Comparative Analysis of Local Control Prediction Using Different Biophysical Models for Non-Small Cell Lung Cancer Patients Undergoing Stereotactic Body Radiotherapy.

PURPOSE: The consistency for predicting local control (LC) data using biophysical models for stereotactic body radiotherapy (SBRT) treatment of lung cancer is unclear. This study aims to compare the results calculated from different models using the treatment planning data. MATERIALS AND METHODS: Treatment plans were designed for 17 patients diagnosed with primary non-small cell lung cancer (NSCLC) using 5 different fraction schemes. The Martel model, Ohri model, and the Tai model were used to predict the 2-year LC value. The Gucken model, Santiago model, and the Tai model were employed to estimate the 3-year LC data. RESULTS: We found that the employed models resulted in completely different LC prediction except for the Gucken and the Santiago models which exhibited quite similar 3-year LC data. The predicted 2-year and 3-year LC values in different models were not only associated with the dose normalization but also associated with the employed fraction schemes. The greatest difference predicted by different models was up to 15.0%. CONCLUSIONS: Our results show that different biophysical models influence the LC prediction and the difference is not only correlated to the dose normalization but also correlated to the employed fraction schemes.

Different definitions of esophagus influence esophageal toxicity prediction for esophageal cancer patients administered simultaneous integrated boost versus standard-dose radiation therapy.

We aim to evaluate whether different definitions of esophagus (DEs) impact on the esophageal toxicity prediction for esophageal cancer (EC) patients administered intensity-modulated radiation therapy with simultaneous integrated boost (SIB-IMRT) vs. standard-dose IMRT (SD-IMRT). The esophagus for 21 patients diagnosed with primary EC were defined in the following four ways: the whole esophagus, including the tumor (ESOwhole); ESOwhole within the treatment field (ESOinfield); ESOinfield, excluding the tumor (ESOinfield-tumor) and ESOwhole, excluding the tumor (ESOwhole-tumor). The difference in the dose variation, acute esophageal toxicity (AET) and late esophageal toxicity (LET) of four DEs were compared. We found that the mean esophageal dose for ESOwhole, ESOinfield, ESOinfield-tumor and ESOwhole-tumor were increased by 7.2 Gy, 10.9 Gy, 4.6 Gy and 2.0 Gy, respectively, in the SIB-IMRT plans. Radiobiological models indicated that a grade ≥ 2 AET was 2.9%, 3.1%, 2.2% and 1.6% higher on average with the Kwint model and 14.6%, 13.2%, 7.2% and 3.4% higher with the Wijsman model for the four DEs. A grade ≥ 3 AET increased by 4.3%, 7.2%, 4.2% and 1.2%, respectively. Additionally, the predicted LET increased by 0.15%, 0.39%, 1.2 × 10-2% and 1.5 × 10-3%. Our study demonstrates that different DEs influence the esophageal toxicity prediction for EC patients administered SIB-IMRT vs. SD-IMRT treatment.

A Dosimetric Study of Using Fixed-Jaw Volumetric Modulated Arc Therapy for the Treatment of Nasopharyngeal Carcinoma with Cervical Lymph Node Metastasis.

PURPOSE: To study the dosimetric difference between fixed-jaw volumetric modulated radiotherapy (FJ-VMAT) and large-field volumetric modulated radiotherapy (LF-VMAT) for nasopharyngeal carcinoma (NPC) with cervical lymph node metastasis. METHODS: Computed tomography (CT) datasets of 10 NPC patients undergoing chemoradiotherapy were used to generate LF-VMAT and FJ-VMAT plans in the Eclipse version 10.0 treatment planning system. These two kinds of plans were then compared with respect to planning-target-volume (PTV) coverage, conformity index (CI), homogeneity index (HI), organ-at-risk sparing, monitor units (MUs) and treatment time (TT). RESULTS: The FJ-VMAT plans provided lower D2% of PGTVnd (PTV of lymph nodes), PTV1 (high-risk PTV) and PTV2 (low-risk PTV) than did the LF-VMAT plans, whereas no significant differences were observed in PGTVnx (PTV of primary nasopharyngeal tumor). The FJ-VMAT plans provided lower doses delivered to the planning organ at risk (OAR) volumes (PRVs) of both brainstem and spinal cord, both parotid glands and normal tissue than did the LF-VMAT plans, whereas no significant differences were observed with respect to the oral cavity and larynx. The MUs of the FJ-VMAT plans (683 ± 87) were increased by 22% ± 12% compared with the LF-VMAT plans (559 ± 62). In terms of the TT, no significant difference was found between the two kinds of plans. CONCLUSIONS: FJ-VMAT was similar or slightly superior to LF-VMAT in terms of PTV coverage and was significantly superior in terms of OAR sparing, at the expense of increased MUs.

Flattening Filter-Free Beams in Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy for Sinonasal Cancer.

