Whole brain radiotherapy with hippocampal avoidance and simultaneous integrated boost for brain metastases: a dosimetric volumetric-modulated arc therapy study

Dosimetric evaluation of LINAC-based single-isocenter multi-target multi-fraction stereotactic radiosurgery with more than 20 targets: comparing MME, HyperArc, and RapidArc

BACKGROUND

To compare the dosimetric quality of three widely used techniques for LINAC-based single-isocenter multi-target multi-fraction stereotactic radiosurgery (fSRS) with more than 20 targets: dynamic conformal arc (DCA) in BrainLAB Multiple Metastases Elements (MME) module and volumetric modulated arc therapy (VMAT) using RapidArc (RA) and HyperArc (HA) in Varian Eclipse.

METHODS

Ten patients who received single-isocenter fSRS with 20-37 targets were retrospectively replanned using MME, RA, and HA. Various dosimetric parameters, such as conformity index (CI), Paddick CI, gradient index (GI), normal brain dose exposures, maximum organ-at-risk (OAR) doses, and beam-on times were extracted and compared among the three techniques. Wilcoxon signed-rank test was used for statistical analysis.

RESULTS

All plans achieved the prescribed dose coverage goal of at least 95% of the planning target volume (PTV). HA plans showed superior conformity compared to RA and MME plans. MME plans showed superior GI compared to RA and HA plans. RA plans resulted in significantly higher low and intermediate dose exposure to normal brain compared to HA and MME plans, especially for lower doses of ≥ 8Gy and ≥ 5Gy. No significant differences were observed in the maximum dose to OARs among the three techniques. The beam-on time of MME plans was about two times longer than RA and HA plans.

CONCLUSIONS

HA plans achieved the best conformity, while MME plans achieved the best dose fall-off for LINAC-based single-isocenter multi-target multi-fraction SRS with more than 20 targets. The choice of the optimal technique should consider the trade-offs between dosimetric quality, beam-on time, and planning effort.

Current status and perspectives of interventional clinical trials for brain metastases: analysis of ClinicalTrials.gov

BACKGROUND

The management of brain metastases (BM), the major cause of cancer morbidity and mortality, is becoming an emerging area of interest. Surgery, whole brain radiation therapy (WBRT), or stereotactic radiosurgery (SRS), have historically been the main focal treatments for BM. However, the introduction of innovative targeted- and immune-based therapies is progressively changing the paradigm of BM treatment, resulting in an increase in clinical trials investigating new therapeutic strategies.

METHODS

Using ClinicalTrials.gov, the largest clinical trial registry with over 400,000 registered trials, we performed an analysis of phase II and phase III ongoing trials evaluating different systemic therapies, radiotherapy (RT), and surgery given alone or in combination in patients with BM.

RESULTS

One hundred sixty-eight trials, 133 phase II and 35 phase III; the largest part having primarily the curative treatment of patients with BM from lung cancer, breast cancer and melanoma, were selected. One hundred sixty-three trials used systemic therapies. One hundred thirteen used tyrosine kinase inhibitors, more frequently Osimertinib, Icotinib and Pyrotinib, 50 used monoclonal antibodies, more frequently Trastuzumab, Pembrolizumab, Nivolumab, 20 used conventional chemotherapies whilst no oncological active drugs were used in 6 trials. Ninety-six trials include RT; 54 as exclusive treatment and 42 in combination with systemic therapies.

CONCLUSION

Systemic targeted- and/or immune-based therapies, combined or not with RT, are increasingly used in the routine of BM treatment. SRS is progressively replacing WBRT. All these trials intend to address multiple questions on the management of patients with BMs, including the recommended upfront treatment for different cancer histologies and the optimal timing between systemic therapies and radiation regarding brain control and neurocognitive outcome and quality of life.

RapidPlan hippocampal sparing whole brain model version 2-how far can we reduce the dose?

