Histogram reduction method for calculating complication probabilities for three-dimensional treatment planning evaluations

Treatment plan comparison between helical tomotherapy and MLC-based IMRT using radiobiological measures

The rapid implementation of advanced treatment planning and delivery technologies for radiation therapy has brought new challenges in evaluating the most effective treatment modality. Intensity-modulated radiotherapy (IMRT) using multi-leaf collimators (MLC) and helical tomotherapy (HT) are becoming popular modes of treatment delivery and their application and effectiveness continues to be investigated. Presently, there are several treatment planning systems (TPS) that can generate and optimize IMRT plans based on user-defined objective functions for the internal target volume (ITV) and organs at risk (OAR). However, the radiobiological parameters of the different tumours and normal tissues are typically not taken into account during dose prescription and optimization of a treatment plan or during plan evaluation. The suitability of a treatment plan is typically decided based on dosimetric criteria such as dose-volume histograms (DVH), maximum, minimum, mean and standard deviation of the dose distribution. For a more comprehensive treatment plan evaluation, the biologically effective uniform dose (D) is applied together with the complication-free tumour control probability (P(+)). Its utilization is demonstrated using three clinical cases that were planned with two different forms of IMRT. In this study, three different cancer types at different anatomical sites were investigated: head and neck, lung and prostate cancers. For each cancer type, a linac MLC-based step-and-shoot IMRT plan and a HT plan were developed. The MLC-based IMRT treatment plans were developed on the Philips treatment-planning platform, using the Pinnacle 7.6 software release. For the tomotherapy HiArt plans, the dedicated tomotherapy treatment planning station was used, running version 2.1.2. By using D as the common prescription point of the treatment plans and plotting the tissue response probabilities versus D for a range of prescription doses, a number of plan trials can be compared based on radiobiological measures. The applied plan evaluation method shows that in the head and neck cancer case the HT treatment gives better results than MLC-based IMRT in terms of expected clinical outcome P(+) of 62.2% and 46.0%, D to the ITV of 72.3 Gy and 70.7 Gy, respectively). In the lung cancer and prostate cancer cases, the MLC-based IMRT plans are better over the clinically useful dose prescription range. For the lung cancer case, the HT and MLC-based IMRT plans give a P(+) of 66.9% and 72.9%, D to the ITV of 64.0 Gy and 66.9 Gy, respectively. Similarly, for the prostate cancer case, the two radiation modalities give a P(+) of 68.7% and 72.2%, D to the ITV of 86.0 Gy and 85.9 Gy, respectively. If a higher risk of complications (higher than 5%) could be allowed, the complication-free tumour control could increase by over 40%, 2% and 30% compared to the initial dose prescription for the three cancer cases, respectively. Both MLC-based IMRT and HT can encompass the often-large ITV required while they minimize the volume of the organs at risk receiving high doses. Radiobiological evaluation of treatment plans may provide an improved correlation of the delivered treatment with the clinical outcome by taking into account the dose-response characteristics of the irradiated targets and normal tissues. There may exist clinical cases, which may look dosimetrically similar but in radiobiological terms may be quite different. In such situations, traditional dose-based evaluation tools can be complemented by the use of P(+)--D diagrams to effectively evaluate and compare treatment plans.

Intensity modulated radiation therapy versus three-dimensional conformal radiation therapy for the treatment of high grade glioma: a dosimetric comparison

The present study compared the dosimetry of intensity-modulated radiation therapy (IMRT) and three-dimensional conformal radiation therapy (3D-CRT) techniques in patients treated for high-grade glioma. A total of 20 patients underwent computed tomography treatment planning in conjunction with magnetic resonance imaging fusion. Prescription dose and normal-tissue constraints were identical for the 3D-CRT and IMRT plans. The prescribed dose was 59.4 Gy delivered at 1.8 Gy per fraction using 4-10 MV photons. Normal-tissue dose constraints were 50-54 Gy for the optic chiasm and nerves, and 55-60 Gy for the brainstem. The IMRT plan yielded superior target coverage as compared with the 3D-CRT plan. Specifically, minimum and mean planning target volume cone down doses were 54.52 Gy and 61.74 Gy for IMRT and 50.56 Gy and 60.06 Gy for 3D-CRT (p < or = 0.01). The IMRT plan reduced the percent volume of brainstem receiving a dose greater than 45 Gy by 31% (p = 0.004) and the percent volume of brain receiving a dose greater than 18 Gy, 24 Gy, and 45 Gy by 10% (p = 0.059), 14% (p = 0.015), and 40% (p < or = 0.0001) respectively. With IMRT, the percent volume of optic chiasm receiving more than 45 Gy was also reduced by 30.40% (p = 0.047). As compared with 3D-CRT, IMRT significantly increased the tumor control probability (p < or = 0.005) and lowered the normal-tissue complication probability for brain and brainstem (p < 0.033). Intensity-modulated radiation therapy improved target coverage and reduced radiation dose to the brain, brainstem, and optic chiasm. With the availability of new cancer imaging tools and more effective systemic agents, IMRT may be used to intensify tumor doses while minimizing toxicity, therefore potentially improving outcomes in patients with high-grade glioma.

Normal tissue complication probability modelling of tissue fibrosis following breast radiotherapy

Cosmetic late effects of radiotherapy such as tissue fibrosis are increasingly regarded as being of importance. It is generally considered that the complication probability of a radiotherapy plan is dependent on the dose uniformity, and can be reduced by using better compensation to remove dose hotspots. This work aimed to model the effects of improved dose homogeneity on complication probability. The Lyman and relative seriality NTCP models were fitted to clinical fibrosis data for the breast collated from the literature. Breast outlines were obtained from a commercially available Rando phantom using the Osiris system. Multislice breast treatment plans were produced using a variety of compensation methods. Dose-volume histograms (DVHs) obtained for each treatment plan were reduced to simple numerical parameters using the equivalent uniform dose and effective volume DVH reduction methods. These parameters were input into the models to obtain complication probability predictions. The fitted model parameters were consistent with a parallel tissue architecture. Conventional clinical plans generally showed reducing complication probabilities with increasing compensation sophistication. Extremely homogenous plans representing idealized IMRT treatments showed increased complication probabilities compared to conventional planning methods, as a result of increased dose to areas receiving sub-prescription doses using conventional techniques.

EUCLID: an outcome analysis tool for high-dimensional clinical studies

Treatment management decisions in three-dimensional conformal radiation therapy (3DCRT) and intensity-modulated radiation therapy (IMRT) are usually made based on the dose distributions in the target and surrounding normal tissue. These decisions may include, for example, the choice of one treatment over another and the level of tumour dose escalation. Furthermore, biological predictors such as tumour control probability (TCP) and normal tissue complication probability (NTCP), whose parameters available in the literature are only population-based estimates, are often used to assess and compare plans. However, a number of other clinical, biological and physiological factors also affect the outcome of radiotherapy treatment and are often not considered in the treatment planning and evaluation process. A statistical outcome analysis tool, EUCLID, for direct use by radiation oncologists and medical physicists was developed. The tool builds a mathematical model to predict an outcome probability based on a large number of clinical, biological, physiological and dosimetric factors. EUCLID can first analyse a large set of patients, such as from a clinical trial, to derive regression correlation coefficients between these factors and a given outcome. It can then apply such a model to an individual patient at the time of treatment to derive the probability of that outcome, allowing the physician to individualize the treatment based on medical evidence that encompasses a wide range of factors. The software's flexibility allows the clinicians to explore several avenues to select the best predictors of a given outcome. Its link to record-and-verify systems and data spreadsheets allows for a rapid and practical data collection and manipulation. A wide range of statistical information about the study population, including demographics and correlations between different factors, is available. A large number of one- and two-dimensional plots, histograms and survival curves allow for an easy visual analysis of the population. Several visual and analytical methods are available to quantify the predictive power of the multivariate regression model. The EUCLID tool can be readily integrated with treatment planning and record-and-verify systems.

How does performance of ultrasound tissue typing affect design of prostate IMRT dose-painting protocols?

PURPOSE

To investigate how the performance characteristics of ultrasound tissue typing (UTT) affect the design of a population-based prostate dose-painting protocol.

METHODS AND MATERIALS

The performance of UTT is evaluated using the receiver operating characteristic curve. As the imager's sensitivity increases, more tumors are detected, but the specificity worsens, causing more false-positive results. The UTT tumor map, obtained with a specific sensitivity and specificity setup, was used with the patient's CT image to guide intensity-modulated radiotherapy (IMRT) planning. The optimal escalation dose to the UTT positive region, as well as the safe dose to the negative background, was obtained by maximizing the uncomplicated control (i.e., a combination of tumor control probability and weighted normal tissue complication probability). For high- and low-risk tumors, IMRT plans guided by conventional ultrasound or UTT with a one-dimensional or two-dimensional spectrum analysis technique were compared with an IMRT plan in which the whole prostate was dose escalated.