PURPOSE: To evaluate the dosimetric impacts of flattening filter-free (FFF) beams in intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for sinonasal cancer. METHODS: For fourteen cases, IMRT and VMAT planning was performed using 6-MV photon beams with both conventional flattened and FFF modes. The four types of plans were compared in terms of target dose homogeneity and conformity, organ-at-risk (OAR) sparing, number of monitor units (MUs) per fraction, treatment time and pure beam-on time. RESULTS: FFF beams led to comparable target dose homogeneity, conformity, increased number of MUs and lower doses to the spinal cord, brainstem and normal tissue, compared with flattened beams in both IMRT and VMAT. FFF beams in IMRT resulted in improvements by up to 5.4% for sparing of the contralateral optic structures, with shortened treatment time by 9.5%. However, FFF beams provided comparable overall OAR sparing and treatment time in VMAT. With FFF mode, VMAT yielded inferior homogeneity and superior conformity compared with IMRT, with comparable overall OAR sparing and significantly shorter treatment time. CONCLUSIONS: Using FFF beams in IMRT and VMAT is feasible for the treatment of sinonasal cancer. Our results suggest that the delivery mode of FFF beams may play an encouraging role with better sparing of contralateral optic OARs and treatment efficiency in IMRT, but yield comparable results in VMAT.

A simple optimization approach for improving target dose homogeneity in intensity-modulated radiotherapy for sinonasal cancer.

Homogeneous target dose distribution in intensity-modulated radiotherapy (IMRT) for sinonasal cancer (SNC) is challenging to achieve. To solve this problem, we established and evaluated a basal-dose-compensation (BDC) optimization approach, in which the treatment plan is further optimized based on the initial plans. Generally acceptable initial IMRT plans for thirteen patients were created and further optimized individually by (1) the BDC approach and (2) a local-dose-control (LDC) approach, in which the initial plan is further optimized by addressing hot and cold spots. We compared the plan qualities, total planning time and monitor units (MUs) among the initial, BDC, LDC IMRT plans and volumetric modulated arc therapy (VMAT) plans. The BDC approach provided significantly superior dose homogeneity/conformity by 23%-48%/6%-9% compared with both the initial and LDC IMRT plans, as well as reduced doses to the organs at risk (OARs) by up to 18%, with acceptable MU numbers. Compared with VMAT, BDC IMRT yielded superior homogeneity, inferior conformity and comparable overall OAR sparing. The planning of BDC, LDC IMRT and VMAT required 30, 59 and 58 minutes on average, respectively. Our results indicated that the BDC optimization approach can achieve significantly better dose distributions with shorter planning time in the IMRT for SNC.

Volumetric modulated arc therapy vs. c-IMRT for the treatment of upper thoracic esophageal cancer.

OBJECTIVE: To compare plans using volumetric-modulated arc therapy (VMAT) with conventional sliding window intensity-modulated radiation therapy (c-IMRT) to treat upper thoracic esophageal cancer (EC). METHODS: CT datasets of 11 patients with upper thoracic EC were identified. Four plans were generated for each patient: c-IMRT with 5 fields (5F) and VMAT with a single arc (1A), two arcs (2A), or three arcs (3A). The prescribed doses were 64 Gy/32 F for the primary tumor (PTV64). The dose-volume histogram data, the number of monitoring units (MUs) and the treatment time (TT) for the different plans were compared. RESULTS: All of the plans generated similar dose distributions for PTVs and organs at risk (OARs), except that the 2A- and 3A-VMAT plans yielded a significantly higher conformity index (CI) than the c-IMRT plan. The CI of the PTV64 was improved by increasing the number of arcs in the VMAT plans. The maximum spinal cord dose and the planning risk volume of the spinal cord dose for the two techniques were similar. The 2A- and 3A-VMAT plans yielded lower mean lung doses and heart V50 values than the c-IMRT. The V20 and V30 for the lungs in all of the VMAT plans were lower than those in the c-IMRT plan, at the expense of increasing V5, V10 and V13. The VMAT plan resulted in significant reductions in MUs and TT. CONCLUSION: The 2A-VMAT plan appeared to spare the lungs from moderate-dose irradiation most effectively of all plans, at the expense of increasing the low-dose irradiation volume, and also significantly reduced the number of required MUs and the TT. The CI of the PTVs and the OARs was improved by increasing the arc-number from 1 to 2; however, no significant improvement was observed using the 3A-VMAT, except for an increase in the TT.

Simultaneous modulated accelerated radiation therapy for esophageal cancer: a feasibility study.

