The linear-quadratic model and fractionated stereotactic radiotherapy

Efficacy and toxicity of primary re-irradiation for malignant spinal cord compression based on radiobiological modelling: a phase II clinical trial

BACKGROUND

The efficacy and safety of primary re-irradiation for MSCC are not known. Our aim was to establish the efficacy and safety of biologically effective dose-based re-irradiation.

METHODS

Patients presenting with MSCC at a previously irradiated spine segment, and not proceeding with surgical decompression, were eligible. A 3 Gray per fraction experimental schedule (minimum 18 Gy/6 fractions, maximum 30 Gy/10 fractions) was used, delivering a maximum cumulative spinal dose of 100 Gy2 if the interval since the last radiotherapy was within 6 months, or 130 Gy2 if longer. The primary outcome was a change in mobility from week 1 to week 5 post-treatment, as assessed by the Tomita score. The RTOG SOMA score was used to screen for spinal toxicity, and an MRI performed to assess for radiation-induced myelopathy (RIM).

RESULTS

Twenty-two patients were enroled, of whom eleven were evaluable for the primary outcome. Nine of eleven (81.8%) had stable or improved Tomita scores at 5 weeks. One of eight (12.5%) evaluable for late toxicity developed RIM.

CONCLUSIONS

Re-irradiation is an efficacious treatment for MSCC. There is a risk of RIM with a cumulative dose of 120 Gy2.

CLINICAL TRIAL REGISTRATION

Cancer Trials Ireland (ICORG 07-11); NCT00974168.

A modified protocol of mandibular osteoradionecrosis induction in rats with external beam radiation therapy

OBJECTIVE

To propose a modified protocol of mandibular osteoradionecrosis induction in rats with external beam radiation therapy.

MATERIAL AND METHODS

A total of 45 male Wistar rats were used in this study. Firstly, 25 rats were divided into 5 groups (n = 5) according to the radiation dose protocol: without irradiation and irradiated with 15 Gy, 20 Gy, 25 Gy, or 30 Gy using a linear accelerator. Secondly, 15 other rats were divided into 3 groups (n = 5) according to the time of extraction of the three right mandibular molars: 7, 10, or 14 days after irradiation of 20 Gy. Lastly, dental extractions were performed in 5 other rats without irradiation (C-E10) for comparison with those of the group of dental extractions 10 days after irradiation (I-E10).

RESULTS

The irradiated animals survived throughout the study period only at single doses of 15 Gy and 20 Gy. The suitable time for dental extractions after irradiation to induce mandibular osteoradionecrosis was defined as 10 days. Macroscopic evaluation of the right hemimandibles showed presence of osteoradionecrosis in I-E10 group and complete gingival healing in C-E10 group.

CONCLUSION

A single radiation dose of 20 Gy focused on head and neck region combined with the extraction of the three mandibular molars 10 days after irradiation constitutes a feasible protocol of mandibular osteoradionecrosis induction in rats with external beam radiation therapy.

CLINICAL RELEVANCE

Establishing a solid and widely available protocol of mandibular osteoradionecrosis induction is essential in the search for methods to prevent this complex disease.

Re-Irradiation of Brain Metastases and Metastatic Spinal Cord Compression: Clinical Practice Suggestions

The recent improvements of therapeutic approaches in oncology have allowed a certain number of patients with advanced disease to survive much longer than in the past. So, the number of cases with brain metastases and metastatic spinal cord compression has increased, as has the possibility of developing a recurrence in areas of the central nervous system already treated with radiotherapy.

Clinicians are reluctant to perform re-irradiation of the brain, because of the risk of severe side effects. The tolerance dose for the brain to a single course of radiotherapy is 50–60 Gy in 2 Gy daily fractions. New metastases appear in 22–73% of the cases after whole brain radiotherapy, but the percentage of re-irradiated patients is 3–10%. An accurate selection must be made before giving an indication to re-irradiation. Patients with Karnofsky performance status >70, age <65 years, controlled primary and no extracranial metastases are those with the best prognosis. The absence of extracranial disease was the most significant factor in conditioning survival, and maximum tumor diameter was the only variable associated with an increased risk of unacceptable acute and/or chronic neurotoxicity. Re-treatment of brain metastases can be done with whole brain radiotherapy, stereotactic radiosurgery or fractionated stereotactic radiotherapy. Most patients had no relevant radiation-induced toxicity after a second course of whole brain radiotherapy or stereotactic radiosurgery. There are few data on fractionated stereotactic radiotherapy in the re-irradiation of brain metastases.

In general, the incidence of an “in-field” recurrence of spinal metastasis varies from 2.5–11% of cases and can occur 2–40 months after the first radiotherapy cycle. Radiation-induced myelopathy can occur months or years (6 months-7 years) after radiotherapy, and the pathogenesis remains obscure. Higher radiotherapy doses, larger doses per fraction, and previous exposure to radiation could be associated with a higher probability of developing radiation-induced myelopathy. Experimental data indicate that also the total dose of the first and second radiotherapy, interval to re-treatment, length of the irradiated spinal cord, and age of the treated animals influence the risk of radiation-induced myelopathy. An α/β ratio of 1.9–3 Gy could be generally the reference value for fractionated radiotherapy. However, when fraction sizes are up to 5 Gy, the linear-quadratic equation become a less valid model. The early diagnosis of relapse is crucial in conditioning response to re-treatment.