RESULTS

For all imaging modalities, the specificity of 0.9 was chosen to reduce complications resulting from high false-positive results. If the primary tumors were low risk, the IMRT plans guided by all imaging modalities achieved high tumor control probability and reduced the normal tissue complication probability significantly compared with the plan with whole gland dose escalation. However, if the primary tumors were high risk, the accuracy of the imaging modality was critical to maintain the tumor control probability and normal tissue complication probability at acceptable levels.

CONCLUSION

The performance characteristics of an imager have important implications in dose painting and should be considered in the design of dose-painting protocols.

Individualized image guided iso-NTCP based liver cancer SBRT

A highly individualized stereotactic body radiotherapy (SBRT) strategy was developed to allow a wide spectrum of patients with liver cancer to be treated. This phase I/II study encompasses individualization of immobilization, radiation planning, PTV margin determination, image guidance strategy and prescription dose. Active breathing control breath hold is used to immobilize the liver when feasible. Image guidance strategies include orthogonal MV images and orthogonal kV fluoroscopy using the diaphragm for a surrogate for the liver, and kV cone beam CT using the liver or tumour for guidance. The prescription dose is individualized to maintain the same estimated risk of radiation-induced liver disease (RILD), based on a normal tissue complication probability (NTCP) model, with a maximum permitted dose of 60 Gy in 6 fractions. Since August 2003, 79 patients with hepatocellular carcinoma (33), intrahepatic cholangiocarcinoma (12) and liver metastases (34) were treated. The median tumour volume was 293 cm3 (2.9-3 088 cm3). The median prescribed dose was 36.6 Gy (24.0 Gy-57.0 Gy) in 6 fractions. The median effective liver volume irradiated was 45% (9-80%). Sixty percent of patients were treated with breath hold to immobilize their liver. Intra-fraction reproducibility (sigma) of the liver with repeat breath holds was excellent (1.5 mm); however inter-fraction reproducibility (sigma) was worse (3.4 mm). Image guidance reduced the residual systematic and random setup errors significantly.

The use of spatial dose gradients and probability density function to evaluate the effect of internal organ motion for prostate IMRT treatment planning

The aim of this study is to investigate the effects of internal organ motion on IMRT treatment planning of prostate patients using a spatial dose gradient and probability density function. Spatial dose distributions were generated from a Pinnacle3 planning system using a co-planar, five-field intensity modulated radiation therapy (IMRT) technique. Five plans were created for each patient using equally spaced beams but shifting the angular displacement of the beam by 15 degree increments. Dose profiles taken through the isocentre in anterior-posterior (A-P), right-left (R-L) and superior-inferior (S-I) directions for IMRT plans were analysed by exporting RTOG file data from Pinnacle. The convolution of the 'static' dose distribution D0(x, y, z) and probability density function (PDF), denoted as P(x, y, z), was used to analyse the combined effect of repositioning error and internal organ motion. Organ motion leads to an enlarged beam penumbra. The amount of percentage mean dose deviation (PMDD) depends on the dose gradient and organ motion probability density function. Organ motion dose sensitivity was defined by the rate of change in PMDD with standard deviation of motion PDF and was found to increase with the maximum dose gradient in anterior, posterior, left and right directions. Due to common inferior and superior field borders of the field segments, the sharpest dose gradient will occur in the inferior or both superior and inferior penumbrae. Thus, prostate motion in the S-I direction produces the highest dose difference. The PMDD is within 2.5% when standard deviation is less than 5 mm, but the PMDD is over 2.5% in the inferior direction when standard deviation is higher than 5 mm in the inferior direction. Verification of prostate organ motion in the inferior directions is essential. The margin of the planning target volume (PTV) significantly impacts on the confidence of tumour control probability (TCP) and level of normal tissue complication probability (NTCP). Smaller margins help to reduce the dose to normal tissues, but may compromise the dose coverage of the PTV. Lower rectal NTCP can be achieved by either a smaller margin or a steeper dose gradient between PTV and rectum. With the same DVH control points, the rectum has lower complication in the seven-beam technique used in this study because of the steeper dose gradient between the target volume and rectum. The relationship between dose gradient and rectal complication can be used to evaluate IMRT treatment planning. The dose gradient analysis is a powerful tool to improve IMRT treatment plans and can be used for QA checking of treatment plans for prostate patients.

Relationships between rectal wall dose-volume constraints and radiobiologic indices of toxicity for patients with prostate cancer

PURPOSE

The purpose of this article was to investigate how exceeding specified rectal wall dose-volume constraints impacts on the risk of late rectal bleeding by using radiobiologic calculations.

METHODS AND MATERIALS

Dose-volume histograms (DVH) of the rectal wall of 250 patients with prostate cancer were analyzed. All patients were treated by three-dimensional conformal radiation therapy, receiving mean target doses of 80 Gy. To study the main features of the patient population, the average and the standard deviation of the distribution of DVHs were generated. The mean dose <D>, generalized equivalent uniform dose formulation (gEUD), modified equivalent uniform dose formulation (mEUD)(0), and normal tissue complication probability (NTCP) distributions were also produced. The DVHs set was then binned into eight classes on the basis of the exceeding or the fulfilling of three dose-volume constraints: V(40) = 60%, V(50) = 50%, and V(70) = 25%. Comparisons were made between them by <D>, gEUD, mEUD(0), and NTCP.

RESULTS

The radiobiologic calculations suggest that late rectal toxicity is mostly influenced by V(70). The gEUD and mEUD(0) are risk factors of toxicity always concordant with NTCP, inside each DVH class. The mean dose, although a reliable index, may be misleading in critical situations.

CONCLUSIONS

Both in three-dimensional conformal radiation therapy and particularly in intensity-modulated radiation therapy, it should be known what the relative importance of each specified dose-volume constraint is for each organ at risk. This requires a greater awareness of radiobiologic properties of tissues and radiobiologic indices may help to gradually become aware of this issue.

Incidence of late rectal bleeding in high-dose conformal radiotherapy of prostate cancer using equivalent uniform dose-based and dose-volume-based normal tissue complication probability models

PURPOSE

Accurate modeling of rectal complications based on dose-volume histogram (DVH) data are necessary to allow safe dose escalation in radiotherapy of prostate cancer. We applied different equivalent uniform dose (EUD)-based and dose-volume-based normal tissue complication probability (NTCP) models to rectal wall DVHs and follow-up data for 319 prostate cancer patients to identify the dosimetric factors most predictive for Grade > or = 2 rectal bleeding.

METHODS AND MATERIALS

Data for 319 patients treated at the William Beaumont Hospital with three-dimensional conformal radiotherapy (3D-CRT) under an adaptive radiotherapy protocol were used for this study. The following models were considered: (1) Lyman model and (2) logit-formula with DVH reduced to generalized EUD, (3) serial reconstruction unit (RU) model, (4) Poisson-EUD model, and (5) mean dose- and (6) cutoff dose-logistic regression model. The parameters and their confidence intervals were determined using maximum likelihood estimation.

RESULTS

Of the patients, 51 (16.0%) showed Grade 2 or higher bleeding. As assessed qualitatively and quantitatively, the Lyman- and Logit-EUD, serial RU, and Poisson-EUD model fitted the data very well. Rectal wall mean dose did not correlate to Grade 2 or higher bleeding. For the cutoff dose model, the volume receiving > 73.7 Gy showed most significant correlation to bleeding. However, this model fitted the data more poorly than the EUD-based models.

CONCLUSIONS

Our study clearly confirms a volume effect for late rectal bleeding. This can be described very well by the EUD-like models, of which the serial RU- and Poisson-EUD model can describe the data with only two parameters. Dose-volume-based cutoff-dose models performed worse.

Early clinical and radiological pulmonary complications following breast cancer radiation therapy: NTCP fit with four different models

OBJECTIVE

To fit four different NTCP (Normal Tissue Complication Probability) models to prospectively collected data on short-term pulmonary complications following breast cancer radiotherapy (RT).

