Tolerance of normal tissue to therapeutic irradiation

Class solutions for conformal external beam prostate radiotherapy

PURPOSE

To determine a class solution coplanar plan from comparisons of three-field (3F), four-field (4F), and six-field (6F) plans in conformal non-intensity-modulated prostate radiotherapy.

METHODS AND MATERIALS

Doses to two clinical target volumes, prostate only (PO) and prostate plus seminal vesicles (PSV) were evaluated in each of 10 patients using a variety of 3F, 4F, and 6F plans with a planning target volume margin of 10 mm. All plans were prescribed to 64 and 74 Gy. The class solution plan for each of 3F, 4F, and 6F was chosen from a variety of symmetrical and asymmetrical field arrangements that had been previously assessed. The class solution plans, 3F (0, 90, 270 degrees ), 4F (35, 90, 270, 325 degrees ), and 6F (50/lat/25) were compared with reference plans: 3F (0, 120, 240 degrees ), 4F (0, 90, 180, 270 degrees ), and 6F (55, 90, 125, 235, 270, 305 degrees ). Rectal volumes irradiated to greater than 50% (V(50)), 80% (V(80)), and 90% (V(90)) of the prescribed dose, normal tissue complication probabilities (NTCP) for rectum, bladder, and femoral heads (FH), and tumor control probabilities (TCP) were assessed. FH tolerance was set at 52 Gy to 10% volume.

RESULTS

The field arrangement that gave the lowest irradiated rectal volume with acceptable bladder and FH doses was a 3F (0, 90, 270 degrees ) class solution plan. This plan gave a reduction in rectal V(80) of 1.2-12.4% for the PO group and 2.3-23.8% for the PSV group compared with the other plans. The reduction in rectal V(90) was 0.2-11.9% for the PO group and 1.5-23.3% for the PSV group using the 3F (0, 90, 270 degrees ) plan. This plan provided one of the lowest rectal NTCPs, but the difference was not significant when compared with the 4F class solution plan. When target volumes with 10-mm margins remain unchanged to 74 Gy, the irradiated rectal volumes for all plans were higher and rectal NTCPs can be trebled.

CONCLUSION

The use of appropriate beam arrangements can provide a class solution plan using only 3 fields compared with 4 or 6 fields for the parameters considered. Both 3F (0, 90, 270 degrees ) and 4F (35, 90, 270, 325 degrees ) plans can be used as a class solution plan. Other practical issues that may influence the choice of class solution include delivery time with smaller number of fields, ease of verification, the use of 10-mm multileaf collimation vs. conformal blocks, and field shape fitting limitations when using dynamic wedges.

Boron neutron capture therapy of brain tumors: clinical trials at the finnish facility using boronophenylalanine

Two clinical trials are currently running at the Finnish dedicated boron neutron capture therapy (BNCT) facility. Between May 1999 and December 2001, 18 patients with supratentorial glioblastoma were treated with boronophenylalanine (BPA)-based BNCT within a context of a prospective clinical trial (protocol P-01). All patients underwent prior surgery, but none had received conventional radiotherapy or cancer chemotherapy before BNCT. BPA-fructose was given as 2-h infusion at BPA-dosages ranging from 290 to 400 mg/kg prior to neutron beam irradiation, which was given as a single fraction from two fields. The average planning target volume dose ranged from 30 to 61 Gy (W), and the average normal brain dose from 3 to 6 Gy (W). The treatment was generally well tolerated, and none of the patients have died during the first months following BNCT. The estimated 1-year overall survival is 61%. In another trial (protocol P-03), three patients with recurring or progressing glioblastoma following surgery and conventional cranial radiotherapy to 50-60 Gy, were treated with BPA-based BNCT using the BPA dosage of 290 mg/kg. The average planning target dose in these patients was 25-29 Gy (W), and the average whole brain dose 2-3 Gy (W). All three patients tolerated brain reirradiation with BNCT, and none died during the first three months following BNCT. We conclude that BPA-based BNCT has been relatively well tolerated both in previously irradiated and unirradiated glioblastoma patients. Efficacy comparisons with conventional photon radiation are difficult due to patient selection and confounding factors such as other treatments given, but the results support continuation of clinical research on BPA-based BNCT.

