Tolerance of normal tissue to therapeutic irradiation

Fractionated stereotactic radiotherapy in low-grade astrocytomas: Long-term outcome and prognostic factors

PURPOSE

To evaluate outcome after fractionated stereotactic radiotherapy (RT) of patients with World Health Organization Grade 2 astrocytoma in terms of progression-free survival, overall survival, toxicity, quality of life, and prognostic factors.

METHODS AND MATERIALS

Between 1984 and 2000, 143 patients with histologically proven Grade 2 astrocytoma were treated with fractionated stereotactic RT at our institution. The evaluation of the quality of life and toxicity was based on neurologic examinations and the Karnofsky performance score. Univariate analysis was performed on seven potential prognosticators and multivariate analysis on four prognosticators.

RESULTS

The median follow-up was 44 months. The actuarial overall survival and progression-free survival was 58% and 39% at 5 years, respectively. Out-of-field recurrences occurred in 1 patient (1.2%). We did not observe a dose-response relationship. Overall survival and progression-free survival were significantly correlated with the absence of contrast media enhancement before RT (p <0.01). Toxicity was mild and included severe side effects of European Organization for Research and Treatment of Cancer/Radiation Therapy Oncology Group Grade 3 in only 4 patients (2.8%). The Karnofsky performance score improved in most patients.

CONCLUSION

Fractionated stereotactic RT is effective and has low toxicity in the treatment of Grade 2 gliomas. The rate of field border recurrences was not increased compared with after conventional RT. Exceeding the tumor dose did not improve the tumor control rate but did enhance toxicity. Pretherapeutic contrast media enhancement should be interpreted as a sign of higher grade tumor elements.

The impact of geometric uncertainty on hypofractionated external beam radiation therapy of prostate cancer

PURPOSE

Recent publications indicate alpha/beta for prostate carcinoma could be lower than assumed. Therefore, hypofractionation might increase the therapeutic ratio. However, patient repositioning and organ motion may affect hypofractionated treatments more than conventional treatments. Our purpose is to evaluate the potential impact of geometric uncertainties on hypofractionated treatments.

METHODS AND MATERIALS

Tumor control probability (TCP) and normal tissue complication probability (NTCP) are calculated for simulated conventional and hypofractionated treatments, assuming alpha/beta of 1.5 Gy for prostate and 3.0 Gy for rectum. A Monte Carlo simulation randomly samples systematic and random displacements and produces the cumulative dose distribution for the prostate and rectum. The limiting number of fractions and the impact of different alpha/beta values are also explored.

RESULTS

A consistent but small reduction in TCP is seen with hypofractionation (generally <1%) as a result of geometric uncertainties. Escalated hypofractionation seems to allow large TCP gains ( approximately 20%) without increasing NTCP. Treatments of five fractions seem to affect outcome minimally. The alpha/beta value has a much greater impact on TCP than geometric uncertainties.

CONCLUSION

The potential increased influence of geometric uncertainties on hypofractionation seems small. Limited knowledge of radiobiologic response is likely a greater obstacle to prostate hypofractionation than geometric uncertainties.

Laparotomy wound recurrence of endometrial carcinoma

OBJECTIVES

Most endometrial cancer relapses are either pelvic or distant metastases. Recurrences in the laparotomy scar are extremely rare, as to our knowledge this is only the sixth reported case and the first treated with brachytherapy. We also present a review of the literature with an emphasis on radiation therapy treatment.

CASE

A 64-year-old woman underwent total abdominal hysterectomy and bilateral salpingo-oophorectomy for IIIA endometrial adenocarcinoma, followed by systemic chemotherapy and pelvic external-beam radiotherapy. Three years later, a recurrence in the laparotomy scar was resected and additional chemotherapy was administered. A solitary mass in the abdominal wound was then found 4 years after that and was reirradiated by combining external-beam radiation therapy and interstitial brachytherapy after complete resection. Histology of the abdominal wall implants was very similar to that of the primary tumour.

CONCLUSIONS

Laparotomy wound recurrence (LWR) for endometrial cancer usually appears as a solitary mass that grows slowly without concomitant failure sites a few years after hysterectomy. In these six patients there is no common histology pattern that could suggest predictive factors for LWR. Common postoperative irradiation does not deliver sufficient a dose to the anterior abdominal wall to prevent this kind of failure.

Radiation Tolerance of the Rat Spinal Cord after Single and Split Doses of Photons and Carbon Ions1

The sensitivity of the rat spinal cord to single and split doses of radiation and the resulting relative biological effectiveness (RBE) were determined for carbon-ion irradiations (12C) in the plateau and Bragg-peak regions. The cranial part of the cervical and thoracic spinal cords of 180 rats were irradiated with one or two fractions of 12C ions or photons, respectively. Dose-response curves for the end point symptomatic myelopathy were established, and the resulting values for the ED50 (dose for 50% complication probability) were used to determine the RBEs. A median latency for myelopathy of 167 days (range, 121-288 days) was found. The ED50 values were 17.1 +/- 0.8 Gy, 24.9 +/- 0.7 Gy (one and two fractions, 12C plateau) and 13.9 +/- 0.8, 15.8 +/- 0.7 Gy (one and two fractions, 12C Bragg peak), respectively. For photons we obtained ED50 values of 24.5 +/- 0.8 Gy for single doses and 34.2 +/- 0.7 Gy when two fractions were applied. The corresponding RBEs were 1.43 +/- 0.08, 1.37 +/- 0.12 (one and two fractions, 12C plateau) and 1.76 +/- 0.05, 2.16 +/- 0.11 (one and two fractions, 12C Bragg peak), respectively. Hematoxylin and eosin staining revealed necrosis of the white matter in the spinal cord in all symptomatic animals. In summary, from one- and two-fraction photon, 12C plateau and Bragg-peak irradiation of the rat spinal cord, we have established RBEs as well as the individual ED50's. From the latter there is a clear indication of repair processes for fractionated photons and 12C plateau ions which are significantly reduced by using Bragg-peak ions. Additional studies are being carried with 6 and 18 fractions to further refine and define the RBE and ED50 values and estimate the alpha/beta ratios.

Three-dimensional conformal radiotherapy in the radical treatment of non-small cell lung cancer

Patients with locally advanced, inoperable, non-small cell lung cancer (NSCLC) have a poor prognosis mainly due to failure of local control after treatment with radical radiotherapy. This overview addresses the role of three-dimensional conformal radiotherapy (3D CRT) in trying to improve survival and reduce toxicity for patients with NSCLC. Current techniques of 3D CRT are analysed and discussed. They include imaging, target volume definition, optimisation of the delivery of radiotherapy through improvement of set-up inaccuracy and reduction of organ motion, dosimetry and implementation and verification issues; the overview concludes with the clinical results of 3D CRT.

Inverse treatment planning by physically constrained minimization of a biological objective function

In the current state-of-the art of clinical inverse planning, the design of clinically acceptable IMRT plans is predominantly based on the optimization of physical rather than biological objective functions. A major impetus for this trend is the unproven predictive power of radiobiological models, which is largely due to the scarcity of data sets for an accurate evaluation of the model parameters. On the other hand, these models do capture the currently known dose-volume effects in tissue dose-response, which should be accounted for in the process of optimization. In order to incorporate radiobiological information in clinical treatment planning optimization, we propose a hybrid physico-biological approach to inverse treatment planning based on the application of a continuous penalty function method to the constrained minimization of a biological objective. The objective is defined as the weighted sum of normal tissue complication probabilities evaluated with the Lyman normal-tissue complication probability model. Physical constraints specify the admissible minimum and maximum target dose. The continuous penalty function method is then used to find an approximate solution of the resulting large-scale constrained minimization problem. Plans generated by our approach are compared to ones produced by a commercial planning system incorporating physical optimization. The comparisons show clinically negligible differences, with the advantage that the hybrid technique does not require specifications of any dose-volume constraints to the normal tissues. This indicates that the proposed hybrid physico-biological method can be used for the generation of clinically acceptable plans.

Effet volume en radiothérapie [II]. Deuxième partie : volume et tolérance des tissus sains

The first part of our work has focused on the relationship between tumor volume and tumor control. Indeed, it is well known that the importance of irradiated volume could be a main parameter of radiation-induced complications. Numerous mathematical models have described the correlation between the irradiated volume and the risk of adverse effects. These models should predict the complication rate of each treatment planning. At the present time late effects have been the most studied. In this report we firstly propose a review of different mathematical models described for volume effect. Secondly, we will discuss whether these theoretical considerations can influence our view of radiation treatment planning optimization.