Radioprotective Effect of Sodium Selenite on Mandible of Irradiated Rats

The purpose of this study was to test the radioprotective effect of selenium in the bone microarchitecture of irradiated rats mandibles. Forty rats were separated into 4 groups with 10 animals: control group (CG), irradiated group (IG), sodium selenite group (SSG) and sodium selenite irradiated group (SSIG). A single dose of 0.8 mg/kg sodium selenite was administered intraperitoneally in the SSG and SSIG groups. One hour later, animals of IG and SSIG groups were irradiated with 15 Gy of x-rays. Forty days after radiation a bilateral extraction of the mandibular first molars was performed. After the extraction procedure, five rats were killed after fifteen days and others five after thirty days. Micro- computed tomography was used to evaluate cortical and trabecular bone of each rat. The mean and standard deviation of each bone microarchitecture parameter were analyzed using the statistical test of two-way Analysis of Variance (ANOVA). At 15 days, the bone volume presented higher values in the CG and SSG groups (p=0.001). The same groups presented statistically significant higher values when bone volume fraction (p<0.001) and trabecular thickness (p<0.001) were analyzed. At 30 days, it was observed that in relation to the bone volume fraction, SSG group presented the highest value while SSIG group had the lowest value, with statistically significant difference (p=0.016). Sodium selenite demonstrated a median radioprotective effect in the bone microarchitecture of irradiated mandibles, which indicates the substance may be a potential radioprotective agent against chronic effects of high doses of ionizing radiation.

Positron emission tomography for staging locally advanced cervical cancer and assessing intensity modulated radiotherapy approach

AIMS

To evaluate toxicity and outcome of concomitant chemotherapy and intensity modulated radiotherapy (IMRT) with 18-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸FDG-PET/CT) based simultaneous integrated boost (SIB) of locally advanced cervical cancer (LACC).

METHODS

Patients with LACC underwent chemo-radiation with IMRT and SIB. Staging and follow-up were performed with clinical evaluation and CT, MRI, ¹⁸FDG-PET/CT. SIB was done on positive nodes with ¹⁸FDG-PET/CT based planning. CT-based planning high-dose-rate brachytherapy (HDR-BT) was delivered as subsequent boost to the primary tumor. Cisplatin concomitant chemotherapy was administered during IMRT.

RESULTS

Fourteen patients with cervical cancer were prospectively recruited between August 2014 and June 2017, 13 (93%) had a LACC, one (7%) patient was not evaluable because ¹⁸FDG-PET/CT evidenced metastases to the liver undetected by previous CT/MRI. Patients had a median age of 59 years, a median Karnofsky performance status of 100%, and a prevalence of squamous cell carcinoma histology (85%). SIB was delivered on 23 positive lymph nodes. IMRT median dose to the pelvis was 48.6 Gy in 27 fractions, SIB median dose 54 Gy in 27 fractions, HDR-BT boost median dose 21 Gy in 3 fractions. After a median follow-up of 30 months, 2-year local control and distant control were 86% and 86%, respectively. There were no grade 4 acute and/or late toxicities.

CONCLUSIONS

The ¹⁸FDG-PET/CT influenced stage assessment and RT treatment planning due to its high specificity in distant metastases and nodal involvement detection. The IMRT with SIB for positive nodes was an effective therapy with acceptable toxicity in LACC.

Meloxicam as a Radiation-Protective Agent on Mandibles of Irradiated Rats

This study evaluated the action of ionizing radiation and the possible radioprotective effect of the non-steroidal anti-inflammatory drug meloxicam on the bone physiology of rat mandibles by assessing the alveolar socket healing and bone strength. Forty male Wistar rats were divided in 4 groups (n=10): control (CG), irradiated (IG), meloxicam (MG), meloxicam irradiated (MIG). A dose of 0.2 mg/kg meloxicam was administered to MG and MIG. After this, IG and MIG were irradiated with 15 Gy radiation dose in the mandible. Forty days after the above procedures, the mandibular first molars were extracted and the animals were killed after 15 or 30 days (n=5). Micro-computed tomography and bending test were used to evaluate alveolar socket healing and bone strength, respectively. At 15 days, bone volume, bone volume fraction and trabecular thickness were higher in the CG and MG than in the IG and MIG; and trabecular separation was higher in the IG compared with the others. At 30 days, there was a difference only in trabecular separation, which was higher in IG than in CG and MG, and MIG did not differ from the others. Bone strength was lower in IG compared with CG and MG, and MIG did not differ from the others. In conclusion, the ionizing radiation affected the bone physiology of rat mandibles, delaying the alveolar socket healing and reducing the bone strength. Moreover, the meloxicam had a positive effect on the trabecular separation in alveolar socket healing and on the bone strength.

Hypofractionated radiotherapy with simultaneous integrated boost (SIB) plus temozolomide in good prognosis patients with glioblastoma: a multicenter phase II study by the Brain Study Group of the Italian Association of Radiation Oncology (AIRO)

INTRODUCTION

A multicenter phase II study for assessing the efficacy and the toxicity of hypofractionated radiotherapy with SIB plus temozolomide in patients with glioblastoma was carried out by the Brain Study Group of the Italian Association of Radiation Oncology.

METHODS

Twenty-four patients with newly diagnosed glioblastoma belonging to Recursive Partitioning Analysis classes III and IV were enrolled. The prescribed dose was 52.5 Gy in 15 fractions of 3.5 Gy and 67.5 in 15 fractions of 4.5 Gy to the SIB volume. Dose constraints for the hypofractionated schedule were provided. Radiotherapy was associated with concomitant and sequential temozolomide.