Intensity-modulated radiation therapy (IMRT) for locally advanced paranasal sinus tumors: incorporating clinical decisions in the optimization process

PURPOSE

Intensity-modulated radiotherapy (IMRT) plans require decisions about priorities and tradeoffs among competing goals. This study evaluates the incorporation of various clinical decisions into the optimization system, using locally advanced paranasal sinus tumors as a model.

METHODS AND MATERIALS

Thirteen patients with locally advanced paranasal sinus tumors were retrospectively replanned using inverse planning. Two clinical decisions were assumed: (1) Spare both optic pathways (OP), or (2) Spare only the contralateral OP. In each case, adequate tumor coverage (treated to 70 Gy in 35 fractions) was required. Two beamlet IMRT plans were thus developed for each patient using a class solution cost function. By altering one key variable at a time, different levels of risk of OP toxicity and planning target volume (PTV) compromise were compared in a systematic manner. The resulting clinical tradeoffs were analyzed using dosimetric criteria, tumor control probability (TCP), equivalent uniform dose (EUD), and normal tissue complication probability.

RESULTS

Plan comparisons representing the two clinical decisions (sparing both OP and sparing only the contralateral OP), with respect to minimum dose, TCP, V(95), and EUD, demonstrated small, yet statistically significant, differences. However, when individual cases were analyzed further, significant PTV underdosage (>5%) was present in most cases for plans sparing both OP. In 6/13 cases (46%), PTV underdosage was between 5% and 15%, and in 3 cases (23%) was greater than 15%. By comparison, adequate PTV coverage was present in 8/13 cases (62%) for plans sparing only the contralateral OP. Mean target EUD comparisons between the two plans (including 9 cases where a clinical tradeoff between PTV coverage and OP sparing was required) were similar: 68.6 Gy and 69.1 Gy, respectively (p = 0.02). Mean TCP values for those 9 cases were 56.5 vs. 61.7, respectively (p = 0.006).

CONCLUSIONS

In IMRT plans for paranasal sinus tumors, tradeoff values between OP toxicity and PTV coverage can be compared for different clinical decisions. The information derived can then be used to individualize the parameters within the optimization system. This process of determining clinical tradeoffs associated with different clinical decisions may be a useful tool in other sites.

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

PURPOSE

To compare different normal tissue complication probability (NTCP) models to predict the incidence of radiation pneumonitis on the basis of the dose distribution in the lung.

METHODS AND MATERIALS

The data from 382 breast cancer, malignant lymphoma, and inoperable non-small-cell lung cancer patients from two centers were studied. Radiation pneumonitis was scored using the Southwestern Oncology Group criteria. Dose-volume histograms of the lungs were calculated from the dose distributions that were corrected for dose per fraction effects. The dose-volume histogram of each patient was reduced to a single parameter using different local dose-effect relationships. Examples of single parameters were the mean lung dose (MLD) and the volume of lung receiving more than a threshold dose (V(Dth)). The parameters for the different NTCP models were fit to patient data using a maximum likelihood analysis.

RESULTS

The best fit resulted in a linear local dose-effect relationship, with the MLD as the resulting single parameter. The relationship between the MLD and NTCP could be described with a median toxic dose (TD(50)) of 30.8 Gy and a steepness parameter m of 0.37. The best fit for the relationship between the V(Dth) and the NTCP was obtained with a D(th) of 13 Gy. The MLD model was found to be significantly better than the V(Dth) model (p <0.03). However, for 85% of the studied patients, the difference in NTCP calculated with both models was <10%, because of the high correlation between the two parameters. For dose distributions outside the range of the studied dose-volume histograms, the difference in NTCP, using the two models could be >35%. For arbitrary dose distributions, an estimate of the uncertainty in the NTCP could be determined using the probability distribution of the parameter values of the Lyman-Kutcher-Burman model.