Incorporating an improved dose-calculation algorithm in conformal radiotherapy of lung cancer: re-evaluation of dose in normal lung tissue

BACKGROUND AND PURPOSE

The low density of lung tissue causes a reduced attenuation of photons and an increased range of secondary electrons, which is inaccurately predicted by the algorithms incorporated in some commonly available treatment planning systems (TPSs). This study evaluates the differences in dose in normal lung tissue computed using a simple and a more correct algorithm. We also studied the consequences of these differences on the dose-effect relations for radiation-induced lung injury.

MATERIALS AND METHODS

The treatment plans of 68 lung cancer patients initially produced in a TPS using a calculation model that incorporates the equivalent-path length (EPL) inhomogeneity-correction algorithm, were recalculated in a TPS with the convolution-superposition (CS) algorithm. The higher accuracy of the CS algorithm is well-established. Dose distributions in lung were compared using isodoses, dose-volume histograms (DVHs), the mean lung dose (MLD) and the percentage of lung receiving >20 Gy (V20). Published dose-effect relations for local perfusion changes and radiation pneumonitis were re-evaluated.

RESULTS

Evaluation of isodoses showed a consistent overestimation of the dose at the lung/tumor boundary by the EPL algorithm of about 10%. This overprediction of dose was also reflected in a consistent shift of the EPL DVHs for the lungs towards higher doses. The MLD, as determined by the EPL and CS algorithm, differed on average by 17+/-4.5% (+/-1SD). For V20, the average difference was 12+/-5.7% (+/-1SD). For both parameters, a strong correlation was found between the EPL and CS algorithms yielding a straightforward conversion procedure. Re-evaluation of the dose-effect relations showed that lung complications occur at a 12-14% lower dose. The values of the TD(50) parameter for local perfusion reduction and radiation pneumonitis changed from 60.5 and 34.1 Gy to 51.1 and 29.2 Gy, respectively.

CONCLUSIONS

A simple tissue inhomogeneity-correction algorithm like the EPL overestimates the dose to normal lung tissue. Dosimetric parameters for lung injury (e.g. MLD, V20) computed using both algorithms are strongly correlated making an easy conversion feasible. Dose-effect relations should be refitted when more accurate dose data is available.

Influence of MRI on target volume delineation and IMRT planning in nasopharyngeal carcinoma

PURPOSE

To compare CT and MRI target volumes for nasopharyngeal carcinoma (NPC) and evaluate the role of intensity-modulated radiotherapy (IMRT) in treating composite CT+MRI targets.

METHODS AND MATERIALS

CT and T(1)/T(2)-weighted MRI scans were obtained for 8 consecutive NPC patients. Using CT, MRI, and fused CT/MRI, various target volumes (gross target volume, clinical target volume, and planning target volume [PTV]) and critical structures were outlined. For each patient, three treatment plans were developed: (1) a three-dimensional conformal RT (3D-CRT) plan using CT-based targets; (2) a 3D-CRT plan using composite CT+MRI targets; and (3) a IMRT plan using CT+MRI targets. The prescription dose was 57.6 Gy and 70.2 Gy to the initial and boost PTV, respectively. Treatment plans were compared using the PTV dose to 95% volume (D(95)), critical structure dose to 5% organ volume (D(5)), and mean dose.

RESULTS

Compared with CT, the MRI-based targets were 74% larger, more irregularly shaped, and did not always include the CT targets. For CT-based targets, 3D-CRT plans, in general, achieved adequate target coverage and sparing of critical structures. However, when these plans were evaluated using CT+MRI targets, the average PTV D(95) was approximately 60 Gy (14% underdosing), and critical structure doses were significantly worse. The use of IMRT for CT+MRI targets resulted in marked improvement in the PTV coverage and critical structure sparing: average PTV D(95) improved to 69.3 Gy, brainstem D(5) to <43 Gy (19% reduction), spinal cord D(5) to <37 Gy (19% reduction), and the mean dose to the parotids and cochlea reduced to below tolerance (23.7 Gy and 35.6 Gy, respectively).

CONCLUSION

CT/MRI fusion improved the determination of target volumes in NPC. In contrast to 3D-CRT, IMRT planning resulted in significantly improved coverage of composite CT+MRI targets and sparing of critical structures.

Autopsy verifies demyelination and lack of vascular damage in partially reversible radiation myelopathy

STUDY DESIGN

Case report of recovering radiation myelopathy.

OBJECTIVE

To present autopsy and functional imaging findings on a unique case of slowly recovering radiation myelopathy with the aim of the clarification of the underlying mechanism.

PATIENT

The cervical spinal cord and the distal part of the medulla oblongata of a 36-year-old thyroid cancer patient had been incorrectly irradiated with a total dose of 61 Gy and a fraction size of 3.4 Gy (J Neurol Sci 1999; 163:39-43), resulting in incomplete cervical transection with a 5-month latency period following the termination of radiotherapy. This was followed by a 9.5-year spontaneous improvement until her demise, during which the check-ups were supplemented by positron emission tomography (PET) investigations; these indicated increased [18F]deoxyglucose and [15O]butanol uptakes, but a diminished [11C]methionine accumulation by the irradiated spinal cord segment.

RESULTS

Autopsy revealed demyelination (with axonal loss) and neuronal damage in the cervical spinal cord and the distal part of the medulla oblongata. In the same region, only minimal vascular injury (thickening of some of the capillary walls) was detected, but not cell proliferation or chronic inflammation. Bilateral, secondary pyramidal tract degeneration caudal to the irradiated segment was observed. The PET and autopsy findings, although separated by 2 years, are consistent.

CONCLUSIONS

The pathological state of the spinal cord revealed by the autopsy is concordant with the incomplete cervical transection, implying that the functional recovery is supported by a process that probably differs from the restoration of the mechanism destroyed by the radiotherapy. For the restoration of the function, we suggest an altered conduction mechanism of the action potential, involving an increased number of sodium channels along the demyelinated segments of the injured axons, which is fully congruent with the PET findings.

Molecular whole-body cancer staging using positron emission tomography: consequences for therapeutic management and metabolic radiation treatment planning

A prospective analysis was performed in 124 non-small cell lung cancer patients to determine the role of F-18 fluorodeoxyglucose (FDG)-positron emission tomography (PET) for molecular (metabolic) staging (n=63), therapy monitoring after induction-chemotherapy (n=34), and conformal radiation treatment planning (n=27). Staging by FDG-PET was significantly more accurate than CT (p<0.001) and changed therapeutic management in 52% of all patients. After induction-chemotherapy, patients with complete metabolic remission histologically did not show vital tumor cells in contrast to patients with metabolic partial remission or progressive disease. Metabolic radiation treatment planning by PET led to smaller planning target volumes (PTVs) for radiation therapy (between 3% and 21% in 25/27 patients), resulting in a reduction of dose exposure to healthy tissue. In two patients, PET-PTV was larger than CT-based PTV, since PET detected lymph node metastases smaller than 1 cm. FDG-PET provides clinically important information; changes therapeutic management, can predict noninvasively effectiveness of chemotherapy, and may lead to better tumor control with less radiation-induced toxicity.

Induction chemotherapy followed by radical local therapy for locally advanced non-small cell lung cancer

Many patients who receive a diagnosis of non-small cell lung cancer (NSCLC) have locally advanced disease at initial presentation. Historically, these patients were treated with primary thoracic radiation therapy and had poor long-term survival rates, secondary to both progression of local disease and development of distant metastases. With the goal of improving clinical outcomes, multiple concepts of combined-modality therapy for locally advanced NSCLC have been investigated. The rationale for using chemotherapy in the induction regimen is to eliminate subclinical metastatic disease while improving local control. The optimal treatment of locally advanced NSCLC continues to evolve, but combined-modality therapy has led to improved survival rates compared to treatment with radiation alone and has become the new standard of care. This report reviews the major trials that have investigated various combinations of surgery, radiation therapy, and chemotherapy in the treatment of locally advanced NSCLC.

An evaluation of forward and inverse radiotherapy planning using Helax-TMS (version 6.0) for lung cancer patients treated with rtog 93-11 dose-escalation protocol

This study investigated the dosimetric advantages of inversely planned intensity-modulated radiotherapy (IMRT) over forward-planned conventional 3D conformal radiotherapy (3D-CRT) in treating lung cancer patients at escalated dose. Three consecutively accrued patients on the RTOG 93-11 dose-escalation protocol were replanned using IMRT with the same dosimetric rules, so that the isodose distributions and dose-volume histograms could be generated and compared. The Helax-TMS treatment planning system, with an IMRT optimization module (version 6.0), was used. In all cases, a consistent approach of inverse planning and set of dose-volume constraints (DVCs) provided improved critical structure sparing. However, the minimum dose in PTV was generally below that achieved with the corresponding forward planned 3D-CRT.

