Comparing different NTCP models that predict the incidence of radiation pneumonitis. Normal tissue complication probability

Fatal pneumonitis associated with intensity-modulated radiation therapy for mesothelioma

PURPOSE

To describe the initial experience at Dana-Farber Cancer Institute/Brigham and Women's Hospital with intensity-modulated radiation therapy (IMRT) as adjuvant therapy after extrapleural pneumonectomy (EPP) and adjuvant chemotherapy.

METHODS AND MATERIALS

The medical records of patients treated with IMRT after EPP and adjuvant chemotherapy were retrospectively reviewed. IMRT was given to a dose of 54 Gy to the clinical target volume in 1.8 Gy daily fractions. Treatment was delivered with a dynamic multileaf collimator using a sliding window technique. Eleven of 13 patients received heated intraoperative cisplatin chemotherapy (225 mg/m(2)). Two patients received neoadjuvant intravenous cisplatin/pemetrexed, and 10 patients received adjuvant cisplatin/pemetrexed chemotherapy after EPP but before radiation therapy. All patients received at least 2 cycles of intravenous chemotherapy. The contralateral lung was limited to a V20 (volume of lung receiving 20 Gy or more) of 20% and a mean lung dose (MLD) of 15 Gy. All patients underwent fluorodeoxyglucose positron emission tomography (FDG-PET) for staging, and any FDG-avid areas in the hemithorax were given a simultaneous boost of radiotherapy to 60 Gy. Statistical comparisons were done using two-sided t test.

RESULTS

Thirteen patients were treated with IMRT from December 2004 to September 2005. Six patients developed fatal pneumonitis after treatment. The median time from completion of IMRT to the onset of radiation pneumonitis was 30 days (range 5-57 days). Thirty percent of patients (4 of 13) developed acute Grade 3 nausea and vomiting. One patient developed acute Grade 3 thrombocytopenia. The median V20, MLD, and V5 (volume of lung receiving 5 Gy or more) for the patients who developed pneumonitis was 17.6% (range, 15.3-22.3%), 15.2 Gy (range, 13.3-17 Gy), and 98.6% (range, 81-100%), respectively, as compared with 10.9% (range, 5.5-24.7%) (p = 0.08), 12.9 Gy (range, 8.7-16.9 Gy) (p = 0.07), and 90% (range, 66-98.3%) (p = 0.20), respectively, for the patients who did not develop pneumonitis.

CONCLUSIONS

Intensity-modulated RT treatment for mesothelioma after EPP and adjuvant chemotherapy resulted in a high rate of fatal pneumonitis when standard dose parameters were used. We therefore recommend caution in the utilization of this technique. Our data suggest that with IMRT, metrics such as V5 and MLD should be considered in addition to V20 to determine tolerance levels in future patients.

Impact of geometrical uncertainties on 3D CRT and IMRT dose distributions for lung cancer treatment

PURPOSE

To quantify the effect of set-up errors and respiratory motion on dose distributions for non-small cell lung cancer (NSCLC) treatment.

METHODS AND MATERIALS

Irradiations of 5 NSCLC patients were planned with 3 techniques, two (conformal radiation therapy (CRT) and intensity modulated radiation therapy (IMRT1)) with a homogeneous dose in the planning target volume (PTV) and a third (IMRT2) with dose heterogeneity. Set-up errors were simulated for gross target volume (GTV) and organs at risk (OARs). For the GTV, the respiration was also simulated with a periodical motion around a varying average. Two configurations were studied for the breathing motion, to describe the situations of free-breathing (FB) and respiration-correlated (RC) CT scans, each with 2 amplitudes (5 and 10 mm), thus resulting in 4 scenarios (FB_5, FB_10, RC_5 and RC_10). Five thousand treatment courses were simulated, producing probability distributions for the dosimetric parameters.

RESULTS

For CRT and IMRT1, RC_5, RC_10 and FB_5 were associated with a small degradation of the GTV coverage. IMRT2 with FB_10 showed the largest deterioration of the GTV dosimetric indices, reaching 7% for Dmin at the 95% probability level. Removing the systematic error due to the periodic breathing motion was advantageous for a 10 mm respiration amplitude. The estimated probability of radiation pneumonitis and acute complication for the esophagus showed limited sensitivity to geometrical uncertainties. Dmax in the spinal cord and the parameters predicting the risk of late esophageal toxicity were associated to a probability up to 50% of violating the dose tolerances.

CONCLUSIONS

Simulating the effect of geometrical uncertainties on the individual patient plan should become part of the standard pre-treatment verification procedure.

Changes in pulmonary function after incidental lung irradiation for breast cancer: A prospective study

PURPOSE

The aim of this study was to analyze changes in pulmonary function after radiation therapy (RT) for breast cancer.

METHODS AND MATERIALS

A total of 39 consecutive eligible women, who underwent postoperative irradiation for breast cancer, were entered in the study. Spirometry consisting of forced vital capacity (FVC) and forced expiratory volume in 1 s (FEV1), carbon monoxide diffusing capacity (DLCO), and gammagraphic (ventilation and perfusion) pulmonary function tests (PFT) were performed before RT and 6, 12, and 36 months afterwards. Dose-volume and perfusion-weighted parameters were obtained from 3D dose planning: Percentage of lung volume receiving more than a threshold dose (Vi) and between 2 dose levels (V(i-j)). The impact of clinical and dosimetric parameters on PFT changes (Delta PFT) after RT was evaluated by Pearson correlation coefficients and stepwise lineal regression analysis.

RESULTS

No significant differences on mean PFT basal values (before RT) with respect to age, smoking, or previous chemotherapy (CT) were found. All the PFT decreased at 6 to 12 months. Furthermore FVC, FEV(1), and ventilation recovered almost to their previous values, whereas DLCO and perfusion continued to decrease until 36 months (-3.3% and -6.6%, respectively). Perfusion-weighted and interval-scaled dose-volume parameters (pV(i-j)) showed better correlation with Delta PFT (only Delta perfusion reached statistically significance at 36 months). Multivariate analysis showed a significant relation between pV(10-20) and Delta perfusion at 3 years, with a multiple correlation coefficient of 0.48. There were no significant differences related to age, previous chemotherapy, concurrent tamoxifen and smoking, although a tendency toward more perfusion reduction in older and nonsmoker patients was seen.

CONCLUSIONS

Changes in FVC, FEV1 and ventilation were reversible, but not the perfusion and DLCO. We have not found a conclusive mathematical predictive model, provided that the best model only explained 48% of the variability. We suggest the use of dose-perfused volume and interval-scaled parameters (i.e., pV(10-20)) for further studies.

Characteristics of patients who developed radiation pneumonitis requiring steroid therapy after stereotactic irradiation for lung tumors

BACKGROUND

To find possible risk factors for symptomatic radiation pneumonitis (RP) after stereotactic irradiation (STI) for peripheral non-small cell lung cancer (NSCLC), pre-treatment pulmonary function test and dose volume statistics in patients who developed RP requiring steroid intake were retrospectively compared with statistics of those who did not develop RP.

MATERIALS AND METHODS

From 1996 to 2002, 156 patients with Stage I NSCLC received STI at 5 hospitals in Japan. Of those patients, 12 were medicated with steroids for RP after treatment (RP group). For comparison, 31 patients were randomly selected from the remaining 144 patients who received STI but did not receive steroids (control group).

RESULTS

There were no statistical differences in age, sex, tumor size, performance status, forced expiratory volume in 1 sec (FEV1.0%), or percent vital capacity (%VC) between patients medicated with steroids for RP and those who did not have RP and received no steroids. V20 (%) was 7 to 18% (median 8%) in patients medicated with steroids for RP and 2 to 16% (median 7%) in those who did not have RP. No difference was observed in V20, the biologically effectively dose (BED) at the periphery of the planning target volume, or the dose per fraction between the two groups.

CONCLUSIONS

Pre-treatment pulmonary function test (%VC, FEV1.0%), and dose volume statistics V20, total dose, BED, dose per fraction, peripheral dose) were not predictive of RP requiring steroid intake after STI for stage I NSCLC.

The clinical implementation of respiratory-gated intensity-modulated radiotherapy

The clinical use of respiratory-gated radiotherapy and the application of intensity-modulated radiotherapy (IMRT) are 2 relatively new innovations to the treatment of lung cancer. Respiratory gating can reduce the deleterious effects of intrafraction motion, and IMRT can concurrently increase tumor dose homogeneity and reduce dose to critical structures including the lungs, spinal cord, esophagus, and heart. The aim of this work is to describe the clinical implementation of respiratory-gated IMRT for the treatment of non-small cell lung cancer. Documented clinical procedures were developed to include a tumor motion study, gated CT imaging, IMRT treatment planning, and gated IMRT delivery. Treatment planning procedures for respiratory-gated IMRT including beam arrangements and dose-volume constraints were developed. Quality assurance procedures were designed to quantify both the dosimetric and positional accuracy of respiratory-gated IMRT, including film dosimetry dose measurements and Monte Carlo dose calculations for verification and validation of individual patient treatments. Respiratory-gated IMRT is accepted by both treatment staff and patients. The dosimetric and positional quality assurance test results indicate that respiratory-gated IMRT can be delivered accurately. If carefully implemented, respiratory-gated IMRT is a practical alternative to conventional thoracic radiotherapy. For mobile tumors, respiratory-gated radiotherapy is used as the standard of care at our institution. Due to the increased workload, the choice of IMRT is taken on a case-by-case basis, with approximately half of the non-small cell lung cancer patients receiving respiratory-gated IMRT. We are currently evaluating whether superior tumor coverage and limited normal tissue dosing will lead to improvements in local control and survival in non-small cell lung cancer.