RESULTS

Median overall survival (OS) was 15.1 months, while median progression-free survival (PFS) was 8.6 months. Actuarial OS at 12 months was 65.6% ± 0.09, whereas actuarial PFS at 12 months was 41.2% ± 0.10. Status of methylation of MGMT promoter resulted to be a significant prognostic factor for OS. Radiotherapy-related acute toxicity was not relevant. Three patients (12.5%) had G3 myelotoxicity that required temozolomide temporary interruption or dose reduction during the chemotherapy. However, chemotherapy was not definitely discontinued for toxicity in any case. One patient out of 24 (4.2%) developed radionecrosis that required surgical resection with no evidence of disease in the surgical specimen.

CONCLUSIONS

This trial confirms that hypofractionated radiotherapy with SIB and association with temozolomide may be a reasonable and feasible option for good prognosis patients with GBM.

Definitive three-dimensional high-dose-rate brachytherapy for inoperable endometrial cancer

Purpose

To report our experience on high-dose-rate brachytherapy (HDR-BT) in patients with stage I-III endometrial cancer unfit to surgery.

Material and methods

Seventeen patients underwent HDR-BT as definitive treatment. Median age was 79 years (range, 60-95), median Karnofsky performance status 90% (range, 60-100). Histology was endometrial adenocarcinoma in 14 (82%), and non-endometrial in 3 (18%) patients. In 15 (88%) patients, clinical stage was I and in remaining 2 (12%) was III. All patients were evaluated with computed tomography (CT) and endometrial biopsy. Using the Fletcher applicator, a CT-based planning HDR-BT was delivered. Local control (LC) was obtained when there was an interruption of vaginal bleeding in absence of CT-imaging progression.

Results

Fourteen patients underwent HDR-BT alone and three external beam radiotherapy (EBRT) combined with HDR-BT. All patients had a clinical LC, after a median follow-up of 53 months (range, 6-131), 3 and 6 years LC rates were 86% and 69%, respectively. Cancer specific survival (CSS) at 1, 2, and 6 years was 93%, 85%, and 85%, respectively. Age, stage, dose, and type of radiotherapy did not result significant prognostic factors for LC and CSS. Only histology significantly influenced LC: for high-risk histology (i.e., non-endometrial carcinoma or grade [G] 3 endometrial adenocarcinoma) LC was 73% at 1 year and 36% at 6 years; for low-risk histology (i.e., G1-2 endometrial adenocarcinoma) was 100% at 1 and 6 years (p = 0.05). Two (12%) patients had G2 acute toxicity and two others (12%) G1 late toxicity.

Conclusions

Although some limitations of our analysis (relatively few number of patients recruited, retrospective evaluation, and consequent suboptimal patient selection), it confirms effectiveness and safety of definitive HDR-BT for medically inoperable stage I-III endometrial cancer. The best LC was obtained in stage I low-risk histology.

Is upfront stereotactic radiosurgery a rational treatment option for very elderly patients with brain metastases? A retrospective analysis of 106 consecutive patients age 80 years and older

Background

Advanced age has been shown to be a factor predicting poor survival in patients with brain metastases (BM). There have been only a few studies focusing on stereotactic radiosurgery (SRS) for elderly BM patients. The present study aimed to investigate the efficacy and limitations of SRS for very elderly BM patients.

Methods

This was a retrospective observational study analyzing 106 consecutive patients (69 males/37 females) age 80 years and older who received upfront Gamma Knife SRS for BM between January 2009 and October 2015. The median age was 84 years, and the median Karnofsky performance status (KPS) was 70. Fifty-two patients had a solitary BM, and others multiple BM. The median cumulative tumor volume was 3.9 mL and the median dose prescribed was 20 Gy. Overall survival (OS), neurological death rates and distant and local intracranial tumor control rates were analyzed.

Results

No patients were lost to follow-up. Six-month and 12-month OS rates were 54% and 32%, respectively. The median OS time was 7.1 months. Competing risks analysis showed that 6-month and 12-month neurological death rates were 8% and 11%, respectively. In total, 245 / 311 tumors (79%) in 82 patients (77%) with sufficient radiological follow-up data were evaluated. Six-month and 12-month distant BM recurrence rates (per patient) after SRS were 17% and 25%, respectively. Six-month and 12-month rates of local tumor control (per lesion) were 94% and 89%, respectively. Repeat SRS, salvage WBRT and surgical resection were subsequently required in 25, 4 and 1 patient, respectively. Proportional hazard regression analysis showed that KPS ≥ 70 (HR: 0.444, P < .001), controlled primary disease/no extracranial metastases (HR: 0.361, P < .001) and female sex (HR: 0.569, P = 0.028) were independent factors predicting better OS. Similarly, tumor volume (>2 mL) was the only factor predicting a higher rate of local control failure (HR: 12.8, P = 0.003).

Conclusions

The present study suggested an upfront SRS strategy to offer a feasible and effective treatment option for very elderly patients with limited BM. In the majority of patients, neurological death could be delayed or even prevented.

Leksell Gamma Knife treatment for pilocytic astrocytomas: long-term results

OBJECTIVE The purpose of this study was to evaluate long-term treatment results, radiation-related toxicity, and prognostic factors for the progression-free survival (PFS) of patients with pilocytic astrocytomas treated by means of stereotactic radiosurgery with a Leksell Gamma Knife. METHODS A total of 25 patients with pilocytic astrocytomas underwent Gamma Knife surgery during the period 1992-2002. The median target volume was 2700 mm(3) (range 205-25,000 mm(3)). The 18 patients treated with 5 daily fractions received a median minimum target dose of 25 Gy. Doses for the 2 patients treated with 10 fractions over 5 days (2 fractions delivered on the same day at least 6 hours apart) were 23 and 28 Gy. For the 5 patients treated with a single fraction, the minimum target dose ranged from 13 to 20 Gy (median 16 Gy). RESULTS Complete regression occurred in 10 patients (40%) and partial regression in 10 patients (40%). The 10-year overall survival rate was 96% and the 10-year PFS rate was 80%. Target volume appeared to be a significant prognostic factor for PFS (p = 0.037). Temporary Grade 3 toxicity appeared in 2 patients (8%), and these patients were treated with corticosteroids for 2 months. Permanent Grade 4 toxicity appeared in 2 patients (8%) and was associated with neurocognitive dysfunction. In these 2 individuals, the neurocognitive dysfunction was also felt to be in part the result of the additional therapeutic interventions (4 in one case and 6 in the other) required to achieve durable control of their tumors. CONCLUSIONS Radiosurgery represents an alternative treatment modality for small residual or recurrent volumes of pilocytic astrocytomas and provides long-term local control. Target volume appears to be the most important factor affecting PFS.