MATERIALS/METHODS

Four hundred and seventy-five breast cancer patients, referred to the Radiotherapy Department at Stockholm Söder Hospital (1994-1998) for adjuvant post-operative RT were prospectively followed for pulmonary complications 1, 4 and 7 months after the completion of RT. Eighty-seven patients with complete dose-volume histogram (DVH) of the ipsilateral lung were selected for the present analysis. Mean dose to the ipsilateral lateral lung ranged from 2.5 to 18Gy (median 12Gy). Three different endpoints were considered: (1) clinical pneumonitis scored according to CTC-NCIC criteria: asymptomatic (grade 0) vs grade 1 and grade 2; (2) radiological changes assessed with diagnostic chest X-ray: no/slight radiological changes vs moderate/severe; (3) radiological changes assessed with CT: no/slight vs moderate/severe. Four NTCP models were used: the Lyman model with DVH reduced to the equivalent uniform dose (LEUD), the Logit model with DVH reduced to EUD, the Mean Lung Dose (MLD) model and the Relative Seriality (RS) model. The data fitting procedure was done using the maximum likelihood analysis. The analysis was done on the entire population (n=87) and on a subgroup of patients treated with loco-regional RT (n=44).

RESULTS

24/87 patients (28%) developed clinical pneumonitis; 28/81 patients (35%) had radiological side effects on chest X-rays and 11/75 patients (15%) showed radiological density changes on Computed Tomography (CT). The analysis showed that the risk of clinical pneumonitis was a smooth function of EUD (calculated from DVH using n=0.86+/-0.10, best fit result). With LEUD, the relationship between EUD and NTCP could be described with a D(50) of 16.4Gy+/-1.1Gy and a steepness parameter m of 0.36+/-0.7. The results found in the overall population were substantially confirmed in the subgroup of patients treated with loco-regional RT.

CONCLUSIONS

A large group of prospective patient data (87 pts), including grade 1 pneumonitis, were analysed. The four NTCP models fit quite accurately the considered endpoints. EUD or the mean lung dose are robust and simple parameters correlated with the risk of pneumonitis. For all endpoints the D(50) values ranged in an interval between 10 and 20Gy.

The atlas of complication incidence: a proposal for a new standard for reporting the results of radiotherapy protocols

We present a new method of reporting the results of radiotherapy protocols. The dose-volume atlas of complication incidence is a comprehensive and unbiased summary of the dose-volume exposures and complications occurring in patients after treatment. This new tool provides clear and systematic information about the safety of regions of dose-volume exposure previously treated that can be used when considering new treatments. Actuarial and model-dependent versions of the atlas are described. By using the raw data in the appropriate forms of the atlas, logistic regression, Kaplan-Meier, and Cox proportional hazards analysis can be performed, allowing for the independent calculation of dose-volume response. The data required are simple enough that provided compatible definitions of dose, volume, and complications are used, atlases from different protocols are potentially additive, facilitating the meta-analysis of inter-interinstitutional data. If this method were adopted as a standard for reporting the outcome of treatment protocols, a potentially synergistic increase in the utility of each protocol could result.

Integration of Enhanced Optical Tracking Techniques and Imaging in IGRT

In external beam radiotherapy, modern technologies for dynamic dose delivery and beam conformation provide high selectivity in radiation dose administration to the pathological volume. A comparable accuracy level is needed in the 3-D localization of tumor and organs at risk (OARs), in order to accomplish the planned dose distribution in the reality of each irradiation session. In-room imaging techniques for patient setup verification and tumor targeting may benefit of the combined daily use of optical tracking technologies, supported by techniques for the detection and compensation of organ motion events. Multiple solutions to enhance the use of optical tracking for the on-line correction of target localization uncertainties are described, with specific emphasis on the compensation of setup errors, breathing movements and non-rigid deformations. The final goal is the implementation of customized protocols where appropriate external landmarks, to be tracked in real-time by means of non-invasive optical devices, are selected as a function of inner target localization. The presented methodology features high accuracy in patient setup optimization, also providing a valuable tool for on-line patient surveillance, taking into account both breathing and deformation effects. The methodic application of optical tracking is put forward to represent a reliable and low cost procedure for the reduction of safety margins, once the patient-specific correlation between external landmarks and inner structures has been established. Therefore, the integration of optical tracking with in-room imaging devices is proposed as a way to gain higher confidence in the framework of Image Guided Radiation Therapy (IGRT) treatments.

Novel lung IMRT planning algorithms with nonuniform dose delivery strategy to account for respiratory motion

To effectively deliver radiation dose to lung tumors, respiratory motion has to be considered in treatment planning. In this paper we first present a new lung IMRT planning algorithm, referred as the dose shaping (DS) method, that shapes the dose distribution according to the probability distribution of the tumor over the breathing cycle to account for respiratory motion. In IMRT planning a dose-based convolution method was generally adopted to compensate for random organ motion by performing 4-D dose calculations using a tumor motion probability density function. We modified the CON-DOSE method to a dose volume histogram based convolution method (CON-DVH) that allows nonuniform dose distribution to account for respiratory motion. We implemented the two new planning algorithms on an in-house IMRT planning system that uses the Eclipse (Varian, Palo Alto, CA) planning workstation as the dose calculation engine. The new algorithms were compared with (1) the conventional margin extension approach in which margin is generated based on the extreme positions of the tumor, (2) the dose-based convolution method, and (3) gating with 3 mm residual motion. Dose volume histogram, tumor control probability, normal tissue complication probability, and mean lung dose were calculated and used to evaluate the relative performance of these approaches at the end-exhale phase of the respiratory cycle. We recruited six patients in our treatment planning study. The study demonstrated that the two new methods could significantly reduce the ipsilateral normal lung dose and outperformed the margin extension method and the dose-based convolution method. Compared with the gated approach that has the best performance in the low dose region, the two methods we proposed have similar potential to escalate tumor dose, but could be more efficient because dose is delivered continuously.

Étude comparative et mise en œuvre clinique de deux systèmes de radiothérapie asservie à la respiration : bénéfice dosimétrique pour le traitement du cancer du poumon

Breathing can lead to organ motions up to several centimeters. For radiotherapy of lung, these motions are generally taken into account by adding a specific margin around the target. Thus, treated volumes are often too large to allow for the high-dose values requested for local control. To manage respiratory motion, deep-inspiration breath-hold technique (DIBH) and gated radiotherapy are starting being used clinically. DIBH consists in asking the patient to perform breath-hold during the treatment and the image acquisition, DIBH level being measured by a spirometer. Gated radiotherapy consists in treating the patient at a certain phase of the free breathing. Linac is synchronized with the motion of a marker located on the patient chest. Planning images are obtained by a four-dimensional CT (4D-CT) using the same marker. We have assessed the value of these two methods. For lung treatment, compared to a standard treatment, toxicity reduction was mainly due to the lung total volume increase. It is therefore more significant for breath-hold approach. It is also due to the reduction of safety margins, which is similar for both methods. These two techniques, which have specific advantages and drawbacks, are used routinely at Curie Institute for a large proportion of lung patients, but also for some breast, liver or even Hodgkin disease treatments.

Dosimetric effects of patient rotational setup errors on prostate IMRT treatments

The purpose of this work is to determine dose delivery errors that could result from systematic rotational setup errors (DeltaPhi) for prostate cancer patients treated with three-phase sequential boost IMRT. In order to implement this, different rotational setup errors around three Cartesian axes were simulated for five prostate patients and dosimetric indices, such as dose-volume histogram (DVH), tumour control probability (TCP), normal tissue complication probability (NTCP) and equivalent uniform dose (EUD), were employed to evaluate the corresponding dosimetric influences. Rotational setup errors were simulated by adjusting the gantry, collimator and horizontal couch angles of treatment beams and the dosimetric effects were evaluated by recomputing the dose distributions in the treatment planning system. Our results indicated that, for prostate cancer treatment with the three-phase sequential boost IMRT technique, the rotational setup errors do not have significant dosimetric impacts on the cumulative plan. Even in the worst-case scenario with DeltaPhi=3 degrees, the prostate EUD varied within 1.5% and TCP decreased about 1%. For seminal vesicle, slightly larger influences were observed. However, EUD and TCP changes were still within 2%. The influence on sensitive structures, such as rectum and bladder, is also negligible. This study demonstrates that the rotational setup error degrades the dosimetric coverage of target volume in prostate cancer treatment to a certain degree. However, the degradation was not significant for the three-phase sequential boost prostate IMRT technique and for the margin sizes used in our institution.