Modeling radiation pneumonitis risk with clinical, dosimetric, and spatial parameters

PURPOSE

To determine the clinical, dosimetric, and spatial parameters that correlate with radiation pneumonitis.

METHODS AND MATERIALS

Patients treated with high-dose radiation for non-small-cell lung cancer with three-dimensional treatment planning were reviewed for clinical information and radiation pneumonitis (RP) events. Three-dimensional treatment plans for 219 eligible patients were recovered. Treatment plan information, including parameters defining tumor position and dose-volume parameters, was extracted from non-heterogeneity-corrected dose distributions. Correlation to RP events was assessed by Spearman's rank correlation coefficient (R). Mathematical models were generated that correlate with RP.

RESULTS

Of 219 patients, 52 required treatment for RP (median interval, 142 days). Tumor location was the most highly correlated parameter on univariate analysis (R = 0.24). Multiple dose-volume parameters were correlated with RP. Models most frequently selected by bootstrap resampling included tumor position, maximum dose, and D35 (minimum dose to the 35% volume receiving the highest doses) (R = 0.28). The most frequently selected two- or three-parameter models outperformed commonly used metrics, including V20 (fractional volume of normal lung receiving >20 Gy) and mean lung dose (R = 0.18).

CONCLUSIONS

Inferior tumor position was highly correlated with pneumonitis events within our population. Models that account for inferior tumor position and dosimetric information, including both high- and low-dose regions (D(35), International Commission on Radiation Units and Measurements maximum dose), risk-stratify patients more accurately than any single dosimetric or clinical parameter.

Dose-volume factors predicting radiation pneumonitis in patients receiving salvage radiotherapy for postlobectomy locoregional recurrent non-small-cell lung cancer

BACKGROUND

The correlation between treatment-related factors and lung toxicity has not been sufficiently evaluated in salvage radiotherapy.

METHODS

Twenty-one patients with recurrent non-small-cell lung cancer (NSCLC) after lobectomy received salvage radiotherapy to a total dose of 46-60 Gy. The effects of radiotherapy parameters on the development of radiation pneumonitis (RP) were examined using dose-volume histograms.

RESULTS

Grade 1 RP was observed in 4, grade 2 in 2, and grade 3 in 1 patient. Patients who developed RP had a significantly higher value in V dose (V13, V20) parameters and mean lung dose (MLD) than those who did not develop RP. Concerning G2 or higher RP, 3 patients who developed > or = G2 RP had a significantly higher value in V20, V13, and MLD than the remaining patients with P values of 0.01, 0.015, and 0.016, respectively. The mean V20, V13, and MLD in these 3 patients were 27%, 29.3%, and 14.8 Gy, respectively, whereas the mean V20, V13, and MLD in the remaining 18 patients were 15.8%, 18.3%, and 8.8 Gy, respectively. Three of 6 patients with a V20 > or = 20% developed > or = G2 RP whereas this did not occur in the remaining patients (P = 0.015). Similarly, 3 of 6 patients with a V13 > or = 23% developed > or = G2 RP whereas this did not occur in the remaining patients (P = 0.015).

CONCLUSIONS

These data suggest that a somewhat lower V dose value or MLD, as compared with the setting of definitive radiotherapy, could be a surrogate for RP in patients undergoing salvage radiotherapy for recurrent NSCLC.

Final toxicity results of a radiation-dose escalation study in patients with non-small-cell lung cancer (NSCLC): predictors for radiation pneumonitis and fibrosis

PURPOSE

We aimed to report the final toxicity results on a radiation-dose escalation trial designed to test a hypothesis that very high doses of radiation could be safely administered to patients with non-small-cell lung cancer (NSCLC) by quantifying the dose-volume toxicity relationship of the lung.

METHODS AND MATERIALS

A total of 109 patients with unresectable or medically inoperable NSCLC were enrolled and treated with radiation-dose escalation (on the basis of predicted normal-lung toxicity) either alone or with neoadjuvant chemotherapy by use of 3D conformal techniques. Eighty-four patients (77%) received more than 69 Gy, the trial was stopped after the dose reached 103 Gy. Estimated median follow-up was 110 months.

RESULTS

There were 17 (14.6%) Grade 2 to 3 pneumonitis and 15 (13.8%) Grade 2 to 3 fibrosis and no Grade 4 to 5 lung toxicity. Multivariate analyses showed them to be (1) not associated with the dose prescribed to the tumor, and (2) significantly (p<0.001) associated with lung-dosimetric parameters such as the mean lung dose (MLD), volume of lung that received at least 20 Gy (V20), and the normal-tissue complication probability (NTCP) of the lung. If cutoffs are 30% for V20, 20 Gy for MLD, and 10% for NTCP, these factors have positive predictive values of 50% to 71% and negative predictive value of 85% to 89%.

CONCLUSIONS

With long-term follow-up for toxicity, we have demonstrated that much higher doses of radiation than are traditionally administered can be safely delivered to a majority of patients with NSCLC. Quantitative lung dose-volume toxicity-based dose escalation can form the basis for individualized high-dose radiation treatment to maximize the therapeutic ratio in these patients.

Multiple fields may offer better esophagus sparing without increased probability of lung toxicity in optimized IMRT of lung tumors

PURPOSE

To evaluate whether increasing numbers of intensity-modulated radiation therapy (IMRT) fields enhance lung-tumor dose without additional predicted toxicity for difficult planning geometries.

METHODS AND MATERIALS

Data from 8 previous three dimensional conformal radiation therapy (3D-CRT) patients with tumors located in various regions of each lung, but with planning target volumes (PTVs) overlapping part of the esophagus, were used as input. Four optimized-beamlet IMRT plans (1 plan that used the 3D-CRT beam arrangement and 3 plans with 3, 5, or 7 axial, but predominantly one-sided, fields) were compared. For IMRT, the equivalent uniform dose (EUD) in the whole PTV was optimized simultaneously with that in a reduced PTV exclusive of the esophagus. Normal-tissue complication probability-based costlets were used for the esophagus, heart, and lung.

RESULTS

Overall, IMRT plans (optimized by use of EUD to judiciously allow relaxed PTV dose homogeneity) result in better minimum PTV isodose surface coverage and better average EUD values than does conformal planning; dose generally increases with the number of fields. Even 7-field plans do not significantly alter normal-lung mean-dose values or lung volumes that receive more than 13, 20, or 30 Gy.

CONCLUSION

Optimized many-field IMRT plans can lead to escalated lung-tumor dose in the special case of esophagus overlapping PTV, without unacceptable alteration in the dose distribution to normal lung.

Intensity-modulated radiotherapy of breast cancer using direct aperture optimization

BACKGROUND AND PURPOSE

To design a clinically reliable and efficient step-and-shoot IMRT delivery technique for the treatment of breast cancer using direct aperture optimization (DAO). Using DAO, segments are created and optimized within the same optimization process.

PATIENTS AND METHODS

The DAO technique implemented in the Pinnacle treatment planning system, which is called direct machine parameter optimization (DMPO), was used to generate IMRT plans for twelve breast cancer patients. The prescribed dose was 50 Gy. Two DMPO plans were generated. The first approach uses DMPO only; the second technique combines DMPO with two predefined segments (DMPO(segm)), having shapes identical to the conventional tangential fields. The weight of these predefined segments is optimized simultaneously with DMPO. The DMPO plans were compared with normal two-step (TS) IMRT, creating segments after optimizing the intensity.

RESULTS

Dose homogeneity within the target volume was 4.8+/-0.6, 4.3+/-0.5 and 3.8+/-0.5 Gy for the TS, DMPO and DMPO(segm) plans, respectively. Comparing the IMRT plans with an idealized dose distribution obtained using only beamlet optimization, the degradation of the dose distribution was less for the DMPO plans compared with the two-step IMRT approach. Furthermore, this degradation was similar for all patients, while for the two-step IMRT approach it was patient specific.

CONCLUSIONS

An efficient step-and-shoot IMRT solution was developed for the treatment of breast cancer using DMPO combined with two predefined segments.