Radiobiological modeling of two stereotactic body radiotherapy schedules in patients with stage I peripheral non-small cell lung cancer

This study aims to compare the radiobiological response of two stereotactic body radiotherapy (SBRT) schedules for patients with stage I peripheral non-small cell lung cancer (NSCLC) using radiobiological modeling methods. Volumetric modulated arc therapy (VMAT)-based SBRT plans were designed using two dose schedules of 1 × 34 Gy (34 Gy in 1 fraction) and 4 × 12 Gy (48 Gy in 4 fractions) for 19 patients diagnosed with primary stage I NSCLC. Dose to the gross target volume (GTV), planning target volume (PTV), lung and chest wall (CW) were converted to biologically equivalent dose in 2 Gy fraction (EQD2) for comparison. Five different radiobiological models were employed to predict the tumor control probability (TCP) value. Three additional models were utilized to estimate the normal tissue complication probability (NTCP) value for the lung and the modified equivalent uniform dose (mEUD) value to the CW. Our result indicates that the 1 × 34 Gy dose schedule provided a higher EQD2 dose to the tumor, lung and CW. Radiobiological modeling revealed that the TCP value for the tumor, NTCP value for the lung and mEUD value for the CW were 7.4% (in absolute value), 7.2% (in absolute value) and 71.8% (in relative value) higher on average, respectively, using the 1 × 34 Gy dose schedule.

Radiobiological modeling analysis of the optimal fraction scheme in patients with peripheral non-small cell lung cancer undergoing stereotactic body radiotherapy

This study aimed to determine the optimal fraction scheme (FS) in patients with small peripheral non-small cell lung cancer (NSCLC) undergoing stereotactic body radiotherapy (SBRT) with the 4 × 12 Gy scheme as the reference. CT simulation data for sixteen patients diagnosed with primary NSCLC or metastatic tumor with a single peripheral lesion ≤3 cm were used in this study. Volumetric modulated arc therapy (VMAT) plans were designed based on ten different FS of 1 × 25 Gy, 1 × 30 Gy, 1 × 34 Gy, 3 × 15 Gy, 3 × 18 Gy, 3 × 20 Gy, 4 × 12 Gy, 5 × 12 Gy, 6 × 10 Gy and 10 × 7 Gy. Five different radiobiological models were employed to predict the tumor control probability (TCP) value. Three other models were utilized to estimate the normal tissue complication probability (NTCP) value to the lung and the modified equivalent uniform dose (mEUD) value to the chest wall (CW). The 1 × 30 Gy regimen is recommended to achieve 4.2% higher TCP and slightly higher NTCP and mEUD values to the lung and CW compared with the 4 × 12 Gy schedule, respectively. This regimen also greatly shortens the treatment duration. However, the 3 × 15 Gy schedule is suggested in patients where the lung-to-tumor volume ratio is small or where the tumor is adjacent to the CW.

Long-term outcome of moderate hypofractionated stereotactic radiotherapy for meningiomas

PURPOSE

The aim of this work was to evaluate long-term results of moderate hypofractionated stereotactic radiotherapy (hFSRT) for intracranial meningiomas.

PATIENTS AND METHODS

In all, 77 consecutive patients with 80 lesions were included. Median age was 65 years (range 23-82 years), male/female ratio was 21/56, and the median Karnofsky performance status was 90 (range 60-100). In 31 lesions (39 %), diagnosis was based upon clinical and radiological data; 37 lesions were histologically proven as World Health Organization (WHO) grade I and 12 grade II meningiomas. Median treatment volume was 23 cc. Prescribed doses were 45 Gy in 15 fractions of 3 Gy (15 × 3 Gy) or 42 Gy in 14 fractions of 3 Gy (14 × 3 Gy).

RESULTS

After a median follow-up of 56 months, 49 (61 %) lesions received 14 × 3 Gy and 31 (39 %) 15 × 3 Gy. Local control (LC) rate remained unchanged at 84 % at 5 and 10 years. Overall survival and disease-specific survival (DSS) were 76 and 93 % at 5 years, 72 and 89 % at 10 years, respectively. With univariate analysis, previous surgery and WHO grade II tumor were negative prognostic factors for LC and DSS. With multivariate analysis only tumor grade was an independent prognostic factor for LC. No clinically significant acute and/or late toxicities were observed.

CONCLUSION

Moderate hFSRT was effective and safe with an excellent tolerance profile. It can be an alternative treatment option for patients with recurrent or inoperable large meningiomas. The low number of fractions administered with hFSRT led to reduce treatment-related discomfort for patients. Grade II tumor and previous surgery were negative prognosis factors.

Optimizing the flattening filter free beam selection in RapidArc®-based stereotactic body radiotherapy for Stage I lung cancer

OBJECTIVE

To optimize the flattening filter-free (FFF) beam selection in stereotactic body radiotherapy (SBRT) treatment for Stage I lung cancer in different fraction schemes.

