Stereotactic body radiotherapy for lung tumors: Dosimetric analysis and clinical outcome.

INTRODUCTION: Stereotactic body radiotherapy (SBRT) has emerged as an important modality in malignant lung tumor treatment both in early localized primary and oligometastatic setting. This study aims to present the results of lung SBRT both in terms of dosimetry and clinical outcome. MATERIALS AND METHODS: Twenty-seven patients were assessed from 2012 to 2016. Both the primary and oligometastatic lung tumors were evaluated. Respiratory motion management was done employing ANZAI (Siemens, Germany) based four-dimensional computed tomography (CT). Commonly used fractionations were 60 Gy/5 fractions for peripheral tumors and 48 Gy/6 fractions for central tumors. Radiation Therapy Oncology Group toxicity criteria were used for toxicity and whole-body positron emission tomography-CT scan was done at follow-up for response evaluation. RESULTS: Twenty-seven patients were evaluated, 18 (66.7%) patients had a primary, and 9 (33.3%) patients had metastatic lung tumors. The male-to-female ratio for the entire cohort was 2:1. The median age at diagnosis was 65.8 years. Mean planning target volume (PTV) D2cc was 54.9 ± 9.04 Gy and mean internal target volume diameter was 3.0 ± 1.07 cm. Mean V20 Gy, V10 Gy, and V5 Gy of (lungs total-PTV) and (Lung ipsilateral - PTV) were 5.4 ± 4% and 10.9 ± 7.9%, 11.7 ± 5.8% and 24.2 ± 14.0%, and 22.05 ± 12.4% and 33.2 ± 15.3%, respectively. In total 21 (84%) patients and 4 patients (16%) showed a complete and partial response, respectively. One (3%) patient developed Gr 3 radiation pneumonitis. One year local control was in 18 (81%) patients whereas 4 (14%) patients progressed and three patients did not report. A higher prescribed dose significantly correlated with 1 year tumor control (P = 0.036). CONCLUSION: This study infers the feasibility and a favorable outcome for lung cancer amenable to SBRT in addition to being one of the largest clinical experiences for lung stereotactic treatment in our country.

Transabdominal Ultrasonography-Defined Optimal and Definitive Bladder-Filling Protocol With Time Trends During Pelvic Radiation for Cervical Cancer.

PURPOSE: Advanced radiotherapy techniques have emphasized on the importance of accurate target volume localization and delineation. The aim of this study was to determine time taken to achieve moderate bladder volume under physiological conditions, using transabdominal ultrasound. MATERIALS AND METHODS: Patients with cervical cancer undergoing radical radiation with or without concomitant chemotherapy underwent serial ultrasound to estimate bladder filling. With a strict bladder protocol of consuming 1000 mL of water orally over 30 minutes after emptying the bladder, ultrasound was done after 45 minutes from bladder emptying time and repeated at 15-minute interval till 300 (25) mL filling was achieved and repeated every week. RESULTS: Forty-six patients with weekly ultrasound for bladder-filling documentation were evaluated. The mean (standard deviation) bladder volume measured at 45 minutes was 220 (93), 210 (95), 195 (91), 195 (96), and 190 (85) mL (average: 200; median: 195 mL) for the first to fifth week, respectively, and the mean (standard deviation) volume at 75 minutes was 300 (95), 310 (80), 290 (80), 295 (80), and 285 (70) mL (average: 295; median: 300 mL). The mean (standard deviation) time for bladder filling to 300 mL in the first, second, third, fourth, and fifth week was 57 ( 13.5), 67 (16.6), 66 (16.7), 66 (15.5), and 69 (17.1) minutes, respectively. CONCLUSION: Bladder filling to a definitive moderate volume at a reasonably fixed time period in each week of radiation is well tolerated, feasible, and measurable by weekly transabdominal ultrasound measurements.

Comparison between weekly cisplatin-enhanced radiotherapy and cetuximab-enhanced radiotherapy in locally advanced head and neck cancer: first retrospective study in Asian population.

AIM: To present a direct comparison between chemotherapy-enhanced radiotherapy (CERT) and biotherapy-enhanced radiotherapy (BERT) in locally advanced head and neck cancer. METHODS: It is a retrospective analysis of 53 patients with locally advanced head and neck cancer treated from August 2006 to December 2008. For CERT, patients received weekly cisplatin (40 mg/m2 ) and for BERT, a loading dose of 400 mg/m2 of cetuximab given one week prior to radiotherapy followed by 250 mg/m2 given weekly along with radiotherapy. Disease-free survival (DFS) and overall survival (OS) were computed with Kaplan-Meier curve with log-rank test for comparison between the two groups. Multivariate Cox proportional hazards regression analysis was performed to estimate the impact of known relevant prognostic factors on DFS and OS. RESULTS: The median DFS was significantly better with CERT than BERT group (50.82 vs 11.66 months; P = 0.031). The 3 years DFS was significantly higher in CERT group than in BERT group (60.0% vs 14.3%; P = 0.022). The median OS was significantly better with CERT than BERT group (53.61 vs 32.55 months; P = 0.044). The 3 years OS was also significantly higher in CERT group than in BERT group (74.0% vs 42.1%; P = 0.032). There were no significant differences in acute toxicities of all grade and grade ≥3 between the two groups. The compliance to treatment and assisted feeding dependency for more than 6 months duration were also not significantly different. CONCLUSION: CERT is associated with better outcome with no significantly increased acute toxicities compared to BERT.