Extracranial Radiosurgery (Stereotactic Body Radiation Therapy) for Oligometastases

Extracranial radiosurgery, also known as stereotactic body radiation therapy (SBRT), is an increasingly used method of treatment of limited cancer metastases located in a variety of organs/sites including the spine, lungs, liver, and other areas in the abdomen and pelvis. The techniques used to perform SBRT were initially modeled after intracranial radiosurgery, although considerable evolution in technique and conduct has occurred for extracranial applications. Unlike intracranial radiosurgery, SBRT requires characterization and accounting for inherent organ movement including breathing motion. Potent dose hypofractionation schedules have been used with SBRT such that the treatment is generally both ablative and convenient. Because the treatment is severely damaging to tissues within and about the target, the volume of adjacent normal tissue must be strictly minimized to avoid toxic late effects. Outcomes in various sites show very high rates of local control with toxicity mostly related to tubular tissues like the airways and bowels. With proper conduct though, SBRT can be an extremely effective treatment option for oligometastases.

Role of gross tumor volume on outcome and of dose parameters on toxicity of patients undergoing chemoradiotherapy for locally advanced non-small cell lung cancer

The aim of this retrospective study was to evaluate the prognostic role of gross tumor volume (GTV) on survival of locally advanced NSCLC patients, regardless of TNM stage, and to analyze whether GTV and other radiotherapy (RT) parameters were important for the development of lung toxicity. Thirty-two patients with locally advanced NSCLC (stage IIIA bulky/IIIB) treated with chemoradiotherapy were retrospectively analyzed. Patients received induction chemotherapy followed by combination treatment (27 patients) or induction chemotherapy followed by RT alone (5 patients). Thoracic RT consisted in 60 Gy, with standard fractionation and was the same for all 32 patients. Dose volume histograms were collected from the 3D treatment plans and GTV, planning target volume, mean lung dose, volume of lung receiving more than 20 Gy or more than 30 Gy were analyzed. Survival was significantly longer in patients with a GTV < 100 cm(3) compared with patients having GTV > 100 cm(3) (p = 0.03). In a multivariate analysis only N-status and GTV were predictors of survival with a risk ratio of 0.51 and 0.62, respectively. Ten patients (31%) developed radiation pneumonitis grade 2 or higher. None of the RT parameters examined correlated significantly with the development of lung toxicity. In locally advanced NSCLC, GTV and N-status play a prognostic role even in patients at the same clinical stage and receiving a combination of chemo- and radiotherapy. This could imply a reassessment of the current staging system in patients with non-resectable NSCLC to better identify those patients who would benefit more from the combined treatment, despite its higher toxicity.

Comparative planning evaluation of intensity-modulatedradiotherapy techniques for complex lung cancer cases

BACKGROUND AND PURPOSE

Lung cancer treatment can be one of the most challenging fields in radiotherapy. The aim of the present study was to compare different modalities of radiation delivery based on a balanced scoring scheme for target coverage and normal tissue avoidance.

PATIENTS AND METHODS

Treatment plans were developed for 15 patients with stage III inoperable non-small cell lung cancer using 3D conformal technique and intensity-modulated radiotherapy (IMRT). Elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate PTV2 and 1cm margin around elective nodes for PTV1 resulting in PTV1 volumes larger than 1000 cm(3) in 13 of the 15 patients. 3D conformal and IMRT plans were generated on a commercial treatment planning system (TheraPlan Plus, Nucletron) with various combinations of beam energies and gantry angles. A 'dose quality factor' (DQF) was introduced to correlate the plan quality with patient specific parameters.

RESULTS

A good correlation was found between the quality of the plans and the overlap between PTV1 and lungs. The patient feature factor (PFF), which is a product of several pertinent characteristics, was introduced to facilitate the choice of a particular technique for a particular patient.

CONCLUSIONS

This approach may allow the evaluation of different treatment options prior to actual planning, subject to validation in larger prospective data sets.

The impact of heterogeneity correction on dosimetric parameters that predict for radiation pneumonitis

PURPOSE

To determine if heterogeneity correction significantly affects commonly measured dosimetric parameters predicting pulmonary toxicity in patients receiving radiation for lung cancer.

METHODS AND MATERIALS

Sixty-eight patients treated for lung cancer were evaluated. The conformal treatment technique mostly employed anteroposterior/posterior-anterior fields and off-cord obliques. The percent total lung volume receiving 20 Gy or higher (V20) and mean lung dose (MLD) were correlated with the incidence of radiation pneumonitis. Parameters from both heterogeneity-corrected and heterogeneity-uncorrected plans were used to assess this risk.

RESULTS

Univariate analysis revealed a significant correlation between the development of radiation pneumonitis and both V20 and MLD. A best-fit line to a plot of V20 from the homogeneous plan against the corresponding V20 heterogeneous value produced a slope of 1.00 and zero offset, indicating no difference between the two parameters. For MLD, a similarly significant correlation is seen between the heterogeneous and homogeneous parameters, indicating a 4% difference when correcting for heterogeneity. A significant correlation was also observed between the MLD and V20 parameters (p < 0.0001).

CONCLUSIONS

A high degree of correlation exists between heterogeneity-corrected and heterogeneity-uncorrected dosimetric parameters for lung and the risk of developing pneumonitis. Either V20 or MLD predicts the pneumonitis risk with similar effect.

Attempts to predict the long-term decrease in lung function due to radiotherapy of non-small cell lung cancer

PURPOSE

To obtain a model which can predict long-term decrease in lung function due to radiation damage from dose-volume data for patients with non-small cell lung cancer.

PATIENTS AND METHODS

27 patients were included, all long-term survivors after radical radiation therapy. For each patient a regression analysis was performed on a post-RT succession of measurements of FEV1 in order to estimate the decrease after 2 years and a standard error (SE) on this regression estimate. The modelling was based on dose-volume histograms (DVH) exported from the treatment planning system, and involved fits of threshold models, a mean lung dose model as well as more complex models based on the relative damaged volume (rdV).

RESULTS

Decreases after 2 years of up to 28% in FEV1 was measured (median 10%), with significant day-to-day variation in FEV1 for the individual patient. The threshold models predicted the long-term decrease in FEV1 well when the SE was interpreted as the uncertainty of the measured decrease. The best threshold value, marginally, was 30 Gy with an R(2) of 0.46. The mean lung dose model did not perform so well. A complex model based on rdV performed better than any of the other models (R(2)=0.52).

CONCLUSION

The long-term decrease in FEV1 could be predicted from a simple dose-volume model when the SE was interpreted as the uncertainty of the measured decrease.

Clinical validation of the LKB model and parameter sets for predicting radiation-induced pneumonitis from breast cancer radiotherapy

The choice of the appropriate model and parameter set in determining the relation between the incidence of radiation pneumonitis and dose distribution in the lung is of great importance, especially in the case of breast radiotherapy where the observed incidence is fairly low. From our previous study based on 150 breast cancer patients, where the fits of dose-volume models to clinical data were estimated (Tsougos et al 2005 Evaluation of dose-response models and parameters predicting radiation induced pneumonitis using clinical data from breast cancer radiotherapy Phys. Med. Biol. 50 3535-54), one could get the impression that the relative seriality is significantly better than the LKB NTCP model. However, the estimation of the different NTCP models was based on their goodness-of-fit on clinical data, using various sets of published parameters from other groups, and this fact may provisionally justify the results. Hence, we sought to investigate further the LKB model, by applying different published parameter sets for the very same group of patients, in order to be able to compare the results. It was shown that, depending on the parameter set applied, the LKB model is able to predict the incidence of radiation pneumonitis with acceptable accuracy, especially when implemented on a sub-group of patients (120) receiving [see text]|EUD higher than 8 Gy. In conclusion, the goodness-of-fit of a certain radiobiological model on a given clinical case is closely related to the selection of the proper scoring criteria and parameter set as well as to the compatibility of the clinical case from which the data were derived.

The use of lung dose-volume histograms in predicting post-radiation pneumonitis after non-conventionally fractionated radiotherapy for thoracic carcinoma

AIMS

To assess the use of lung dose-volume histogram (DVH) parameters (specifically V20Gy) in the prediction of radiation pneumonitis for non-conventional fraction sizes used in the treatment of lung cancer.

MATERIALS AND METHODS

Patients requiring computed tomography planning for thoracic radiotherapy between January 1999 and January 2002 were identified. The patients receiving radical or high-dose palliative radiotherapy had DVH produced routinely during planning. These were retrospectively reviewed and the case notes accessed for additional pre-treatment parameters, demographics and evidence of radiation pneumonitis. The severity of the pneumonitis was then scored using Radiation Therapy Oncology Group criteria. Data were analysed using the SPSS computer program.

RESULTS

One hundred and sixty consecutive patients were reviewed. Ninety patients received hypofractionated treatment (fraction size > 2.5 Gy) and 57 continuous hyperfractionated accelerated radiation therapy (CHART) (fraction size 1.5 Gy). Lung V20Gy values ranged from 3% to 53%, with a median value of 24%. Only six patients reported grade 2, and 16 patients grade 3 pneumonitis. Two patients developed fatal, grade 5 pneumonitis. No correlation between pneumonitis score and V20Gy or other possible predictive factors was found.