Evaluation of Standard Tangential Irradiation versus Breast Ring Technique Using Three-Dimensional Tools in Cancerous Large Breasts

Aims and background

In patients with large breasts, tangential irradiation after lumpectomy is technically difficult. Tangential plans of large breasts comprise a large volume of the lung, axilla and heart, as well as an important volume of the opposite breast and lung.

Methods

Instead of classical positioning of the breast, we encircled the breast with a plastic polyvinyl ring-shaped tube. All five left-sided breast cancer patients underwent CT scan planning with and without the plastic ring in conventional treatment positioning. Skin treatment portals at the midline and mid axilla were marked with radio-opaque markers. The scan volume encompassed the region from just below the diaphragm to the lung apex. Patients' plans were evaluated with regard to dose-volume coverage of the breast planning target volume, ipsilateral lung, contralateral lung, heart and contralateral breast. End points were maximum dose, minimum dose, and mean dose delivered to the target or critical structure.

Results

As expected, the average volume of the left lung treated above a tolerance dose of 2000 cGy was less than 10% in the ringed breast, whereas in the other method without the ring the corresponding lung volume was 30%. The cardiac volume receiving a dose over 4000 cGy was 2% in the ringed breast and 18% in the breast without a ring.

Conclusions

With the use of a simple technique with a fairly low expenditure, acute skin reactions and late cardiac and lung morbidity can be minimized in patients with large breasts.

Radiation tolerance of normal temporal bone structures: implications for gamma knife stereotactic radiosurgery

Popular current thought states that hearing loss and facial weakness after radiosurgery of vestibular schwannomas is a function of cranial nerve damage. Although this may be true in some cases, the middle and inner ear contain rich networks of other sensitive structures that are at risk after radiotherapy and that may contribute to toxicity afterward. We reviewed the limited reported data regarding radiation tolerance of external, middle, and inner ear structures, and perspectives for therapy with gamma knife stereotactic radiosurgery are addressed.

Effects of radiation on normal tissue: consequences and mechanisms

The use of radiation therapy to treat cancer inevitably involves exposure of normal tissues. As a result, patients may experience symptoms associated with damage to normal tissue during the course of therapy for a few weeks after therapy or months or years later. Symptoms may be due to cell death or wound healing initiated within irradiated tissue, and may be precipitated by exposure to further injury or trauma. Many factors contribute to risk and severity of normal tissue reactions; these factors are site specific and vary with time after treatment. Treatments that reduce the risk or severity of damage to normal tissue or that facilitate the healing of radiation injury are being developed. These could greatly improve the quality of life of patients treated for cancer.

Does prone positioning reduce small bowel dose in pelvic radiation with intensity-modulated radiotherapy for gynecologic cancer?

PURPOSE

Intensity-modulated radiotherapy (IMRT) has been shown to reduce the radiation dose to small bowel in pelvic RT in gynecology patients. Prone positioning has also been used to decrease small bowel dose by displacement of small bowel from the RT field in these patients. The purpose of this study was to determine whether the combination of both IMRT and prone positioning on a belly board can reduce small bowel dose further in gynecologic cancer patients undergoing pelvic RT.

METHODS AND MATERIALS

IMRT plans for pelvic RT were computed in 16 patients with gynecologic cancer who had undergone planning CT scans in both the supine and the prone positions on a belly board. For the gross tumor volume, the uterus, cervix, and tumor (or postoperative region) were traced. The clinical target volume was defined as the vessels and lymph nodes from the obturator level to the aortic bifurcation, presacral region, and upper 4 cm of the vagina, in addition to gross tumor volume. The planning target volume was defined as a 2-cm margin in addition to the gross tumor volume and upper 4 cm of the vagina, and 1.5 cm for lymph nodes and vessels. Normal tissue regions of interest included small bowel, large bowel, and bladder. IMRT plans using (1) the limited arc technique (180 degrees arc length) and (2) the extended arc technique (340 degrees arc length) were computed. Dose-volume histograms for normal tissue structures and target were compared between the supine and prone IMRT plans using the paired t test.

RESULTS

Prone positioning on a belly board decreased the small bowel dose in gynecologic pelvic IMRT, and the magnitude of improvement depended on the specific IMRT technique used. With the limited arc technique, prone positioning significantly decreased the irradiated small bowel volume at the 25-50-Gy dose levels compared with supine positioning. Small bowel volumes receiving > or =45 Gy decreased from 19% to 12.5% (p = 0.005) with prone positioning. With the extended arc technique, the decrease in irradiated small bowel volume was less marked, but remained detectable in the 35-45-Gy dose levels. Small bowel volumes receiving > or =45 Gy decreased from 13.6% to 10.1% (p = 0.03) with prone positioning. The effect of prone positioning on large bowel and bladder was variable. Large bowel volumes receiving > or =45 Gy increased with prone positioning from 16.5% to 20.6% (p = 0.02) in the limited arc technique and was unaffected in the extended arc technique.

CONCLUSION

These preliminary data suggest that prone positioning on a belly board can reduce the small bowel dose further in gynecology patients treated with pelvic RT, and that the dose reduction depends on the IMRT technique used.

From physical dose constraints to equivalent uniform dose constraints in inverse radiotherapy planning

Optimization algorithms in inverse radiotherapy planning need information about the desired dose distribution. Usually the planner defines physical dose constraints for each structure of the treatment plan, either in form of minimum and maximum doses or as dose-volume constraints. The concept of equivalent uniform dose (EUD) was designed to describe dose distributions with a higher clinical relevance. In this paper, we present a method to consider the EUD as an optimization constraint by using the method of projections onto convex sets (POCS). In each iteration of the optimization loop, for the actual dose distribution of an organ that violates an EUD constraint a new dose distribution is calculated that satisfies the EUD constraint, leading to voxel-based physical dose constraints. The new dose distribution is found by projecting the current one onto the convex set of all dose distributions fulfilling the EUD constraint. The algorithm is easy to integrate into existing inverse planning systems, and it allows the planner to choose between physical and EUD constraints separately for each structure. A clinical case of a head and neck tumor is optimized using three different sets of constraints: physical constraints for all structures, physical constraints for the target and EUD constraints for the organs at risk, and EUD constraints for all structures. The results show that the POCS method converges stable and given EUD constraints are reached closely.

[Optimization criteria in intensity-modulated radiotherapy]

The present paper provides an overview on the inverse treatment planning for the assessment of intensity-modulated fields. The problem is to find the optimal dose distribution for given attributes of the irradiated tissue. The attributes of the optimal dose distribution are delineated by an objective function. In practice, models are used that evaluate the physical dose distribution, either directly or through their radiobiological effects. In the simplest case, the squared deviation of the achieved dose distribution is minimized to the prescribed dose distribution. For organs structured in parallel, it is common to introduce dose-volume constraints. Another approach is to optimize a value for the probability of complication-free tumor control. The complication probability for normal tissue, in turn, is a rather complex function. However, using the relative seriality, a simple model can be devised with a certain approximation. Other models of "effective dose" are also presented.

Optimizer convergence and local minima errors and their clinical importance

Two of the errors common in the inverse treatment planning optimization have been investigated. The first error is the optimizer convergence error, which appears because of non-perfect convergence to the global or local solution, usually caused by a non-zero stopping criterion. The second error is the local minima error, which occurs when the objective function is not convex and/or the feasible solution space is not convex. The magnitude of the errors, their relative importance in comparison to other errors as well as their clinical significance in terms of tumour control probability (TCP) and normal tissue complication probability (NTCP) were investigated. Two inherently different optimizers, a stochastic simulated annealing and deterministic gradient method were compared on a clinical example. It was found that for typical optimization the optimizer convergence errors are rather small, especially compared to other convergence errors, e.g., convergence errors due to inaccuracy of the current dose calculation algorithms. This indicates that stopping criteria could often be relaxed leading into optimization speed-ups. The local minima errors were also found to be relatively small and typically in the range of the dose calculation convergence errors. Even for the cases where significantly higher objective function scores were obtained the local minima errors were not significantly higher. Clinical evaluation of the optimizer convergence error showed good correlation between the convergence of the clinical TCP or NTCP measures and convergence of the physical dose distribution. On the other hand, the local minima errors resulted in significantly different TCP or NTCP values (up to a factor of 2) indicating clinical importance of the local minima produced by physical optimization.

