V150% but this was at the expense of high rectal dose. TomoTherapy and CK MLC plans achieved PTV V150% and V200% but the bladder dose was higher compared to CK IC plans. VMAT exhibited excellent PTV coverage based on V100 and OAR sparing, but without any ability to achieve the high intra-prostatic doses of HDR (V150% and V200%). SBRT techniques can be used to deliver hypofractionated radiotherapy to the PTV V100%. Based on the comparison of "physical" dose distributions, SBRT cannot presently achieve the same high intraprostatic doses as HDR BT while respecting the OAR constraints. SBRT still remains an attractive treatment option for delivering hypofractionated treatments for prostate cancer compared to HDR BT, in particular as it is less invasive and less resource intensive. Long-term outcomes of clinical trials comparing HDR BT and SBRT "prostate boosts" may show whether the high intraprostatic doses are clinically significant and correlate with outcomes.

Prostate Stereotactic Body Radiation Therapy With Halcyon 2.0: Treatment Plans Comparison Based on RTOG 0938 Protocol

Purpose

The aim of this study is to investigate the feasibility of prostate stereotactic body radiation therapy treatment with a newly developed Varian Halcyon^TM 2.0 machine by comparing radiotherapy plans with previously delivered CyberKnife G4 plans created with the previous version of CyberKnife Treatment Planning System Multiplan 4.6.1.

Methods

Fifteen previously treated prostate stereotactic body radiation therapy treatment CyberKnife plans were re-planned retrospectively according to the Radiation Therapy Oncology Group 0938 protocol on a Halcyon^TM 2.0 machine with a prescription of 3625 cGy in five fractions.

Results

All re-plans on a Halcyon^TM 2.0 were able to meet the Radiation Therapy Oncology Group 0938 protocol goals and constraints. The re-plans decreased the maximum dose to skin and urethra, mean doses to the bladder and rectum, and also improve the conformity index and the Planning Target Volume coverage. However, D1cc to the rectum, D1cc and D10% to the bladder increased with no statistically significant differences (p > 0.05) with the re-plans.

Conclusion

The Halcyon^TM 2.0 can generate stereotactic body radiation therapy treatment prostate plans created based on the Radiation Therapy Oncology Group 0938 protocol by delivering adequate coverage to the target while sparing healthy tissues.

Efficacy and safety of stereotactic radiosurgery for pulmonary metastases from osteosarcoma: Experience in 73 patients

Osteosarcoma pulmonary metastases are typically treated with resection and/or chemotherapy. We hypothesize that stereotactic radiosurgery (SRS) can be an alternative to surgery that can achieve high rates of local control with limited toxicity. From January 2005 to December 2013, 73 patients who developed pulmonary metastasis during period of adjuvant chemotherapy or follow-up were analyzed. 33 patients were treated by stereotactic radiosurgery using the body gamma-knife system. A total dose of 50 Gy was delivered at 5 Gy/fraction to the 50% isodose line covering the planning target volume, whereas a total dose of 70 Gy was delivered at 7 Gy/fraction to the gross target volume. The other 40 patients were treated by surgical resection. Four-year progression-free survival rate, four-year survival rate, median time of PRPFS (post-relapse progress-free survival) and PROS (post-relapse overall survival) in SRS group were parallel to that in surgical group. Patients tolerated gamma knife radiosurgery well. Our study demonstrates that SRS is well-tolerated with excellent local control and less complications. SRS should be considered as a potential option in patients with pulmonary metastases from osteosarcoma, especially in those who are medically inoperable, refuse surgery.

Hypo-fractionated SBRT for localized prostate cancer: a German bi-center single treatment group feasibility trial

BACKGROUND

For prostate cancer treatment, treatment options with minimal side effects are desired. External beam radiation therapy (EBRT) is non-invasive, standard of care and delivered in either conventional fractionation over 8 weeks or with moderate hypo-fractionation over about 5 weeks. Recent advances in radiotherapy technology have made extreme hypo-fractionated stereotactic body radiation therapy (SBRT) of prostate cancer feasible, which has not yet been introduced as a standard treatment method in Germany. Initial results from other countries are promising, but long-term results are not yet available. The aim of this study is to investigate feasibility and effectiveness of SBRT for prostate cancer in Germany.