Whole-brain radiotherapy has been the standard palliative treatment for patients with brain metastases due to its effectiveness, availability, and ease of administration. Recent clinical trials have shown that limiting radiation dose to the hippocampus is associated with decreased cognitive toxicity. In this study, we updated an existing Knowledge Based Planning model to further reduce dose to the hippocampus and improve other dosimetric plan quality characteristics. Forty-two clinical cases were contoured according to guidelines. A new dosimetric scorecard was created as an objective measure for plan quality. The new Hippocampal Sparing Whole Brain Version 2 (HSWBv2) model adopted a complex recursive training process and was validated with five additional cases. HSWBv2 treatment plans were generated on the Varian Halcyon^TM and TrueBeam^TM systems and compared against plans generated from the existing (HSWBv1) model released in 2016. On the Halcyon^TM platform, 42 cases were re-planned. Hippocampal D_100% from HSWBv2 and HSWBv1 models had an average dose of 5.75 Gy and 6.46 Gy, respectively (p < 0.001). HSWBv2 model also achieved a hippocampal D_mean of 7.49 Gy, vs 8.10 Gy in HSWBv1 model (p < 0.001). Hippocampal D_0.03CC from HSWBv2 model was 9.86 Gy, in contrast to 10.57 Gy in HSWBv1 (p < 0.001). For PTV_3000, D_98% and D_2% from HSWBv2 model were 28.27 Gy and 31.81 Gy, respectively, compared to 28.08 Gy (p = 0.020) and 32.66 Gy from HSWBv1 (p < 0.001). Among several other dosimetric quality improvements, there was a significant reduction in PTV_3000 V_105% from 35.35% (HSWBv1) to 6.44% (HSWBv2) (p < 0.001). On 5 additional validation cases, dosimetric improvements were also observed on TrueBeam^TM. In comparison to published data, the HSWBv2 model achieved higher quality hippocampal avoidance whole brain radiation therapy treatment plans through further reductions in hippocampal dose while improving target coverage and dose conformity/homogeneity. HSWBv2 model is shared publicly.

Reirradiation of Whole Brain for Recurrent Brain Metastases: A Case Report of Lung Cancer With 12-Year Survival

Whole brain radiotherapy (WBRT) for brain metastases (BMs) was considered to be dose limited. Reirradiation of WBRT for recurrent BM has always been challenged. Here, we report a patient with multiple BMs of non-small-cell lung cancer (NSCLC), who received two courses of WBRT at the interval of 5 years with the cumulative administration dose for whole brain as 70 Gy and a boost for the local site as 30 Gy. Furthermore, after experiencing relapse in the brain, he underwent extra gamma knife (GK) radiotherapy for local brain metastasis for the third time after 5 years. The overall survival was 12 years since he was initially diagnosed with NSCLC with multiple brain metastases. Meanwhile, each time of radiotherapy brought a good tumor response to brain metastasis. Outstandingly, during the whole survival, he had a good quality of life (QoL) with Karnofsky Performance Score (KPS) above 80. Even after the last GK was executed, he had just a mild neurocognitive defect. In conclusion, with the cautious evaluation of a patient, we suggest that reirradiation of WBRT could be a choice, and the cumulative radiation dose of the brain may be individually modified.

Brain metastases of lung cancer: comparison of survival outcomes among whole brain radiotherapy, whole brain radiotherapy with consecutive boost, and simultaneous integrated boost

PURPOSE

Radiotherapy is the mainstay for treating brain metastasis (BM). The objective of this study is to evaluate the overall survival (OS) of patients with BM of lung cancer treated with different radiotherapy modalities.

METHODS

Patients with BM of lung cancer who underwent radiotherapy between July 2007 and November 2017 were collected, and their baseline demographics, clinicopathological characteristics and treatments were recorded. Survival was estimated by the Kaplan-Meier method and compared by using the log-rank test. Univariate and multivariate analysis of the prognostic factors were performed using the Cox proportional hazard regression model.