CONCLUSION

The 15% grade 2-5 pneumonitis rate we document is at the lower end of the spectrum reported in other studies. This suggests that using published data on limiting V20Gy values to reduce the risk of radiation pneumonitis can be extrapolated to planning treatment with non-conventionally fractionated radiotherapy.

A normal tissue dose response model of dynamic repair processes

A model is presented for serial, critical element complication mechanisms for irradiated volumes from length scales of a few millimetres up to the entire organ. The central element of the model is the description of radiation complication as the failure of a dynamic repair process. The nature of the repair process is seen as reestablishing the structural organization of the tissue, rather than mere replenishment of lost cells. The interactions between the cells, such as migration, involved in the repair process are assumed to have finite ranges, which limits the repair capacity and is the defining property of a finite-sized reconstruction unit. Since the details of the repair processes are largely unknown, the development aims to make the most general assumptions about them. The model employs analogies and methods from thermodynamics and statistical physics. An explicit analytical form of the dose response of the reconstruction unit for total, partial and inhomogeneous irradiation is derived. The use of the model is demonstrated with data from animal spinal cord experiments and clinical data about heart, lung and rectum. The three-parameter model lends a new perspective to the equivalent uniform dose formalism and the established serial and parallel complication models. Its implications for dose optimization are discussed.

Re-Examining the Role of Elective Nodal Irradiation

OBJECTIVE

Elective nodal irradiation (ENI) of regional lymphatics has been a foundational paradigm for radiation oncologists in the treatment of nonsmall-cell lung cancer (NSCLC), but its utility has recently been called into question. This review summarizes the controversies surrounding ENI and reviews the therapeutic options available to treat regional lymphatics in NSCLC.

METHODS

Local failure after conventional radiotherapy (RT) occurs in 40% to 80% of patients fueling the investigation of more aggressive RT regimens. As the dose is increased and accelerated the volume of normal lung tissue treated becomes a limiting factor. Thus elimination of ENI followed by further dose escalation has become a commonly pursued solution. When ENI is excluded, treatment is restricted to clinically positive disease and negative lymph node stations are left untreated.

RESULTS

Radiographic and surgical data suggest our ability to determine the true extent of disease is imperfect and therefore the elimination of ENI likely leaves microscopic NSCLC untreated.

CONCLUSIONS

At our institution we have concluded that the prophylactic treatment of regional lymph nodes is best reserved for patients most likely to achieve local control and are designing treatment protocols including chemotherapy to take advantage of this improvement in local control.

Monte Carlo-based lung cancer treatment planning incorporating PET-defined target volumes

Despite the well-known benefits of positron emission tomography (PET) imaging in lung cancer diagnosis and staging, the poor spatial resolution of PET has limited its use in radiotherapy planning. Methods used for segmenting tumor from normal tissue, such as threshold boundaries using a fraction of the standardized uptake value (SUV), are subject to uncertainties. The issue of respiratory motion in the thorax confounds the problem of accurate target definition. In this work, we evaluate how changing the PET-defined target volume by varying the threshold value in the segmentation process impacts target and normal lung tissue doses. For each of eight lung cancer patients we retrospectively generated multiple PET-target volumes; each target volume corresponds to those voxels with intensities above a given threshold level, defined by a percentage of the maximum voxel intensity. PET-defined targets were compared to those from CT; CT targets comprise a composite volume generated from breath-hold inhale and exhale datasets; the CT dataset therefore also includes the extents of tumor motion. Treatment plans using Monte Carlo dose calculation were generated for all targets; the dose uniformity was approximately 100+/-5% within the internal target volume (ITV) (formed by a uniform 8-mm expansion of the composite gross target volume (GTV)). In all cases differences were observed in the generalized equivalent uniform doses (gEUDs) to the targets and in the mean lung doses (MLDs) and normal tissue complication probabilities (NTCPs) to the normal lung tissues. The magnitudes of the dose differences were found to depend on the target volume, location, and amount of irradiated normal lung tissue, and in many instances were clinically meaningful (greater than a single 2 Gy fraction). For those patients studied, results indicate that accurate dosimetry using PET volumes is highly dependent on accurate target segmentation. Further study with correlation to clinical outcome will be helpful in determining how to apply these various PET and CT volumes in treatment planning, to potentially improve local tumor control and reduce normal tissue toxicities.

Acute esophageal toxicity in non-small cell lung cancer patients after high dose conformal radiotherapy

BACKGROUND AND PURPOSE

To correlate acute esophageal toxicity with dosimetric and clinical parameters for non-small cell lung cancer (NSCLC) patients treated with radiotherapy (RT) alone or with chemo-radiotherapy (CRT).

PATIENTS AND METHODS

We analyzed the data of 156 patients with medically inoperable or locally advanced NSCLC. Seventy-four patients were irradiated with high dose RT only, 45 patients with sequential CRT (Gemicitabine/Cisplatin) and 37 patients with concurrent CRT (Cisplatin daily 6 mg/m(2)). The radiation dose delivered ranged from 49.5 to 94.5 Gy (2.25-2.75 Gy per fraction) with an overall treatment time of 5-6 weeks. For all patients the maximal acute esophageal toxicity (RTOG/EORTC criteria) was scored and related to dose-volume parameters, as well as to clinical and treatment-related parameters. All parameters were tested univariable and multivariable in a binary logistic regression model. The toxicity data of a homogeneous subgroup was fitted to the Lyman-Kutcher-Burman model.

RESULTS

Grade 2 acute esophageal toxicity or higher occurred in 27% (n=42) of the patient population of which nine patients developed grade 3 toxicity and one patient grade 4. All 10 patients with grade>or=3 esophageal toxicity received concurrent CRT. At multivariable analysis, the most significant clinical parameter to predict acute esophageal toxicity was the concurrent use of CRT. The most significant dosimetric parameter was the esophagus volume that received at least 35 Gy. The data of the patients who did not receive concurrent CRT were well described by the Lyman-Kutcher-Burman normal tissue complication probability model. The optimal fit of the data of non-concurrent treated patients to this model was obtained using the following values for the parameters: TD(50)=47 Gy (41-60 Gy), n=0.69 (0.18-6.3) and m=0.36 (0.25-0.55) where the numbers between brackets denote the 95% confidence interval. Acute esophageal toxicity was not significantly increased for patients treated with sequential CRT.

CONCLUSION

Both concurrent CRT and the volume that receives at least 35 Gy were predictors of acute esophageal toxicity.

Radiation pneumonitis and pulmonary fibrosis in non-small-cell lung cancer: pulmonary function, prediction, and prevention

Although radiotherapy improves locoregional control and survival in patients with non-small-cell lung cancer, radiation pneumonitis is a common treatment-related toxicity. Many pulmonary function tests are not significantly altered by pulmonary toxicity of irradiation, but reductions in D(L(CO)), the diffusing capacity of carbon monoxide, are more commonly associated with pneumonitis. Several patient-specific factors (e.g. age, smoking history, tumor location, performance score, gender) and treatment-specific factors (e.g. chemotherapy regimen and dose) have been proposed as potential predictors of the risk of radiation pneumonitis, but these have not been consistently demonstrated across different studies. The risk of radiation pneumonitis also seems to increase as the cumulative dose of radiation to normal lung tissue increases, as measured by dose-volume histograms. However, controversy persists about which dosimetric parameter optimally predicts the risk of radiation pneumonitis, and whether the volume of lung or the dose of radiation is more important. Radiation oncologists ought to consider these dosimetric factors when designing radiation treatment plans for all patients who receive thoracic radiotherapy. Newer radiotherapy techniques and technologies may reduce the exposure of normal lung to irradiation. Several medications have also been evaluated for their ability to reduce radiation pneumonitis in animals and humans, including corticosteroids, amifostine, ACE inhibitors or angiotensin II type 1 receptor blockers, pentoxifylline, melatonin, carvedilol, and manganese superoxide dismutase-plasmid/liposome. Additional research is warranted to determine the efficacy of these medications and identify nonpharmacologic strategies to predict and prevent radiation pneumonitis.

Body Mass Index Predicts the Incidence of Radiation Pneumonitis in Breast Cancer Patients

In patients receiving breast radiotherapy, the risk of radiation pneumonitis has been associated with the volume of irradiated lung, and concomitant methotrexate, paclitaxel, and tamoxifen therapy. Many of the studies of radiation pneumonitis are based on estimates of pulmonary risk using central lung distance that is calculated using two-dimensional techniques. With the treatment of internal mammary nodes and three-dimensional treatment planning for breast cancer becoming increasingly more common, there is a need to further consider the impact of dose-volume metrics in assessing radiation pneumonitis risk. We herein present a case control study assessing the impact of clinical and dose-volume metrics on the development of radiation pneumonitis in patients receiving sequential chemotherapy and local-regional radiotherapy.

Esophagus sparing with IMRT in lung tumor irradiation: An EUD-based optimization technique

PURPOSE

The aim of this study was to evaluate (1) the use of generalized equivalent uniform dose (gEUD) to optimize dose escalation of lung tumors when the esophagus overlaps the planning target volume (PTV) and (2) the potential benefit of further dose escalation in only the part of the PTV that does not overlap the esophagus.