Limitation of conventional two dimensional radiation therapy planning in nasopharyngeal carcinoma

PURPOSE

To assess the adequacy of coverage of gross tumor volume (GTV) with traditional two dimensional (2D) radiation therapy (RT) planning in patients with nasopharyngeal cancer (NPC).

MATERIALS AND METHODS

The study comprised 94 of 179 patients treated with definitive RT between 1993 and 1997. The inclusion requirement was the availability of a digitally archived pretreatment magnetic resonance imaging. The digital images were used to record the precise location of the GTV in the sagittal plane. As a separate procedure, sagittal dose distributions for each treatment phase were created by digitizing the simulation field parameters into treatment planning software without knowledge of the GTV. The location of the GTV and dose distribution in the sagittal plane were superimposed on each other and GTV coverage by the 50, 90 and 95% isodose lines determined for each phase of treatment.

RESULTS

The 1997 tumour node metastasis (TNM) stage distribution was: 7 (8%) stage I, 16 (16%) stage II, 30 (32%) stage III and 41 (44%) stage IV. Median follow-up was 4.4 years. Median primary dose was 66 Gy. The actuarial 5-year overall survival, disease free survival and local relapse free rates were 88, 54 and 66%, respectively. The GTV was covered by the 50, 90 and 95% isodose lines for all phases of the multiphase plan in only 53, 20 and 9% of patients, respectively. The GTV was more likely to be undercovered in the latter phases of the plan particularly in those patients with advanced T category.

CONCLUSION

2D RT planning has significant limitations in achieving adequate GTV coverage in NPC. We strongly recommend 3D planning using either conformal techniques of dose delivery or intensity modulated radiation therapy for the treatment of these patients.

Is the Renal Dosimetry for [90Y-DOTA0, Tyr3]Octreotide Accurate Enough to Predict Thresholds for Individual Patients?

The accuracy in the dosimetry for radionuclide therapy shows a great contrast to that obtained in external beam radiotherapy. The dosimetry for [(90)Y-DOTA(0), Tyr(3)] octreotide is evaluated in patients to see whether the accuracy of the dosimetry is high enough to distinguish the probability for radiation nephropathy. The 5% threshold for late end-point nephropathy at 23 Gy with external beam radiotherapy becomes with (90)Y therapy at least 30-35 Gy, when it is given in three or more fractions. More accurate linear-quadratic (LQ) model parameters are, however, needed to predict a more precise threshold for renal damage in this dose rate region. The average MIRD-based dose to the kidneys was 27 +/- 4 Gy (N = 52) with no evidence for renal damage. The variance in the dose is only caused by the high variability in renal uptake kinetics of the compound. Using the actual kidney volumes instead of the phantom values lowered the kidney dose considerably, but the variance in the dose greatly increased. As the peptide specifically localizes in the kidney cortex, the dose to the cortex increased up to a factor 1.5 compared to the MIRD whole kidney dose. Both the sum of uncertainties of ? 40% in the actual dose to the kidneys and the unknown maximum tolerable kidney dose for internal therapy make that a fixed injected activity of 13.32 GBq together with a patient-averaged dosimetry is as good as patient-kinetics specific dosimetry using the MIRD method.

Risk of long-term complications after TFG-beta1-guided very-high-dose thoracic radiotherapy

PURPOSE

To report the incidence of late complications in long-term survivors of very-high-dose thoracic radiotherapy (RT) treated on a prospective clinical trial.

METHODS AND MATERIALS

Patients with locally advanced or medically inoperable non-small-cell lung cancer received three-dimensional conformal RT to the primary tumor and radiographically involved lymph nodes to a dose of 73.6 Gy at 1.6 Gy twice daily. If the plasma transforming growth factor-beta1 (TGF-beta1) level was normal after 73.6 Gy, additional twice-daily RT was delivered to successively higher total doses until the maximal tolerated dose was reached. Patients within a given dose level were followed for 6 months before escalation to the next dose level was permitted. Late complications were defined according to Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria.

RESULTS

Thirty-eight patients were enrolled between 1996 and 1999. Twenty-four patients were not eligible for radiation dose escalation beyond 73.6 Gy because of persistently abnormal TGF-beta1 levels. Fourteen patients received dose escalation (80 Gy in 8; 86.4 Gy in 6). Grade 3 or greater late complications occurred in 4 of 24, 1 of 8, and 2 of 6 patients treated to 73.6, 80, and 86.4 Gy, respectively. The corresponding patient numbers with late Grade 4-5 toxicity were 3 of 24, 0 of 6, and 0 of 8. Overall, 7 (18%) of the 38 patients developed Grade 3-5 late toxicity. Nonpulmonary complications predominated (4 of 7). Five (71%) of seven serious complications developed within 11 months after RT; however, the remaining two complications (29%) occurred very late (at 43 and 62 months). The 5-year actuarial risk of late Grade 3-5 complications was 33%.

CONCLUSION

Long-term survivors of very-high-dose RT for non-small-cell lung cancer have a significant risk of severe treatment-related complications. At these high dose levels, the predominant toxicity may no longer be pulmonary. All Grade 4-5 complications occurred in patients whose dose was limited to 73.6 Gy because of a persistently elevated TGF-beta1. Thus, persistently elevated plasma TGF-beta1 levels toward the end of RT may identify patients at greatest risk of severe complications.

Estimation of parameters of dose-volume models and their confidence limits

Predictions of the normal-tissue complication probability (NTCP) for the ranking of treatment plans are based on fits of dose-volume models to clinical and/or experimental data. In the literature several different fit methods are used. In this work frequently used methods and techniques to fit NTCP models to dose response data for establishing dose-volume effects, are discussed. The techniques are tested for their usability with dose-volume data and NTCP models. Different methods to estimate the confidence intervals of the model parameters are part of this study. From a critical-volume (CV) model with biologically realistic parameters a primary dataset was generated, serving as the reference for this study and describable by the NTCP model. The CV model was fitted to this dataset. From the resulting parameters and the CV model, 1000 secondary datasets were generated by Monte Carlo simulation. All secondary datasets were fitted to obtain 1000 parameter sets of the CV model. Thus the 'real' spread in fit results due to statistical spreading in the data is obtained and has been compared with estimates of the confidence intervals obtained by different methods applied to the primary dataset. The confidence limits of the parameters of one dataset were estimated using the methods, employing the covariance matrix, the jackknife method and directly from the likelihood landscape. These results were compared with the spread of the parameters, obtained from the secondary parameter sets. For the estimation of confidence intervals on NTCP predictions, three methods were tested. Firstly, propagation of errors using the covariance matrix was used. Secondly, the meaning of the width of a bundle of curves that resulted from parameters that were within the one standard deviation region in the likelihood space was investigated. Thirdly, many parameter sets and their likelihood were used to create a likelihood-weighted probability distribution of the NTCP. It is concluded that for the type of dose response data used here, only a full likelihood analysis will produce reliable results. The often-used approximations, such as the usage of the covariance matrix, produce inconsistent confidence limits on both the parameter sets and the resulting NTCP values.

Quantification of rat retinal growth and vascular population changes after single and split doses of proton irradiation: translational study using stereology methods

This study quantified architectural and population changes in the rat retinal vasculature after proton irradiation using stereology. A 100 MeV conformal proton beam delivered 8, 14, 20 and 28 Gy as single and split doses to the whole eye. The vascular networks were prepared from retinal digests. Stereological methods were used to obtain the area of the retina and unbiased estimates of microvessel/artery/vein endothelial, pericyte and smooth muscle population, and vessel length. The retinal area increased progressively in the unirradiated, age-matched controls and in the retinas irradiated with 8 and 14 Gy, indicating uniform progressive retinal growth. No growth occurred after 20 and 28 Gy. Regression analysis of total endothelial cell number in all vessels (arteries, veins and capillaries) after irradiation documented a progressive time- and dose-dependent cell loss occurring over 15 to 24 months. The difference from controls was significant (P<0.01) after 28 Gy given in single and split doses and after 20 Gy given as a split dose (P<0.05). Total vessel length in microvessel was significantly shortened at 20 and 28 Gy compared to that of controls (P<0.05). No evident dose recovery was observed in the endothelial populations after split doses. At 10 Gy, the rate of endothelial cell loss, a dose parameter used to characterize the time- and dose-dependent loss of the endothelial population, was doubled.

Radiation therapy of the pelvic and paraaortic lymph nodes in cervical carcinoma: a prospective three-dimensional analysis of patient positioning and treatment technique

PURPOSE

Pelvic box fields in prone position are the standard treatment for patients with cervical carcinomas. The issue investigated in this report is whether this technique should also be used when extending the planning target volume to the paraaortic region.