Comparison of non-coplanar and coplanar irradiation techniques to treat cancer of the pancreas

We compared two different techniques of pancreatic irradiation using measures associated with normal tissue complications. Seven consecutive patients with pancreatic cancer were planned for both coplanar and non-coplanar (NCP) external beam radiation treatments, using the same defined anatomical volumes for each patient, in each case. Each pair of plans was then compared using a range of objective criteria. Individual normal tissues were assessed against traditional tolerance limits. Selected dose-points, normal tissue complication probability (NTCP) and equivalent uniform doses (EUD) were also compared, as were indices combining information from individual tissues - total NTCP and total weighted EUD. All individual normal tissues doses were within established tolerance limits. For NCP relative to coplanar planning, NTCP and EUD were lower for all individual tissues in four cases and one case, respectively, i.e. in most cases a benefit to one tissue was offset by detriment to others. Summary measures demonstrated overall benefits for NCP techniques, with the total NTCP in six patients, and with the total weighted EUD in all patients. NCP techniques show potentially useful benefits. We present a new objective measure, the total weighted EUD, which may be particularly useful comparing plans where there are multiple critical tissues.

Sphincter-preserving radiation therapy for rectal cancer: a simulation study using three-dimensional computerized technology

BACKGROUND

The acquisition of detailed computerized tomography (CT) imaging at the time of simulation, along with three-dimensional (3D) treatment planning software has been integrated with radiation delivery hardware to create the modality known as 3D conformal radiotherapy (3DXRT). This approach provides, in theory, a means to selectively subtract the anal sphincter from the high-dose field of irradiation in patients with stage II and III adenocarcinomas of the mid-rectum scheduled for low anterior resection (LAR).

HYPOTHESIS

Implementation of 3DXRT with sphincter blocking may be a feasible strategy to reduce the dose of radiation distributed to the anal canal without reduction in the dose distribution to the gross tumour volume (GTV) plus adequate margins.

METHODS

Pretreatment simulation CT scans of 10 patients with rectal cancers located between 5 and 10 cm from the anal verge were retrieved from a computerized database. Radiation oncologists and colorectal surgeons defined the contours of the GTV and the anal sphincter, respectively, on successive CT scan slices. These contours provided the volumetric data required to quantify dose distribution and compute dose-volume histograms. The standard mode of pelvic irradiation planned with CT simulation was compared with a 'virtual CT simulation' approach, in which a sphincter block was added to the protocol.

RESULTS

The mean distance of tumours from the anal verge was 6.3 cm. In the virtual simulation treatment plan, a 2-cm margin separated the sphincter block from the lower limit of the GTV. The mean volume of the anal sphincter was 16.1 +/- 3.5 cm(3). The dose distributed to the GTV in the real plan and in the virtual simulated block plan were 51.7 +/- 1.4 and 51.6 +/- 1.4 Gy respectively (P = 0.85). By comparison the mean dose distributed to the anal sphincter was dramatically reduced by using a sphincter block (33.2 +/- 12 Gy vs 6.4 +/- 4.1 Gy, P < 0.001).

CONCLUSION

During a course of radiotherapy for most low- or mid-rectal cancers, the anal canal is included within the field of irradiation with a mean dose distribution to the sphincter of 33 Gy. Evaluation of 3DXRT with full sphincter block (mid-rectum) and partial sphincter block (distal rectum) is a feasible strategy to decrease the volume of anal sphincter carried to full dose without reduction in dose to the GTV. This approach, by minimizing treatment-induced damage to the anal sphincter, might improve functional outcome of LAR.

Rectal bleeding, fecal incontinence, and high stool frequency after conformal radiotherapy for prostate cancer: normal tissue complication probability modeling

PURPOSE

To analyze whether inclusion of predisposing clinical features in the Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model improves the estimation of late gastrointestinal toxicity.

METHODS AND MATERIALS

This study includes 468 prostate cancer patients participating in a randomized trial comparing 68 with 78 Gy. We fitted the probability of developing late toxicity within 3 years (rectal bleeding, high stool frequency, and fecal incontinence) with the original, and a modified LKB model, in which a clinical feature (e.g., history of abdominal surgery) was taken into account by fitting subset specific TD50s. The ratio of these TD50s is the dose-modifying factor for that clinical feature. Dose distributions of anorectal (bleeding and frequency) and anal wall (fecal incontinence) were used.

RESULTS

The modified LKB model gave significantly better fits than the original LKB model. Patients with a history of abdominal surgery had a lower tolerance to radiation than did patients without previous surgery, with a dose-modifying factor of 1.1 for bleeding and of 2.5 for fecal incontinence. The dose-response curve for bleeding was approximately two times steeper than that for frequency and three times steeper than that for fecal incontinence.

CONCLUSIONS

Inclusion of predisposing clinical features significantly improved the estimation of the NTCP. For patients with a history of abdominal surgery, more severe dose constraints should therefore be used during treatment plan optimization.

Reduction of cardiac and pulmonary complication probabilities after breathing adapted radiotherapy for breast cancer

PURPOSE

Substantial reductions of cardio-pulmonary radiation doses can be achieved using voluntary deep inspiration breath-hold (DIBH) or free breathing inspiration gating (IG) in radiotherapy after conserving surgery for breast cancer. The purpose of this study is to evaluate the radiobiological implications of such dosimetric benefits.

METHODS AND MATERIALS

Patients from previously reported studies were pooled for a total of 33 patients. All patients underwent DIBH and free breathing (FB) scans, and 17 patients underwent an additional IG scan. Tangential conformal treatment plans covering the remaining breast, internal mammary, and periclavicular nodes were optimized for each scan, prescription dose 48 Gy. Normal tissue complication probabilities were calculated using the relative seriality model for the heart, and the model proposed by Burman et al. for the lung.

RESULTS

Previous computed tomography studies showed that both voluntary DIBH and IG provided reduction of the lung V50 (relative volume receiving more than 50% of prescription dose) on the order of 30-40%, and a 80-90% reduction of the heart V50 for left-sided cancers. Corresponding pneumonitis probability of 28.1% (range, 0.7-95.6%) for FB could be reduced to 2.6% (range, 0.1-40.1%) for IG, and 4.3% (range, 0.1-59%) for DIBH. The cardiac mortality probability could be reduced from 4.8% (range, 0.1-23.4%) in FB to 0.5% (range, 0.1-2.6%) for IG and 0.1% (range, 0-3.0%) for DIBH.

CONCLUSIONS

Remarkable potential is shown for simple voluntary DIBH and free breathing IG to reduce the risk of both cardiac mortality and pneumonitis for the common technique of adjuvant tangential breast irradiation.

Fractionated stereotactic radiotherapy for pediatric patients with retinoblastoma

In this report, we discuss the application of a modified Gill‐Thomas‐Cosman (GTC) relocatable head frame to enable fractionated stereotactic radiotherapy (SRT) of infants under anesthesia. This system has been used to treat two infants, ages 12 and 18 months, for bilateral retinoblastoma on a Varian 6/100 linear accelerator. The GTC head frame was used to reproducibly position and treat the orbits of these children to between 2520 cGy and 3960 cGy in 180‐cGy fractions. A standard head and neck tray, with accompanying thermoplastic mask, was adapted to mount to the head frame to enable these treatments. We found the maximum average deviation in the repeat fixations, as compared with the initial fitting data, to be ±2mm. The overall average difference and standard deviation in measurement was 0.47±0.63mm for the first case and 0.19±0.94mm for the second case, with a combined average of 0.35±0.79mm overall from a total of 381 point measurements. The stereotactic treatment plan (Radionics®) incorporated a single isocenter for each orbit and 3 or 4 arcs per isocenter. An intercomparison has been made between this technique and a standard lateral field technique, designed using the stereotactic radiosurgery (SRS) planning system. Dose‐volume histograms and corresponding normal tissue complication probabilities (NTCP) based on pediatric bone growth inhibition have been calculated for each method for the orbital bone areas. We found that the NTCP is reduced from 95% or more in the standard treatment method to 16% or less with SRT. Use of the modified head frame provides excellent setup reproducibility, facilitates access to patients for anesthesia, and reduces the chances of a poor cosmetic result in these growing children.

PACS number: 87.53.Ly

Damage assessment in gastric cancer treatment with adjuvant radiochemotherapy: calculation of the NTCP's from the differential HDV of the organs at risk

OBJECTIVE

To calculate the Normal Tissue Complication Probabilities (NTCP) for the liver, right kidney, left kidney and spinal cord, as well as the global Uncomplicated Tumour Control Probability (UTCP) in gastric cancer patients who underwent a treatment with radiotherapy after radical surgery in our environment.

