Cardiac Exposure in the Dynamic Conformal Arc Therapy, Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy of Lung Cancer

Dosimetric evaluation of SBRT treatment plans of non-central lung tumours: clinical experience

Objectives:

Lung cancer is the most commonly diagnosed cancer in Canada and the leading cause of cancer-related mortality in both men and women in North America. Surgery is usually the primary treatment option for early-stage non-small cell lung cancer (NSCLC). However, for patients who may not be suitable candidates for surgery, stereotactic body radiation therapy (SBRT) is an alternative method of treatment. SBRT has proven to be an effective technique for treating NSCLC patients by focally administering high radiation dose to the tumour with acceptable risk of toxicity to surrounding healthy tissues. The goal of this comprehensive retrospective dosimetric study is to compare the dosimetric parameters between three-dimensional conformal radiation therapy (3DCRT) and volumetric-modulated arc therapy (VMAT) lung SBRT treatment plans for two prescription doses.

Methods:

We retrospectively analysed and compared lung SBRT treatment plans of 263 patients treated with either a 3DCRT non-coplanar or with 2–3 VMAT arcs technique at 48 Gy in 4 fractions (48 Gy/4) or 50 Gy in 5 fractions (50 Gy/5) prescribed to the planning target volume (PTV), typically encompassing the 80% isodose volume. All patients were treated on either a Varian 21EX or TrueBeam linear accelerator using 6-MV or 10-MV photon beams.

Results:

The mean PTV V95% and V100% for treatment plans at 48 Gy/4 are 99·4 ± 0·6% and 96·0 ± 1·0%, respectively, for 3DCRT and 99·7 ± 0·4% and 96·4 ± 3·4%, respectively, for VMAT. The corresponding mean PTV V95% and V100% at 50 Gy/5 are 99·0 ± 1·4% and 95·5 ± 2·5% for 3DCRT and 99·5 ± 0·8% and 96·1 ± 1·6% for VMAT. The CIRI and HI5/95 for the PTV at 48 Gy/4 are 1·1 ± 0·1 and 1·2 ± 0·0 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The corresponding CIRI and HI5/95 at 50 Gy/5 are 1·1 ± 0·1 and 1·3 ± 0·1 for 3DCRT and 1·0 ± 0·1 and 1·2 ± 0·0 for VMAT. The mean R50% and D2cm at 48 Gy/4 are 5·0 ± 0·8 and 61·2 ± 7·0% for 3DCRT and 4·9 ± 0·8 and 57·8 ± 7·9% for VMAT. The corresponding R50% and D2cm at 50 Gy/5 are 4·7 ± 0·5 and 65·5 ± 9·4% for 3DCRT and 4·7 ± 0·7 and 60·0 ± 7·2% for VMAT.

Conclusion:

The use of 3DCRT or VMAT technique for lung SBRT is an efficient and reliable method for achieving dose conformity, rapid dose fall-off and minimising doses to the organs at risk. The VMAT technique resulted in improved dose conformity, rapid dose fall-off from the PTV compared to 3DCRT, although the magnitude may not be clinically significant.

Re-irradiation in locally recurrent lung cancer patients

PURPOSE

Lung cancer remains one of the tumour diagnoses with high lethality, although innovative treatment approaches have yielded improvements in local control and survival rates. There is still no consensus on how to treat local relapse in patients after first-line treatments. Radiotherapy may be considered in this situation; however, data supporting its effectiveness are rare. The purpose of this retrospective analysis was to evaluate outcomes of patients re-irradiated for thoracic tumours in terms of overall survival (OS), local progression-free survival (LPFS), toxicity and dose-volume parameters.

PATIENTS AND METHODS

Sixty-two patients with locally recurrent previously irradiated lung cancer were analysed retrospectively (NSCLC n = 52, SCLC n = 10). Target volumes both in lung and mediastinum were re-irradiated with conventional three-dimensional or intensity-modulated radiotherapy techniques. Median overall dose of re-irradiation was 38.5 Gy (range 20-60 Gy) with a median single dose per fraction of 2 Gy (1.8-3.0 Gy). Clinical documents and treatment plans were evaluated.