CONCLUSION

The maximum likelihood method revealed that the underlying local dose-effect relation for radiation pneumonitis was linear (the MLD model), rather than a step function (the V(Dth) model). Thus, for the studied patient population, the MLD was the most accurate predictor for the incidence of radiation pneumonitis.

Combining dosimetry for targeted radionuclide and external beam therapies using the biologically effective dose

It is not uncommon for a patient to receive both external beam and targeted radionuclide therapy during the course of a cancer treatment. The total dose received by the tumor and by normal tissues will therefore be subject to the contributions of both treatment modalities. However, the two treatments are generally applied independently of one another, with little attention paid to the combined effect. With the availability of patient-specific three-dimensional dosimetry for radionuclide therapies, it is pertinent now to consider the combined effect of the two treatments, and to investigate how dosimetry for this situation may be carried out. Methodology has been developed to allow a combination of dose information from the two types of therapy. The biologically effective dose (BED) has been employed to address the issue of inequivalence of biological effect of the two therapies. Dose distributions have been represented as distributions of BED, and the net effect resulting from the combination of these two therapies demonstrated through a combination of BED maps. Examples are presented of cases in which this analysis of a combined therapy provides a more favorable treatment than either therapy alone. For one patient the ratio of the mean spinal cord dose to the mean CTV dose was calculated for both an external beam therapy alone and for a combined therapy and was found to be 0.40 and 0.16, respectively.

Predictors of radiation-induced esophageal toxicity in patients with non-small-cell lung cancer treated with three-dimensional conformal radiotherapy

PURPOSE

To evaluate the incidence and clinical/dosimetric predictors of acute and late Radiation Therapy Oncology Group Grade 3-5 esophageal toxicity in patients with non-small-cell lung cancer (NSCLC) treated with definitive three-dimensional conformal radiotherapy (3D-CRT).

METHODS AND MATERIALS

We retrospectively reviewed the charts of 207 consecutive patients with NSCLC who were treated with high-dose, definitive 3D-CRT between March 1991 and December 1998. This population consisted of 107 men and 100 women. The median age was 67 years (range 31-90). The following patient and treatment parameters were studied: age, gender, race, performance status, sequential chemotherapy, concurrent chemotherapy, presence of subcarinal nodes, pretreatment weight loss, mean dose to the entire esophagus, maximal point dose to the esophagus, and percentage of volume of esophagus receiving >55 Gy. All doses are reported without heterogeneity corrections. The median prescription dose to the isocenter in this population was 70 Gy (range 60-74) delivered in 2-Gy daily fractions. All patients were treated once daily. Acute and late esophageal toxicities were graded by Radiation Therapy Oncology Group criteria. Patient and clinical/dosimetric factors were coded and correlated with acute and late Grade 3-5 esophageal toxicity using univariate and multivariate regression analyses.

RESULTS

Of 207 patients, 16 (8%) developed acute (10 patients) or late (13 patients) Grade 3-5 esophageal toxicity. Seven patients had both acute and late Grade 3-5 esophageal toxicity. One patient died (Grade 5 esophageal toxicity) of late esophageal perforation. Concurrent chemotherapy, maximal point dose to the esophagus >58 Gy, and a mean dose to the entire esophagus >34 Gy were significantly associated with a risk of Grade 3-5 esophageal toxicity on univariate analysis. Concurrent chemotherapy and maximal point dose to the esophagus >58 Gy retained significance on multivariate analysis. Of 207 patients, 53 (26%) received concurrent chemotherapy. Fourteen (88%) of the 16 patients who developed Grade 3-5 esophageal toxicity had received concurrent chemotherapy (p = 0.0001, Pearson's chi-square test). No case of Grade 3-5 esophageal toxicity occurred in patients who received a maximal point dose to the esophagus of <58 Gy (p = 0.0001, Fisher's exact test, two-tail). Only 2 patients developed Grade 3-5 esophageal toxicity in the absence of concurrent chemotherapy; both received a maximal esophageal point dose >69 Gy. All assessable patients who developed Grade 3-5 esophageal toxicity had a mean dose to the entire esophagus >34 Gy (p = 0.0351, Pearson's chi-square test). However, the mean dose was not predictive on multivariate analysis.