METHODS/DESIGN

This German bi-center single group trial (HYPOSTAT) is designed to evaluate feasibility and effectiveness, as measured by toxicity and PSA-response, respectively, of an extreme hypo-fractionated SBRT regimen with five fractions of 7 Gy in treatment of localized low and intermediate risk prostate cancer. The target volume includes the prostate with or without the base of seminal vesicles depending on risk stratification and uncertainty margins that are kept at 3-5 mm. SBRT treatment is delivered with the robotic CyberKnife system, which was recently introduced in Germany. Acute and late toxicity after one year will be evaluated according to Common Terminology Criteria for Adverse Events (CTCAE v. 4.0), Radiation Therapy Oncology Group (RTOG) and International Prostate Symptom Score (IPSS) Scores. The quality of life will be assessed before and after treatment with the EORTC QLQ C30 questionnaire. Hypothesizing that the proportion of patients with grade 2 side effects or higher is less or equal than 2.8%, thus markedly lower than the standard EBRT percentage (17.5%), the recruitment target is 85 patients.

DISCUSSION

The HYPOSTAT trial aims at demonstrating short term feasibility of extreme hypo-fractioned SBRT for the treatment of prostate cancer and might be used as the pilot study for a multi-center multi-platform or for randomized-controlled trials comparing conventional radiotherapy with SBRT for localized prostate cancer in the future. The study concept of patient enrollment, follow up and evaluation by multiple public university clinics and actual patient treatment in dedicated private radiosurgery practices with high-tech radiation equipment is unique for clinical trials.

STUDY STATUS

The study is ongoing and currently recruiting patients.

TRIAL REGISTRATION

Registration number: NCT02635256 ( clinicaltrials.gov ). Registered 8 December 2015.

Optimal planning strategy among various arc arrangements for prostate stereotactic body radiotherapy with volumetric modulated arc therapy technique

BACKGROUND

The aim of this study was to determine the optimal strategy among various arc arrangements in prostate plans of stereotactic body radiotherapy with volumetric modulated arc therapy (SBRT-VMAT).

PATIENTS AND METHODS

To investigate how arc arrangements affect dosimetric and biological metrics, SBRT-VMAT plans for eighteen patients were generated with arrangements of single-full arc (1FA), single-partial arc (1PA), double-full arc (2FA), and double-partial arc (2PA). All plans were calculated by the Acuros XB calculation algorithm. Dosimetric and radiobiological metrics for target volumes and organs at risk (OARs) were evaluated from dosevolume histograms.

RESULTS

All plans were highly conformal (CI<1.05, CN=0.91) and homogeneous (HI=0.09-0.12) for target volumes. For OARs, there was no difference in the bladder dose, while there was a significant difference in the rectum and both femoral head doses. Plans using 1PA and 2PA showed a strong reduction to the mean rectum dose compared to plans using 1FA and 2FA. Contrastively, the D2% and mean dose in both femoral heads were always lower in plans using 1FA and 2FA. The average tumor control probability and normal tissue complication probability were comparable in plans using all arc arrangements.

CONCLUSIONS

The use of 1PA had a more effective delivery time and produced equivalent target coverage with better rectal sparing, although all plans using four arc arrangements showed generally similar for dosimetric and biological metrics. However, the D2% and mean dose in femoral heads increased slightly and remained within the tolerance. Therefore, this study suggests that the use of 1PA is an attractive choice for delivering prostate SBRT-VMAT.

Prostate-specific antigen kinetics after primary stereotactic body radiation therapy using CyberKnife for localized prostate cancer

PURPOSE

To assess prostate-specific antigen (PSA) kinetics and report on the oncologic outcomes for patients with localized prostate cancer treated with stereotactic body radiation therapy (SBRT) using CyberKnife.

METHODS

We extracted the list and data of 39 patients with clinically localized prostate cancer who had undergone primary SBRT using CyberKnife between January 2008 and December 2012 from the Smart Prostate Cancer database system of Seoul St. Mary's Hospital. Changes in PSA over time, PSA velocity, and PSA nadir were evaluated from the completion of SBRT using CyberKnife. Biochemical recurrence (BCR)-free survival after primary SBRT using CyberKnife was determined using Kaplan-Meier analysis.

RESULTS

The rate of PSA decrease was maximal in the first month (median -3.34 ng/mL/mo), which then fell gradually with median values of -1.51, -0.32, -0.28, -0.20, and -0.03 ng/mL/mo for durations of 3, 6, 9, 12, and 24 months after SBRT using CyberKnife, respectively. The median PSA nadir was 0.31 ng/mL after a median 23 months. Kaplan-Meier analysis calculates an actuarial 5-year BCR-free survival after SBRT using CyberKnife as 80.8%.