RESULTS

Median follow-up was 8.2 months (range 0-27 months). OS following re-irradiation was 9.3 months (range: 0-27 months) and LPFS was 6.5 months (range: 0-24 months). OS and LPFS were not affected by histology, total dose or patient age and gender. OS was improved in patients whose re-irradiation volumes included less than two mediastinal lymph node stations (p = 0.016). Twelve patients suffered from pneumonitis ≥grade II (19%) and two from pneumonitis grade III. One patient presumably died from pneumonitis grade V. A slight decline in forced expiratory volume (FEV₁) was detected in post-re-irradiation lung function testing.

CONCLUSIONS

Re-irradiation is an option for patients with tumour recurrence to control local progression and lower the symptom burden. Oncological outcome appears to be affected by size, location of mediastinal target volumes and lung function. Prospective clinical trials are warranted to substantiate the role of re-irradiation in recurrent lung cancer.

Comparison of Flattening Filter and Flattening Filter-Free Volumetric Modulated Arc Radiotherapy in Patients with Locally Advanced Nasopharyngeal Carcinoma

BACKGROUND This study aimed to investigate the therapeutic role of flattening filter-free (FFF) mode in volumetric modulated arc therapy (VMAT) compared with flattening filter (FF) mode in patients with locally advanced nasopharyngeal carcinoma (NPC). MATERIAL AND METHODS Ten previously treated patients with NPC underwent treatment re-planning with FFF and FF VMAT. Radiotherapy dose distribution on planning target volume (PTV), organs at risk (OAR), target conformity index (CI), total monitor units (MUs), and therapeutic time were compared. RESULTS Maximum and mean radiotherapy dose in PTV and PGTV (primary lesions of NPC and cervical lymph node metastases) in FFF VMAT planning were significantly increased compared with FF VMAT planning, but PTV and OAR showed no significant differences. The CI value of PTV in FFF VMAT planning was significantly reduced compared with FF planning (P<0.05). No differences were found for the maximum radiotherapy dose in the spinal cord and left and right optic nerve, and the mean radiotherapy dose in the brainstem, left and right parotid gland (P>0.05). The maximum dose in the brainstem in the FFF planning was significantly higher compared with FF planning (P>0.05). The maximum radiotherapy dose in left and right crystalline lens (P<0.05) in FFF planning was significantly reduced compared with FF planning. The total hop count in FFF planning was significantly increased compared with FF planning (P<0.05). CONCLUSIONS Both 6 MV X-ray FFF mode and FF mode in the treatment of patients with NPC showed that FFF VMAT planning provided improved protection for OAR.

Cholecystokinin attenuates radiation-induced lung cancer cell apoptosis by modulating p53 gene transcription

The deregulation of p53 in cancer cells is one of the important factors by which cancer cells escape from the immune surveillance. Cholecystokinin (CCK) has strong bioactivity in the regulation of a number of cell activities. This study tests a hypothesis that CCK interferes with p53 expression to affect the apoptotic process in lung cancer (tumor) cells. In this study, tumor-bearing mice and A549 cells (a tumor cell line) were irradiated. The expression of CCK and p53 in tumor cells was assessed with RT-qPCR and Western blotting. The binding of p300 to the promoter of p53 was evaluated by chromatin immunoprecipitation. We observed that, with a given amount and within a given period, small doses/more sessions of irradiation markedly increased the levels of CCK in the sera and tumor cells, which were positively correlated with the tumor growth in mice and negatively correlated with tumor cell apoptosis. CCK increased the levels of histone acetyltransferase p300 and repressed the levels of nuclear factor-kB at the p53 promoter locus in tumor cells, which suppressed the expression of p53. In conclusion, CCK plays an important role in attenuating the radiation-induced lung cancer cell apoptosis. CCK may be a novel therapeutic target in the treatment of lung cancers.

Radiation-induced heart disease in lung cancer radiotherapy: A dosimetric update

BACKGROUND

Radiation-induced heart disease (RIHD), which affects the patients' prognosis with both acute and late side effects, has been published extensively in the radiotherapy of breast cancer, lymphoma and other benign diseases. Studies on RIHD in lung cancer radiotherapy, however, are less extensive and clear even though the patients with lung cancer are delivered with higher doses to the heart during radiation treatment.