CONCLUSION

Concurrent chemotherapy and the maximal esophageal point dose were significantly associated with a risk of Grade 3-5 esophageal toxicity in patients with NSCLC treated with high-dose 3D-CRT. In patients who received concurrent chemotherapy, the threshold maximal esophageal point dose for Grade 3-5 esophageal toxicity was 58 Gy. An insufficient number of patients developed Grade 3-5 esophageal toxicity in the absence of chemotherapy to allow a valid statistical analysis of the relationship between the maximal esophageal point dose and esophagitis.

Inverse and forward optimization of one- and two-dimensional intensity-modulated radiation therapy-based treatment of concave-shaped planning target volumes: the case of prostate cancer

BACKGROUND

Intensity-modulated radiation therapy (IMRT) was suggested as a suitable technique to protect the rectal wall, while maintaining a satisfactory planning target volume (PTV) irradiation in the case of high-dose radiotherapy of prostate cancer. However, up to now, few investigations tried to estimate the expected benefit with respect to conventional three-dimensional (3D) conformal radiotherapy (CRT).

PURPOSE

Estimating the expected clinical gain coming from both 1D and 2D IMRT against 3DCRT, in the case of prostate cancer by mean of radiobiological models. In order to enhance the impact of IMRT, the case of concave-shaped PTV including prostate and seminal vesicles (P+SV) was considered.

MATERIALS AND METHODS

Five patients with concave-shaped PTV including P+SV were selected. Two different sets of constraints were applied during planning: in the first one a quite large inhomogeneity of the dose distribution within the PTV was accepted (set (a)); in the other set (set (b)) a greater homogeneity was required. Tumor control probability (TCP) and normal tissue control probability (NTCP) indices were calculated through the Webb-Nahum and the Lyman-Kutcher models, respectively. Considering a dose interval from 64.8 to 100.8 Gy, the value giving a 5% NTCP for the rectum was found (D(NTCP(rectum)=5%)) using two different methods, and the corresponding TCP(NTCP(rectum)=5%) and NTCP(NTCP(rectum)=5%) for the other critical structures were derived. With the first method, the inverse optimization of the plans was performed just at a fixed 75.6 Gy ICRU dose; with the second method (applied to 2/5 patients) inverse treatment plannings were re-optimized at many dose levels (from 64.8 to 108 Gy with 3.6 Gy intervals). In this case, three different values of alpha/beta (10, 3, 1.5)were used for TCP calculation. The 3DCRT plan consisted of a 3-fields technique; in the IMRT plans, five equi-spaced beams were applied. The Helios Inverse Planning software from Varian was used for both the 2D IMRT and the 1D IMRT inverse optimization, the last one being performed fixing only one available pair of leaves for modulation. A previously proposed forward 1D IMRT 'class solution' technique was also considered, keeping the same irradiation geometry of the inversely optimized IMRT techniques.