RESULTS

A total of 144 patients were enrolled, of whom 77 underwent whole-brain radiotherapy (WBRT), 39 underwent whole brain radiotherapy with consecutive boost (WBRT + boost), and 28 underwent integrated simultaneous integrated boost intensity-modulated radiotherapy (SIB-IMRT). The OS in SIB-IMRT group was significantly longer than that in WBRT group (median OS 14 (95% confidence interval [CI] 8.8-19.1) vs.7 (95% CI 5.5-8.5) months, log-rank p < 0.001) and WBRT + boost group (median OS: 14 (95% CI 8.8-19.1) vs.11 (95% CI 8.3-13.7) months, log-rank p = 0.037). Multivariable analysis showed that mortality risk of patients treated with SIB-IMRT decrease by 56, 59, 64 and 64% in unadjusted model (hazard ratio [HR] = 0.44; 95% CI 0.28-0.70, p < 0.001), model 1 (HR = 0.41; 95% CI 0.26-0.65, p < 0.001), model 2 (HR = 0.36; 95% CI 0.21-0.61, p < 0.001), and model 3 (HR = 0.36; 95% CI 0.21-0.61, p < 0.001).

CONCLUSIONS

For patients with BM of lung cancer, SIB-IMRT seems to be associated with a more favorable prognosis.

Sparing the hippocampus and the hypothalamic- pituitary region during whole brain radiotherapy: a volumetric modulated arc therapy planning study

BACKGROUND

Feasibility testing of a simultaneous sparing approach of hippocampus, hypothalamus and pituitary gland in patients undergoing whole-brain radiotherapy (WBRT) with and without a concomitant boost to metastatic sites.

INTRODUCTION

Cognitive impairment and hormonal dysfunction are common side effects of cranial radiotherapy. A reduced dose application to the patho-physiologically involved functional brain areas, i.e. hippocampus, hypothalamus and pituitary gland, could reduce these common side effects. While hippocampal sparing is already a common practice to improve cognitive outcome, technical experience of additional combined sparing of the hypothalamus/pituitary gland (HT-P) is insufficient.

METHODS

Twenty patients were included in the planning study. In 11 patients, a total dose of 36 Gy of WBRT (2 Gy per fraction) plus a simultaneous integrated boost (SIB) of 9 Gy (0.5 Gy per fraction, total dose: 45 Gy) to the brain metastases was applied. In 9 patients, prophylactic cranial irradiation (PCI) was simulated with a total dose of 30 Gy (2 Gy per fraction). In both patient cohorts, a sparing approach of the hippocampus and the HT-P area was simulated during WBRT. For all treatment plans, volumetric modulated arc therapy (VMAT) was used. Quality assurance included assessment of homogeneity, conformality and target coverage.

RESULTS

The mean dose to the hippocampus and HT-P region was limited to less than 50% of the prescribed dose to the planning target volume (PTV) in all treatment plans. Dose homogeneity (HI) of the target volume was satisfying (median HI = 0.16 for WBRT+SIB and 0.1 for PCI) and target coverage (conformation number, CN) was not compromised (median CN = 0.82 for SIB and 0.86 for PCI).

CONCLUSION

Simultaneous dose reduction to the hippocampus and the HT-P area did not compromise the PTV coverage in patients undergoing WBRT+SIB or PCI using VMAT. While the feasibility of the presented approach is promising, prospective neurologic, endocrine outcome and safety studies are required.

Early experience with hippocampal avoidance whole brain radiation therapy and simultaneous integrated boost for brain metastases

PURPOSE

Cranial irradiation results in cognitive decline, which is hypothesized to be partially attributable to hippocampal injury and stem cell loss. Recent advances allow for targeted reduction of radiation dose to the hippocampi while maintaining adequate dose coverage to the brain parenchyma and additional increasing dose to brain metastases, a approach called hippocampal avoidance whole brain radiation therapy with a simultaneous integrated boost (HA-WBRT + SIB.) We review our early clinical experience with HA-WBRT + SIB.

