Javedan K, Stevens CW, Forster K.

Radiation Oncology,1 H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida, USA. khosrow.javedan@moffitt.org

Abstract

The present work investigated the potential of compensator-based intensity-modulated radiation therapy (CB-IMRT) as an alternative to multileaf collimator (MLC)-based intensity-modulated radiation therapy (IMRT) to treat malignant pleural mesothelioma (MPM) post extrapleural pneumonectomy. Treatment plans for 4 right-sided and 1 left-sided MPM post-surgery cases were generated using a commercial treatment planning system, XIO/CMS (Computerized Medical Systems, St. Louis, MO). We used a 7-gantry-angle arrangement with 6 MV beams to generate these plans. The maximum required field size was 30 x 40 cm. We evaluated IMRT plans with brass compensators (.Decimal, Sanford, FL) by examining isodose distributions, dose-volume histograms, metrics to quantify conformal plan quality, and homogeneity. Quality assurance was performed for one of the compensator plans. Conformal dose distributions were achieved with CB-IMRT for all 5 cases, the average planning target volume (PTV) coverage being 95.1% of the PTV volume receiving the full prescription dose. The average lung V20 (volume of lung receiving 20 Gy) was 1.8%, the mean lung dose was 6.7 Gy, and the average contralateral kidney V15 was 0.6%. The average liver dose V30 was 34.0% for the right-sided cases and 10% for the left-sided case. The average monitor units (MUs) per fraction were 980 MUs for the 45-Gy prescriptions (mean: 50 Gy) and 1083 MUs for the 50-Gy prescriptions (mean: 54 Gy). Post surgery, CB-IMRT for MPM is a feasible IMRT technique for treatment with a single isocenter. Compensator plans achieved dose objectives and were safely delivered on a Siemens Oncor machine (Siemens Medical Solutions, Malvern, PA). These plans showed acceptably conformal dose distributions as confirmed by multiple measurement techniques. Not all linear accelerators can deliver large-field MLC-based IMRT, but most can deliver a maximum conformal field of 40 x 40 cm. It is possible and reasonable to deliver IMRT with compensators for fields this size with most conventional linear accelerators.

Gaspar LE, Ding M.

University of Colorado Denver, Department of Radiation Oncology, Campus Mail Stop F-706, 1665 North Ursula Street, Suite 1032, P.O. Box 6510, Aurora, CO 80045, USA. Laurie.Gaspar@uchsc.edu

Abstract

Intensity-modulated radiation therapy (IMRT) is a sophisticated form of three-dimensional treatment planning and delivery. In some situations, IMRT allows more conformal radiation therapy to complex targets within the lung. As problems related to organ motion are increasingly addressed, the use of IMRT in the treatment of lung cancer, particularly in non-small cell lung cancer and mesothelioma, continues to rise.

Jang SY, Liu HH, Mohan R.

Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX.

Abstract

Purpose: To investigate potential dose calculation errors in the low-dose regions and identify causes of such errors for intensity-modulated radiotherapy (IMRT).

Methods and Materials: The IMRT treatment plans of 23 patients with lung cancer and mesothelioma were reviewed. Of these patients, 15 had severe pulmonary complications after radiotherapy. Two commercial treatment-planning systems (TPSs) and a Monte Carlo system were used to calculate and compare dose distributions and dose-volume parameters of the target volumes and critical structures. The effect of tissue heterogeneity, multileaf collimator (MLC) modeling, beam modeling, and other factors that could contribute to the differences in IMRT dose calculations were analyzed.

Results: In the commercial TPS-generated IMRT plans, dose calculation errors primarily occurred in the low-dose regions of IMRT plans (<50% of the radiation dose prescribed for the tumor). Although errors in the dose-volume histograms of the normal lung were small (<5%) above 10 Gy, underestimation of dose <10 Gy was found to be up to 25% in patients with mesothelioma or large target volumes. These errors were found to be caused by inadequate modeling of MLC transmission and leaf scatter in commercial TPSs. The degree of low-dose errors depends on the target volumes and the degree of intensity modulation.

Conclusions: Secondary radiation from MLCs contributes a significant portion of low dose in IMRT plans. Dose underestimation could occur in conventional IMRT dose calculations if such low-dose radiation is not properly accounted for.

Miles EF, Larrier NA, Kelsey CR, Hubbs JL, Ma J, Yoo S, Marks LB.