METHODS AND MATERIALS

The treatment-planning computed tomography (CT) scans of patients with primary lung tumors located in different regions of the left and right lung were used for the optimization of beamlet intensity modulated radiation therapy (IMRT) plans. In all cases, the PTV overlapped part of the esophagus. The dose in the PTV was maximized according to 7 different primary cost functions: 2 plans that made use of mean dose (MD) (the reference plan, in which the 95% isodose surface covered the PTV and a second plan that had no constraint on the minimum isodose), 3 plans based on maximizing gEUD for the whole PTV with ever increasing assumptions for tumor aggressiveness, and 2 plans that used different gEUD values in 2 simultaneous, overlapping target volumes (the whole PTV and the PTV minus esophagus). Beam arrangements and NTCP-based costlets for the organs at risk (OARs) were kept identical to the original conformal plan for each case. Regardless of optimization method, the relative ranking of the resulting plans was evaluated in terms of the absence of cold spots within the PTV and the final gEUD computed for the whole PTV.

RESULTS

Because the MD-optimized plans lacked a constraint on minimum PTV coverage, they resulted in cold spots that affected approximately 5% of the PTV volume. When optimizing over the whole PTV volume, gEUD-optimized plans resulted in higher equivalent uniform PTV doses than did the reference plan while still maintaining normal-tissue constraints. However, only under the assumption of extremely aggressive tumors could cold spots in the PTV be avoided. Generally, high-level overall results are obtained when optimization in the whole PTV is also associated with a second simultaneous optimization in the PTV minus overlapping portions of the esophagus.

CONCLUSIONS

Intensity modulated radiation therapy optimizations that utilize gEUD-based cost functions for the PTV and NTCP-based constraints for the OARs result in increased doses to large portions of the PTV in cases where the PTV overlaps the esophagus, while still maintaining (and confining to the overlap region) minimum dose coverage equivalent to the homogeneous PTV optimization cases.

New concepts for phase I trials: evaluating new drugs combined with radiation therapy

The rationale for delivering concomitant chemoradiation is not only to increase tumor cell kill but also to achieve a synergistic effect of chemotherapy and radiation. Combination of chemotherapy and radiotherapy has yielded encouraging results in patients with locally advanced diseases. Our increased knowledge of cancer at the molecular level has transformed our understanding of tumor radiation resistance. Preclinical models have shown that several biologic agents designed to target specifically these molecular processes are radiosensitizing agents. Many of these agents are in the process of clinical evaluation with radiotherapy. The translation of these findings into the clinical setting will be feasible only if early phase I trials demonstrate their safety when combined with ionizing radiation. The combination of new drugs and radiation might not necessarily be equivalent to the toxicity of the new drug plus the usual toxicity of radiation. The doses and schedule to be explored for the new drug might vary from those assessed for the new drug alone. Inappropriate evaluation of a combination regimen can result in unjustified abandonment of a combination, or adoption of a regimen at toxic dose levels because of poor toxicity monitoring. Beside the 'in field' radiation dose-dependent symptoms, 'outside the field' symptoms that are not dose dependent might be identified. Specific and long-term clinical evaluation will be required to identify potentially harmful interactions. It will be necessary to rethink phase I strategies, toxicity endpoints, and trial designs and concepts in order to fully optimize these regimens.

Non-small cell lung cancer therapy-related pulmonary toxicity: an update on radiation pneumonitis and fibrosis

Successful treatment of non-small cell lung cancer requires adequate local and systemic disease control. Although it has been shown to have superior results, high-dose radiation therapy is not a current practice largely because of concerns of normal tissue toxicity. This article reviews and updates the possible mechanism of radiation-induced pneumonitis and fibrosis, their associations with dose intensity, and the role they may play in making treatment decisions. The commonly used clinical terminology and grading systems are summarized. Pneumonitis and fibrosis after 3-dimensional conformal high-dose radiation are reviewed, including recent updates from radiation dose escalation trials. Chemotherapy- and chemoradiation-related lung toxicities are also discussed. Individual susceptibility and potential predictive models are examined; dose and 3-dimensional dosimetric parameters are reviewed along with estimation of normal tissue complication probability and biologic predictive assays. Based on the risk levels of toxicity for each patient, future clinical trials may be designed to maximize individual therapeutic gain.

Pulmonary toxicity associated with the treatment of non-small cell lung cancer and the effects of cytoprotective strategies

Concurrent chemoradiation regimens for the treatment of non-small cell lung cancer have resulted in improved treatment outcomes. However, they are also more toxic. Acute esophagitis and pneumonitis are experienced by a large number of treated patients. Cytoprotective agents are used to reduce treatment-related toxicity. The cytoprotectant amifostine has been shown to reduce some of the toxicity associated with concurrent chemoradiation. Clinical studies of its role in reducing esophagitis and radiation pneumonitis are discussed. Lung irradiation also leads to a reduction in lung diffusion capacity (DLCO). The magnitude of this reduction is related to the volume of lung irradiated as well as to the use and timing of chemotherapy. Concurrent chemoradiation regimens result in a larger reduction in DLCO than radiation alone. Small changes in DLCO can be detected with sensitive pulmonary function tests, but are subclinical. Larger reductions in DLCO correlate with significant clinical symptoms. Preliminary data show that amifostine can significantly decrease the treatment-related reduction in DLCO associated with concurrent chemoradiation (42% v 24%; P = .004). Additional studies are being designed to verify these results and to further define the evolving role of cytoprotection in cancer care.

Use of principal component analysis to evaluate the partial organ tolerance of normal tissues to radiation

PURPOSE

To describe a novel method of analyzing partial volume effects of normal tissues to radiation. With this approach, principal component analysis (PCA) is used to efficiently describe the variance in cumulative dose-volume histogram (cDVH) morphology. The independent features of cDVHs that describe the largest variance are then investigated regarding complication risk.

METHODS AND MATERIALS

Principal component analysis was used to describe the variance in the morphology of normal tissue cDVHs, irrespective of complication, by summarizing the largest source of variation within the first principal component (PC), the next largest in the second PC, and so on. Plots relating the most meaningful PCs were constructed. Ideally, cDVHs associated with a complication would yield PC values that could be easily segregated from cDVHs without a complication. Two data sets were evaluated with this approach: 90 parotid gland cDVHs (36 with complications) and 203 liver cDVHs (19 with complications).

RESULTS

Ninety-four percent and 80% of the variation in cDVH morphology was described with two PCs for the parotid gland and the liver data sets, respectively. Plots of the first and second PC values on a Cartesian plane for both data sets revealed "clusters." For the parotid gland, one cluster contained PCs from parotid gland cDVHs with complications, and the other primarily contained PCs from cDVHs without complications. The first PC value, corresponding to a larger volume treated with 10-60 Gy (2 Gy per fraction), was more likely to be larger in parotid gland cDVHs associated with complications than those without complications. In the plots of PC values of liver cDVHs, whole liver radiation cDVHs were segregated from the other cDVHs. There was a trend for cDVHs with a higher first PC, corresponding to increased volume treated with approximately 10-40 Gy (1.5 Gy b.i.d.), to be associated with increased risk of complication. For partial liver radiation cDVHs there was a trend for cDVHs with a higher first PC, corresponding to an increased volume treated with 5-50 Gy, to be associated with a complication. For each data set, logistic regression modeling revealed that the first PC was significantly associated with a complication developing (p < 0.02).

CONCLUSIONS

Principal component analysis can be used to summarize the variance in parallel normal tissue cDVHs, and it can help segregate cDVHs at high or low risk for complications.

Evaluation of dose–response models and parameters predicting radiation induced pneumonitis using clinical data from breast cancer radiotherapy

The purpose of this work is to evaluate the predictive strength of the relative seriality, parallel and LKB normal tissue complication probability (NTCP) models regarding the incidence of radiation pneumonitis, in a large group of patients following breast cancer radiotherapy, and furthermore, to illustrate statistical methods for examining whether certain published radiobiological parameters are compatible with a clinical treatment methodology and patient group characteristics. The study is based on 150 consecutive patients who received radiation therapy for breast cancer. For each patient, the 3D dose distribution delivered to lung and the clinical treatment outcome were available. Clinical symptoms and radiological findings, along with a patient questionnaire, were used to assess the manifestation of radiation-induced complications. Using this material, different methods of estimating the likelihood of radiation effects were evaluated. This was attempted by analysing patient data based on their full dose distributions and associating the calculated complication rates with the clinical follow-up records. Additionally, the need for an update of the criteria that are being used in the current clinical practice was also examined. The patient material was selected without any conscious bias regarding the radiotherapy treatment technique used. The treatment data of each patient were applied to the relative seriality, LKB and parallel NTCP models, using published parameter sets. Of the 150 patients, 15 experienced radiation-induced pneumonitis (grade 2) according to the radiation pneumonitis scoring criteria used. Of the NTCP models examined, the relative seriality model was able to predict the incidence of radiation pneumonitis with acceptable accuracy, although radiation pneumonitis was developed by only a few patients. In the case of modern breast radiotherapy, radiobiological modelling appears to be very sensitive to model and parameter selection giving clinically acceptable results in certain cases selectively (relative seriality model with Seppenwoolde et al and Gagliardi et al parameter sets). The use of published parameters should be considered as safe only after their examination using local clinical data. The variation of inter-patient radiosensitivity seems to play a significant role in the prediction of such low incidence rate complications. Scoring grades were combined to give stronger evidence of radiation pneumonitis since their differences could not be strictly associated with dose. This obviously reveals a weakness of the scoring related to this endpoint, and implies that the probability of radiation pneumonitis induction may be too low to be statistically analysed with high accuracy, at least with the latest advances of dose delivery in breast radiotherapy.