MATERIALS AND METHODS

We evaluated treatments and clinical outcomes for patients treated with HA-WBRT + SIB between 2014 and 2018.

RESULTS

A total of 32 patients (median age, 63.5 years, range 45.3-78.8 years) completed HA-WBRT + SIB. Median follow-up for patients alive at the time of analysis was 11.3 months. The most common histology was non-small cell lung cancer (n = 22). Most patients (n = 25) were prescribed with WBRT dose of 30 Gy with SIB to 37.5 Gy in 15 fractions. Volumetric modulated arc therapy reduced treatment time (p < 0.0001). Median freedom from intracranial progression and overall survival from completion of treatment were 11.4 months and 19.6 months, respectively. Karnofsky Performance Status was associated with improved survival (p = 0.008). The most common toxicities were alopecia, fatigue, and nausea. Five patients developed cognitive impairment, including grade 1 (n = 3), grade 2 (n = 1), and grade 3 (n = 1).

CONCLUSION

HA-WBRT + SIB demonstrated durable intracranial disease control with modest side effects and merits further investigation as a means of WBRT toxicity reduction while improving long-term locoregional control in the brain.

Stereotactic radiosurgery combined with targeted/ immunotherapy in patients with melanoma brain metastasis

BACKGROUND

There is limited data on the use of targeted or immunotherapy (TT/IT) in combination with single fraction stereotactic radiosurgery (SRS) in patients with melanoma brain metastasis (MBM). Therefore, we analyzed the outcome and toxicity of SRS alone compared to SRS in combination with TT/IT.

METHODS

Patients with MBM treated with single session SRS at our department between 2014 and 2017 with a minimum follow-up of 3 months after first SRS were included. The primary endpoint of this study was local control (LC). Secondary endpoints were distant intracranial control, radiation necrosis-free survival (RNFS), and overall survival (OS). The local/ distant intracranial control rates, RNFS and OS were analyzed using the Kaplan-Meier method. The log-rank test was used to test differences between groups. Cox proportional hazard model was performed for univariate continuous variables and multivariate analyses.

RESULTS

Twenty-eight patients (17 male and 11 female) with 52 SRS-lesions were included. The median follow-up was 19 months (range 14-24 months) after first SRS. Thirty-six lesions (69.2%) were treated with TT/IT simultaneously (4 weeks before and 4 weeks after SRS), while 16 lesions (30.8%) were treated with SRS alone or with sequential TT/IT. The 1-year local control rate was 100 and 83.3% for SRS with TT/IT and SRS alone (p = 0.023), respectively. The estimated 1-year RNFS was 90.0 and 82.1% for SRS in combination with TT/IT and SRS alone (p = 0.935). The distant intracranial control rate after 1 year was 47.7 and 50% for SRS in combination with TT/IT and SRS alone (p = 0.933). On univariate analysis, the diagnosis-specific Graded Prognostic Assessment including the BRAF status (Melanoma-molGPA) was associated with a significantly improved LC. Neither gender nor SRS-PTV margin had a prognostic impact on LC. V10 and V12 were significantly associated with RNFS (p < 0.001 and p = 0.004).

CONCLUSION

SRS with simultaneous TT/IT significantly improved LC with no significant difference in radiation necrosis rate. The therapy combination appears to be effective and safe. However, prospective studies on SRS with simultaneous TT/IT are necessary and ongoing.

TRIAL REGISTRATION

The institutional review board approved this analysis on 10th of February 2015 and all patients signed informed consent (UE nr. 128-14).