Department of Radiation Oncology, Duke University Medical Center, Durham, NC.

Abstract

Purpose: To assess the safety and efficacy of intensity-modulated radiotherapy (IMRT) after extrapleural pneumonectomy for malignant pleural mesothelioma.

Methods and Materials: Thirteen patients underwent IMRT after extrapleural pneumonectomy between July 2005 and February 2007 at Duke University Medical Center. The clinical target volume was defined as the entire ipsilateral hemithorax, chest wall incisions, including drain sites, and involved nodal stations. The dose prescribed to the planning target volume was 40–55 Gy (median, 45). Toxicity was graded using the modified Common Toxicity Criteria, and the lung dosimetric parameters from the subgroups with and without pneumonitis were compared. Local control and survival were assessed.

Results: The median follow-up after IMRT was 9.5 months. Of the 13 patients, 3 (23%) developed Grade 2 or greater acute pulmonary toxicity (during or within 30 days of IMRT). The median dosimetric parameters for those with and without symptomatic pneumonitis were a mean lung dose (MLD) of 7.9 vs. 7.5 Gy (p = 0.40), percentage of lung volume receiving 20 Gy (V20) of 0.2% vs. 2.3% (p = 0.51), and percentage of lung volume receiving 5 Gy (V20) of 92% vs. 66% (p = 0.36). One patient died of fatal pulmonary toxicity. This patient received a greater MLD (11.4 vs. 7.6 Gy) and had a greater V20 (6.9% vs. 1.9%), and V5 (92% vs. 66%) compared with the median of those without fatal pulmonary toxicity. Local and/or distant failure occurred in 6 patients (46%), and 6 patients (46%) were alive without evidence of recurrence at last follow-up.

Conclusions: With limited follow-up, 45-Gy IMRT provides reasonable local control for mesothelioma after extrapleural pneumonectomy. However, treatment-related pulmonary toxicity remains a significant concern. Care should be taken to minimize the dose to the remaining lung to achieve an acceptable therapeutic ratio.

Sterzing F, Sroka-Perez G, Schubert K, Münter MW, Thieke C, Huber P, Debus J, Herfarth KK.

Department of Radiation Oncology, University of Heidelberg, Germany.

Abstract

Purpose: To evaluate the potential of helical tomotherapy in the adjuvant treatment of malignant pleural mesothelioma and compare target homogeneity, conformity and normal tissue dose with step-and-shoot intensity-modulated radiotherapy.

Methods and materials: Ten patients with malignant pleural mesothelioma who had undergone neoadjuvant chemotherapy with cisplatin and permetrexed followed by extrapleural pneumonectomy (EPP) were treated in our department with 54Gy to the hemithorax delivered by step-and-shoot IMRT. A planning comparison was performed by creating radiation plans for helical tomotherapy. The different plans were compared by analysing target homogeneity using the homogeneity indices HI_max and HI_min and target conformity by using the conformity index CI₉₅. To assess target coverage and normal tissue sparing TV₉₀, TV₉₅ and mean and maximum doses were compared.

Results: Both modalities achieved excellent dose distributions while sparing organs at risk. Target coverage and homogeneity could be increased significantly with helical tomotherapy compared with step-and-shoot IMRT. Mean dose to the contralateral lung could be lowered beyond 5Gy.

Conclusions: Our planning study showed that helical tomotherapy is an excellent option for the adjuvant intensity-modulated radiotherapy of MPM. It is capable of improving target coverage and homogeneity.

Keywords: MPM, Mesothelioma, Step-and-shoot IMRT, Helical tomotherapy

Sterzing F, Schubert K, Sroka-Perez G, Kalz J, Debus J, Herfarth K.

Department of Radiation Oncology, University of Heidelberg, INF 400, 69120, Heidelberg, Germany, florian.sterzing@med.uni-heidelberg.de.

Abstract

Background and Purpose: Helical tomotherapy was introduced into clinical routine at the Department of Radiation Oncology, University Hospital of Heidelberg, Germany, in July 2006. This report is intended to describe the experience with the first 150 patients treated with helical tomotherapy. Patient selection, time effort, handling of daily image guidance with megavoltage (MV) CT, and quality of radiation plans shall be assessed.

