The Impact of Dose Rate on the Tumor Microenvironment Using Flattening-filter-free Beams

AIMS

Recently, dose delivery technology has rapidly evolved with flattening filter-free beams (FFF), and the biological effects of high dose rates are a matter of interest. We hypothesized that FFF beams at different dose rates obtained with modern linear accelerators have different effects on the TME.

MATERIALS AND METHODS

The B16-F10 melanoma syngeneic tumor model was established, and mice were randomized to 2 different doses (2 Gy and 10 Gy) and 3 different dose rates (1 Gy/min, 6 Gy/min, and 14 Gy/min) along with the control group. Euthanasia was performed on the seventh day after RT, and intracardiac blood was collected for a comet assay. Tumors were harvested and examined histomorphologically and immunohistochemically. Statistical analyses were performed using SPSS software version 23 (SPSS Inc., Chicago, IL, USA).

RESULTS

The daily growth rate was uniform, and no difference was observed between tumor volumes across all three dose rates for each dose. Deoxyribonucleic acid (DNA) damage in blood mononuclear cells was not affected by dose or dose rate. In the TME histomorphological examination, the number of mitosis is less in the 10 Gy arm, whereas the pleomorphism score was greater. Nevertheless, varying dose rates had no effect on the number of mitosis or the pleomorphism score. The severity of the inflammation, cell densities in the TME, and expression of immunohistochemical markers were comparable across all doses and dose rates.

CONCLUSION

In our study involving the B16-F10 syngeneic tumor model, varying dose rates obtained with FFF beams had no effect on tumor volume, blood mononuclear cell DNA damage, or TME parameters. However, in order to fully understand the biological impacts of novel techniques, our study should be validated with alternative preclinical setups.

Metastasis-directed radiotherapy for non-small cell lung cancer failured under TKI: A case report and literature review

Although tyrosine kinase inhibitors (TKI) have revolutionized the treatment of anaplastic lymphoma kinase rearranged non-small cell lung cancer (ALKr-NSCLC), radiotherapy (RT) still plays an essential role for treatment of both intracranial and extracranial metastases, particularly for patients experienced a TKI-failure. We reported the case of a 38-year-old woman with metastatic ALKr-NSCLC who received whole-brain radiotherapy (RT) for multiple brain metastases (BMs), initially. After RT, alectinib was initiated and the patient had a good clinico-radiological response in both intracranial and extracranial regions. However, intracranial progression was developed and, stereotactic radiosurgery (SRS) was applied to the four progressed BMs. Two months after SRS, all BMs disappeared. While patient was using alectinib, a recurrent lung lesion, a hilar lymph node and bone metastasis were detected. Stereotactic body radiotherapy (SBRT) was applied to all metastatic sites and, alectinib was continued again. Three months after SBRT, a complete response was obtained. She has been alive with the initial systemic therapy agent for more than 4years without evidence of neither disease nor toxicity. SRS/SBRT may eradicate the TKI-resistant tumoral clones and it may prevent switching the systemic therapy, even if there is a failure.

The Effect of Dose Rate on Tumor Microenvironment in External Beam Radiotherapy

PURPOSE/OBJECTIVE(S)

The fact that treatment can be given at a narrow dose rate range in external radiotherapy (ERT) applications with crude delivery techniques has caused the dose rate to be neglected for a long time. Recently dose delivery technology has rapidly evolved and with the re-introduction of FLASH-RT to the radiation oncology stage, dose rate studies escalated. It is also known that interactions within the tumor microenvironment (TME) play a significant role in tumor prognosis. Herein we aimed to investigate the effect of three different dose rates on TME.

MATERIALS/METHODS

To generate the tumor model, 1 million B16-F10 malignant melanoma cells were subcutaneously injected into the right flank of C57BL/6 mice. RT time was estimated to be 0.5 cm in diameter. Forty-two mice were randomly assigned to the control group, 2 different doses (2 Gy and 10 Gy), and 3 different dose rates (1 Gy/min, 6 Gy/min, and 14 Gy/min). Vernier scale measurements were taken every day to monitor the mice's tumor size. Euthanasia is induced on the seventh day after ERT. Tumor and metastatic organs were harvested, and evaluated histomorphological, and immunohistochemically. Intracardiac blood was collected for the comet assay.

RESULTS

After radiation, the 10 Gy arm's mean tumor size was lower than that of the 2 Gy and control arms (p = 0.01 and p = 0.007). Tumor size did not differ between the 2 Gy and control arms (p = 0.53). Additionally, there was no difference in tumor diameters between low and high doses at different dose rates (p = 0.12, p = 0.21). Blood mononuclear cells in the control arm had less DNA damage than those in the 10 Gy arm (p = 0.04). The 2 Gy and 10 Gy arms did not differ in terms of DNA damage (p = 0.65). Each dose arm was evaluated in terms of dose rates and no significant difference was found (p = 0.79, p = 0.24). The number of mitoses per 10 HPF was assessed during the histological analysis. The number of mitoses in the 10 Gy arm was less than the 2 Gy arm (p = 0.001). There was no difference at different dose rates in the 2 Gy and 10 Gy arms (p = 0.28, p = 0.97). Pleomorphism score was evaluated as mild-moderate and severe (score 1-2-3). In comparison to the 2 Gy and control arms, the 10 Gy arm had a higher pleomorphism score (p = 0.01). The 2 Gy arm and the control arm did not vary from one another (p = 0.04). Pleomorphism scores were comparable across low and high doses at different dose rates (p = 0.35, p = 0.58). Different dose rates resulted in the same staining pattern with aSMA and SOX-10.