METHODS

Treatment plans from 12 patients suffering from Stage I lung cancer were designed using the 6XFFF and 10XFFF beams in different fraction schemes of 4 × 12, 3 × 18 and 1 × 34 Gy. Plans were evaluated mainly in terms of organs at risk (OARs) sparing, normal tissue complication probability (NTCP) estimation and treatment efficiency.

RESULTS

Compared with the 10XFFF beam, 6XFFF beam showed statistically significant lower dose to all the OARs investigated. The percentage of NTCP reduction for both lung and chest wall was about 10% in the fraction schemes of 4 × 12 and 3 × 18 Gy, whereas only 7.4% and 2.6% was obtained in the 1 × 34 Gy scheme. For oesophagus, heart and spinal cord, the reduction was greater with the 6XFFF beam, but their absolute estimates were <10(-6)%. The mean beam-on time for 6XFFF and 10XFFF beams at 4 × 12, 3 × 18 and 1 × 34 Gy schemes were 2.2 ± 0.2 vs 1.5 ± 0.1, 3.3 ± 0.9 vs 2.0 ± 0.5 and 6.3 ± 0.9 vs 3.5 ± 0.4 min, respectively.

CONCLUSION

The 6XFFF beam obtains better OARs sparing and lower incidence of NTCP in SBRT treatment of Stage I lung cancer, whereas the 10XFFF beam improves the treatment efficiency. To balance the OARs sparing and intrafractional variation owing to the prolonged treatment time, the authors recommend using the 6XFFF beam in the 4 × 12 and 3 × 18 Gy schemes but the 10XFFF beam in the 1 × 34 Gy scheme.

ADVANCES IN KNOWLEDGE

This study optimizes the FFF beam selection in different fraction schemes in SBRT treatment of Stage I lung cancer.

Multisession stereotactic radiosurgery for large vestibular schwannomas

OBJECT

Microsurgery is not the only option for larger vestibular schwannomas (VSs); recent reviews have confirmed the feasibility and efficacy of radiosurgery for larger VSs. This study illustrates the outcomes of a series of large VSs after multisession stereotactic radiosurgery (SRS).

METHODS

A series of 33 VSs larger than 8 cm3 (range 8–24 cm3, mean 11 cm3, median 9.4 cm3) were treated using the CyberKnife from 2003 to 2011 with the multisession SRS technique in 2–5 fractions (14–19.5 Gy). Five patients had undergone surgical removal and 5 had ventriculoperitoneal shunts. Nine patients were eligible for but refused surgery. Twelve patients were older than 70 years and 5 were younger than 40 years. Two female patients had neurofibromatosis.

RESULTS

The follow-up period ranged from 12 to 111 months (median 48 months); radiological growth control was achieved in 94% of cases: 19 tumors (58%) displayed no size variation or reduction in tumor diameter; 12 (36%), after a transient enlargement, presented with arrested growth or shrinkage. Seven patients had a volume reduction of more than 50%. Two patients (6%) needed debulking and 2 were treated with ventriculoperitoneal shunts. Actuarial progressionfree survival rates at 1 year and 5 years were 97% and 83%, respectively. Hearing was retained in 7 of the 8 patients with serviceable baseline hearing. Adverse events were limited to 1 case each of vertigo, tongue paresthesia, and trigeminal neuralgia.

CONCLUSIONS

The good control rate obtained with multisession SRS deepens the controversy of the radiobiology of VSs and may extend the indication of radiation therapy (fractionated or SRS) for large VSs to include patients without symptoms of mass effect. The limited number of cases and short follow-up period do not provide sufficient support for widespread application of multisession SRS in young patients. Further studies with multisession SRS are warranted.

Reirradiation with stereotactic body radiotherapy: analysis of human spinal cord tolerance using the generalized linear-quadratic model

AIM

Using the generalized linear-quadratic (gLQ) model, we reanalyzed published dosimetric data from patients with radiation myelopathy (RM) after reirradiation with spinal stereotactic body radiotherapy (SBRT).

MATERIALS & METHODS

Based on a published study, the thecal sac dose of five RM patients and 14 no RM patients were reanalyzed using gLQ model. Maximum point doses (Pmax) in the thecal sac were obtained. The gLQ-based biological effective doses were calculated and normalized (nBEDgLQ) to a 2-Gy equivalent dose (nBEDgLQ = Gy2/2_gLQ). The initial conventional radiotherapy dose, converted to Gy2/2_gLQ, was added.

RESULTS

Total (conventional radiotherapy + SBRT) mean Pmax nBEDgLQ was lower in no RM than RM patients: 59.2 Gy2/2_gLQ (range: 37.5-101.9) versus 94.8 Gy2/2_gLQ (range: 70.2-133.4) (p = 0.0016). The proportion of total Pmax nBEDgLQ accounted for by the SBRT Pmax nBEDgLQ was higher for RM patients. No RMs were seen below a total spinal cord nBEDgLQ of 70 Gy2/2_gLQ.

CONCLUSION

The gLQ-derived spinal cord tolerance for total nBEDgLQ was 70 Gy2/2_gLQ.

Developments in stereotactic ablative radiotherapy for the treatment of early-stage lung cancer

SUMMARY Stereotactic ablative radiotherapy (SABR), also known as stereotactic body radiation therapy, has emerged as an effective treatment for inoperable early-stage non-small-cell lung cancer. SABR differs from conventional radiotherapy by virtue of its tight spatial tolerances and use of oligofractionated radiation. The modern technique is characterized by management of tumor motion, image guidance before each fraction and specialized radiation delivery techniques. The result is a highly conformal target dose with a sharp gradient that spares normal tissues with great accuracy. This enables delivery of very potent (ablative) doses, causing more rapid and durable responses than traditional radiation therapy treatment regimens can achieve. The established techniques, new developments and ongoing questions related to SABR for early-stage non-small-cell lung cancer are reviewed herein.