Critical neurological structure sparing radiosurgery of vestibular schwannoma: dosimetric comparison of different techniques and dose prescription methods.

AIM: To investigate potential sparing of critical neurological structures (CNSs) during radiosurgery of vestibular schwannoma (VS) employing different techniques and dose prescription methods. MATERIALS AND METHODS: Fused CT and MRI datasets of eight patients with unilateral VS representing a wide range of target volume (0.48 to 12.08 cc; mean = 3.56 cc), shape and proximity to CNSs such as cochlea, trigeminal nerve and brainstem were re-planned employing static conformal field (SCF), dynamic conformal arc (DCA) and intensity modulated radiosurgery (IMRS) techniques. For every patient, five plans were created for a fixed margin dose of 12 Gy prescribed at 80% in three plans (SCF_80%, DCA_80%, and IMRS_80%) and 50% in another two plans (SCF_50% and DCA_50%). All plans were compared using standard dosimetric indices. RESULTS: Primary goal of every plan to cover ≥99% of target volume with 12 Gy was fulfilled for all patients with minimum significant dose to target (D99) ≥11.99 Gy. Best conformity index (CI Paddick = 0.62 ± 0.12) was observed in SCF_80% and DCA_80% plans whereas; sharpest dose gradient index of 3.40 ± 0.40 was resulted from DCA_50%. All five plans resulted similar maximum dose to brainstem (11.04 ± 2.23 to 11.53 ± 1.10 Gy), cochlea (9.02 ± 1.79 to 10.15 ± 1.26 Gy) and trigeminal nerve (11.55 ± 1.38 to 12.19 ± 2.12 Gy). Among 80% prescription plans, IMRS_80% reduces mean and D5 (P < 0.05) to all CNSs. Prescription of dose at 50% isodose sharpened the dose gradient and significantly (P < 0.05) reduced mean dose and D5 to all CNSs at the cost of target conformity (P = 0.01). Mean dose to cochlea and trigeminal nerve were least at 4.53 ± 0.86 and 6.95 ± 2.02 Gy from SCF_50% and highest at 6.65 ± 0.70 and 8.40 ± 2.11 Gy from DCA_80% plans respectively. CONCLUSION: This dosimetric data provides a guideline for choosing optimum treatment option and scope of inter institutional dosimetric comparison for further improvement in radiosurgery of Vestibular Schwannoma (VS).

Analysis of dose-volume parameters predicting radiation pneumonitis in patients with esophageal cancer treated with 3D-conformal radiation therapy or IMRT.

PURPOSE: Multimodality therapy for esophageal cancer can cause various kinds of treatment-related sequelae, especially pulmonary toxicities. This prospective study aims to investigate the clinical and dosimetric parameters predicting lung injury in patients undergoing radiation therapy for esophageal cancer. METHODS: Forty-five esophageal cancer patients were prospectively analyzed. The pulmonary toxicities (or sequelae) were evaluated by comparing chest X-ray films, pulmonary function tests and symptoms caused by pulmonary damage before and after treatment. All patients were treated with either three-dimensional radiotherapy (3DCRT) or with intensity-modulated radiotherapy (IMRT). The planning dose volume histogram was used to compute the lung volumes receiving more than 5, 10, 20 and 30 Gy (V5, V10, V20, V30) and mean lung dose. RESULTS: V20 was larger in the IMRT group than in the 3DCRT group (p = 0.002). V20 (>15%) and V30 (>20%) resulted in a statistically significant increase in the occurrence of chronic pneumonitis (p = 0.03) and acute pneumonitis (p = 0.007), respectively. CONCLUSIONS: The study signifies that a larger volume of lung receives lower doses because of multiple beam arrangement and a smaller volume of lung receives higher doses because of better dose conformity in IMRT plans. Acute pneumonitis correlates more with V30 values, whereas chronic pneumonitis was predominantly seen in patients with higher V20 values.

Set-up uncertainties: online correction with X-ray volume imaging.

AIM: To determine interfractional three-dimensional set-up errors using X-ray volumetric imaging (XVI). MATERIALS AND METHODS: Between December 2007 and August 2009, 125 patients were taken up for image-guided radiotherapy using online XVI. After matching of reference and acquired volume view images, set-up errors in three translation directions were recorded and corrected online before treatment each day. Mean displacements, population systematic (Σ), and random (σ) errors were calculated and analyzed using SPSS (v16) software. Optimum clinical target volume (CTV) to planning target volume (PTV) margin was calculated using Van Herk's (2.5Σ + 0.7 σ) and Stroom's (2Σ + 0.7 σ) formula. RESULTS: Patients were grouped in 4 cohorts, namely brain, head and neck, thorax, and abdomen-pelvis. The mean vector displacement recorded were 0.18 cm, 0.15 cm, 0.36 cm, and 0.35 cm for brain, head and neck, thorax, and abdomen-pelvis, respectively. Analysis of individual mean set-up errors revealed good agreement with the proposed 0.3 cm isotropic margins for brain and 0.5 cm isotropic margins for head-neck. Similarly, 0.5 cm circumferential and 1 cm craniocaudal proposed margins were in agreement with thorax and abdomen-pelvic cases. CONCLUSION: The calculated mean displacements were well within CTV-PTV margin estimates of Van Herk (90% population coverage to minimum 95% prescribed dose) and Stroom (99% target volume coverage by 95% prescribed dose). Employing these individualized margins in a particular cohort ensure comparable target coverage as described in literature, which is further improved if XVI-aided set-up error detection and correction is used before treatment.