AIM: To establish the feasibility of simultaneous modulated accelerated radiation therapy (SMART) in esophageal cancer (EC). METHODS: Computed tomography (CT) datasets of 10 patients with upper or middle thoracic squamous cell EC undergoing chemoradiotherapy were used to generate SMART, conventionally-fractionated three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiation therapy (cf-IMRT) plans, respectively. The gross target volume (GTV) of the esophagus, positive regional lymph nodes (LN), and suspected lymph nodes (LN ±) were contoured for each patient. The clinical target volume (CTV) was delineated with 2-cm longitudinal and 0.5- to 1.0-cm radial margins with respect to the GTV and with 0.5-cm uniform margins for LN and LN(±). For the SMART plans, there were two planning target volumes (PTVs): PTV66 = (GTV + LN) + 0.5 cm and PTV54 = CTV + 0.5 cm. For the 3DCRT and cf-IMRT plans, there was only a single PTV: PTV60 = CTV + 0.5 cm. The prescribed dose for the SMART plans was 66 Gy/30 F to PTV66 and 54 Gy/30 F to PTV54. The dose prescription to the PTV60 for both the 3DCRT and cf-IMRT plans was set to 60 Gy/30 F. All the plans were generated on the Eclipse 10.0 treatment planning system. Fulfillment of the dose criteria for the PTVs received the highest priority, followed by the spinal cord, heart, and lungs. The dose-volume histograms were compared. RESULTS: Clinically acceptable plans were achieved for all the SMART, cf-IMRT, and 3DCRT plans. Compared with the 3DCRT plans, the SMART plans increased the dose delivered to the primary tumor (66 Gy vs 60 Gy), with improved sparing of normal tissues in all patients. The Dmax of the spinal cord, V20 of the lungs, and Dmean and V50 of the heart for the SMART and 3DCRT plans were as follows: 38.5 ± 2.0 vs 44.7 ± 0.8 (P = 0.002), 17.1 ± 4.0 vs 25.8 ± 5.0 (P = 0.000), 14.4 ± 7.5 vs 21.4 ± 11.1 (P = 0.000), and 4.9 ± 3.4 vs 12.9 ± 7.6 (P = 0.000), respectively. In contrast to the cf-IMRT plans, the SMART plans permitted a simultaneous dose escalation (6 Gy) to the primary tumor while demonstrating a significant trend of a lower irradiation dose to all organs at risk except the spinal cord, for which no significant difference was found. CONCLUSION: SMART offers the potential for a 6 Gy simultaneous escalation in the irradiation dose delivered to the primary tumor of EC and improves the sparing of normal tissues.

Effect of beam arrangement on oral cavity dose in external beam radiotherapy of nasopharyngeal carcinoma.

This study compared the oral cavity dose between the routine 7-beam intensity-modulated radiotherapy (IMRT) beam arrangement and 2 other 7-beam IMRT with the conventional radiotherapy beam arrangements in the treatment of nasopharyngeal carcinoma (NPC). Ten NPC patients treated by the 7-beam routine IMRT technique (IMRT-7R) between April 2009 and June 2009 were recruited. Using the same computed tomography data, target information, and dose constraints for all the contoured structures, 2 IMRT plans with alternative beam arrangements (IMRT-7M and IMRT-7P) by avoiding the anterior facial beam and 1 conventional radiotherapy plan (CONRT) were computed using the Pinnacle treatment planning system. Dose-volume histograms were generated for the planning target volumes (PTVs) and oral cavity from which the dose parameters and the conformity index of the PTV were recorded for dosimetric comparisons among the plans with different beam arrangements. The dose distributions to the PTVs were similar among the 3 IMRT beam arrangements, whereas the differences were significant between IMRT-7R and CONRT plans. For the oral cavity dose, the 3 IMRT beam arrangements did not show significant difference. Compared with IMRT-7R, CONRT plan showed a significantly lower mean dose, V30 and V-40, whereas the V-60 was significantly higher. The 2 suggested alternative beam arrangements did not significantly reduce the oral cavity dose. The impact of varying the beam angles in IMRT of NPC did not give noticeable effect on the target and oral cavity. Compared with IMRT, the 2-D conventional radiotherapy irradiated a greater high-dose volume in the oral cavity.

[Dosimetric comparison between intensity-modulated radiotherapy and conformal radiotherapy for upper thoracic esophageal carcinoma].

BACKGROUND AND OBJECTIVE: Treatment planning for radiotherapy of upper thoracic esophageal carcinoma is challenging due to the anatomical features. The difficulty may be resolved by intensity-modulated radiotherapy (IMRT). This study was to compare the dosimetric advantages of IMRT to that of conformal radiotherapy (CRT) for upper thoracic esophageal carcinoma, and to explore the clinical application of IMRT. METHODS: Eleven patients with upper thoracic esophageal carcinoma were enrolled. In addition to the actually used CRT plan, a five-field IMRT plan was generated for each case. The parameters of dose volume histogram for targets and organs at risk were compared between two techniques. RESULTS: For the planning target volume (PTV) of tumor and para-tumor tissues, the mean dose, maximal dose, doses covering 99% and 95% volume were similar in IMRT and CRT plans (P>0.05). However, IMRT plan had a higher conformity index than CRT plan (0.68+/-0.04 vs. 0.46+/-0.11, P<0.01). For the PTV of supraclavicular region, IMRT plan showed a better dose heterogeneity index than CRT plan (1.17+/-0.05 vs. 1.33+/-0.15, P=0.01). IMRT plan had lower maximal dose to the planning risk volume of the spinal cord (44.4 Gy vs. 52.5 Gy, P<0.05) and lower lung volume received dose of 10 Gy or higher [(32+/-6)% vs. (35+/-9)%, P<0.05] than CRT plan. CONCLUSION: For the upper thoracic esophageal carcinoma, IMRT has more conformal distribution of dose and better spinal cord sparing than CRT, and can reduce the volume of lung that received dose of 10 Gy or higher.