MATERIALS AND METHODS

In a prospective study of eight consecutive patients with cervical carcinomas, two patient positions (prone and supine) and three radiation techniques (A, anteroposterior/posteroanterior opposed fields; B, four-field box; and C, three-field technique) were examined concerning the dose to critical organs. The analysis was based on three-dimensional planning, dose-volume histograms and normal tissue complication probabilities (NTCP).

RESULTS

Compared to the prone position, the supine position led to improved organ sparing in four of seven organs (liver, both kidneys, spinal canal). In two of seven organs (rectum and bladder) no difference between prone and supine position was observed. The best sparing of small bowel was achieved in prone position. Technique B followed by technique C in the supine position resulted in the best overall sparing of critical organs concerning the volumes receiving the respective TD(5/5) doses or more. Mean NTCP values for liver, rectum and bladder were below 1.0%. The highest values of up to 12% were found for both kidneys in prone position with C and for the spinal canal with A in the prone and supine position.

CONCLUSION

According to this analysis, for the treatment of the pelvic and paraaortic lymph node regions together, supine position and technique B (alternatively C) should be preferred despite the advantages of prone position on belly boards for pelvic irradiation alone.

Focal fractionated radiotherapy for intramedullary spinal arteriovenous malformations: 10-year experience

OBJECT

Radiosurgical treatment of spinal arteriovenous malformations (AVMs) is becoming a practical therapeutic option as methodology improves, but no comparative study has yet been published on focal fractionated radiotherapy. The authors report their experience with conventional and hypofractionated radiotherapy for spinal AVM.

METHODS

Candidates for this study were patients who experienced symptoms due to an intramedullary AVM but were ineligible for embolization or surgery. Of 21 patients with spinal AVMs, 10 cases in a 10-year period met this criterion. Angiography and contrast-enhanced computerized tomography scanning were used for treatment planning in all cases. Fractionated radiotherapy was performed using a linear accelerator, extracranial immobilization system, and frequent orthogonal linacographic verification. The starting radiation dose was 32 Gy in two, 36 Gy in three, and 40 Gy in two patients, in a regimen involving 1.8 to 2-Gy daily fractions; this was recently changed to a hypofractionation schedule of 30 Gy (in eight sessions) in one and 20 Gy (in four sessions) in two patients.

RESULTS

The follow-up period ranged from 26 to 124 months (median of 49 months). There were no hemorrhages nor any adverse reactions attributable to irradiation. Of the seven patients who consented to undergo follow-up angiography, the nidus size decreased in five, but complete obliteration did not occur in any patient.

CONCLUSIONS

Because no patient experienced adverse effects, the maximum tolerable radiation dose for the spinal cord associated with an AVM could not be identified, although it presumably is higher than those administered. The lack of rebleeding in patients in whom complete angiographic occlusion was absent suggests that the natural history of spinal AVMs may be less aggressive than previously reported.

Radiotherapy of small intracranial tumours with different advanced techniques using photon and proton beams: a treatment planning study

BACKGROUND AND PURPOSE

The potential benefits and limitations of five different radiation techniques, 3D conformal radiotherapy (3DCRT), stereotactic arc therapy (SRS/T), intensity modulated radiotherapy with photons (IMRT), and radiotherapy with protons (spot scanning (SSp) or passive scattering (PSp)), have been assessed using comparative treatment planning methods in a cohort of patients presenting with 'benign' brain tumours.

MATERIAL AND METHODS

Plans for five acoustic neurinomas, five meningiomas, and two pituitary adenomas were computed for all modalities using computed tomography (CT) scans to delineate planning target volume and organs at risk (OARs) and to predict dose distributions. Dose-volume histograms were used for physical and simple biological evaluation.

RESULTS

Proton techniques were shown to be superior to all photon approaches for the irradiation of small brain lesions in terms of target dose uniformity and conformity and in terms of sparing OARs. No major differences were observed between the results of the photon techniques, which were generally good for target coverage. Minimum target doses ranged from 81% with SRS/T to 93% with IMRT. The volume receiving more than 95% of the dose ranged from 95% (SRS/T) to 99% (PSp). No clear patterns of coverage dependence upon target shape were observed. Maximum brain stem irradiation ranged from 60% with IMRT to 26% with protons and the conformity index from 4.4 with IMRT to 2.5 with protons. Considering the rather long life expectancy of the patients suffering from meningiomas, neurinomas, and pituitary adenomas, the most important aspect to be considered, other than target coverage, is toxicity and in the long term, the possibility of secondary tumour induction. Considering these aspects, proton irradiation should be the irradiation technique of choice, when available. If not, IMRT, or even 3DCRT, techniques can provide an acceptable compromise, even without recurring to unconventional treatments like SRS/T, which require complex installations and high machine occupancy.

Stereology techniques have--or should have--a role in preclinical radiation therapy

A paper by Kubinova et al. (Radiat. Res. 000, 000-000, 2003) introduced to radiation biology the techniques of stereology required to quantify the dose response of irradiated brain populations. A paper by Mao et al. (Radiat. Res. 000, 000-000, 2003) and earlier papers by Archambeau et al. applied these techniques to quantify the population changes in the vasculature of the retina. This presentation reviews in broad terms the evolution of the need to quantify population and kinetic techniques and how the need has been met. The in vitro and in vivo descriptive and clonogenic techniques used regularly in radiation biology and in clinical therapy will not be replaced by stereology. While stereology is applicable to all tissue, it proves to be an important technique that allows the investigator to quantify cell population parameters in late-responding and non-proliferative populations.

Stereology techniques in radiation biology

Clinicians involved in conventional radiation therapy are very concerned about the dose-response relationships of normal tissues. Before proceeding to new clinical protocols, radiation biologists involved with conformal proton therapy believe it is necessary to quantify the dose response and tolerance of the organs and tissues that will be irradiated. An important focus is on the vasculature. This presentation reviews the methodology and format of using confocal microscopy and stereological methods to quantify tissue parameters, cell number, tissue volume and surface area, and vessel length using the microvasculature as a model tissue. Stereological methods and their concepts are illustrated using an ongoing study of the dose response of the microvessels in proton-irradiated hemibrain. Methods for estimating the volume of the brain and the brain cortex, the total number of endothelial cells in cortical microvessels, the length of cortical microvessels, and the total surface area of cortical microvessel walls are presented step by step in a way understandable for readers with little mathematical background. It is shown that stereological techniques, based on a sound theoretical basis, are powerful and reliable and have been used successfully.

Segmental and dynamic intensity-modulated radiotherapy delivery techniques for micro-multileaf collimator

A leaf sequencing algorithm has been implemented to deliver segmental and dynamic multileaf collimated intensity-modulated radiotherapy (SMLC-IMRT and DMLC-IMRT, respectively) using a linear accelerator equipped with a micro-multileaf collimator (mMLC). The implementation extends a previously published algorithm for the SMLC-IMRT to include the dynamic MLC-IMRT method and several dosimetric considerations. The algorithm has been extended to account for the transmitted radiation and minimize the leakage between opposing and neighboring leaves. The underdosage problem associated with the tongue-and-groove design of the MLC is significantly reduced by synchronizing the MLC leaf movements. The workings of the leaf sequencing parameters have been investigated and the results of the planar dosimetric investigations show that the sequencing parameters affect the measured dose distributions as intended. Investigations of clinical cases suggest that SMLC and DMLC delivery methods produce comparable results with leaf sequences obtained by root-mean-square (RMS) errors specification of 1.5% and lower, approximately corresponding to 20 or more segments. For SMLC-IMRT, there is little to be gained by using an RMS error specification smaller than 2%, approximately corresponding to 15 segments; however, more segments directly translate to longer treatment time and more strain on the MLC. The implemented leaf synchronization method does not increase the required monitor units while it reduces the measured TG underdoses from a maximum of 12% to a maximum of 3% observed with single field measurements of representative clinical cases studied.

Influence of irradiated volume on ureteral injury after intraoperative radiation therapy: experimental study in dogs

PURPOSE

To investigate the role of irradiated volumes at intraoperative radiation therapy in the development of ureteral injury in dogs.

MATERIALS AND METHODS

Sixteen beagle dogs were randomized to receive 30 Gy of intraoperative radiation therapy in the right ureter. Lead shielding ensured that different volumes were irradiated. Six dogs received a 4 x 12-cm field, five dogs a 4 x 8-cm field, and five dogs a 4 x 4-cm field. Follow-up included magnetic resonance (MR) imaging, clinical examination, and resting sequential renography. Twelve months after irradiation, the animals were killed, and autopsy was performed. Functional outcome was defined as MR imaging and renography findings and was evaluated statistically by using the Cochran-Armitage test at a.05 significance level.