Patients and Methods: Between July 2006 and May 2007, 150 patients were treated with helical tomotherapy in the University Hospital of Heidelberg. Mean age was 60 years with a minimum of 30 years and a maximum of 85 years. 79 of these patients received radiotherapy as a part of multimodal treatment pre- or postoperatively, 17 patients received treatment as a combined radiochemotherapy. 76% were treated with curative intent. Radiotherapy sites were central nervous system (n = 7), head and neck (n = 28), thoracic (n = 37), abdominal (n = 58) and skeletal system (n = 20). Most common tumor entities were prostate cancer (n = 28), breast cancer (n = 17), gastrointestinal tumors (n = 19), pharyngeal carcinoma (n = 14), lymphoma (n = 13), metastatic disease (bone n = 14, liver n = 6, lung n = 4, lymph node n = 2), sarcoma (n = 8), malignant pleural mesothelioma (n = 5), ovarian cancer treated with whole abdominal irradiation (n = 4), lung cancer (n = 3), skin malignancies (n = 3), chordoma (n = 2), meningioma (n = 2), one ependymoma and one medulloblastoma treated with craniospinal axis irradiation (n = 2), and others (n = 4). Nine patients were treated with single-fraction radiosurgery, nine with image-guided spinal reirradiation, and twelve patients were treated at multiple targets simultaneously. A pretreatment MV-CT scan was performed in 98.2% of the 3,026 fractions applied. After matching with the kilovoltage planning CT, corrections for translations and rotation around longitudinal axis (roll) were done.

Results: Mean time on table was 24.8 min for the mentioned tumor entities with fractionated radiation, mean treatment time 10.7 min. Mean correction vector after MV-CT registration was 6.9 mm. With helical tomotherapy it was possible to achieve highly conformal dose distributions for targets of all sizes and multiple targets within one procedure. Image guidance with MV-CT allowed daily position correction and safe and precise treatment application. This was feasible even if the desired immobilization was not possible due to obesity, claustrophobia, pain, or neurologic or orthopedic impairment.

Conclusion: Helical tomotherapy and daily image guidance with MV-CT could fast be introduced into daily clinical routine. This technique allows precise intensity-modulated radiotherapy (IMRT) in standard cases and offers new treatment options in a huge variety of difficult cases.

Keywords: Helical tomotherapy – IMRT – IGRT – Megavoltage CT

Kantor G, Mahé MA, Giraud P; et les contributeurs des protocoles, Alapetite C, Durdux C, Fourquet A, Gardner M, Le Prisé E, Maire JP, Richaud P, Vendrely V, Caron J, Dejean C, Lisbona A, Munos C, Zefkili S, Mazal A.

Service de radiothérapie, institut Bergonié, 229, cours de l’Argonne, 33076 Bordeaux cedex, France.

Abstract

After a request for proposal initiated by National Institute against cancer (INCa) in 2005, three French centers in France started tomotherapy in the first semester of 2007. A national policy of evaluation was performed to study the feasibility of this innovative technique and to compare the interest of helicoidal tomotherapy with other modalities of conformal therapy. Common protocols have been designed to facilitate this evaluation. Description of dose, IMRT levels and constraints are achieved according to each selected indication as: sarcoma, head and neck tumors, lung cancer, mesothelioma, bone metastases, anal carcinoma and craniospinal irradiation.

Keywords: Helicoidal tomotherapy; Evaluation

Rice DC, Stevens CW, Correa AM, Vaporciyan AA, Tsao A, Forster KM, Walsh GL, Swisher SG, Hofstetter WL, Mehran RJ, Roth JA, Liao Z, Smythe WR.

Department of Thoracic and Cardiovascular Surgery, University of Texas, MD Anderson Cancer Center, Houston, Texas 77030, USA. drice@mdanderson.org

Abstract

Background: Malignant pleural mesothelioma is a locally aggressive tumor that is usually fatal. Extrapleural pneumonectomy (EPP) followed by hemithoracic irradiation has shown promise, but local failure remains a significant problem. To improve local control, we have used intensity-modulated radiation therapy (IMRT) as it allows better dose distribution to regions at risk of recurrence as well as reduced radiation to surrounding organs.

Methods: One hundred consecutive patients underwent EPP. At a median interval of 2.5 months from surgery, 63 patients received IMRT (median dose 45 Gy) with curative intent. Chemotherapy was not routinely administered.