MATERIAL AND METHOD

In April 2000, a postoperative chemotherapy (QT-RT) protocol started in the province of Malaga for Gastric Adenocarcinomas with postsurgical stage II or higher (pT3-4 and/or pN+). This clinical protocol served as a base for our NTCP and UTCP retrospective theorical study. A virtual simulation and a 3D planning were made in all cases. The differential HDV, selected for each patient were obtained for the 4 organs at risk (OR). Hystograms reduction was made by the Kutcher and Burman's Effective Volume method. NTCP calculations by Lyman's models. The following variables were calculated: maximal dose for each organ (Dmax), Effective Volume (Veff), TD50 (Veff/Vref); NTCP for each organ of the patient; global UTCP for each patient. Differences between the 2 treatment techniques were analysed (2-field versus 4-field technique). For the NTCP calculations the computer application Albireo 1.0(R) was used.

RESULTS

29 patients to assess with an average age of 54 +/- 10 years (range: 38-71); 65.5% men/34.5% women. The technique used was the field technique AP-PA in the 51.7% (15) and with 4 fields in 48.3% (14) of the cases. The global damage is estimated in 16% with a range between 0 and 37%. This goes up to 25% with the 2-field technique, with a wide range between 2 and 48% and it remains reduced to 4%, within a range between 0 and 12% when 4 fields are used. There were significant differences concerning the estimated damage probability (NTCP) on liver, spinal cord and left kidney, depending on the use of two or four fields.

CONCLUSION

NTCP and the global UTCP values of the organs at risk allow to compare a technique net benefit from another in each particular case, although in our theoretical study the comparison was done among the patients. It is important to stress that the calculations of the TCP and NTCP have a limited quantitative signification but they are useful and beneficial in order to decide between treatment plans when they are supported by the clinical knowledge.

A novel radiation therapy technique for malignant pleural mesothelioma combining electrons with intensity-modulated photons

BACKGROUND AND PURPOSE

To investigate the feasibility and potential benefits of combining electron and photon intensity modulated radiotherapy (IMRT) for patients with malignant pleural mesothelioma (MPM).

PATIENTS AND METHODS

The planning CT images of 11 MPM patients, six after extrapleural pneumonectomy (EPP) and five after pleurectomy/decortication (P/D), were used for this study. These cases were planned with photon IMRT alone and photon IMRT combined with electrons (IMRT+e). The latter approach incorporated the electron dose into the inverse planning optimization. The resulting doses to the planning target volume (PTV) and relevant critical structures were compared.

RESULTS

For all patients, the PTV was well covered and doses to critical structures were clinically acceptable for all patients with both techniques. However, IMRT+e exhibited a distinct advantage in reducing the doses to the liver, ipsilateral kidney, contralateral kidney, and heart (P=0.002, 0.003, 0.025, and 0.001, respectively).

CONCLUSIONS

This study showed that IMRT or IMRT+e is a viable treatment modality for MPM patients. Both plans can provide excellent target coverage and normal tissue sparing, but with the addition of electron beams, the critical structures can be further spared. Additional refining of the electron contribution is expected to further reduce radiation-induced morbidity.

Decomposition analysis of differential dose volume histograms

Dose volume histograms are a common tool to assess the value of a treatment plan for various forms of radiation therapy treatment. The purpose of this work is to introduce, validate, and apply a set of tools to analyze differential dose volume histograms by decomposing them into physically and clinically meaningful normal distributions. A weighted sum of the decomposed normal distributions (e.g., weighted dose) is proposed as a new measure of target dose, rather than the more unstable point dose. The method and its theory are presented and validated using simulated distributions. Additional validation is performed by analyzing simple four field box techniques encompassing a predefined target, using different treatment energies inside a water phantom. Furthermore, two clinical situations are analyzed using this methodology to illustrate practical usefulness. A comparison of a treatment plan for a breast patient using a tangential field setup with wedges is compared to a comparable geometry using dose compensators. Finally, a normal tissue complication probability (NTCP) calculation is refined using this decomposition. The NTCP calculation is performed on a liver as organ at risk in a treatment of a mesothelioma patient with involvement of the right lung. The comparison of the wedged breast treatment versus the compensator technique yields comparable classical dose parameters (e.g., conformity index approximately = 1 and equal dose at the ICRU dose point). The methodology proposed here shows a 4% difference in weighted dose outlining the difference in treatment using a single parameter instead of at least two in a classical analysis (e.g., mean dose, and maximal dose, or total dose variance). NTCP-calculations for the mesothelioma case are generated automatically and show a 3% decrease with respect to the classical calculation. The decrease is slightly dependant on the fractionation and on the alpha/beta-value utilized. In conclusion, this method is able to distinguish clinically important differences between treatment plans using a single parameter. This methodology shows promise as an objective tool for analyzing NTCP and doses in larger studies, as the only information needed is the dose volume histogram.

IMRT: Improvement in treatment planning efficiency using NTCP calculation independent of the dose-volume-histogram

The normal tissue complication probability (NTCP) is a predictor of radiobiological effect for organs at risk (OAR). The calculation of the NTCP is based on the dose-volume-histogram (DVH) which is generated by the treatment planning system after calculation of the 3D dose distribution. Including the NTCP in the objective function for intensity modulated radiation therapy (IMRT) plan optimization would make the planning more effective in reducing the postradiation effects. However, doing so would lengthen the total planning time. The purpose of this work is to establish a method for NTCP determination, independent of a DVH calculation, as a quality assurance check and also as a mean of improving the treatment planning efficiency. In the study, the CTs of ten randomly selected prostate patients were used. IMRT optimization was performed with a PINNACLE3 V 6.2b planning system, using planning target volume (PTV) with margins in the range of 2 to 10 mm. The DVH control points of the PTV and OAR were adapted from the prescriptions of Radiation Therapy Oncology Group protocol P-0126 for an escalated prescribed dose of 82 Gy. This paper presents a new model for the determination of the rectal NTCP (R(NTCP)). The method uses a special function, named GVN (from Gy, Volume, NTCP), which describes the R(NTCP) if 1 cm3 of the volume of intersection of the PTV and rectum (R(int)) is irradiated uniformly by a dose of 1 Gy. The function was "geometrically" normalized using a prostate-prostate ratio (PPR) of the patients' prostates. A correction of the R(NTCP) for different prescribed doses, ranging from 70 to 82 Gy, was employed in our model. The argument of the normalized function is the R(int), and parameters are the prescribed dose, prostate volume, PTV margin, and PPR. The R(NTCPs) of another group of patients were calculated by the new method and the resulting difference was < +/- 5% in comparison to the NTCP calculated by the PINNACLE3 software where Kutcher's dose-response model for NTCP calculation is adopted.

A modelling study of the potential influence of low dose hypersensitivity on radiation treatment planning

BACKGROUND AND PURPOSE

Low dose hyper-radiosensitivity (HRS) has been observed in both normal tissues and tumours. This modelling study explores the possible impact of HRS on radiation treatment planning.

PATIENTS AND METHODS

The interplay between volume-effect and HRS was studied in an idealized comparison of partial versus whole organ irradiation. In the further studies, CT scans of three previously scanned patients were used to estimate normal tissue complication probability (NTCP) for the kidneys after a conformal and a conventional treatment plan with and without consideration of HRS.

RESULTS

Idealized treatment plans were compared as pairs of a conventional and a conformal plan both treating the same target volume to the same dose per fraction. Contour maps of the difference in NTCP between paired plans showed a strong dependence on the magnitude of both the volume effect and the HRS effect. For more clinically realistic treatment plans with NTCP calculated for the kidney, the balance between the sparing due to the LQ effect and the increased sensitivity due to the HRS effect was dependent on both the dose distribution and the fractionation.

CONCLUSIONS

HRS may potentially affect radiotherapy treatment planning and the relative importance of HRS is larger in a tissue or organ with a pronounced volume effect. If HRS is expressed in some normal tissues or organs, this could offset much of the sparing predicted by the LQ formalism. However, in some clinical situations the NTCP calculated with correction for HRS may still be lower than the NTCP calculated from the uncorrected physical doses.

Conformity index: a review

We present a critical analysis of the conformity indices described in the literature and an evaluation of their field of application. Three-dimensional conformal radiotherapy, with or without intensity modulation, is based on medical imaging techniques, three-dimensional dosimetry software, compression accessories, and verification procedures. It consists of delineating target volumes and critical healthy tissues to select the best combination of beams. This approach allows better adaptation of the isodose to the tumor volume, while limiting irradiation of healthy tissues. Tools must be developed to evaluate the quality of proposed treatment plans. Dosimetry software provides the dose distribution in each CT section and dose-volume histograms without really indicating the degree of conformity. The conformity index is a complementary tool that attributes a score to a treatment plan or that can compare several treatment plans for the same patient. The future of conformal index in everyday practice therefore remains unclear.