RESULTS

Twelve months after therapy, ureteral obstruction with consecutive hydronephrosis of the right kidney was observed in four of six animals that received the largest volume of irradiation. Two dogs that received the medium volume developed ureteral obstruction. None of the five dogs that received the smallest volume showed abnormal findings (P <.05). The irradiated parts of the ureters in all dogs showed abnormal histopathologic findings, such as fibrosis.

CONCLUSION

The probability of ureteral obstruction following intraoperative radiation therapy increases with the irradiated partial volume of the ureter.

Biological response to radiation therapy

In an investigation by the Swedish Cancer Society, the present status, critical issues and future aspects and potentials were described by an expert group for each of nine major areas of radiation therapy research. This article deals with biological response to radiation. Separate sections deal with molecular responses to radiation, the stem cell and clonogenic cell concepts and the importance of cell proliferation, cell and tissue responses to doses above and below 1 Gy, respectively, the potential role of intercellular signalling pathways, the so-called bystander effect and radiation biology-based therapy planning and treatment optimization.

The method of intercepts in parameter space for the analysis of local minima caused by dose-volume constraints

The local minima problem in radiotherapy optimization has been a concern for both researchers and physicians. In this work, local minima induced by dose-volume histogram (DVH) constraints are discussed. The non-convex property of the feasible set formed by DVH constraints is discussed in beam weight space. An intuitive explanation of the origin of this type of local minima is given by a two-beam model setup. Some interesting properties and insights about the DVH-induced local minima are found. Based on this, a heuristic non-random initial guess sampling method is proposed and applied to a clinical nasopharyngeal case, where some significantly different local minima are located.

Dosimetric considerations for patients with HIP prostheses undergoing pelvic irradiation. Report of the AAPM Radiation Therapy Committee Task Group 63

This document is the report of a task group of the Radiation Therapy Committee of the AAPM and has been prepared primarily to advise hospital physicists involved in external beam treatment of patients with pelvic malignancies who have high atomic number (Z) hip prostheses. The purpose of the report is to make the radiation oncology community aware of the problems arising from the presence of these devices in the radiation beam, to quantify the dose perturbations they cause, and, finally, to provide recommendations for treatment planning and delivery. Some of the data and recommendations are also applicable to patients having implanted high-Z prosthetic devices such as pins, humeral head replacements. The scientific understanding and methodology of clinical dosimetry for these situations is still incomplete. This report is intended to reflect the current state of scientific understanding and technical methodology in clinical dosimetry for radiation oncology patients with high-Z hip prostheses.

Planejamento tridimensional para radioterapia de tumores de esôfago: comparação de técnicas de tratamento e análise de probabilidade de complicações

Para comparar diversas técnicas de irradiação para o câncer de esôfago, foi utilizado sistema de planejamento tridimensional. Em um paciente com carcinoma espinocelular de esôfago médio, foram estudadas as seguintes técnicas de tratamento: dois campos ântero-posteriores e dois campos látero-laterais paralelos e opostos, três campos em "Y" e em "T" e quatro campos em "X". Foram obtidos os histogramas dose-volume, considerando como órgãos de risco medula espinhal e pulmões. Os resultados foram analisados de acordo com as recomendações da Normal Tissue Complication Probability (NTCP) e Tumor Control Probability (TCP). Quanto às doses de irradiação em pulmão, a melhor opção foi a técnica em dois campos ântero-posteriores paralelos e opostos. A medula foi mais poupada quando se utilizaram campos látero-laterais. Sugerimos a combinação de pelo menos duas técnicas de tratamento: ântero-posterior e as técnicas com campos em "Y", "T" ou látero-laterais, para o balanceamento das doses em pulmões e medula espinhal. Ou, ainda, a utilização de técnicas de três campos durante todo o tratamento.

Use of ibritumomab tiuxetan anti-CD20 radioimmunotherapy in a non-Hodgkin's lymphoma patient previously treated with a yttrium-90-labeled anti-CD22 monoclonal antibody

Ibritumomab tiuxetan is a novel radioimmunotherapeutic agent that has a high response rate in relapsed or chemotherapy-refractory CD20+ B-cell non-Hodgkin's lymphoma. Whereas chemotherapy agents can successfully be used multiple times in a given patient, there are few data on the repeated use of radioimmunotherapy in terms of efficacy or morbidity, and no reports as yet involving radioconjugates that target different antigens We report on a patient who was treated successfully with yttrium-90-labeled humanized anti-CD22 monoclonal antibody (90Y-epratuzumab). Upon relapse 3 years later, the patient was treated again with radioimmunotherapy consisting of 90Y-ibritumomab tiuxetan anti-CD20 monoclonal antibody, with a good response and acceptable bone marrow suppression. This case report demonstrates the potential for repeated treatments with radioimmunotherapy agents in patients with chemotherapy-refractory non-Hodgkin's lymphoma.

CT evaluation of patient deep inspiration self-breath-holding: how precisely can patients reproduce the tumor position in the absence of respiratory monitoring devices?

The aim of the present study was to evaluate the reproducibility of tumor position under patient deep inspiration self-breath-holding in the absence of respiratory monitoring devices, as well as to compare the reproducibility of deep inspiration self-breath-holding on the verbal command of a radiation technologist (Passive mode) with that initiated by patients' own estimation (Active mode). Twenty patients with lung cancer were shown how the tumor and diaphragm move during the respiration cycle. Patients were instructed to hold their breath during deep inspiration and reproduce identical tumor position as well as possible either by the Active mode or by the Passive mode. After patients had practiced self-breath-holding during deep inspiration, a set of three CT scans was obtained for each of the two modes of self-breath-holding (6 CT scans total) to obtain randomly timed images of 2 mm thickness in the vicinity of the tumor. The first three scans were performed during breath-hold using the Active mode, and next three scans were using the Passive mode. Maximum difference in tumor position for the three CT scans was then calculated along three axes: cranial-caudal (C-C); anterior-posterior (A-P); and right-left (R-L). In the 20 patients who underwent analysis of self-breath-holding, mean maximum difference in tumor position obtained under breath-hold using the Active and the Passive modes were: 2.2 and 3.1 mm along the C-C axis; 1.4 and 2.4 mm along the A-P axis; and 1.3 and 2.2 mm along the R-L axis, respectively. These differences in all axes were significantly smaller (p<0.05) for the Active mode than for the Passive mode. Most tumors displayed maximal respiratory movement along the C-C axis, and minimal movement along the R-L axis, but tumors located in the upper lung displayed maximal movement along the A-P axis. Significant correlation (p<0.05) was observed between differences along three axes in either mode of breath-hold. In conclusion, the reproducibility of tumor position under self-breath-holding by patients during deep inspiration after sufficient practice and in the absence of respiratory monitoring devices was satisfactorily accurate, and differences in tumor position were smaller under breath-holding using the Active mode than using the Passive mode. We believe this new technique is likely to prove extremely useful for the irradiation of lung tumors with a small internal margin and for reduced proportion of high-dose irradiated normal lung to total lung volume.

Simultaneous integrated boost intensity-modulated radiotherapy for locally advanced head-and-neck squamous cell carcinomas. I: dosimetric results

PURPOSE

This report describes the dosimetric analyses of a Phase I/II protocol, designed to examine the capabilities of an institutionally developed intensity-modulated radiotherapy (IMRT) system with respect to dose escalation. The protocol employed stringent dosimetric guidelines in the treatment of locally advanced head-and-neck squamous cell carcinomas (HNSCC) with radiotherapy alone using IMRT and the simultaneous integrated boost (SIB) technique.

METHODS AND MATERIALS

The first 14 patients enrolled on the protocol were included in this analysis. Escalating doses of 68.1 Gy (6 patients), 70.8 Gy (6 patients), and 73.8 Gy (2 patients) were delivered to the gross tumor volume (GTV) in 30 fractions. Simultaneously, constant dose coverage was given to the subclinical disease and the electively treated nodal regions, which received 60 Gy and 54 Gy, respectively, in all three cohorts. Parotid glands were spared to the degree possible without compromising target coverage. The following indices are reported for the GTV: (1) dose to specified percent volumes (e.g., D(98) and D(2)); (2) homogeneity index defined as the ratio (D(2) - D(98))/D(prescription); (3) biologically equivalent uniform dose (EUD); and (4) an index of conformality, PITV, defined as the ratio of volume enclosed within the prescribed isodose surface to the target volume. Treatments were planned and delivered with nine 6-MV photon beams using the multileaf collimator (MLC) "sliding window" technique.