Principles of radiobiology of stereotactic radiosurgery and clinical applications in the central nervous system

Stereotactic radiosurgery (SRS) has become an important treatment option for intracranial lesions and has recently been adapted to treat lesions outside the brain. Many studies have shown the effectiveness of SRS for the treatment of benign and metastatic tumors. Although DNA damage has been thought to be the principal form of radiation-induced damage, recent studies have shown that vascular endothelial damage is perhaps more important in the setting of high radiation doses per fraction such as those used in SRS. Furthermore, it has been shown that molecular responses to radiation differ based on dose per fraction. The principles of classical radiobiology are reviewed with explanation on why fractionation of radiotherapy allows optimization of the therapeutic ratio. The current understanding of the molecular responses that occur soon after the delivery of high radiation doses per fraction is also reviewed. A summary of current clinical evidence of radiation tolerance to SRS of brain, brainstem, optic chiasm and spinal cord is also provided. Recent advances in understanding the molecular basis of SRS response have uncovered a different biological response than previously thought. Further understanding of these molecular mechanisms will allow for the development of targeted radiosensitizers and radioprotectors to optimize the therapeutic ratio.

Re-irradiation: outcome, cumulative dose and toxicity in patients retreated with stereotactic radiotherapy in the abdominal or pelvic region

The purpose of the present study was to explore the outcome, cumulative dose in tumor and organs at risk and toxicity after extra-cranial stereotactic re-irradiation. Twenty-seven patients were evaluated who had been re-irradiated with stereotactic body radiotherapy (SBRT) after conventional radiotherapy (CRT). The dose summation of the SBRT and CRT plans was done by dose point calculations accounting for fraction size by the linear-quadratic model. Efficacy and toxicity was scored by looking at the reduction in tumor size, pain and bleeding. Symptomatic response was observed in 96% of the patients. The median maximum SBRT dose to the tumor was 90 Gy₃ (range: 42-420 Gy₃). The median cumulative dose for the rectum, bowel and bladder resulted in 104 Gy₃, 98 Gy₃ and 113 Gy₃, respectively. No grades 5, 4 and 3 acute and late toxicity was observed. In conclusion: re-irradiation to the same region using extra-cranial stereotactic radiotherapy is feasible and resulted in a 96% symptomatic response with low toxicity.

Isoeffect calculations with the linear quadratic and its extensions: An examination of model-dependent estimates at doses relevant to hypofractionation

The linear quadratic is the standard model for calculating isoeffects in the range of conventional dose per fraction. However, the use of hypofractionation and stereotactic body radiation therapy can call for isoeffect calculations for large doses per fraction. The purpose of this work is to investigate the linear quadratic at large doses per fraction. The linear quadratic is compared to models that incorporate effects such as dose protraction, whose purpose is to extend the useful range of the linear quadratic to larger doses. The linear quadratic and extended linear quadratic models are fit to 4 data sets. The model-predicted isoeffects for these data sets are calculated. It is found that the linear quadratic and extended linear quadratic predict different isoeffect curves for certain data sets. However, for these data sets, by appropriate selection of a α/β ratio, the linear quadratic can well approximate the extended linear quadratic models. In particular, it is found that a α/β ratio of 0.5 well approximates the extended linear quadratic isoeffect curve for 2 prostate cell lines for conventional and moderate doses per fraction.

Stereotactic Radiosurgery of Cranial Nonvestibular Schwannomas: Results of Single- and Multisession Radiosurgery

BACKGROUND:

Surgical resection of nonvestibular cranial schwannomas carries a considerable risk of postoperative complications. Stereotactic radiosurgery (SRS) offers a non-invasive treatment alternative. The efficacy and safety of multi-session SRS of nonvestibular cranial schwannomas has not been well studied.

OBJECTIVE:

To analyze the results of single- and multi-session SRS of nonvestibular cranial schwannomas.

METHODS:

From 2001 to 2007, 42 lesions in 40 patients were treated with SRS at Stanford University Medical Center, targeting schwannomas of cranial nerves IV (n = 1), V (n = 18), VII (n = 6), X (n = 5), XII (n = 2), jugular foramen (n = 8), and cavernous sinus (n = 2). SRS was delivered to a median marginal dose of 18 Gy (range, 15-33 Gy) in 1 to 3 sessions, targeting a median tumor volume of 3.2 cm3 (range, 0.1-23.7 cm3). The median doses for treatments in 1 (n = 18), 2 (n = 9), and 3 (n = 15) sessions were 17.5, 20, and 18 Gy, respectively.

RESULTS:

With a median follow-up of 29 months (range, 6-84 months), tumor control was achieved in 41 of the 42 lesions. Eighteen of 42 lesions (43%) decreased in size; 23 tumors (55%) remained stable. There were 2 cases of new or worsening cranial nerve deficits in patients treated in single session; no patient treated with multi-session SRS experienced any cranial nerve toxicity (P = 0.18).

CONCLUSION:

SRS of nonvestibular cranial schwannomas provides excellent tumor control with minimal risk of complications. There was a trend towards decreased complications with multi-session SRS.

Assessment of the alpha/beta ratios for arteriovenous malformations, meningiomas, acoustic neuromas, and the optic chiasma

PURPOSE

To determine alpha/beta (alpha/beta) values of arteriovenous malformations (AVM), meningiomas, acoustic neuromas (AN), and the optic chiasma using clinical data.