Diffusion tensor imaging: possible implications for radiotherapy treatment planning of patients with high-grade glioma

AIMS

Radiotherapy treatment planning for high-grade gliomas (HGG) is hampered by the inability to image peri-tumoural white-matter infiltration. Diffusion tensor imaging (DTI) is an imaging technique that seems to show white-matter abnormalities resulting from tumour infiltration that cannot be visualised by conventional computed tomography or magnetic resonance imaging (MRI). We propose a new term, the image-based high-risk volume (IHV) for such abnormalities, which are distinct from the gross-tumour volume (GTV). For IHV based on DTI, we use the term IHVDTI. This study assesses the value of DTI for the individualisation of radiotherapy treatment planning for patients with HGG.

METHODS

Seven patients with biopsy-proven HGG were included in a theoretical planning exercise, comparing standard planning techniques with individualised plans based on DTI. Standard plans were generated using a 2.5 cm clinical target volume (CTV) margin added to the GTV. For DTI-based plans, the CTV was generated by adding a 1 cm margin to the IHVDTI. Estimates of normal tissue complication probability (NTCP) were calculated and used to estimate the level of dose escalation that could be achieved using the DTI-based plans.

RESULTS

The use of DTI resulted in non-uniform margins being added to the GTV to encompass areas at high risk of tumour involvement, but, in six out of seven cases, the IHVDTI was encapsulated by the standard CTV margin. In all cases, DTI could be used to reduce the size of the planning-target volume (PTV) (mean 35%, range 18-46%), resulting in escalated doses (mean 67 Gy, range 64-74 Gy), with NTCP levels that matched the conventional treatment plans.

CONCLUSION

DTI can be used to individualise radiotherapy target volumes, and reduction in the CTV permits modest dose escalation without an increase in NTCP. DTI may also be helpful in stratifying patients according to the degree of white-matter infiltration.

Long-term results of high-dose conformal radiotherapy for patients with medically inoperable T1–3N0 non–small-cell lung cancer: Is low incidence of regional failure due to incidental nodal irradiation?

PURPOSE

To report the results of high-dose conformal irradiation and examine incidental nodal irradiation and nodal failure in patients with inoperable early-stage non-small-cell lung cancer (NSCLC).

METHODS AND MATERIALS

This analysis included patients with inoperable CT-staged T1-3N0M0 NSCLC treated on our prospective dose-escalation trial. Patients were treated with radiation alone (total dose, 63-102.9 Gy in 2.1-Gy daily fractions) with a three-dimensional conformal technique without intentional nodal irradiation. Bilateral highest mediastinal and upper/lower paratracheal, prevascular and retrotracheal, sub- and para-aortic, subcarinal, paraesophageal, and ipsilateral hilar regions were delineated individually. Nodal failure and doses of incidental irradiation were studied.

RESULTS

The potential median follow-up was 104 months. For patients who completed protocol treatment, median survival was 31 months. The actuarial overall survival rate was 86%, 61%, 43%, and 21% and the cause-specific survival rate was 89%, 70%, 53%, and 35% at 1, 2, 3, and 5 years, respectively. Weight loss (p = 0.008) and radiation dose in Gy (p = 0.013) were significantly associated with overall survival. In only 22% and 13% of patients examined did ipsilateral hilar and paratracheal (and subaortic for left-sided tumor) nodal regions receive a dose of > or = 40 Gy, respectively. Less than 10% of all other nodal regions received a dose of > or = 40 Gy. No patients failed initially at nodal sites.

CONCLUSIONS

Radiation dose is positively associated with overall survival in patients with medically inoperable T1-3N0 NSCLC, though long-term results remain poor. The nodal failure rate is low and does not seem to be due to high-dose incidental irradiation.

Evaluation of image-guided radiation therapy (IGRT) technologies and their impact on the outcomes of hypofractionated prostate cancer treatments: A radiobiologic analysis

PURPOSE

To quantify the mitigation of geometric uncertainties achieved with the application of various patient setup techniques during the delivery of hypofractionated prostate cancer treatments, using tumor control probability (TCP) and normal tissue complication probability.

METHODS AND MATERIALS

Five prostate cancer patients with approximately 16 treatment CT studies, taken during the course of their radiation therapy (77 total), were analyzed. All patients were planned twice with an 18 MV six-field conformal technique, with 10- and 5-mm margin sizes, with various hypofractionation schedules (5 to 35 fractions). Subsequently, four clinically relevant patient setup techniques (laser guided and image guided) were simulated to deliver such schedules.

RESULTS

As hypothesized, the impact of geometric uncertainties on clinical outcomes increased with more hypofractionated schedules. However, the absolute gain in TCP due to hypofractionation (up to 21.8% increase) was significantly higher compared with the losses due to geometric uncertainties (up to 8.6% decrease).

CONCLUSIONS

The results of this study suggest that, although the impact of geometric uncertainties on the treatment outcomes increases as the number of fractions decrease, the reduction in TCP due to the uncertainties does not significantly offset the expected theoretical gain in TCP by hypofractionation.

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.

Feasibility of using intensity-modulated radiotherapy to improve lung sparing in treatment planning for distal esophageal cancer

BACKGROUND AND PURPOSE

To evaluate the feasibility whether intensity-modulated radiotherapy (IMRT) can be used to reduce doses to normal lung than three-dimensional conformal radiotherapy (3 DCRT) in treating distal esophageal malignancies.

PATIENTS AND METHODS

Ten patient cases with cancer of the distal esophagus were selected for a retrospective treatment-planning study. IMRT plans using four, seven, and nine beams (4B, 7B, and 9B) were developed for each patient and compared with the 3 DCRT plan used clinically. IMRT and 3 DCRT plans were evaluated with respect to PTV coverage and dose-volumes to irradiated normal structures, with statistical comparison made between the two types of plans using the Wilcoxon matched-pair signed-rank test.

RESULTS

IMRT plans (4B, 7B, 9B) reduced total lung volume treated above 10 Gy (V(10)), 20 Gy (V(20)), mean lung dose (MLD), biological effective volume (V(eff)), and lung integral dose (P<0.05). The median absolute improvement with IMRT over 3DCRT was approximately 10% for V(10), 5% for V(20), and 2.5 Gy for MLD. IMRT improved the PTV heterogeneity (P<0.05), yet conformity was better with 7B-9B IMRT plans. No clinically meaningful differences were observed with respect to the irradiated volumes of spinal cord, heart, liver, or total body integral doses.

CONCLUSIONS

Dose-volume of exposed normal lung can be reduced with IMRT, though clinical investigations are warranted to assess IMRT treatment outcome of esophagus cancers.

Biophysical analysis of the acute toxicity of radiotherapy in Hodgkin’s lymphoma—a comparison between extended field and involved field radiotherapy based on the data of the German Hodgkin Study Group

PURPOSE

To determine biophysical parameters from the complication probability data during and after radiotherapy of Hodgkin's lymphoma (HL), based on the number of gastrointestinal side effects that were found in the multicenter HD8 trial of the German Hodgkin Lymphoma Study Group.

METHODS AND MATERIALS

Between 1993 and 1998, 1204 patients with newly diagnosed, histology-proven HL in clinical Stages I/IIA/IIB with defined risk factors and stage IIIA without risk factors were enrolled into the multicenter HD8 study. Patients were randomized to receive two cycles of COPP (cyclophosphamide, vincristine, procarbazine, prednisone) alternating with two cycles of ABVD (doxorubicin, bleomycin, vinblastine, dacarbazine) followed by radiotherapy (RT) of 30 Gy extended field plus 10 Gy to bulky disease (Arm A) or 30 Gy involved field plus 10 Gy to bulky disease (Arm B). For 910 patients, the rates of acute gastrointestinal side effects during and after RT could be determined. Comparison showed differences between Arms A and B (Grade 1-2: 16.6 vs. 3.9; Grade 3-4: 0.9 vs. 0.2; p < 0.001). From the dose-volume histograms for a "standard patient" (volume intestine 2300 cm3), we determined the normal tissue complication probability (NTCP) (V, D, m, n, TD50), the biophysical parameter TD50, and n (volume dependent) in such a manner that the observed NTCP in Arm A in cases of supradiaphragmatic involvement only and in cases of infradiaphragmatic involvement correlated with the calculated values.