RESULTS

Mean doses to 98% of GTV were 68.4 Gy, 70.5 Gy, and 70.8 Gy, and average GTV dose homogeneity was 6.7%, 7.6%, and 8.8% for the three cohorts. The average doses to the parotid gland proximal to and distant from GTV were 41.3 Gy and 25.7 Gy, respectively. Dose distributions measured in phantom showed good agreement with calculations.

CONCLUSIONS

Treatment of locally advanced HNSCC using SIB-IMRT as described is feasible. Treatment planning and delivery are safer and more efficient than with conventional three-dimensional processes. Predicted dose distributions can be accurately delivered with excellent conformality using dynamic MLC. At least one of the parotid glands can be adequately spared. Patient follow-up continues and will allow eventual quantitative correlation of delivered dose distributions with clinical outcomes.

Radiation pneumonitis following treatment of non-small-cell lung cancer with continuous hyperfractionated accelerated radiotherapy (CHART)

PURPOSE

To determine whether partial volume lung irradiation influences the risk of developing acute radiation pneumonitis after the treatment of non-small-cell lung cancer with continuous hyperfractionated accelerated radiotherapy (CHART).

METHODS AND MATERIALS

We conducted an analysis of 32 patients treated with CHART at the Gloucestershire Oncology Center. Twelve patients were treated using conventional two-dimensional treatment techniques and received elective nodal irradiation (ENI). Their treatment plans were subsequently recapitulated using a three-dimensional treatment planning system. Twenty patients were planned using this system from the outset. For these patients, elective nodal irradiation was omitted. Dose-volume histograms (DVH) were constructed and several parameters analyzed for their ability to predict for the development of pneumonitis.

RESULTS

Univariate analysis revealed that the percentage lung volume receiving more than 20 Gy (V20) and the mean lung dose are of predictive value for the development of pneumonitis after CHART. There is a strong correlation between these two parameters. Importantly, partial volume lung irradiation using CHART appears to be better tolerated than conventionally fractionated radiotherapy. The omission of ENI considerably reduces V20. Using a commonly employed 3-beam technique it was also noted that the shape of the planning target volume (PTV) in the transverse plane (expressed as an elliptical index) affects the conformity of the V20 isodose to the PTV. This influences the scope for dose escalation with irregularly shaped tumors.

CONCLUSIONS

In relation to acute radiation pneumonitis, CHART appears to have a superior therapeutic index than conventionally fractionated radiotherapy. V20 and mean lung dose are useful factors for predicting the risk of this complication. The use of these parameters will aid the selection of optimal treatment plans and provides a basis for future dose escalation studies.

Tolerance of organs at risk in small-volume, hypofractionated, image-guided radiotherapy for primary and metastatic lung cancers

PURPOSE

To determine the organ at risk and the maximum tolerated dose (MTD) of radiation that could be delivered to lung cancer using small-volume, image-guided radiotherapy (IGRT) using hypofractionated, coplanar, and noncoplanar multiple fields.

MATERIALS AND METHODS

Patients with measurable lung cancer (except small-cell lung cancer) 6 cm or less in diameter for whom surgery was not indicated were eligible for this study. Internal target volume was determined using averaged CT under normal breathing, and for patients with large respiratory motion, using two additional CT scans with breath-holding at the expiratory and inspiratory phases in the same table position. Patients were localized at the isocenter after three-dimensional treatment planning. Their setup was corrected by comparing two linacographies that were orthogonal at the isocenter with corresponding digitally reconstructed images. Megavoltage X-rays using noncoplanar multiple static ports or arcs were used to cover the parenchymal tumor mass. Prophylactic nodal irradiation was not performed. The radiation dose was started at 60 Gy in 8 fractions over 2 weeks (60 Gy/8 Fr/2 weeks) for peripheral lesions 3.0 cm or less, and at 48 Gy/8 Fr/2 weeks at the isocenter for central lesions or tumors more than 3.0 cm at their greatest dimension.

RESULTS

Fifty-seven lesions in 45 patients were treated. Tumor size ranged from 0.6 to 6.0 cm, with a median of 2.6 cm. Using the starting dose, 1 patient with a central lesion died of a radiation-induced ulcer in the esophagus after receiving 48 Gy/8 Fr at isocenter. Although the contour of esophagus received 80% or less of the prescribed dose in the planning, recontouring of esophagus in retrospective review revealed that 1 cc of esophagus might have received 42.5 Gy, with the maximum dose of 50.5 Gy. One patient with a peripheral lesion experienced Grade 2 pain at the internal chest wall or visceral pleura after receiving 54 Gy/8 Fr. No adverse respiratory reaction was noted in the symptoms or respiratory function tests. The 3-year local control rate was 80.4% +/- 7.1% (a standard error) with a median follow-up period of 17 months for survivors. Because of the Grade 5 toxicity, we have halted this Phase I/II study and are planning to rearrange the protocol setting accordingly. The 3-year local control rate was 69.6 +/- 10.6% for patients who received 48 Gy and 100% for patients who received 60 Gy (p = 0.0442).

CONCLUSIONS

Small-volume IGRT using 60 Gy in eight fractions is highly effective for the local control of lung tumors, but MTD has not been determined in this study. The organs at risk are extrapleural organs such as the esophagus and internal chest wall/visceral pleura rather than the pulmonary parenchyma in the present protocol setting. Consideration of the uncertainty in the contouring of normal structures is critically important, as is uncertainty in setup of patients and internal organ in the high-dose hypofractionated IGRT.

Prediction of the benefits from dose-escalated hypofractionated intensity-modulated radiotherapy for prostate cancer

PURPOSE

To estimate the benefits of dose escalation in hypofractionated intensity-modulated radiotherapy (IMRT) for prostate cancer, using radiobiologic modeling and incorporating positional uncertainties of organs.

MATERIALS AND METHODS

Biologically based mathematical models for describing the relationships between tumor control probability (TCP) and normal-tissue complication probability (NTCP) vs. dose were used to describe some of the results available in the literature. The values of the model parameters were then used together with the value of 1.5 Gy for the prostate cancer alpha/beta ratio to predict the responses in a hypofractionated 3 Gy/fraction IMRT trial at the Christie Hospital, taking into account patient movement characteristics between dose fractions.

RESULTS

Compared with the current three-dimensional conformal radiotherapy technique (total dose of 50 Gy to the planning target volume in 16 fractions), the use of IMRT to escalate the dose to the prostate was predicted to increase the TCP by 5%, 16%, and 22% for the three dose levels, respectively, of 54, 57, and 60 Gy delivered using 3 Gy per fraction while keeping the late rectal complications (>/=Grade 2 RTOG scale) at about the same level of 5%. Further increases in TCP could be achieved by reducing the uncertainty in daily target position, especially for the last stage of the trial, where up to 6% further increase in TCP should be gained.

CONCLUSIONS

Dose escalation to the prostate using IMRT to deliver daily doses of 3 Gy was predicted to significantly increase tumor control without increasing late rectal complications, and currently this prediction is being tested in a clinical trial.

A new irradiation system for lung cancer combining linear accelerator, computed tomography, patient self-breath-holding, and patient-directed beam-control without respiratory monitoring devices

PURPOSE

To introduce and assess a new irradiation technique for lung cancer that utilizes a linear accelerator and computed tomography (CT) scanner combination, along with a novel switching mechanism, which enables patients to synchronize the duration of irradiation with self-breath-holding without respiratory monitoring devices.

MATERIALS AND METHODS

A newly developed treatment unit, a linear accelerator combined with a CT scanner (CT-linac), was used for irradiation. A novel switching mechanism, connected directly to the console of the linear accelerator, enabled the patient to control the radiation beam to correspond with the duration of self-breath-holding during a session determined by a radiation technologist. Twenty patients with lung cancer were enrolled in this study. All patients were instructed in the technique of breath-holding during the inspiration phase using visualization of respiratory motion through fluoroscopy as a teaching aid. CT scans under patients' self-breath-holding were repeated three times, and differences in tumor position on CT images were measured. The reproducibility of tumor position was visually evaluated on electronic portal images (EPI).

RESULTS

Mean maximum differences in tumor position under patients' self-breath-holding were 2.2 mm in the cranial-caudal direction, 1.4 mm in the anterior-posterior direction, and 1.3 mm in the right-left direction. Switching of the radiation beam was delayed less than 0.1 s behind patient switching. EPIs were used to determine that reproducibility of tumor position was satisfactorily accurate.