METHODS AND MATERIALS

Data of dose/fractionation schedules form the literature, iso-effective for a specific clinical outcome, were analysed using the Fraction Equivalent plot (FE) method and the Tucker method. Established safe dose/fractionation schedules for the optic chiasma were used to determine its alpha/beta value.

RESULTS

With the FE plot method, an alpha/beta value of 3.76 Gray (Gy) (95% confidence level [CL]: 2.8-4.6 Gy) for meningiomas, 2.4 Gy (95% CL: 0.8-3.9 Gy) for acoustic neuroma, and 14.7 Gy (95% CL: 3.8-25.7 Gy) for arteriovenous malformations were determined. The respective alpha/beta values using the Tucker method were 3.3 Gy (95%CL: 2.2-6.8 Gy), 1.77 Gy (95%CL: 1.3-3.0 Gy) and -57 Gy (95%CL: -79.6 to -35.2 Gy). No meaningful alpha/beta values could be determined for the optic chiasma.

CONCLUSION

Acoustic neuromas with a low alpha/beta value would show no lesion intrinsic benefit from fractionation. Meningiomas probably benefit from a hypofractionated schedule. The high alpha/beta value for AVM can be explained but needs further research. Fractionation versus radiosurgery can be considered when the primary objective is to avoid normal tissue damage.

Validation of histologic changes induced by external irradiation in mandibular bone. An experimental animal model

The present experimental study sought to determine the effect of high-dose irradiation on the rat mandible in order to establish an experimental model of radiogenic bone damage. The left mandibles of 20 adult Wistar rats were irradiated (single fraction 1500cGy, total dose 60Gy) by means of a hypofractionated stereotactic radiotherapy (hfSRT) over a period of 6 weeks. Follow-up was 6 weeks (group 1, n=10) and 12 weeks (group 2, n=10). The contralateral mandibles as well as 5 non-irradiated animals served as controls. Primary endpoints were fibrosis, loss of cell count, decreased immunohistochemical labelling for bone morphogenetic protein-2 (BMP-2) and osteocalcin as well as increased expression of transforming growth factor (TGF-beta). Cell loss, progressive fibrosis, and focal necrosis were detected in all irradiated sites. Quantitative measurement revealed 32.0+/-8.7% and 37.3+/-9.5% empty osteocyte lacunae for groups 1 and 2 resp., compared to 16.3+/-4.7% and 18.9+/-4.9% on the contralateral side and 7.9+/-1.7% for unirradiated controls (Mann-Whitney U test; p<.01). BMP-2 and osteocalcin labelling showed a marked decrease in irradiated and contralateral sides while TGF-beta was expressed strongly in irradiated sites only (for all p<.05). External hypofractionated irradiation with a total dose of 60Gy is feasible in rats and yields all histologic changes attributed to osteoradionecrosis (ORN) after a follow-up of 6 weeks. The irradiation protocol is suitable for an assessment of regenerative options in severe radiogenic bone damage. As a split mouth design entails major inaccuracies healthy animals have to be used as controls.

Clinical results of stereotactic body frame based fractionated radiation therapy for primary or metastatic thoracic tumors

The aim of this study was to evaluate the treatment outcomes of stereotactic body radiation therapy for treating primary or metastatic thoracic tumors using a stereotactic body frame. Between January 1998 and February 2004, 101 lesions from 91 patients with thoracic tumors were prospectively reviewed. A dose of 10-12 Gy per fraction was given three to four times over consecutive days to a total dose of 30-48 Gy (median 40 Gy). The overall response rate was 82%, with 20 (22%) complete responses and 55 (60%) partial responses. The one- and two-year local progression free survival rates were 90% and 81%, respectively. The patients who received 48 Gy showed a better local tumor control than those who received less than 48 Gy (Fisher exact test; p = 0.004). No pulmonary complications greater than a RTOG toxicity criteria grade 2 were observed. The experience of stereotactic body frame based radiation therapy appears to be a safe and promising treatment modality for the local management of primary or metastatic lung tumors. The optimal total dose, fractionation schedule and treatment volume need to be determined after a further follow-up of these results.

Comparison of early complications for patients with convexity and parasagittal meningiomas treated with either stereotactic radiosurgery or fractionated stereotactic radiotherapy

OBJECTIVE

Patients with convexity and parasagittal (CPS) meningiomas treated with stereotactic radiosurgery (SRS) have been shown to be at risk for posttreatment symptomatic peritumoral edema (SPTE). We sought to analyze the pattern of this complication and compare it with the SPTE experienced in our patients treated with fractionated stereotactic radiotherapy.

METHODS

From January 2003 to October 2005, 32 patients with CPS meningiomas were treated. Thirty patients with a total of 38 lesions had sufficient follow-up for analysis. Group A (n = 14) patients were treated with single fraction SRS, and Group B (n = 16) patients were treated with fractionated stereotactic radiotherapy. The lesion volume was different between the two groups with the Group B median volume (7.46 cm) being larger than that for Group A (2.84 cm) (P = 0.0008). Conversely age, follow-up, sex, prior surgical events, number of lesions, tumor location, and atypical histology did not differ between these groups. The median marginal dose for patients in Group A was 14 Gy (range, 12.5-18 Gy). For Group B, six patients received a median marginal dose of 50.4 Gy in 28 fractions, and 10 patients received a marginal dose of 25 Gy in five fractions.

RESULTS

Seven of the 30 patients treated in this series developed posttreatment SPTE. The incidence of SPTE in Group A (six of 14 patients) was significantly higher than that in Group B (one of 16 patients) (P = 0.031). The median time to onset of SPTE in the six patients in Group A was 4 months. In Group B, one patient had onset of SPTE in 3 months. On univariate analysis, larger tumor volume (P = 0.0014) and tumor margin dose >14 Gy in patients undergoing SRS (P = 0.031) was associated with onset of SPTE. Age, previous surgery, and tumor location were not associated with onset of SPTE.