CONCLUSION

In our study involving the B16-F10 syngeneic tumor model, we could not find a significant effect of three different dose rates on TME. With constantly improving treatment techniques, larger dose rates are going to be achieved. Owing to this, protocols should also list dose rate as a treatment variable. This project was supported by the TÜBİTAK, Short Term R&D Funding Program.

Hyaluronic acid spacer in focal prostate reirradiation: A single centre experience

PURPOSE

The optimal management of locally recurrent prostate cancer after curative radiotherapy is still unknown. In this study, we evaluated the preliminary results of reirradiation using stereotactic body radiotherapy for locally recurrent prostate cancer after initial definitive local radiotherapy.

MATERIALS AND METHODS

Between April 2016 and February 2019, 11 patients with recurrent disease at the previously irradiated prostate were treated. Local recurrence was detected by radiological with or without functional imaging modalities including prostate multiparametric/pelvic MRI or positron-emission tomography-computerised tomography with (⁶⁸Ga)-labelled prostate-specific membrane antigen performed after rising prostate specific antigen serum level during follow-up. All patients received stereotactic body radiotherapy to the recurrent nodule to a total dose of 30Gy in five fractions. Hyaluronic acid spacer was injected between prostate and rectum in seven patients to decrease the rectal dose. Acute toxicity was evaluated by using Common Terminology Criteria for Adverse Events version 4.0, and late toxicity was evaluated by using Radiation Therapy Oncology Group/European Organisation for Research and Treatment of Cancer late radiation morbidity scoring schema.

RESULTS

At the diagnosis, the median age was 64 years, and the mean prostate specific antigen serum concentration was 17.7ng/mL. The median interval time between local recurrence and initial definitive radiotherapy was 63 months. Mean prostate specific antigen concentration nadir value during follow-up was 0.43ng/mL. With a median follow up of 19 months, three patients developed either local or distant relapse. One patient had grade 3 acute rectal toxicity, and one patient had grade 2 late urinary toxicity. We did not observe any acute or late toxicity due to hyaluronic acid spacer injection.

CONCLUSION

Reirradiation after local recurrence following initial definitive radiotherapy together with hyaluronic acid spacer use seems to be effective and safe.

Robotic Stereotactic Body Radiation Therapy in Patients With Recurrent or Metastatic Abdominopelvic Tumors: A Single Institute Experience

BACKGROUND

The aim of this study was to evaluate the efficacy and toxicity of robotic CyberKnife (Accuray Incorporated, Sunnyvale, California)-based stereotactic body radiation therapy (SBRT) in patients with recurrent or metastatic abdominopelvic tumors.

METHODS AND MATERIALS

A total of 69 patients treated between May 2008 and January 2011 were evaluated retrospectively. Indication for SBRT was persistent disease in 3 (4%) patients, local recurrence in 29 (42%) patients, regional recurrence in 13 (19%) patients, and oligometastatic disease in 24 (35%) patients. Forty-two (61%) patients were previously irradiated to the same region and 27 (39%) patients were treated for the first time. The median age was 59 years (range, 24-86 years). There were 31 (45%) male and 38 (55%) female patients. The median total dose was 30 Gy (range, 15-60 Gy) delivered with a median 3 fractions (range, 2-5 fractions). The tumor response to treatment was assessed by computed tomography, magnetic resonance imaging, or positron emission tomography.

RESULTS

At the 12-month (range, 2-44 months) median follow-up, local control was 65% and median overall survival (OS) was 20 months. A larger gross tumor volume (≥ 67 cm(3)) was significantly correlated with worse 1-year OS (81% vs 48%, P = .03). The patients with local recurrence occurring <11 months had a significantly shorter 1-year local control rate than patients with ≥ 11 months (31% vs 91%, P < .001). Grade 3-4 acute and late toxicities were seen in 7% and 15% of patients, respectively. The patients with previous radiotherapy history had significantly higher rate of acute toxicity (19% vs 0%, P = .019). Late toxicity was significantly higher in pelvic tumors than in abdominal tumors (3% vs 28%, P = .004).

CONCLUSION

The SBRT seems to be feasible and resulted in good treatment outcomes in patients with recurrent or metastatic abdominopelvic tumors.

Robotic Stereotactic Radiosurgery in Patients with Unresectable Glomus Jugulare Tumors

We evaluated the treatment results of robotic stereotactic radiosurgery (SRS) in our patients with unresectable glomus jugulare tumors (GJTs). The medical charts of fourteen patients with GJT, who were treated with robotic SRS, were retrospectively evaluated. The gross tumor volume was described as the clinical target volume. The median dose to the tumor was 25 Gy in median 5 fractions. The dose was normalized to 80% isodose line. All patients were evaluated for tumor growth and clinical outcome every 6 months in the first 2 years and then annually. Median follow-up was 39 months (range, 7–60 months). Lesions were stable in 8 patients, and tumor regression was observed in 6 patients. We did not observe any treatment related toxicity in our patients. In conclusion, according to our early experience, robotic SRS seems to be successful treatment option in the management of unresectable GJTs.

Malignant pleural mesothelioma with brain metastasis

Malignant pleural mesothelioma (MPM) is a rare neoplasm associated with poor prognosis. Local disease progression is the major cause of death rather than distant metastasis. Intracranial metastases are seen very rarely. Herein, we report a case of MPM with brain metastasis treated with cranial irradiation.