CONCLUSIONS

The reproducibility of tumor position, during patient self-breath-holding synchronized with patient-initiated radiation and without a respiratory monitoring device, was sufficiently accurate. This novel irradiation technique for lung tumors using a combination CT-linac offers reduced PTV, sufficient reproducibility, and decreased duration of treatment.

Stereotactic conformal radiotherapy for posterior fossa tumours: a modelling study for potential improvement in therapeutic ratio

PURPOSE

To investigate the optimal technique of stereotactic conformal radiotherapy (SCRT) for posterior fossa tumours.

MATERIAL AND METHODS

SCRT planning image data sets of four patients with posterior fossa tumours constituted the study material. Based on the operative notes and preoperative imaging, a clinical target volume (CTV) was drawn for each patient. An additional CTV representative of a typical posterior fossa tumour was also drawn on each patient's localisation scans. Therefore a total of eight CTVs differing in their size and location were used for further work. A margin of 5 mm was grown in three dimensions to result in a final planning target volume (PTV). Beam arrangements studied were conformal bilateral parallel pair, a three-field coplanar arrangement with two bilateral and a vertex beam, two three-field non-coplanar techniques and a six-field non-coplanar technique with conformation achieved by micromultileaf collimator (mMLC). Normal structures contoured included normal posterior fossa brain (excluding PTV), brain stem, cochleae, optic apparatus, pituitary-hypothalamic axis (PHA), supratentorial brain and the temporal lobes. Comparative evaluation of plans was done with dose volume histograms (DVH), conformity index (CI) and dose heterogeneity (DH).

RESULTS

In all plans, the 95% isodose line covered at least 99% of the PTV with acceptable dose heterogeneity. As compared to the baseline bilateral conformal parallel pair plan, all other plans achieved significantly more sparing of the normal posterior fossa brain at the 95 and 80% dose prescription levels with superior CI (at 95% isodose). The six-field technique resulted in maximum sparing as compared to the bilateral plan with a mean additional sparing of 74% (46.2 cm3) and 55% (33.83) at 95 and 80% dose prescription level, respectively (P<0.0001). Among the three field plans, the technique of bilateral and vertex fields resulted in least doses to cochlea and also irradiated the least volume of brain stem and PHA. Comparison of this technique to the six-field technique did not show any significant difference in sparing of normal structures in the posteriorly placed tumours. In anteriorly placed tumours, the six-field technique was the most optimal irrespective of the size of the target volumes.

CONCLUSIONS

A six-field plan SCRT achieves the most significant sparing of the normal tissues for localised irradiation in posterior fossa tumours, particularly for anteriorly located tumours. A relatively simpler three-field plan with bilateral and a vertex beam is equally good for tumours that are placed posteriorly and away from the brain stem.

Re-irradiation in conjunction with liposomal doxorubicin for the treatment of skin metastases of recurrent breast cancer: a radiobiological approach and 2 year of follow-up

Thirty patients with local relapses after radical mastectomy and radiotherapy and undergoing infusion of liposomal doxorubicin (40 mg/m(2) monthly for 6 months) were randomized to receive re-irradiation. Radiotherapy was with either 17 fractions of 1.8 Gy, 5 days a week (N=15, group A) or 4 Gy plus two fractions of 3 Gy the 1st week and six fractions of 3 Gy given every second day (N=15, group B). Eight patients from group A (53.3%) and nine patients (60%) from group B demonstrating a clinically complete response (P=0.9). Grade I/II acute skin toxicity was monitored in 26.6% of patients in group A versus 73.3% in group B. The radiation schedule of group A seems superior for grade I/II acute (P=0.027) and late (P=0.015) skin toxicity. The linear quadratic model enabled the prediction of tumor response as well as normal skin reactions.

Radiation exposure of normal temporal bone structures during stereotactically guided gamma knife surgery for vestibular schwannomas

OBJECT

The dosimetry of radiation exposure of healthy inner, middle, and external ear structures that leads to hearing loss, tinnitus, facial weakness, dizziness, vertigo, and imbalance after gamma knife surgery (GKS) for vestibular schwannomas (VSs) is unknown. The authors quantified the dose of radiation received by these structures after GKS for VS to assess the likelihood that these doses contributed to postradiosurgery complications.

METHODS

A retrospective study was performed using a prospectively acquired database of a consecutive series of 54 patients with VS who were treated with GKS during a 3.5-year period at an "open unit" gamma knife center. Point doses were measured for 18 healthy temporal bone structures in each patient, with the anatomical position of each sampling point confirmed by a fellowship-trained neurootologist. These values were compared against single-dose equivalents for the 5-year tolerance dose for a 5% risk of complications and the 5-year tolerance dose for a 50% risk of complications, which were calculated using known 2-Gy/fraction thresholds for chronic otitis, chondromalacia, and osseous necrosis, as well as the tumor margin dose and typical tumor margin prescription doses for patients in whom hearing preservation was attempted. External and middle ear doses were uniformly low. The intratemporal facial nerve is susceptible to unintentionally high radiation exposure at the fundus of the internal auditory canal, with higher than tumor margin doses detected in 26% of cases. In the cochlea, the basal turn near the modiolus and its inferior portion are most susceptible, with doses greater than 12 Gy detected in 10.8 and 14.8% of cases. In the vestibular labyrinth, the ampulated ends of the lateral and posterior semicircular canals are most susceptible, with doses greater than 12 Gy detected in 7.4 and 5.1% of cases.

CONCLUSIONS

Doses delivered to middle and external ear structures are unlikely to contribute to post-GKS complications, but unexpectedly high doses may be delivered to sensitive areas of the intratemporal facial nerve and inner ear. Unintentional delivery of high doses to the stria vascularis, the sensory neuroepithelium of the inner ear organs and/or their ganglia, may play a role in the development of post-GKS tinnitus, hearing loss, dizziness, vertigo, and imbalance. Minimizing treatment complications post-GKS for VS requires precise dose planning conformality with the three-dimensional surface of the tumor.

Stricture of the proximal esophagus in head and neck carcinoma patients after radiotherapy

BACKGROUND

It is well recognized that many patients with head and neck carcinoma have problems with food intake and malnutrition. The objective of the current study was to determine the clinical pattern of patients with nonneoplastic stricture of the upper esophagus after radiotherapy for head and neck carcinoma.

METHODS

A retrospective chart study of 22 patients with stricture of the proximal esophagus diagnosed between 1993 and 1999 at Karolinska Hospital was performed. The dose volume histograms of the first 2 cm and 5 cm, respectively, of the proximal esophagus were calculated.

RESULTS

Five of the patients (23%) had total obliteration. The first 2 cm of the esophagus received at least 60 grays (Gy) in > 80% of the volume. Radiation injury was not reported to occur at doses < 60 Gy. There was a correlation found between dysphagia during radiotherapy and the development of proximal esophageal stricture. Stricture was diagnosed 1-60 months (median, 6 months) after radiotherapy. In 18 patients, the stricture was treated with single or repeated endoscopic dilation. These treatments allowed a nearly normal diet in 78% of the patients.

CONCLUSIONS

Stricture of the upper esophagus is one deglutition disorder that is reported to occur after radiotherapy for head and neck carcinoma. In the current study, the authors emphasize the importance of knowing the tolerance of the normal esophagus to irradiation as well as early diagnosis of stricture of the proximal esophagus because this condition may lead to physical and emotional distress.

Clinical evaluation of dynamic arc conformal radiotherapy for paraaortic lymph node metastasis

PURPOSE

This study was performed to evaluate the efficacy and safety of dynamic arc conformal radiotherapy, a simple intensity modulated radiation therapy (IMRT), for the treatment of paraaortic lymph node metastases.

MATERIALS AND METHODS

Twenty-nine patients with paraaortic lymph node metastases were enrolled in this study. The total planned dose was 55-60 Gy. A computed tomography (CT) simulator was used in the treatment planning.

RESULTS

The total radiation dose delivered was 50-63.4 Gy (median 60 Gy). Sixteen of 29 patients showed local tumor shrinkage on CT, and the 2 year in-field recurrence free survival rate was 58%. Acute Grade 1 and Grade 2 gastrointestinal disorders occurred in 31% and 17%, respectively, and acute Grade 2 liver dysfunction occurred in 7%. As a late complication, Grade 1 and Grade 2 liver dysfunction occurred in six patients (21%) and five patients (17%), respectively. There was no renal dysfunction or myelopathy detected.

CONCLUSION

Dynamic arc conformal radiotherapy, a simple IMRT, is a safe and effective treatment method for paraaortic lymph node metastasis.