Role of Radiosurgery/Stereotactic Radiotherapy in Oligometastatic Disease: Brain Oligometastases

During the natural history of oncologic diseases, approximately 20-40% of patients affected by cancer will develop brain metastases. Non-small lung cancer, breast cancer, and melanoma are the primaries that are most likely to metastasize into the brain. To date, the role of Radiosurgery/Stereotactic Radiotherapy (SRS/SRT) without Whole brain irradiation (WBRT) is a well-recognized treatment option for patients with limited intracranial disease (1-4 BMs) and a life-expectancy of more than 3-6 months. In the current review, we focused on randomized studies that evaluate the potential benefit of radiosurgery/stereotactic radiotherapy for brain oligometastases. To date, no difference in overall survival has been observed between SRS/SRT alone compared to WBRT plus SRS. Notably, SRS alone achieved higher local control rates compared to WBRT. A possible strength of SRS adoption is the potential decreased neurocognitive impairment.

Modern radiotherapy in cancer treatment during pregnancy

Breast cancer, gynecological malignancies and lymphomas are the most frequently diagnosed tumors in pregnant women. The feasibility of radiotherapy during pregnancy remains a subject of debate and clinicians continue to hesitate on this approach, trying to avoid radiotherapy in most cases. Since the 1990s, several technological advances, including intensity modulated and image guided radiation delivery, have been implemented in radiation oncology to improve the radiation treatment in terms of effectiveness and tolerability. It remains uncertain which short- and long-term health effects the radiation exposure of the fetus may have through advanced radiotherapy techniques. The present systematic literature review aims to summarize the limited current evidences of the feasibility and clinical results of "modern" radiotherapy procedures for the treatment of the most frequently diagnosed tumors in pregnant women.

First experience and clinical results using a new non-coplanar mono-isocenter technique (HyperArc™) for Linac-based VMAT radiosurgery in brain metastases

INTRODUCTION

Radiosurgery (SRS) or stereotactic fractionated radiotherapy (SFRT) is increasing in the treatment of brain metastases (BMs). Aim of the present study was to evaluate the safety and effectiveness of SRS/SFRT for BMs, using a new mono-isocenter non-coplanar solution (HyperArc™ Varian Medical System).

METHODS

BMs patients with a diameter inferior to 3 cm, a life expectancy of more than 3 months and a good performance status, were eligible for Linac-based volumetric modulated arc therapy (VMAT) SFRT/SRS with HyperArc™. A retrospective analysis of patients and BMs was performed.

RESULTS

From August 2017 to May 2018, 381 BMs in 64 patients were treated and 246 BMs (43 patients, median number of BMs: 5) of them were suitable for analysis. With a median FU time of 6 months, 244 out 246 (99%) BMs were controlled (18% complete response; 41% partial response, 40% stable disease), 2 BMs showed a progression, at the first control. No acute or late toxicities were reported. Median overall survival (OS) has not yet been achieved, while median time to progression was 5 months. In univariate analysis, statistically negative prognostic factors for OS were histology of primary tumor (p = 0.009): lung/breast cancer had better survival rates as compared to others. Cumulative intracranial volume disease ≥ 15 cc and systemic progression disease were independent prognostic factors for OS at univariate (p = 0.04; p = 0.005) and multivariate (p = 0.04; p = 0.009) analysis, respectively.

CONCLUSION

The present first clinical data show that SFRT/SRS with HyperArc™ is safe and effective for BMs patients. The utilization of SFRT/SRS for BMs is promising and should be further explored in randomized trials.

Dummy Run of Quality Assurance Program before Prospective Study of Hippocampus-Sparing Whole-Brain Radiotherapy and Simultaneous Integrated Boost for Multiple Brain Metastases from Non-small Cell Lung Cancer: Korean Radiation Oncology Group (KROG) 17-06 Study

Purpose

Lung Cancer Subcommittee of Korean Radiation Oncology Group (KROG) has recently launched a prospective clinical trial (KROG 17-06) of hippocampus-sparing whole brain radiotherapy (HS-WBRT) with simultaneous integrated boost (SIB) in treating multiple brain metastases from non-small cell lung cancer. In order to improve trial quality, dummy run studies among the participating institutions were designed. This work reported the results of two-step dummy run procedures of the KROG 17-06 study.