RESULTS

With the first method, the average gains in TCP(NTCP(rectum)=5%) of the 2D IMRT technique, with respect 3DCRT, were 10.3 and 7.8%, depending on the choice of the DVHs constraints during the inverse optimization procedure (set (a) and set (b), respectively). The average gain (DeltaTCP(NTCP(rectum)=5%)) coming from the inverse 1D IMRT optimization was 5.0%, when fixing the set (b) DVHs constraints. Concerning the forward 1D IMRT optimization, the average gain in TCP(NTCP(rectum)=5%) was 4.5%. The gain was found to be correlated with the degree of overlapping between rectum and PTV. When comparing 2D IMRT and 1D IMRT, in the case of the more realistic set (b) constraints, DeltaTCP(NTCP(rectum)=5%) was always less than 3%, excepting one patient with a very large overlap region. Basing our choice on this result, the second method was applied to this patient and one of the remaining. Through the inverse re-optimization of the treatment plans at each dose level, the gain in TCP(NTCP(rectum)=5%) of the inverse 2D technique was significantly higher than the ones obtained by applying the first method (concerning the two patients: +6.1% and +2.4%), while no significant benefit was found for inverse 1D. The impact of changing the alpha/beta ratio was less evident in the patient with the lower gain in TCP(NTCP(rectum)=5%).

CONCLUSIONS

The expected benefit due to IMRT with respect to 3DCRT seems to be relevant when the overlap between PTV and rectum is high. Moreover, the difference between the inverse 2D and the simpler inverse or forward 1D IMRT techniques resulted in being relatively modest, with the exception of one patient, having a very large overlap between rectum and PTV. Optimizing the inverse planning at each dose level to find TCP(NTCP(rectum)=5%)e level to find TCP(NTCP(rectum)=5%) can improve the performances of inverse 2D IMRT, against a significant increase of the time for planning. These results suggest the importance of selecting the patients that could have significant benefit from the application of IMRT.

Defining the optimal dose of radiation after incomplete resection of central neurocytomas

PURPOSE

Central neurocytomas are uncommon benign central nervous system tumors. There is uncertainty regarding the most appropriate radiation dose after incomplete resection. This analysis was performed to determine the optimal dose.

METHODS AND MATERIALS

All cases reported since 1982 were reviewed for age, gender, resection status, total dose, dose per fraction, local control, and overall survival. Additional data were obtained from the authors. The inclusion criteria were incomplete resection, postoperative irradiation, complete data, and 12 months' minimal follow-up. Two groups were formed according to the equivalent dose in 2-Gy fractions (EQD2): group A (40.0-53.6 Gy) and group B (54.0-62.2 Gy). Local control and survival were compared using Kaplan-Meier analysis and the log-rank test.

RESULTS

Eighty-nine patients (group A 42, group B 47) met the inclusion criteria. At 5 years, the local control rate was 98% for group B vs. 69% for group A. At 10 years, it was 89% vs. 65% (p = 0.0066). The 5- and 10-year survival rate was 98% for group B vs. 88% for group A (p = 0.1).

CONCLUSIONS

Our data suggest that a EQD2 > or =54 Gy significantly improves local control in patients with subtotally resected neurocytomas. Although the difference in survival was not significant, a trend toward better survival was noted after a EQD2 of > or =54 Gy.

Physical aspects of yttrium-90 microsphere therapy for nonresectable hepatic tumors

Administration of yttrium-90 microspheres via the hepatic artery is an attractive approach to selectively deliver therapeutic doses of radiation to liver malignancies. This procedure allows delivering radiation absorbed doses in excess of 100 Gy to the tumors without significant liver toxicity. The microsphere therapy involves different specialties including medical oncology, radiation oncology, nuclear medicine, interventional radiology, medical physics, and radiation safety. We have treated 80 patients with nonresectable hepatic tumors with yttrium-90 microspheres during the past two years on an institutional study protocol. The nominal radiation absorbed dose to the tumor in this study was 150 Gy. Required activity was calculated based on the nominal radiation absorbed dose and patient's liver volume obtained from the CT scan, assuming a uniform distribution of the microspheres within the liver. Microspheres were administered via a catheter placed into the hepatic artery. The actual radiation absorbed doses to tumors and normal liver tissue were calculated retrospectively based on the patient's 99mTc-MAA study and CT scans. As expected, the activity uptake within the liver was found to be highly nonuniform and multifold tumor to nontumor uptake was observed. A partition model was used to calculate the radiation absorbed dose within each region. For a typical patient the calculated radiation absorbed doses to the tumor and liver were 402 and 118 Gy, respectively. The radiation safety procedure involves confinement of the source and proper disposal of the contaminated materials. The average exposure rates at 1 m from the patients and on contact just anterior to the liver were 6 and 135 uSv/h, respectively. The special physics and dosimetry protocol developed for this procedure is presented.