RESULTS

Of 1,204 patients randomized, 1,064 patients were informative for the comparison of study arms. The median observation time was 54 months. The overall survival for all eligible patients was 91%, and freedom from treatment failure was 83%. Survival rates at 5 years after start of RT revealed no differences in terms of freedom from treatment failure (85.8% in Arm A, 84.2% in Arm B) and overall survival (90.8% and 92.4%). There were also no differences between the two arms in terms of complete remission, progressive disease, relapse, death, and secondary neoplasias. In contrast, acute side effects, including leukopenia, thrombocytopenia, nausea, gastrointestinal toxicity, and pharyngeal toxicity, were more frequent in the extended field arm. Concerning gastrointestinal toxicity, the different radiation treatment volumes resulted in different NTCPs. On the basis of these findings, values of n = 0.09 and TD50 = 32 Gy were derived. However, this biophysical model is sensitive to variations of the parameters. A deviation of 1% of TD50 results in a deviation of 10% of the NTCP.

CONCLUSION

Radiotherapy volume reduction from extended field to involved field after two cycles of COPP/ABVD chemotherapy gives similar results and less toxicity in patients with early-stage, unfavorable HL. Biophysical parameters could be determined from the complication probability data after RT of HL. Because of the exponential dependence, this biophysical model is unstable. It represents a "start model" until further data can be incorporated.

Concomitant GRID boost for Gamma Knife radiosurgery

We developed an integrated GRID boost technique for Gamma Knife radiosurgery. The technique generates an array of high dose spots within the target volume via a grid of 4-mm shots. These high dose areas were placed over a conventional Gamma Knife plan where a peripheral dose covers the full target volume. The beam weights of the 4-mm shots were optimized iteratively to maximize the integral dose inside the target volume. To investigate the target volume coverage and the dose to the adjacent normal brain tissue for the technique, we compared the GRID boosted treatment plans with conventional Gamma Knife treatment plans using physical and biological indices such as dose-volume histogram (DVH), DVH-derived indices, equivalent uniform dose (EUD), tumor control probabilities (TCP), and normal tissue complication probabilities (NTCP). We found significant increase in the target volume indices such as mean dose (5%-34%; average 14%), TCP (4%-45%; average 21%), and EUD (2%-22%; average 11%) for the GRID boost technique. No significant change in the peripheral dose coverage for the target volume was found per RTOG protocol. In addition, the EUD and the NTCP for the normal brain adjacent to the target (i.e., the near region) were decreased for the GRID boost technique. In conclusion, we demonstrated a new technique for Gamma Knife radiosurgery that can escalate the dose to the target while sparing the adjacent normal brain tissue.

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.

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.

Results of a phase I dose-escalation study using three-dimensional conformal radiotherapy in the treatment of inoperable nonsmall cell lung carcinoma

BACKGROUND

The objective of this study was to report the results of a Phase I dose-escalation study using three-dimensional conformal radiation therapy (3D-CRT) for the treatment of patients with nonsmall cell lung carcinoma (NSCLC).

METHODS

Between 1991 and 2003, 104 patients were enrolled for 3D-CRT at Memorial Sloan-Kettering Cancer Center. The median patient age was 69 years. Twenty-eight percent of patients had Stage I-II NSCLC, 33% of patients had Stage IIIA NSCLC, 32% of patients had Stage IIIB NSCLC, and 6% of patients had recurrent NSCLC. Induction chemotherapy was received by 16% of patients. Radiation was delivered in daily fractions of 1.8 grays (Gy) for doses < or = 81.0 Gy and in daily fractions of 2.0 Gy for higher doses. Accrual at a dose level was complete when 10 patients received the intended dose without unacceptable acute morbidity.

RESULTS

After an incident of fatal acute radiation pneumonitis at the starting dose of 70.2 Gy, the protocol was modified to limit normal tissue complication probabilities (NTCP) to < 25%. The dose was then escalated from 70.2 Gy, to 75.6 Gy, 81.0 Gy, and 84.0 Gy, with at least 10 patients treated at each dose level. Unacceptable pulmonary toxicity occurred at 90.0 Gy. Subsequently, another 10 patients were accrued at the 84.0 Gy level with acceptable toxicity. Thus, 84.0 Gy was the maximum tolerated dose (MTD). The crude late pulmonary toxicity rate was 7%, the 2-year local control rate was 52%, the disease-free survival rate was 33%, and the overall survival rate was 40%. The median survival was 21.1 months. Overall survival was improved significantly in patients who received > or = 80.0 Gy.

CONCLUSIONS

The MTD of 3D-CRT for NSCLC with an NTCP constraint of 25% was 84.0 Gy in the current study. There was a suggestion of improved survival in patients who received 80.0 Gy.

Method to account for dose fractionation in analysis of IMRT plans: Modified equivalent uniform dose

PURPOSE

To propose a modified equivalent uniform dose (mEUD) to account for dose fractionation using the biologically effective dose without losing the advantages of the generalized equivalent uniform dose (gEUD) and to report the calculated mEUD and gEUD in clinically used intensity-modulated radiotherapy (IMRT) plans.

METHODS AND MATERIALS

The proposed mEUD replaces the dose to each voxel in the gEUD formulation by a biologically effective dose with a normalization factor. We propose to use the term mEUD(D(o))(/n(o)) that includes the total dose (D(o)) and number of fractions (n(o)) and to use the term mEUD(o) that includes the same total dose but a standard fraction size of 2 Gy. A total of 41 IMRT plans for patients with nasopharyngeal cancer treated at our institution between October 1997 and March 2002 were selected for the study. The gEUD and mEUD were calculated for the planning gross tumor volume (pGTV), planning clinical tumor volume (pCTV), parotid glands, and spinal cord. The prescription dose for these patients was 70 Gy to >95% of the pGTV and 59.4 Gy to >95% of the pCTV in 33 fractions.

RESULTS

The calculated average gEUD was 72.2 +/- 2.4 Gy for the pGTV, 54.2 +/- 7.1 Gy for the pCTV, 26.7 +/- 4.2 Gy for the parotid glands, and 34.1 +/- 6.8 Gy for the spinal cord. The calculated average mEUD(D(o))(/n(o)) using 33 fractions was 71.7 +/- 3.5 Gy for mEUD(70/33) of the pGTV, 49.9 +/- 7.9 Gy for mEUD(59.5/33) of the pCTV, 27.6 +/- 4.8 Gy for mEUD(26/33) of the parotid glands, and 32.7 +/- 7.8 Gy for mEUD(45/33) of the spinal cord.

CONCLUSION

The proposed mEUD, combining the gEUD with the biologically effective dose, preserves all advantages of the gEUD while reflecting the fractionation effects and linear and quadratic survival characteristics.

Image-guided adaptive radiation therapy (IGART): Radiobiological and dose escalation considerations for localized carcinoma of the prostate

The goal of this work was to evaluate the efficacy of various image-guided adaptive radiation therapy (IGART) techniques to deliver and escalate dose to the prostate in the presence of geometric uncertainties. Five prostate patients with 15-16 treatment CT studies each were retrospectively analyzed. All patients were planned with an 18 MV, six-field conformal technique with a 10 mm margin size and an initial prescription of 70 Gy in 35 fractions. The adaptive strategy employed in this work for patient-specific dose escalation was to increase the prescription dose in 2 Gy-per-fraction increments until the rectum normal tissue complication probability (NTCP) reached a level equal to that of the nominal plan NTCP (i.e., iso-NTCP dose escalation). The various target localization techniques simulated were: (1) daily laser-guided alignment to skin tattoo marks that represents treatment without image-guidance, (2) alignment to bony landmarks with daily portal images, and (3) alignment to the clinical target volume (CTV) with daily CT images. Techniques (1) and (3) were resimulated with a reduced margin size of 5 mm to investigate further dose escalation. When delivering the original clinical prescription dose of 70 Gy in 35 fractions, the "CTV registration" technique yielded the highest tumor control probability (TCP) most frequently, followed by the "bone registration" and "tattoo registration" techniques. However, the differences in TCP among the three techniques were minor when the margin size was 10 mm (< or = 1.1 %). Reducing the margin size to 5 mm significantly degraded the TCP values of the "tattoo registration" technique in two of the five patients, where a large difference was found compared to the other techniques (< or = 11.8 %). The "CTV registration" technique, however, did maintain similar TCP values compared to their 10 mm margin counterpart. In terms of normal tissue sparing, the technique producing the lowest NTCP varied from patient to patient. Reducing the margin size seemed the only sure way to reduce the NTCP significantly, irrespective of the IGART technique employed. In escalating the dose with the iso-NTCP constraint, the largest average gain in dose was observed with the "tattoo registration" technique, followed by the "CTV registration" and "bone registration" techniques. This is attributed to the fact that in three of the five patients, the "tattoo registration" technique yielded the lowest NTCP, hence a greater window of opportunity to escalate the dose was possible with this technique. However, the variation among the five patients was also largest with the "tattoo registration" technique where, in the case of one patient, the required dose actually needed to be below the original prescription dose of 70 Gy to satisfy the iso-NTCP constraint. This was not the case with the "CTV registration" technique where positive and similar dose escalation was allowed on all five patients. Based on these data, an attractive dose escalation strategy may be to implement the "CTV registration" technique (for consistent dosimetric coverage) for daily target localization in combination with a margin reduction (for increased normal tissue sparing).