Materials and Methods

Two steps tested hippocampus contouring variability and radiation therapy planning compliance. In the first step, the variation of the hippocampus delineation was investigated for two representative cases using the Dice similarity coefficients. In the second step, the participating institutions were requested to generate a HS-WBRT with SIB treatment plan for another representative case. The compliance of the treatment plans to the planning protocol was evaluated.

Results

In the first step, the median Dice similarity coefficients of the hippocampus contours for two other dummy run cases changed from 0.669 (range, 0.073 to 0.712) to 0.690 (range, 0.522 to 0.750) and from 0.291 (range, 0.219 to 0.522) to 0.412 (range, 0.264 to 0.598) after providing the hippocampus contouring feedback. In the second step, with providing additional plan priority and extended dose constraints to the target volumes and normal structures, we observed the improved compliance of the treatment plans to the planning protocol.

Conclusion

The dummy run studies demonstrated the notable inter-institutional variability in delineating the hippocampus and treatment plan generation, which could be decreased through feedback from the trial center.

Cognitive impairment and morphological changes after radiation therapy in brain tumors: A review

Life expectancy of patients treated for brain tumors has lengthened due to the therapeutic improvements. Cognitive impairment has been described following brain radiotherapy, but the mechanisms leading to this adverse event remain mostly unknown. Technical evolutions aim at enhancing the therapeutic ratio. Sparing of the healthy tissues has been improved using various approaches; however, few dose constraints have been established regarding brain structures associated with cognitive functions. The aims of this literature review are to report the main brain areas involved in cognitive adverse effects induced by radiotherapy as described in literature, to better understand brain radiosensitivity and to describe potential future improvements.

Dosimetric Study and Neurocognitive Function of Hippocampal-Sparing Whole-Brain Radiotherapy

Objective:

To investigate the feasibility of hippocampal-sparing whole-brain radiotherapy and reduction in neurocognitive function impairment after radiotherapy.

Methods:

Forty-three patients with brain metastases were selected. Whole-brain radiotherapy was performed in 22 patients, with 3-dimensional conformal radiotherapy in parallel opposed fields. Twenty-one patients had significant difference. Planning parameter values and neurocognitive function scores in 2 groups were statistically analyzed.

Results:

Homogeneity index in the 3-dimensional conformal radiotherapy group and tomotherapy group was 0.12 ± 0.02 and 0.36 ± 0.03, respectively, with a significant difference (P < .05). The homogeneity of target doses was better in the tomotherapy group than in the 3-dimensional conformal radiotherapy group. There was a statistical significance in D_mean and D_max between the 2 groups (P < .05). The dose in hippocampal was less in the tomotherapy group than in the other group. D_mean and D_max of the left hippocampus declined to 20.14% and 35.39% of prescription dose, respectively, and D_mean and D_max of the right hippocampus declined to 19.92% and 35.14% of prescription dose, respectively. Neurocognitive function score between the 2 groups before treatment and 1 month after treatment had no significant difference (P > .05), while there was a significant difference in 3 and 6 months after treatment (P < .05). Neurocognitive function score was higher in the tomotherapy group than in the other group. No level III or above adverse reactions were observed.

Conclusions:

Hippocampal-sparing whole-brain radiotherapy in brain metastases treatment is feasible. Homogeneity index value is higher in the tomotherapy group than in the 3-dimensional conformal radiotherapy group. All V_95% in the 2 groups meet the requirements. Hippocampal sparing could avoid neurocognitive function impairment to some extent.

Hippocampal dose during Linac-based stereotactic radiotherapy for brain metastases: An observational study

INTRODUCTION

Aim of the present study is to evaluate homolateral and contralateral hippocampus (H-H, C-H, respectively) dose during Fractionated Stereotactic Radiotherapy (FSRT) or Radiosurgery (SRS) for brain metastases (BM).