CONCLUSIONS

PSA decline occurred rapidly in the first month, and then the rate of PSA decline fell off steadily over time throughout 2 years after treatment. Also, SBRT using CyberKnife leads to long-term favorable BCR-free survival in localized prostate cancer.

Treatment plan comparison between stereotactic body radiation therapy techniques for prostate cancer: non-isocentric CyberKnife versus isocentric RapidArc

PURPOSE

The aim of this study was to evaluate the feasibility and dose distribution of two different stereotactic body radiation therapy (SBRT) techniques, isocentric RapidArc (RA) and non-isocentric CyberKnife (CK), for the treatment of localized prostate cancer.

METHODS

Two groups of patients (Groups 1 and 2 with ten patients per group) treated with CK were re-planned with RA. The patients were grouped according to the rectum constraint used (Group1, maximum dose for rectum; Group 2, dose-volume histogram for rectum). The prescription dose was 37.5 Gy in five fractions. The two SBRT techniques were compared by target coverage, normal tissue sparing, and dose distribution parameters. Monitor units (MUs) and the delivery time were likewise compared to assess delivery efficiency.

RESULTS

The RA plans consistently exhibited superior PTV coverage and better rectum sparing at low doses in the both groups. The conformity and heterogeneity indices of the RA plans were better than the CK plans. Additionally, the RA plans resulted in fewer low-dose regions, lower MUs, and faster delivery times than the CK plans.

CONCLUSIONS

The good dosimetric distribution and shorter delivery time make RA an attractive SBRT technique for the treatment of localized prostate cancer.

Stereotactic radiosurgery, a potential alternative treatment for pulmonary metastases from osteosarcoma

Stereotactic radiosurgery (SRS), such as body gamma knife, was reported to achieve excellent rates of local disease control with limited toxicity in many cases of primary or secondary pulmonary tumor, except osteosarcoma. To confirm the value of SRS in pulmonary metastases from osteosarcoma, we reviewed the experience from our institution (Department of Oncology, Affiliated Sixth People's Hospital, Shanghai) and compared the efficiency of SRS with that of surgical resection. From January 2005 to December 2012, we carried out a retrospective investigation of 58 patients (age, 8-59 years; mean, 25.2 years) who were diagnosed with non-metastatic osteosarcoma of the extremity and later developed pulmonary metastasis during the period of adjuvant chemotherapy or follow-up. Among them, 27 patients were treated by SRS using the body gamma-knife system. A total dose of 50 Gy was delivered at 5 Gy/fraction to the 50% isodose line covering the planning target volume, whereas a total dose of 70 Gy was delivered at 7 Gy/fraction to the gross target volume. The other 31 patients were treated by surgical resection. Two-year progression-free survival rate, two-year survival rate, median time of PRPFS (post-relapse progress-free survival) and PROS (post-relapse overall survival) in SRS group were parallel to that in surgical group. All 27 patients tolerated gamma knife radiosurgery well while only 9 patients had grades 1-2 pneumonitis. We believe SRS, compared with surgical resection, is effective and safe in treating pulmonary metastasis from osteosarcoma, especially for those patients who were medically unfit for a resection or who refused surgery.

A single-center study of 100 consecutive patients with localized prostate cancer treated with stereotactic body radiotherapy

BACKGROUND

Radiotherapy is an increasingly preferred treatment option for localized prostate cancer, and stereotactic body radiation therapy (SBRT) a relatively established modality of therapeutic irradiation. The present study analyzes the toxicity and biochemical efficacy of SBRT in 100 consecutive prostate cancer patients treated with CyberKnife Robotic Radiosurgery System.

METHODS

One hundred patients were treated with SBRT at the Radiation Oncology department of San Bortolo Hospital, Vicenza, Italy. All patients included in this IRB-approved protocol-driven prospective study had biopsy-proven prostate cancer. Risk category was low in 41, intermediate in 42, and high in 17 patients. The patients were treated with CyberKnife-SBRT (CK-SBRT), the prescription dose was 35 Gy in five fractions, corresponding to 92 Gy in 2-Gy fractions (α/β =1.5 Gy); 29 patients also received androgen deprivation therapy (ADT).