Pulmonary radiation injury: identification of risk factors associated with regional hypersensitivity

Effective radiation treatment of thoracic tumors is often limited by radiosensitivity of surrounding tissues. Several experimental studies have suggested variations in radiosensitivity of different pulmonary regions. Mice and rat studies in part contradict each other and urge for a more detailed analysis. This study was designed to obtain a more comprehensive insight in radiation injury development, expression, and its regional heterogeneity in lung. The latter is obviously highly critical for optimization of radiotherapy treatment plans and may shed light on the mechanisms of lung dysfunction after irradiation. Six different but volume-equal regions in rat lung were irradiated. Whereas the severity of damage, as seen in histologic analysis, was comparable in all regions, the degree of lung dysfunction, measured as breathing rates, largely varied. During the pneumonitic phase (early: 6-12 weeks), the most sensitive regions contained a substantial part of alveolar lung parenchyma. Also, a trend for hypersensitivity was observed when the heart lay in the irradiation field. In the fibrotic phase (late: 34-38 weeks), lung parenchyma and heart-encompassing regions were the most sensitive. No impact of the heart was observed during the intermediate phase (16-28 weeks). The severity of respiratory dysfunction after partial thoracic irradiation is likely governed by an interaction between pulmonary and cardiac functional deficits. As a repercussion, more severe acute and delayed toxicity should be expected after combined lung and heart irradiation. This should be considered in the process of radiotherapy treatment planning of thoracic malignancies.

Correlation of dosimetric factors and radiation pneumonitis for non-small-cell lung cancer patients in a recently completed dose escalation study

PURPOSE

To determine dosimetric factors for lung, lung subregions, and heart that correlate with radiation pneumonitis (Radiation Therapy Oncology Group Grade 3 or more) in the 78 evaluable patients from a Phase I dose escalation study (1991-2003) of three-dimensional conformal radiation therapy (3D-CRT) of non-small-cell lung cancer.

METHODS AND MATERIALS

There were 10 > or = Grade 3 pneumonitis cases within 6 months after treatment. Dose-volume factors analyzed for univariate correlation with > or = Grade 3 pneumonitis were mean dose (MD), effective uniform dose (d(eff)), normal tissue complication probability (NTCP), parallel model f(dam) and V(D) for 5 < or = D < or = 60 Gy for whole, ipsilateral, contralateral, upper and lower halves of the lungs and heart D05, and mean and maximum doses.

RESULTS

The most significant variables (0.005 < p < 0.006) were ipsilateral lung V(D) for D < 20 Gy. Also significant (p < 0.05) for ipsilateral lung were V(D) for D < 50 Gy, MD, f(dam) and d(eff); for total lung V(D) (D < 50 Gy), MD, f(dam), d(eff) and NTCP; for lower lung V(D) (D < 60 Gy), MD, f(dam) and d(eff). All variables for upper and contralateral lung were insignificant, as were heart variables.

CONCLUSIONS

Previously reported correlations between severe pneumonitis and whole lung V13 and with other dose-volume factors of total lung and lower lung are confirmed. The most significant correlations were for (V05-V13) in ipsilateral lung.

Intensity-modulated radiotherapy for lymphoma involving the mediastinum

PURPOSE

To determine the feasibility, potential advantage, and indications for intensity-modulated radiotherapy (IMRT) in the treatment of Hodgkin's lymphoma or non-Hodgkin's lymphoma involving excessively large mediastinal disease volumes or requiring repeat RT.

METHODS AND MATERIALS

Sixteen patients with Hodgkin's lymphoma (n = 11) or non-Hodgkin's lymphoma (n = 5) undergoing primary radiotherapy or repeat RT delivered via an IMRT plan were studied. The indications for using an IMRT plan were previous mediastinal RT (n = 5) or extremely large mediastinal treatment volumes (n = 11). For each patient, IMRT, conventional parallel-opposed (AP-PA), and three-dimensional conformal (3D-CRT) plans were designed using 6-MV X-rays to deliver doses ranging from 18 to 45 Gy (median, 36 Gy). The plans were compared with regard to dose-volume parameters. The IMRT/AP-PA and IMRT/3D-CRT ratios were calculated for each parameter.

RESULTS

For all patients, the mean lung dose was reduced using IMRT, on average, by 12% compared with AP-PA and 14% compared with 3D-CRT. The planning target volume coverage was also improved using IMRT compared with AP-PA but was not different from the planning target volume coverage obtained with 3D-CRT.

CONCLUSION

In selected patients with Hodgkin's lymphoma and non-Hodgkin's lymphoma involving the mediastinum, IMRT provides improved planning target volume coverage and reduces pulmonary toxicity parameters. It is feasible for RT of large treatment volumes and allows repeat RT of relapsed disease without exceeding cord tolerance. Additional follow-up is necessary to determine whether improvements in dose delivery affect long-term morbidity and disease control.

Nonsurgical Therapy for Stages I and II Non–Small Cell Lung Cancer

For patients who have stages I and II non-small cell lung cancer (NSCLC) and who are unable or unwilling to undergo surgical resection, nonsurgical treatment modalities have been used with curative intent. Conventionally fractionated radiotherapy has been the mainstay of nonsurgical therapy; however, advances in technology and the clinical application of radiobiologic principles have allowed more accurately targeted treatment that delivers higher effective doses to the tumor, while respecting the tolerance of surrounding normal tissues. This article discusses nonsurgical approaches to the treatment of early-stage NSCLC, including several promising techniques, such as radiation dose escalation, altered radiation fractionation, stereotactic radiotherapy, and radiofrequency ablation.

Bases génétiques de la radiosensibilité des cancers du sein

Local-regional radiation therapy is one of the major therapeutic means in the management of breast cancer. Three questions however arise from the important advances achieved in this domain in the past years. The first question concerns the possibilities to identify and overcome the radioresistance of a subset of tumours. The second question is how to recognize women likely to benefit from adjuvant radiation therapy, and therefore to diminish treatment indications in other groups. Finally, the third question is how to identify subjects at high risk for long term injury following breast irradiation, in order to adapt techniques and indications in such populations. The major advances of breast cancer molecular genetics in the past years should provide clinicians with tools to answer these important questions. In this paper, we review the molecular germline (BRCA1, BRCA2, ATM, ...) and somatic (p53, tyrosine kinase receptors, as well as actors of cell cycle, signal transduction, apoptosis, DNA repair ...) main bases of breast cancer radiosensitivity. Recent methods of exploration of the genetic background of both the host and the tumours (gene and protein expression profiles) are also reviewed as major tools of breast cancer management in the next few years.

Fitting late rectal bleeding data using different NTCP models: results from an Italian multi-centric study (AIROPROS0101)

BACKGROUND AND PURPOSE

Recent investigations demonstrated a significant correlation between rectal dose-volume patterns and late rectal toxicity. The reduction of the DVH to a value expressing the probability of complication would be suitable. To fit different normal tissue complication probability (NTCP) models to clinical outcome on late rectal bleeding after external beam radiotherapy (RT) for prostate cancer.

PATIENTS AND METHODS

Rectal dose-volume histograms of the rectum (DVH) and clinical records of 547 prostate cancer patients (pts) pooled from five institutions previously collected and analyzed were considered. All patients were treated in supine position with 3 or 4-field techniques: 123 patients received an ICRU dose between 64 and 70 Gy, 255 patients between 70 and 74 Gy and 169 patients between 74 and 79.2 Gy; 457/547 patients were treated with conformal RT and 203/547 underwent radical prostatectomy before RT. Minimum follow-up was 18 months. Patients were considered as bleeders if showing grade 2/3 late bleeding (slightly modified RTOG/EORTC scoring system) within 18 months after the end of RT. Four NTCP models were considered: (a) the Lyman model with DVH reduced to the equivalent uniform dose (LEUD, coincident with the classical Lyman-Kutcher-Burman, LKB, model), (b) logistic with DVH reduced to EUD (LOGEUD), (c) Poisson coupled to EUD reduction scheme and (d) relative seriality (RS). The parameters for the different models were fit to the patient data using a maximum likelihood analysis. The 68% confidence intervals (CI) of each parameter were also derived.