Intensity modulation in radiotherapy: photons versus protons in the paranasal sinus

PURPOSE

The purpose of this study is to investigate whether successive tightening of normal tissue constraints on an intensity modulated X-ray therapy plan might be able to improve it to the point of clinical comparability with the corresponding intensity modulated proton therapy plan.

MATERIALS AND METHODS

Photon and proton intensity modulated plans were calculated for a paranasal sinus case using nominal dose constraints. Additional photon plans were then calculated in an effort to match the dose-volume histograms of the critical structures to those of the proton plan.

RESULTS

On reducing the low dose contribution to both orbits in the photon plan by tightening the constraints on these structures, an increased dose heterogeneity across the target resulted. When all critical structures were more strictly constrained, target dose homogeneity and conformity was further compromised. An increased integral dose to the non-critical normal tissues was observed for the photon plans as dose was progressively removed from the critical structures.

CONCLUSIONS

Both modalities were found to provide comparable target volume conformation and sparing of critical structures, when the nominal dose constraints were applied. However, the use of intensity modulated protons provided the only method by which critical structures could be spared at all dose levels, whilst simultaneously providing acceptable dose homogeneity within the target volume.

Partial volume rat lung irradiation; assessment of early DNA damage in different lung regions and effect of radical scavengers

PURPOSE

These studies were designed to examine radiation-induced in-field and out-of-field DNA damage in rat lung as a function of dose and various volumes of irradiation. They also determined whether superoxide dismutase (SOD) and nitro-L-arginine methyl ester (L-NAME) protected against this damage.

METHODS AND MATERIALS

The whole lung, or various volumes of the lower or upper lungs of Sprague-Dawley rats were exposed to doses up to 20 Gy of 60Co gamma rays. Radiation-induced DNA damage was quantified in fibroblasts obtained at 18 h after irradiation from both irradiated and shielded lung regions using a micronucleus assay. The radioprotective role of SOD (CuZnSOD: 10 mg/kg body weight; MnSOD: 50-100mg/kg body weight) and L-NAME (0.2 mg/kg body weight.) in vivo was determined by injecting them into rats 30 min before or immediately after a dose of 10 Gy.

RESULTS

Micronucleus formation was approximately linear with dose up to 15 Gy. When 70% of the lung volume was irradiated with 10 Gy, irradiated lower lung gave similar numbers of micronuclei (MN)/binucleate cell (BN) to that observed following whole lung irradiation (0.91 MN/BN), whereas the irradiated upper lung gave only 0.66 MN/BN. Following lower lung irradiation, the shielded upper lung (30% of lung volume) showed substantial (out-of-field) damage (0.43 MN/BN). When 30% of the lung was given 10 Gy, irradiated upper or lower lung showed similar amounts of in-field damage (0.43 MN/BN) but this was smaller than that seen following irradiation of 70% of the lung volume. For 30% lower lung irradiation, the shielded upper lung showed only a small out-of-field effect (0.1 MN/BN). For both volumes of irradiation there was a similar or smaller effect in the shielded lower lung after upper lung irradiation. Injection of SOD before or L-NAME after 10 Gy to the lower 70% lung volume resulted in a reduction in DNA damage both in-field and out-of-field but the percentage was much greater for out-of-field damage (50-60%) than for in-field damage (10-30%). Following whole lung irradiation (10 Gy) significantly greater DNA damage was observed in fibroblasts from the left lung than from the right lung (0.93 MN/BN vs. 0.82 MN/BN). Following whole lung irradiation there was no significant difference in DNA damage observed in fibroblasts from the lower lung and the upper lung.