RESULTS

Median follow-up was 36 months (range, 6-76 months). Acute Grade 2 genitourinary and gastrointestinal toxicity occurred in respectively 12% and 18% of the patients; there were no Grade 3 or higher acute toxicities. Late Grade 1, 2, and 3 genitourinary toxicities occurred in 4%, 3%, and 1% of the patients, respectively; late Grade 1 gastrointestinal toxicity occurred in two patients and Grade 2 toxicity in one patient; no late gastrointestinal toxicities of grade 3 or 4 were observed. Median PSA nadir was 0.45 ng/ml at 36 months for all patients. In the SBRT-monotherapy group, the median PSA nadir at 36 months was 0.62 ng/ml; in the ADT-SBRT group, it was 0.18 ng/ml. Four patients had clinical recurrence: one local, two lymph nodes, and one to the bone. Ninety-six patients had no evidence of biochemical or clinical recurrence. A benign PSA bounce of median 1.08 ng/ml occurred in 12% of the 71 SBRT monotherapy patients at a mean 23 months (range, 18-30 months).

CONCLUSIONS

In this study CK-SBRT has provided promising outcomes in localized prostate cancer with good PSA response, minimal toxicity and patient inconvenience.

Treatment and technical intervention time analysis of a robotic stereotactic radiotherapy system

The purpose of this study is to obtain a better operational knowledge of Stereotactic Body Radiotherapy (SBRT) treatments with CyberKnife(r). An analysis of both In-room Times (IRT) and technical interventions of 5 years of treatments was performed, during which more than 1600 patients were treated for various indications, including liver (21%), lung (29%), intracranial (13%), head and neck (11%) and prostate (7%). Technical interventions were recorded along with the time of the failure, time to the intervention, and the complexity and duration of the repair. Analyses of Time Between Failures (TBF) and Service Disrupting TBF(disr) were performed. Treatment time data and variability per indication and following different system upgrades were evaluated. Large variations of IRTs were found between indications, but also large variations for each indication. The combination of the time reduction Tool (using Iris(r)) and Improved Stop Handling was of major impact to shortening of treatment times. The first implementation of the Iris collimator alone did not lead to significantly shorter IRTs for us except during prostate treatments. This was mostly due to the addition at the same time of larger rotational compensation for prostate treatments (58 instead of 1.58). Significant differences of duration between the first fraction and following fractions of a treatment, representing the necessity of defining imaging parameters and explanation to patients, were found for liver (12 min) and lung treatments using Xsight(r) Spine (5 min). Liver and lung treatments represent the longest IRT's and involve the largest variability's in IRT. The malfunction rate of the system followed a Weibull distribution with the shape and scale parameters of 0.8 and 39.7. Mean TBF(disr) was 68 work hours. 60 to 80% of the service disrupting interventions were resolved within 30-60 min, 5% required external intervention and 30% occurred in the morning. The presented results can be applied in the evaluation of the required machine time in order to implement robotic radiosurgery for different indications. The analytical distributions of IRTs and technical interruptions can be used for simulations.

Analysis of high-dose rate brachytherapy dose distribution resemblance in CyberKnife hypofractionated treatment plans of localized prostate cancer

The present study is to analyze the CyberKnife hypofractionated dose distribution of localized prostate cancer in terms of high-dose rate (HDR) brachytherapy equivalent doses to assess the degree of HDR brachytherapy resemblance of CyberKnife dose distribution. Thirteen randomly selected localized prostate cancer cases treated using CyberKnife with a dose regimen of 36.25Gy in 5 fractions were considered. HDR equivalent doses were calculated for 30Gy in 3 fractions of HDR brachytherapy regimen. The D5% of the target in the CyberKnife hypofractionation was 41.57 ± 2.41Gy. The corresponding HDR fractionation (3 fractions) equivalent dose was 32.81 ± 1.86Gy. The mean HDR fractionation equivalent dose, D98%, was 27.93 ± 0.84Gy. The V100% of the prostate target was 95.57% ± 3.47%. The V100% of the bladder and the rectum were 717.16 and 79.6mm(3), respectively. Analysis of the HDR equivalent dose of CyberKnife dose distribution indicates a comparable resemblance to HDR dose distribution in the peripheral target doses (D98% to D80%) reported in the literature. However, there is a substantial difference observed in the core high-dose regions especially in D10% and D5%. The dose fall-off within the OAR is also superior in reported HDR dose distribution than the HDR equivalent doses of CyberKnife.