RESULTS

Forty six out of five hundred and forty seven patients experienced grade 2/3 late bleeding: 38/46 developed rectal bleeding within 18 months and were then considered as bleeders The risk of rectal bleeding can be well calculated with a 'smooth' function of EUD (with a seriality parameter n equal to 0.23 (CI 0.05), best fit result). Using LEUD the relationship between EUD and NTCP can be described with a TD50 of 81.9 Gy (CI 1.8 Gy) and a steepness parameter m of 0.19 (CI 0.01); when using LOGEUD, TD50 is 82.2 Gy and k is 7.85. Best fit parameters for RS are s=0.49, gamma=1.69, TD50=83.1 Gy. Qualitative as well as quantitative comparisons (chi-squared statistics, P=0.005) show that the models fit the observed complication rates very well. The results found in the overall population were substantially confirmed in the subgroup of radically treated patients (LEUD: n=0.24 m=0.14 TD50=75.8 Gy). If considering just the grade 3 bleeders (n=9) the best fit is found in correspondence of a n-value around 0.06, suggesting that for severe bleeding the rectum is more serial.

CONCLUSIONS

Different NTCP models fit quite accurately the considered clinical data. The results are consistent with a rectum 'less serial' than previously reported investigations when considering grade 2 bleeding while a more serial behaviour was found for severe bleeding. EUD may be considered as a robust and simple parameter correlated with the risk of late rectal bleeding.

Prediction of radiation-induced normal tissue complications in radiotherapy using functional image data

The aim of this study has been to explicitly include the functional heterogeneity of an organ as a factor that contributes to the probability of complication of normal tissues following radiotherapy. Situations for which the inclusion of this information can be advantageous to the design of treatment plans are then investigated. A Java program has been implemented for this purpose. This makes use of a voxelated model of a patient, which is based on registered anatomical and functional data in order to enable functional voxel weighting. Using this model, the functional dose-volume histogram (fDVH) and the functional normal tissue complication probability (fNTCP) are then introduced as extensions to the conventional dose-volume histogram (DVH) and normal tissue complication probability (NTCP). In the presence of functional heterogeneity, these tools are physically more meaningful for plan evaluation than the traditional indices, as they incorporate additional information and are anticipated to show a better correlation with outcome. New parameters m(f), n(f) and TD(50f) are required to replace the m, n and TD(50) parameters. A range of plausible values was investigated, awaiting fitting of these new parameters to patient outcomes where functional data have been measured. As an example, the model is applied to two lung datasets utilizing accurately registered computed tomography (CT) and single photon emission computed tomography (SPECT) perfusion scans. Assuming a linear perfusion-function relationship, the biological index mean perfusion weighted lung dose (MPWLD) has been extracted from integration over outlined regions of interest. In agreement with the MPWLD ranking, the fNTCP predictions reveal that incorporation of functional imaging in radiotherapy treatment planning is most beneficial for organs with a large volume effect and large focal areas of dysfunction. There is, however, no additional advantage in cases presenting with homogeneous function. Although presented for lung radiotherapy, this model is general. It can also be applied to positron emission tomography (PET)-CT or functional magnetic resonance imaging (fMRI)-CT registered data and extended to the functional description of tumour control probability.

Planning evaluation of radiotherapy for complex lung cancer cases using helical tomotherapy

Lung cancer treatment is one of the most challenging fields in radiotherapy. The aim of the present study was to investigate what role helical tomotherapy (HT), a novel approach to the delivery of highly conformal dose distributions using intensity-modulated radiation fan beams, can play in difficult cases with large target volumes typical for many of these patients. Tomotherapy plans were developed for 15 patients with stage III inoperable non-small-cell lung cancer. While not necessarily clinically indicated, elective nodal irradiation was included for all cases to create the most challenging scenarios with large target volumes. A 2 cm margin was used around the gross tumour volume (GTV) to generate primary planning target volume (PTV2) and 1 cm margin around elective nodes for secondary planning target volume (PTV1) resulting in PTV1 volumes larger than 1000 cm3 in 13 of the 15 patients. Tomotherapy plans were created using an inverse treatment planning system (TomoTherapy Inc.) based on superposition/convolution dose calculation for a fan beam thickness of 25 mm and a pitch factor between 0.3 and 0.8. For comparison, plans were created using an intensity-modulated radiation therapy (IMRT) approach planned on a commercial treatment planning system (TheraplanPlus, Nucletron). Tomotherapy delivery times for the large target volumes were estimated to be between 4 and 19 min. Using a prescribed dose of 60 Gy to PTV2 and 46 Gy to PTV1, the mean lung dose was 23.8+/-4.6 Gy. A 'dose quality factor' was introduced to correlate the plan outcome with patient specific parameters. A good correlation was found between the quality of the HT plans and the IMRT plans with HT being slightly better in most cases. The overlap between lung and PTV was found to be a good indicator of plan quality for HT. The mean lung dose was found to increase by approximately 0.9 Gy per percent overlap volume. Helical tomotherapy planning resulted in highly conformal dose distributions. It allowed easy achievement of two different dose levels in the target simultaneously. As the overlap between PTV and lung volume is a major predictor of mean lung dose, future work will be directed to control of margins. Work is underway to investigate the possibility of breath-hold techniques for tomotherapy delivery to facilitate this aim.

How can we further improve radiotherapy for stage-III non-small-cell lung cancer?

Combined modality treatment in advanced NSCLC has produced some gain in treatment outcome. Local control as addressed by radiotherapy is still a significant site of failure. Doses higher than achieved by conventional conformal radiotherapy are shown to result in better control rates. Volume restriction seems to be the most important issue in dose escalation. Integration of PET imaging into target definition, omission of clinically uninvolved lymph-node areas and measures to decrease set-up and movement uncertainties are explored. Introduction of risk estimation based on dose-volume analysis for dose prescription may further optimise individual treatment.

A challenge to traditional radiation oncology

PURPOSE

To investigate and compare the biologically effective doses, equivalent doses in 2-Gy fractions, log tumor cells killed, and late effects that can be estimated for the large fractions in short overall times that are now being delivered in various clinically used schedules in several countries for the treatment of cancer in human lungs, liver, and kidney.

METHODS AND MATERIALS

Linear quadratic (LQ) modeling is employed with only the standard assumptions that tumor alpha/beta ratio is 10 Gy, pneumonitis and late complication alpha/beta ratios are 3 Gy, that intrinsic radiosensitivity of tumor cells is 0.35 ln/Gy, that no tumor repopulation occurs within 2 weeks, and that LQ modeling is valid up to 23 Gy per fraction. As well as the planning target volume (PTV), we propose a practical term called the prescription isodose volume (PIV) to be used in this discussion. In the ideal case of 100% conformity, PIV equals PTV, but usually PIV is larger than the PTV. Biologically effective doses (BED) in Gy(10) for tumors or Gy(3) for normal lung are calculated and converted to equivalent doses in 2 Gy fractions (= normalized total doses [NTD]), and to estimated log cell kill. How such large biologic doses might be delivered to tissues is discussed.

RESULTS

Tumor cell kill varies between 16 and 27 logs to base 10 for schedules from 4F x 12 Gy to 3F x 23 Gy. The rationale for the high end of this scale is the possible presence of hypoxic or otherwise extraordinarily resistant cells, but how many tumors and which ones require such doses is not known. How can such large doses be tolerated? In "parallel type organs," it is shown to be theoretically possible, provided that suitably small volumes are irradiated, with rapid fall-off of dose outside the PTV, and a mean dose (excluding PTV and allowing for local fraction size) to both lungs of less than 19 Gy NTD. If suitably small PTVs were used, local late BEDs have been given which were as large as 600 Gy(3), equivalent to 2 Gy x 180F = 360 Gy in 2-Gy fractions, with remarkably few complications reported clinically. Questions of concurrent chemotherapy and microscopic extension of lung tumor cells are discussed briefly.

CONCLUSIONS

Such large doses can apparently be given, with suitable precautions and experience. Ongoing clinical trials from an increasing number of centers will be reporting the results of tumor control and complications from this new modality of biologically higher doses.

Regional differences in lung radiosensitivity after radiotherapy for non-small-cell lung cancer

PURPOSE

To study regional differences in lung radiosensitivity by evaluating the incidence of radiation pneumonitis (RP) in relation to regional dose distributions.

METHODS AND MATERIALS

Registered chest CT and single photon emission CT lung perfusion scans were obtained in 106 patients before curative or radical radiotherapy for non-small-cell lung cancer. The mean lung dose (MLD) was calculated. The single photon-emission CT perfusion data were used to weigh the MLD with perfusion, resulting in the mean perfusion-weighted lung dose. In addition, the lungs were geometrically divided into different subvolumes. The mean regional dose (MRD) for each region was calculated and weighted with the perfusion of each region to obtain the mean perfusion-weighted regional dose. RP was defined as respiratory symptoms requiring steroids. The incidence of RP for patients with tumors in a specific subvolume was calculated. The normal tissue complication probability (NTCP) parameter values for the TD(50), and an offset NTCP parameter for tumor location were fitted for both lungs and for each lung subvolume to the observed data using maximum likelihood analysis.