CONCLUSIONS

With partial lung irradiation the lower lung sustains more in-field DNA damage following irradiation than the upper lung, whereas out-of-field effects are observed primarily in the upper lung (i.e. following lower lung irradiation). Following whole lung irradiation the left lung sustains more damage than the right lung but there is no difference between the upper and lower lung. The protective effects of SOD and L-NAME suggest that inflammatory cytokines induced by the irradiation may be involved in the initiation of a reaction resulting in the production of reactive oxyradicals and nitric oxide that cause indirect DNA damage both in and out of the radiation field.

Is there a dose-effect relationship for the treatment of symptomatic vertebral hemangioma?

PURPOSE

Symptomatic vertebral hemangiomas are rare vascular lesions. Radiotherapy is the most common treatment. Because of a lack of information in the literature, uncertainty exists about the total radiation dose to be applied.

METHODS AND MATERIALS

Individual data from our own and published patients with symptomatic vertebral hemangioma treated with radiotherapy alone were obtained. The data were pooled, and the impact of the total dose on complete pain relief was evaluated using the chi-square test. Because different single-fraction doses were used, the equivalent dose in 2-Gy fractions (EQD(2)) was used for the analysis.

RESULTS

Complete data could be obtained from 117 patients. Patients were categorized according to total dose (EQD(2)) into two groups of similar size (Group A: 20-34 Gy, n = 62; and Group B: 36-44 Gy, n = 55). Radiation-induced complete pain relief was achieved in 39% (24/62) of the patients in Group A and in 82% (45/55) of the patients in Group B. The difference was statistically significant (p = 0.003).

CONCLUSIONS

The data suggest a dose-effect relationship in the radiotherapy of symptomatic vertebral hemangiomas. We recommend a total radiation dose 36-40 Gy with a dose per fraction of 2.0 Gy.

Primary intraspinal primitive neuroectodermal tumor: report of two cases and review of the literature

BACKGROUND

Primary intraspinal primitive neuroectodermal tumor (PNET) is a very rare tumor entity. The optimal therapeutic approach is not known yet. We report on two women with primary intraspinal PNETs and review the literature. We describe the typical course of the disease, compare our patients to the other 17 cases reported until today, and discuss therapeutic options.

PATIENTS AND METHOD

Case A: In a 49-year-old woman with an intraspinal PNET at L2, laminectomy and a gross tumor removal was accomplished. Postoperative radiation was performed from T12 to L3 to a dose of 50.4 Gy. Subsequently she was treated with chemotherapy containing vincristine, cisplatinum and lomustine. Case B: A 29-year-old woman presented with intramedullary PNET lesions at T1-3 and T10-11. Due to the multifocal location, she received a primary craniospinal axis irradiation to a dose of 35.2 Gy plus a boost to the tumor region to a total dose of 53.2 Gy.

RESULTS

Both patients developed multilocular intraspinal relapses with meningeosis neoplastica 17 and 6 months from radiation therapy and underwent palliative chemotherapy. Case A died 23 months, case B 17 months after primary diagnosis.

CONCLUSION

Despite modern treatment with microsurgery, irradiation and chemotherapy in primary intraspinal PNETs, local relapse or dissemination in most cases lead to death within a few months. An improvement of treatment outcome can only be achieved by intensification through multidisciplinary treatment.

Beam orientation selection for intensity-modulated radiation therapy based on target equivalent uniform dose maximization

PURPOSE

To develop an automated beam-orientation selection procedure for intensity-modulated radiotherapy (IMRT), and to determine if a small number of beams picked by this automated procedure can yield results comparable to a large number of manually placed orientations.