Results: Tumors were right sided in 66 patients (66%) and nonepithelioid in 33 (33%). American Joint Committee on Cancer pathology stage was I in 6 patients (6%), II in 7 (7%), III in 72 (72%), and IV (T4) in 15 (15%). Fifty-four patients (54%) had ipsilateral nodal metastases. Perioperative mortality was 8%. Median overall survival (n = 100) was 10.2 months. For patients who received IMRT (n = 63), median overall and 3-year survival was 14.2 months and 20%. Of these, node-negative patients with epithelioid histology (n = 18) had median and 3-year survival of 28 months and 41%. Distant recurrences occurred in 33 of 61 evaluable patients (54%). Eight patients (13%) had local or regional recurrence, 5 of whom also recurred distally. Only 3 patients (5%) had recurrence within the irradiated field.

Conclusions: Intensity-modulated radiation therapy after EPP results in excellent local control for malignant pleural mesothelioma; however, distant metastases remain a significant problem and limit survival. This provides a strong rationale for combining aggressive local regimens with systemic therapy.

Krayenbuehl J, Oertel S, Davis JB, Ciernik IF.

Department of Radiation Oncology, Zurich University Hospital, Zurich, Switzerland.

Abstract

Purpose: The optimal technique for postoperative radiotherapy (RT) after extrapleural pleuropneumonectomy (EPP) of malignant pleural mesothelioma (MPM) remains debated.

Methods and Materials: The data from 8 right-sided and 9 left-sided consecutive cases of MPM treated with RT after radical EPP were reviewed. Of the 17 patients, 8 had been treated with three-dimensional (3D) conformal RT (3D-CRT) and 9 with intensity-modulated RT (IMRT) with 6-MV photons. The clinical outcome and adverse events were assessed. For comparative planning, each case was replanned with 3D-CRT using photons and electrons or with IMRT. Homogeneity, doses to the organs at risk, and target volume coverage were analyzed.

Results:Both techniques yielded acceptable plans. The dose coverage and homogeneity of IMRT increased by 7.7% for the first planning target volume and 9.7% for the second planning target volume, ensuring ≥95% of the prescribed dose compared with 3D-CRT (p < 0.01). Compared with 3D-CRT, IMRT increased the dose to the contralateral lung, with an increase in the mean lung dose of 7.8 Gy and an increase in the volume receiving 13 Gy and 20 Gy by 20.5% and 7.2%, respectively (p < 0.01). A negligible dose increase to the contralateral kidney and liver was observed. No differences were seen for the spinal cord and ipsilateral kidney. Two adverse events of clinical relevant lung toxicity were observed with IMRT.

Conclusion: Intensity-modulated RT and 3D-CRT are both suitable for adjuvant RT. IMRT improves the planning target volume coverage but delivered greater doses to the organs at risk. Rigid dose constraints for the lung should be respected.

Allen AM, Schofield D, Hacker F, Court LE, Czerminska M.

Department of Radiation Oncology, Dana-Farber Cancer Institute, Brigham and Women’s Hospital, Harvard Medical School, Boston, MA.

Abstract

Purpose: To improve the target coverage and normal tissue sparing of intensity-modulated radiotherapy (IMRT) for mesothelioma after extrapleural pneumonectomy.

Methods and Materials: Thirteen plans from patients previously treated with IMRT for mesothelioma were replanned using a restricted field technique. This technique was novel in two ways. It limited the entrance beams to 200° around the target and three to four beams per case had their field apertures restricted down to the level of the heart or liver to further limit the contralateral lung dose. New constraints were added that included a mean lung dose of <9.5 Gy and volume receiving ≥5 Gy of <55%.

Results: In all cases, the planning target volume coverage was excellent, with an average of 97% coverage of the planning target volume by the target dose. No change was seen in the target coverage with the new technique. The heart, kidneys, and esophagus were all kept under tolerance in all cases. The average mean lung dose, volume receiving ≥20 Gy, and volume receiving ≥5 Gy with the new technique was 6.6 Gy, 3.0%, and 50.8%, respectively, compared with 13.8 Gy, 15%, and 90% with the previous technique (p < 0.0001 for all three comparisons). The maximal value for any case in the cohort was 8.0 Gy, 7.3%, and 57.5% for the mean lung dose, volume receiving ≥20 Gy, and volume receiving ≥5 Gy, respectively.

Conclusion: Restricted field IMRT provides an improved method to deliver IMRT to a complex target after extrapleural pneumonectomy. An upcoming Phase I trial will provide validation of these results.

Keywords: Intensity-modulated radiotherapy, IMRT, Mesothelioma, Optimization