RESULTS

The incidence of RP correlated significantly with the MLD and MRD of the posterior, caudal, ipsilateral, central, and peripheral lung subvolumes (p between 0.05 and 0.002); no correlation was seen for the anterior, cranial, and contralateral regions Similarly, a statistically significant correlation was observed between the incidence of RP and the perfusion-weighted MLD and perfusion-weighted MRD for all regions, except the anterior lung region. For this region, the dose-effect relation improved remarkably after weighting the local dose with the local perfusion. A statistically significant difference (p = 0.01) in the incidence of RP was found between patients with cranial and caudal tumors (11% and 40%, respectively). Therefore, a dose-independent offset NTCP parameter for caudal tumors was included in the NTCP model, improving most correlations significantly, confirming that patients with caudal tumors have a greater probability of developing RP.

CONCLUSION

The incidence of RP correlated significantly with the MLD and MRD of most lung regions, except for the anterior, cranial, and contralateral regions. Weighting the local dose with the local perfusion improved the dose-effect relation for the anterior lung region. Irradiation of caudally located lung tumors resulted in a greater risk of RP than irradiation of tumors located in other parts of the lungs.

Sensitivity of treatment plan optimisation for prostate cancer using the equivalent uniform dose (EUD) with respect to the rectal wall volume parameter

BACKGROUND AND PURPOSE

To analyse the sensitivity of plan optimisation of prostate cancer treatments with respect to changes in the volume parameter (n), when the EUD is used to control the dose in the rectal wall.

PATIENTS AND METHODS

A series of plans was defined, by varying n over a range between 0.08 and 1, and testing different cost functions and beam arrangements. In all cases, the aim was to minimise the EUD in the rectal wall, while ensuring specific dose coverage of the PTV, and limiting the dose in the other OARs. The results were evaluated in terms of 3-D dose distribution and with respect to the current clinical knowledge about late rectal toxicity after irradiation.

RESULTS

Different values of n lead to very similar dose distributions over the PTV (differences in mean dose < 1 Gy, differences in dose given to 99% of the volume < 1%). For the rectal wall, the following observations were made: (a) all cumulative DVH curves crossed each other around 60 Gy; (b) the rectal wall volume receiving doses between 30 and 45 Gy could change by 45 and 30%, respectively, depending on the value of n; (c) for doses higher than 70Gy the differences were typically within 5%. Different values of n also affected the position of isodose surfaces. The distance between the 70 and the 30 Gy isodose curves changed in the AP direction by a factor of 3 when n decreased from 1 to 0.08. High values of n were associated with less dose conformity and a larger volume (at least 20%) of normal tissues receiving 50 Gy or more. All DVHs for the rectal wall were below published dose toxicity thresholds except when the prescribed dose was escalated up to 86 Gy.

CONCLUSIONS

In most cases, the solutions associated with n values up to 0.25 produced similar dose distribution in the rectal wall for doses above 45 Gy, complying with the dose-toxicity thresholds we analysed. The choice of a specific value of n in the optimisation requires an analysis of its effects on the dose distribution for the rectal wall, but also on other aspects, such as the value of the dose to the non-involved normal tissues.

Correlation of gross tumor volume excursion with potential benefits of respiratory gating

PURPOSE

To test the hypothesis that the magnitude of thoracic tumor motion can be used to determine the desirability of respiratory gating.

METHODS AND MATERIALS

Twenty patients to be treated for lung tumors had computed tomography image data sets acquired under assisted breath hold at normal inspiration (100% tidal volume), at full expiration (0% tidal volume), and under free breathing. A radiation oncologist outlined gross tumor volumes (GTVs) on the breath-hold computed tomographic images. These data sets were registered to the free-breathing image data set. Two sets of treatment plans were generated: one based on an internal target volume explicitly formed from assessment of the excursion of the clinical target volume (CTV) through the respiratory cycle, representing an ungated treatment, and the other based on the 0% tidal volume CTV, representing a gated treatment with little margin for residual motion. Dose-volume statistics were correlated to the magnitude of the motion of the center of the GTV during respiration.

RESULTS

Patients whose GTVs were >100 cm(3) showed little decrease in lung dose under gating. The other patients showed a correlation between the excursion of the center of the GTV and a reduction in potential lung toxicity. As residual motion increased, the benefits of respiratory gating increased.

CONCLUSION

Gating seems to be advantageous for patients whose GTVs are <100 cm(3) and for whom the center of the GTV exhibits significant motion, provided residual motion under gating is kept small.

Dose–volume response analyses of late rectal bleeding after radiotherapy for prostate cancer

PURPOSE

To compare the fits of various normal tissue complication probability (NTCP) models to a common set of late rectal toxicity data, with the aim of identifying the best model for predicting late rectal injury after irradiation.

METHODS AND MATERIALS

Late toxicity data from 128 prostate cancer patients treated on protocol with three-dimensional conformal radiotherapy at The University of Texas M.D. Anderson Cancer Center (UTMDACC) were analyzed. The dose-volume histogram for total rectal volume, including contents, was obtained for each patient, and the presence or absence of Grade 2 or worse rectal bleeding within 2 years of treatment was scored. Five different NTCP models were fitted to the data using maximum likelihood analysis: the Lyman model, the mean dose model, a parallel architecture model, and models based on either a cutoff dose or a cutoff volume.

RESULTS

All five of the NTCP models considered provided very similar fits to the UTMDACC rectal bleeding data. In particular, none of the more highly parameterized models (the four-parameter parallel model, three-parameter Lyman model, or three-parameter cutoff dose and volume models) provided a better fit than the simplest of the models, the two-parameter NTCP model describing rectal bleeding as a probit function of mean dose to rectum.

CONCLUSION

No dose-volume response model has yet been identified that provides a better description of the UTMDACC rectal toxicity data than the mean dose model. Because this model has relatively low predictive accuracy, the need to identify a better model remains.

Significance of plasma transforming growth factor-beta levels in radiotherapy for non-small-cell lung cancer

PURPOSE

In dose-escalation studies of radiotherapy (RT) for non-small-cell lung cancer (NSCLC), radiation pneumonitis (RP) is the most important dose-limiting complication. Transforming growth factor-beta1 (TGF-beta1) has been reported to be associated with the incidence of RP. It has been proposed that serial measurements of plasma TGF-beta1 can be valuable to estimate the risk of RP and to decide whether additional dose-escalation can be safely applied. The aim of this study was to evaluate prospectively the time course of TGF-beta1 levels in patients irradiated for NSCLC in relation to the development of RP and dose-volume parameters.

METHODS AND MATERIALS

Plasma samples were obtained in 68 patients irradiated for medically inoperable or locally advanced NSCLC (dose range, 60.8-94.5 Gy) before and 4, 6, and 18 weeks after the start of RT. Plasma TGF-beta1 levels were determined using a bioassay on the basis of TGF-beta1-induced plasminogen activator inhibitor-1 expression in mink lung cells. All patients underwent chest computed tomography scans before RT that were repeated at 18 weeks after RT. The computed tomography data were used to calculate the mean lung dose (MLD) and to score the radiation-induced radiologic changes. RP was defined on the basis of the presence of either radiographic changes or clinical symptoms. Symptomatic RP was scored according to the Common Toxicity Criteria (Grade 1 or worse) and the Southwestern Oncology Group criteria (Grade 2 or worse). Multivariate analyses were performed to investigate which factors (pre- or posttreatment TGF-beta1 level, MLD) were associated with the incidence of RP. To improve our understanding of the time course of TGF-beta1 levels, we performed a multivariate analysis to investigate which factors (pre-RT TGF-beta1 level, MLD, RP) were independently associated with the posttreatment TGF-beta1 levels.

RESULTS

The pre-RT TGF-beta1 levels were increased in patients with NSCLC (median 21 ng/mL, range, 5-103 ng/mL) compared with healthy individuals (range, 4-12 ng/mL). On average, the TGF-beta1 levels normalized toward the end of treatment and remained stable until 18 weeks after RT. In 29 patients, however, TGF-beta1 was increased at the end of RT with respect to the pre-RT value. The multivariate analyses revealed that the MLD was the only variable that correlated significantly with the risk of both radiographic RP (p = 0.05) and symptomatic RP, independent of the scoring system used (p = 0.05 and 0.03 for Southwestern Oncology Group and Common Toxicity Criteria systems, respectively). The TGF-beta1 level at the end of RT was significantly associated with the MLD (p <0.001) and pre-RT TGF-beta1 level (p = 0.001).

CONCLUSION

The MLD correlated significantly with the incidence of both radiographic and symptomatic RP. The results of our study did not confirm the reports that increased levels of TGF-beta1 at the end of RT are an independent additional risk factor for developing symptomatic RP. However, the TGF-beta1 level at the end of a RT was significantly associated with the MLD and the pre-RT level.