METHODS

In this article, after extensive literature search and analysis, we reviewed the current evidence on RIHD in lung cancer patients after their radiation treatments and investigated the potential risk factors for RIHD as compared to other types of cancers.

RESULT

Cardiac toxicity has been found highly relevant in lung cancer radiotherapy. So far, the crude incidence of cardiac complications in the lung cancer patients after radiotherapy has been up to 33%.

CONCLUSION

The dose to the heart, the lobar location of tumor, the treatment modality, the history of heart and pulmonary disease and smoking were considered as potential risk factors for RIHD in lung cancer radiotherapy. As treatment techniques improve over the time with better prognosis for lung cancer survivors, an improved prediction model can be established to further reduce the cardiac toxicity in lung cancer radiotherapy.

Predictive parameters for selection of electronic tissue compensation radiotherapy in early-stage breast cancer patients after breast-conserving surgery

Electronic tissue compensation (eComp) is an external beam planning technique allowing user to manually generate dynamic beam fluence to produce more uniform or modulated dose distribution. In this study, we compared the effectiveness between conventional three-dimensional conformal radiotherapy (3DCRT) and eComp for whole breast irradiation. 3DCRT and eComp planning techniques were used to generate treatment plans for 60 whole breast patients, respectively. The planning goal was to cover 95% of the planning target volume (PTV) with 95% of the prescription dose while minimizing doses to lung, heart, and skin. Comparing to 3DCRT plans, on the average, eComp treatment planning process was about 7 minutes longer, but resulted in lower lung V20Gy, lower mean skin dose, with similar heart dose. The benefits were more pronounced for larger breast patients. Statistical analyses were performed between critical organ doses and patient anatomic features, i.e., central lung distance (CLD), maximal heart distance (MHD), maximal heart length (MHL) and breast separation (BS) to explore any correlations and planning method selection. It was found that to keep the lung V20Gy lower than 20% and mean skin dose lower than 85% of the prescription dose, eComp was the preferred method for patients with more than 2.3 cm CLD or larger than 22.5 cm BS. The study results may be useful in providing a handy criterion in clinical practice allowing us to easily choose between different planning techniques to satisfy the planning goal with minimal increase in complexity and cost.

A New Score for Estimating Survival After Definitive Radiochemotherapy of Limited Disease Small Cell Lung Cancers

INTRODUCTION

Most patients with limited disease small cell lung cancer (LD-SCLC) receive definitive radiochemotherapy. Some patients cannot withstand combined modality treatments. Patients with short life expectancies should receive less time-consuming programs. For patients with favorable prognoses, cure while avoiding late toxicity is important. Personalized treatment programs are required. An instrument to estimate the survival after radiochemotherapy of LD-SCLC was created.

METHODS

Seventy-one patients receiving definitive radiochemotherapy for LD-SCLC were retrospectively analyzed. Eight factors were evaluated for survival including gender, age, Karnofsky performance score, T-stage, N-stage, tumor substage, number of pack years, and pre-radiotherapy hemoglobin level. Factors that were significant (p < 0.05) or showed a trend (p ≤ 0.08) on multivariate analyses were incorporated in the score. Scoring points were derived from 2-year survival rates divided by 10 and added to scores for individual patients.

RESULTS

On multivariate analysis, gender (p = 0.03), performance score (p < 0.001), and pre-radiotherapy hemoglobin level (p = 0.04) were significant, and tumor substage showed a trend (p = 0.08). Taking into account the 2-year survival rates of these factors, scores for single patients ranged from 9 to 26 points. Three groups were identified: 9-13, 14-18, and 19-26 points. One-year survival rates were 8, 73, and 100 %, respectively (p < 0.001). Two-year survival rates were 0, 35, and 87 %, respectively (p < 0.001). The 3-year survival rates were 0, 19, and 75 %, respectively (p < 0.001).

CONCLUSION

This score including three groups with significantly different survival rates is a helpful instrument for personalization of therapy for patients with LD-SCLC. When using this instrument, the limitations if this study must be taken into account.