MATERIALS & METHODS

Patients with BM<5, size≤30mm, KPS≥80 and a life expectancy>3months, were considered for SRS/FSRT (total dose 15-30Gy, 1-5 fractions). For each BM, a Flattening Filter Free (FFF) Volumetric Modulated Arc Therapy (VMAT) plan was generated with one or two arcs. Hippocampi were not considered during optimizations phase and were contoured and evaluated retrospectively in terms of dose: the Dmedian, Dmean, D0.1cc and the V1Gy, V2Gy, V5Gy and V10Gy were analyzed.

RESULTS

From April 2014 to December 2015, 81 BM were treated with FFF-FSRT/SRS. For the H-H, the average values of Dmedian, Dmean and D0.1cc were 1.5Gy, 1.54Gy and 2.2Gy, respectively, while the V1Gy, V2Gy, V5Gy and V10Gy values were 25%, 8.9%, 8.9% and 2.1%, respectively. For the C-H, the average Dmedian, Dmean and D0.1cc were 0.7Gy, 0.7Gy, 0.9Gy, respectively, while the average values of V1Gy, V2Gy, V5Gy and V10Gy were 18%, 10.2%, 2.8% and 1.4%, respectively. Tumor dimension, tumor cranial-caudal length and the distance between BM and H-H were correlated to Dmedian, Dmean and D0.1cc. For C-H, only the distance from PTV was correlated with a dose reduction.

CONCLUSION

During FFF-FSRT/SRS, hippocampus received a negligible dose. Despite its clinical significance is still under evaluation, in patients with a long life expectancy, H-H should be considered during Linac-based FSRT/SRS.

Hippocampal-Sparing Whole-Brain Radiotherapy for Lung Cancer

Brain metastases occur in 20% to 40% of lung cancer patients. Whole-brain radiotherapy (WBRT) has long been considered the treatment of choice for many patients with lung cancer, because of its wide availability, ease of delivery, and effectiveness in prolonging survival. However, WBRT is also associated with several side effects, such as decline in memory and other cognitive functions. There exists significant preclinical and clinical evidence that radiation-induced injury to the hippocampus correlates with neurocognitive decline of patients who receive WBRT. Technological advances in treatment planning and delivery facilitate the use of hippocampal-sparing (HS) WBRT as prophylactic cranial irradiation or the primary treatment modality for lung cancer patients with brain metastases. In this review, we provide a detailed and comprehensive discussion of the safety profile, techniques for hippocampus-sparing, and the clinical evidence of HS-WBRT for lung cancer patients.

Whole brain radiotherapy with adjuvant or concomitant boost in brain metastasis: dosimetric comparison between helical and volumetric IMRT technique

BACKGROUND

To compare and evaluate the possible advantages related to the use of VMAT and helical IMRT and two different modalities of boost delivering, adjuvant stereotactic boost (SRS) or simultaneous integrated boost (SIB), in the treatment of brain metastasis (BM) in RPA classes I-II patients.

METHODS

Ten patients were treated with helical IMRT, 5 of them with SRS after whole brain radiotherapy (WBRT) and 5 with SIB. MRI co-registration with planning CT was mandatory and prescribed doses were 30 Gy in 10 fractions (fr) for WBRT and 15Gy/1fr or 45Gy/10fr in SRS or SIB, respectively. For each patient, 4 "treatment plans" (VMAT SRS and SIB, helical IMRT SRS and SIB) were calculated and accepted if PTV boost was included in 95 % isodose and dose constraints of the main organs at risk were respected without major deviations. Homogeneity Index (HI), Conformal Index (CI) and Conformal Number (CN) were considered to compare the different plans. Moreover, time of treatment delivery was calculated and considered in the analysis.