Carbogen gas and radiotherapy outcomes in prostate cancer

Prostate cancer hypoxia is associated with inferior prognosis and resistance to treatment. The use of androgen deprivation therapy, both prior to and during radiotherapy, may exacerbate underlying hypoxia. Whilst larger radiation doses per fraction may achieve therapeutic gain, this is balanced by the reduced opportunity for re-oxygenation to take place during the course of treatment. Improving the underlying hypoxic tumour environment may therefore improve the treatment outcomes. Strategies to combat tumour hypoxia, with particular focus on the use of carbogen gas breathing concurrently with radiotherapy, is the subject of this review.

Comparison of quality of life after stereotactic body radiotherapy and surgery for early-stage prostate cancer

Background

As the long-term efficacy of stereotactic body radiation therapy (SBRT) becomes established and other prostate cancer treatment approaches are refined and improved, examination of quality of life (QOL) following prostate cancer treatment is critical in driving both patient and clinical treatment decisions. We present the first study to compare QOL after SBRT and radical prostatectomy, with QOL assessed at approximately the same times pre- and post-treatment and using the same validated QOL instrument.

Methods

Patients with clinically localized prostate cancer were treated with either radical prostatectomy (n = 123 Spanish patients) or SBRT (n = 216 American patients). QOL was assessed using the Expanded Prostate Cancer Index Composite (EPIC) grouped into urinary, sexual, and bowel domains. For comparison purposes, SBRT EPIC data at baseline, 3 weeks, 5, 11, 24, and 36 months were compared to surgery data at baseline, 1, 6, 12, 24, and 36 months. Differences in patient characteristics between the two groups were assessed using Chi-squared tests for categorical variables and t-tests for continuous variables. Generalized estimating equation (GEE) models were constructed for each EPIC scale to account for correlation among repeated measures and used to assess the effect of treatment on QOL.

Results

The largest differences in QOL occurred in the first 1–6 months after treatment, with larger declines following surgery in urinary and sexual QOL as compared to SBRT, and a larger decline in bowel QOL following SBRT as compared to surgery. Long-term urinary and sexual QOL declines remained clinically significantly lower for surgery patients but not for SBRT patients.

Conclusions

Overall, these results may have implications for patient and physician clinical decision making which are often influenced by QOL. These differences in sexual, urinary and bowel QOL should be closely considered in selecting the right treatment, especially in evaluating the value of non-invasive treatments, such as SBRT.

Equivalent normalized total dose estimates in cyberknife radiotherapy dose delivery in prostate cancer hypofractionation regimens

As the α/β value of prostate is very small and lower than the surrounding critical organs, hypofractionated radiotherapy became a vital mode of treatment of prostate cancer. Cyberknife (Accuray Inc., Sunnyvale, CA, USA) treatment for localized prostate cancer is performed in hypofractionated dose regimen alone. Effective dose escalation in the hypofractionated regimen can be estimated if the corresponding conventional 2 Gy per fraction equivalent normalized total dose (NTD) distribution is known. The present study aims to analyze the hypofractionated dose distribution of localized prostate cancer in terms of equivalent NTD. Randomly selected 12 localized prostate cases treated in cyberknife with a dose regimen of 36.25 Gy in 5 fractions were considered. The 2 Gy per fraction equivalent NTDs were calculated using the formula derived from the linear quadratic (LQ) model. Dose distributions were analyzed with the corresponding NTDs. The conformity index for the prescribed target dose of 36.25 Gy equivalent to the NTD dose of 90.63 Gy (α/β = 1.5) or 74.31 Gy (α/β = 3) was ranging between 1.15 and 1.73 with a mean value of 1.32 ± 0.15. The D5% of the target was 111.41 ± 8.66 Gy for α/β = 1.5 and 90.15 ± 6.57 Gy for α/β = 3. Similarly, the D95% was 91.98 ± 3.77 Gy for α/β = 1.5 and 75.35 ± 2.88 Gy for α/β = 3. The mean values of bladder and rectal volume receiving the prescribed dose of 36.25 Gy were 0.83 cm3 and 0.086 cm3, respectively. NTD dose analysis shows an escalated dose distribution within the target for low α/β (1.5 Gy) with reasonable sparing of organs at risk. However, the higher α/β of prostate (3 Gy) is not encouraging the fact of dose escalation in cyberknife hypofractionated dose regimen of localized prostate cancer.