CONCLUSION

Despite larger lesion volumes, fractionated stereotactic radiotherapy is associated with less risk of posttreatment SPTE than SRS for patients with CPS meningiomas in our series. For patients treated with SRS, smaller volume and dose <14 Gy seems to be safe. Longer follow-up will be required to compare late complications and tumor control rates in these patients.

Long-term results of stereotactic proton beam radiotherapy for acoustic neuromas

BACKGROUND AND PURPOSE

A retrospective study evaluating the role of hypofractionated stereotactic proton beam therapy for acoustic neuromas.

MATERIALS AND METHODS

The data of 51 patients treated with hypofractionation (3 fractions) and followed up for a minimum of 2 years, were analyzed. Mean dose prescribed to ICRU reference point (isocenter) was 26 cobalt gray equivalent (CGyE) in 3 fractions. Mean minimum tumor dose was 21.4 CGyE/3. Cranial nerve functions were evaluated clinically. Serial MR Scans were used to evaluate local control.

RESULTS

With a mean clinical and radiological follow-up of 72 and 60 months respectively, the 5-year results showed a 98% local control, with a hearing preservation of 42%, a facial nerve preservation of 90.5% and a trigeminal nerve preservation of 93%.

CONCLUSION

For those patients harboring large acoustic neuromas that are inoperable, hypofractionated stereotactic proton beam offers long-term control with minimal side-effects.

CHAINED LIGHTNING

RADIOSURGERY IS FUNDAMENTALLY the harnessing of energy and delivering it to a focal target for a therapeutic effect. The evolution of radiosurgical technology and practice has served toward refining methodologies for better conformal energy delivery. In the past, this has resulted in developing strategies for improved beam generation and delivery. Ultimately, however, our current instrumentation and treatment modalities may be approaching a practical limit with regard to further optimizing energy containment.

In looking forward, several strategies are emerging to circumvent these limitations and improve conformal radiosurgery. Refinement of imaging techniques through functional imaging and nanoprobes for cancer detection may benefit lesion localization and targeting. Methods for enhancing the biological effect while reducing radiation-induced changes are being examined through dose fractionation schedules. Radiosensitizers and photosensitizers are being investigated as agents for modulating the biological response of tissues to radiation and alternative energy forms. Discovery of new energy modalities is being pursued through development of microplanar beams, free electron lasers, and high-intensity focused ultrasound. The exploration of these future possibilities will provide the tools for radiosurgical treatment of a broader spectrum of diseases for the next generation.

Enhanced survival and cure of F98 glioma-bearing rats following intracerebral delivery of carboplatin in combination with photon irradiation

PURPOSE

The goal of the present study was to evaluate the efficacy of intracerebral (i.c.) administration of carboplatin by means of convection-enhanced delivery (CED) in combination with fractionated, external beam photon irradiation for the treatment of F98 glioma-bearing rats.

EXPERIMENTAL DESIGN

Carboplatin (20 microg/20 microL) was administrated i.c. by CED to F98 glioma-bearing rats, 13 days after stereotactic implantation of 10(3) tumor cells. One day following initiation of CED, a 24-Gy X-ray dose was administered in three daily fractions of 8 Gy each. Photon irradiation was carried out using either a conventional (6 MV) linear accelerator or a monochromatic synchrotron source (80 keV) at the European Synchrotron Radiation Facility. The primary end point of this study was overall survival.

RESULTS

The median survival times were 79 and 60 days and the corresponding percent increase in life spans were 182% and 114%, respectively, for the combination of carboplatin chemotherapy and irradiation with either 6-MV or 80-keV photons. A subset of long-term survivors (>200 days) were observed in both chemoradiotherapy groups: 16.6% and 8.3% for 6 MV and 80 keV, respectively. In contrast, the median survival times for 6-MV or 80-keV irradiated controls, chemotherapy alone, and untreated controls were 42, 51, 45, and 28 days, respectively.

CONCLUSIONS

Our results convincingly show the therapeutic efficacy of i.c. administration of carboplatin by means of CED in combination with either 6-MV or 80-keV photons. Further studies are warranted to optimize this combination of chemoradiotherapy for malignant gliomas.

Extending the linear–quadratic model for large fraction doses pertinent to stereotactic radiotherapy

Ongoing clinical trials designed to explore the use of extracranial stereotactic radiosurgery (ESR) for different tumour sites use large doses per fraction (15, 20, 30 Gy or even larger). The question of whether the linear-quadratic (LQ) model is appropriate to describe radiation response for such large fraction doses has been raised and has not been answered definitively. It has been proposed that mechanism-based models, such as the lethal-potentially lethal (LPL) model, could be more appropriate for such large fraction/acute doses. However, such models are not well characterized with clinical data and they are generally not easy to use. The purpose of this work is to modify the LQ model to more accurately describe radiation response for high fraction/acute doses. A new parameter is introduced in the modified LQ (MLQ) model. The new parameter introduced is characterized based both on in vitro cell survival data of several human tumour cell lines and in vivo animal iso-effect curves. The MLQ model produces a better fit to the iso-effect data than the LQ model. For a high single dose irradiation, the prediction of the MLQ is consistent with that from the LPL model. Unlike the LPL model, the MLQ model retains the simplicity of the LQ model and uses the well-characterized alpha and beta parameters. This work indicates that the standard LQ model can lead to erroneous results when used to calculate iso-effects with large fraction doses, such as those used for ESR. We present a solution to this problem.