RESULTS

Volume of brain metastasis ranged between 1.43 and 51.01 cc (mean 12.89 ± 6.37 ml) and 3 patients had double lesions. V95% resulted over 95 % in the average for each kind of technique, but the "target coverage" was inadequate for VMAT planning with two sites. The HI resulted close to the ideal value of zero in all cases; VMAT-SIB, VMAT-SRS, Helical IMRT-SIB and Helical IMRT-SRS showed mean CI of 2.15, 2.10, 2.44 and 1.66, respectively (optimal range: 1.5-2.0). Helical IMRT-SRS was related to the best and reliable finding of CN (0.66). The mean of treatment time was 210 s, 467 s, 440 s, 1598 s, respectively, for VMAT-SIB, VMAT-SRS, Helical IMRT-SIB and Helical IMRT-SRS.

CONCLUSIONS

This dosimetric comparison show that helical IMRT obtain better target coverage and respect of CI and CN; VMAT could be acceptable in solitary metastasis. SIB modality can be considered as a good choice for clinical and logistic compliance; literature's preliminary data are confirming also a radiobiological benefit for SIB. Helical IMRT-SRS seems less effective for the long time of treatment compared to other techniques.

Dosimetric study of different radiotherapy planning approaches for hippocampal avoidance whole-brain radiation therapy (HA-WBRT) based on fused CT and MRI imaging

The purpose of this study was to compare the dosimetric characteristics for hippocampal avoidance (HA) between the treatment plans based on fused CT and MRI imaging during whole brain radiotherapy (WBRT) pertaining to: (1) 3-dimensional conformal radiotherapy (3D-CRT), (2) dynamic intensity modulated radiation therapy (dIMRT), and (3) RapidArc for patients with brain metastases. In our study, HA was defined as hippocampus beyond 5 mm, and planning target volume (PTV) was obtained subtracting HA volume from the volume of whole brain. There were 10 selected patients diagnosed with brain metastases receiving WBRT. These patients received plans for 3D-CRT (two fields), dIMRT (seven non-coplanar fields) and RapidArc (dual arc). The prescribed dose 30 Gy in 10 fractions was delivered to the whole-brain clinical target volume of patients. On the premise of meeting the clinical requirements, we compared target dose distribution, target coverage (TC), homogeneity index (HI), dose of organs at risk (OARs), monitor units (MU) and treatment time between the above three radiotherapy plans. V90 %, V95 % and TC of PTV for 3D-CRT plan were lowest of the three plans. V90 %, V95 % and HI of PTV in RapidArc plan were superior to the other two plans. TC of PTV in RapidArc plan was similar with dIMRT plan (P > 0.05). 3D-CRT was the optimal plan in the three plans for hippocampal protection. The median dose (Dmedian) and the maximum doses (Dmax) of hippocampus in 3D-CRT were 4.95, 10.87 Gy, which were lowest among the three planning approaches (P < 0.05). Dmedian and Dmax of hippocampus in dIMRT were 10.68, 14.11 Gy. Dmedian and Dmax of hippocampus in RapidArc were 10.30 gGy, 13.92 Gy. These parameters of the last two plans pertain to no significant difference (P > 0.05). When WBRT (30 Gy,10F) was equivalent to single dose 2 Gy,NTDmean of hippocampus in 3D-CRT, dIMRT and RapidArc were reduced to 3.60, 8.47, 8.20 Gy2, respectively. In addition, compared with dIMRT, MU of RapidArc was reduced and the treatment time was shortened by nearly 25 %. All three radiotherapy planning approaches in our study can meet the clinical requirements of HA. Although TC in 3D-CRT was lowest, hippocampus was protected best by this plan. So many radiation fields and the design of non-coplanar fields lead to the complication of dIMRT. TC and HI in RapidArc were superior to the other two plans with the precise of meeting the clinical requirements. The difference in protection for hippocampus between dIMRT and RapidArc was statistically significant. In addition, RapidArc can remarkably reduce MU and the treatment time.