IMRT versus conventional 3DCRT on prostate and normal tissue dosimetry using an endorectal balloon for prostate immobilization

This study was undertaken to compare prostate and normal tissue dosimetry in prostate cancer patients treated with intensity-modulated radiation therapy (IMRT) and conventional 3-dimensional conformal radiotherapy (3DCRT) using an endorectal balloon for prostate immobilization. Ten prostate cancer patients were studied using both IMRT and conventional 3DCRT at Houston Veterans Affairs Medical Center. For IMRT, the prescription was 70 Gy at 2 Gy/fraction at the 83.4% isodose line, allowing no more than 15% of the rectum and 33% of the bladder to receive above 68 and 65 Gy, respectively. For conventional 3DCRT, a 6-field arrangement with lateral and oblique fields was used to deliver 76 Gy at 2Gy/fraction, ensuring complete tumor coverage by the 72-Gy isodose line. Mean doses for prostate and seminal vesicles were 75.10 and 75.11 Gy, respectively, for IMRT and 75.40 and 75.02 Gy, respectively, for 3DCRT (p > 0.218). 3DCRT delivered significantly higher doses to 33%, 50%, and 66% volumes of rectum by 3.55, 6.64, and 10.18 Gy, respectively (p < 0.002), and upper rectum by 7.26, 9.86, and 9.16 Gy, respectively (p < 0.007). 3DCRT also delivered higher doses to femur volumes of 33% and 50% by 9.38 and 10.19 Gy, respectively, (p < 0.001). Insignificant differences in tumor control probability (TCP) values between IMRT and 3DCRT were calculated for prostate (p = 0.320) and seminal vesicles (p = 0.289). Compared to 3DCRT, IMRT resulted in significantly reduced normal tissue complication probability (NTCP) only for upper rectum (p = 0.025) and femurs (p = 0.021). This study demonstrates that IMRT achieves superior normal tissue avoidance, especially for rectum and femurs compared to 3DCRT, with comparable target dose escalation.

Impact of geometric uncertainties on evaluation of treatment techniques for prostate cancer

PURPOSE

To assess the impact of patient repositioning and internal organ motion on prostate treatment plans using three-dimensional conformal and intensity-modulated radiotherapy.

METHODS AND MATERIALS

Four-field, six-field, and simplified intensity-modulated arc therapy plans were generated for 5 prostate cancer patients. The planning target volume was created by adding a 1-cm margin to the clinical target volume. A convolution model was used to estimate the effect of random geometric uncertainties during treatment. Dose statistics, tumor control probabilities, and normal tissue complication probabilities were compared with and without the presence of uncertainty. The impact of systematic uncertainties was also investigated.

RESULTS

Compared with the planned treatments, the delivered dose distribution with random geometric uncertainties displayed an increase in the apparent minimal dose to the prostate and seminal vesicles and a decrease in the rectal volume receiving a high dose. This increased the tumor control probabilities and decreased the normal tissue complication probabilities. Changes were seen in the percentage of prostate volume receiving 100% and 95% of the prescribed dose, and the minimal dose and tumor control probabilities for the target volume. In addition, the volume receiving at least 65 Gy, the minimal dose, and normal tissue complication probabilities changed considerably for the rectum. The simplified intensity-modulated arc therapy technique was the most sensitive to systematic errors, especially in the anterior-posterior and superior-inferior directions.

CONCLUSION

Geometric uncertainties should be considered when evaluating treatment plans. Contrary to the widely held belief, increased conformation of the dose distribution is not always associated with increased sensitivity to random geometric uncertainties if a sufficient planning target volume margin is used. Systematic errors may have a variable effect, depending on the treatment technique used.

Optimum parameters in a model for tumour control probability including interpatient heterogeneity

A model for computing tumour control probability (TCP) is studied which embodies a dependence on the size of the irradiated volume, the density of clonogenic cells and the dose received, together with the alpha and beta parameters of the linear quadratic model of cell kill. The model can be used to describe situations where both the dose and the clonogenic cell densities are inhomogeneously distributed; however there is still uncertainty about its radiobiological parameters and the author aims to establish parameters for four types of tumour. In its simplest form, when the volumes are spherical, the clonogenic cell density is considered constant throughout the volume and the dose is uniform, the model has been used (by D.J. Brenner, 1993) to predict the radiobiological parameter alpha which allows the model to best fit the observed clinical data for four types of tumour. Here a new set of fits to the data presented by Brenner is constructed using a model which includes the distribution of radiosensitivity across a heterogeneous patient population. It is shown that this leads to a different set of optimum radiobiological parameters when the clonogenic cell density is of the order of 107 cells cm-3.

Comparison of end normal inspiration and expiration for gated intensity modulated radiation therapy (IMRT) of lung cancer

BACKGROUND AND PURPOSE

Gated delivery of radiation during part of the respiration cycle may improve the treatment of lung cancer with intensity modulated radiation therapy (IMRT). In terms of the respiration phase for gated treatment, normal end-expiration (EE) is more stable but normal end-inspiration (EI) increases lung volume. We compare the relative merit of using EI and EE in gated IMRT for sparing normal lung tissue.

PATIENTS AND METHODS

Ten patients received EI and EE respiration-triggered CT scans in the treatment position. An IMRT plan for a prescription dose of 70 Gy was generated for each patient and at each respiration phase. The optimization constraints included target dose uniformity, less than 35% of the total lung receiving 20 Gy or more and maximum cord dose <or=45 Gy. We compared planning target volume (PTV) coverage, mean lung dose, percentage of total lung receiving 20 Gy or more (V(20)) and lung normal tissue complication probability (NTCP).

RESULTS

For 9 of the 10 patients, cord and lung doses were acceptable and PTV coverage was similar for EE and EI, with lung sparing was equal to or slightly better at EI than at EE. For the 10th patient, lung sparing at EI was significantly better. Patient averaged mean lung dose was 15.4 Gy (range: 7.1-20.4) at EI and 16.3 Gy (range: 6.9-21.9) at EE. The average V(20) was 23.8% (range: 13-36.4) at EI and 25.3% (range: 13-37.3) at EE. The average NTCP at EI was 8 versus 12% at EE.

CONCLUSIONS

Dosimetric indices of lung protection for IMRT plans at EI are better than at EE. For 9 out of the 10 patients in our study, this difference is small. Thus other factors such as reproducibility, reliability and duty cycle at normal end expiration may be more critical for selecting treatment breathing phase.

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.

Clinical impact of the detector size effect in 3D-CRT

OBJECTIVE

The detector size artificially increases the measured penumbra of radiotherapy fields. The aim of this work is to determine the influence of the detector size when planning three-dimensional conformal radiation therapy (3D-CRT) treatments.

MATERIAL AND METHODS

Two anatomical sites of interest in 3D-CRT were studied: prostate and hypophysis chordoma. Conventional 3D-CRT treatments for two cases in these locations were planned with a FOCUS 4.0.0 (Computerized Medical Systems, USA) treatment planning system (TPS) equipped with Fast Fourier Transform Convolution (FFTC) and Multigrid Superposition (MGS) algorithms, making use of beams modelled from radiation profiles measured either with a 2.0 mm diameter detector (PFD(3G) diode) or with a 5.5 mm diameter detector (PTW-31002 ionisation chamber). These detectors cover up the range of detector sizes commonly used to measure radiation profiles for 3D-CRT. Dose-volume histograms (DVHs), radiobiological indexes, tumor control probability (TCP) and normal tissue complication probability (NTCP) were analysed and compared for planning target volumes (PTVs) and organs at risk (OAR) studied.

RESULTS

Important differences in DVH were found. OAR received higher dose levels when a 5.5 mm detector was used to measure profiles compared to the case in which a 2.0 mm detector was used. A 2 Gy increment in the mean rectal dose was found when the larger detector was used. In the same way, NTCP of brain stem in hypophysis chordoma treatments was doubled when this detector was used.

CONCLUSION

The current use of ionisation chambers of about 5 mm active diameter to get the necessary data to model treatment machines in radiotherapy treatment planning systems (TPS) implies a significant overirradiation of OAR close to the PTV in 3D-CRT treatments due to errors in the measured penumbra of beam profiles. To avoid this overirradiation, the measured profiles should either being acquired with a suitable detector size (2-3 mm active diameter) or being deconvoluted.

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.