METHODS AND MATERIALS

The automated beam selection procedure maximizes an unconstrained objective function composed of target equivalent uniform dose (EUD) and critical structure dose-volume histogram (DVH) constraints. Beam orientations are selected from a large feasible set of directions through a series of alternating fluence optimization and orientation alteration steps, until convergence to a stable orientation set. The fluence optimization step adjusts fluences to maximize the objective function. The orientation alteration step substitutes beams in the orientation set currently under consideration with beams of the parent set in the immediate angular vicinity; the altered orientation set is deemed current if it produces a higher objective function value in the fluence optimization step.

RESULTS AND CONCLUSIONS

It is demonstrated, for prostate IMRT planning, that a modest number of appropriately selected beam orientations (3 or 5) can provide dose distributions as satisfactory as those produced by a large number of unselected equispaced orientations. Such selected beam orientations can reduce overall treatment time, thus making IMRT more clinically practical.

Comparative analysis of intensity modulation inverse planning modules of three commercial treatment planning systems applied to head and neck tumour model

BACKGROUND AND PURPOSE

Three commercial treatment planning modules for intensity modulated radiation therapy (IMRT) Inverse Planning, MDS-Nordion Helax-TMS, Varian Cadplan-Helios, and CMS Focus, were compared in an attempt to determine potential application limits or dosimetric differences among various optimisation algorithms.

MATERIALS AND METHODS

A comparative analysis of intensity modulated dose distributions was conducted at planning level on a group of four patients presenting advanced head and neck cancers. In the study, we analysed primarily the static 'step and shoot' multileaf implementation of modulation realisation with some investigation, on the Cadplan-Helios implementation of the 'sliding window', the Varian dynamic approach to IMRT delivery. The whole study was carried out using the inverse planning tools implemented by vendors fully optimising each plan to obtain the best dosimetry given some general plan objectives. To achieve adequate target coverage, optimisation was carried out on Helax-TMS and CMS Focus adding extra margins of 5 or 6mm to the planning target volume (PTV). Beam arrangements were set with five and nine equally spaced fields. The study was conducted with two complexity levels. At the first level, dose-volume constraints were applied only to the target volume and to the spinal cord, while parotid glands were added at the second level. The relative values of dose distributions and dose-volume histograms were compared, together with an estimate of the biological implications in terms of Equivalent Uniform Dose to the target. In the Cadplan-Helios system also the dosimetric implications of the number of intensity levels selected for the discretisation of the fluence matrix were investigated.

RESULTS

With the application of common planning strategies and the proper consideration of treatment planning system (TPS) specific features (e.g. the PTV margin problem), no substantial differences among the three algorithms were demonstrated at the first level for PTV and spinal cord. At the second level of the study differences were outlined for Helax-TMS, where sub-optimal results were obtained with the 5-field geometry. Mainly due to the differences in optimisation volumes, Cadplan-Helios presented significant better sparing of healthy tissue around the PTV, in terms of mean dose to healthy tissue and Irradiated Volume at 50% dose level. Finally, to achieve dosimetrically acceptable and stable results on target, a minimum of eight intensity levels should be applied for the multileaf collimator (MLC) segmentation, giving an average of 1.5 segments per field and per intensity level.

CONCLUSIONS

Results obtained for the three IMRT TPS show in first instance that the optimisation algorithms analysed, as well as the conversion from computed fluences to multileaf sequences implemented in the planning systems can produce substantially equivalent dose plans (for target coverage and organs at risk sparing) if planning is performed with common strategies and once a strong understanding of each system feature is achieved. Secondly, a limited number of dose levels (about eight) is adequate at planning level.

PET-guided IMRT for cervical carcinoma with positive para-aortic lymph nodes-a dose-escalation treatment planning study

PURPOSE

To evaluate a treatment planning method for dose escalation to the para-aortic lymph nodes (PALNs) based on positron emission tomography (PET) with intensity-modulated radiotherapy (IMRT) for cervical cancer patients with PALN involvement. One goal of this process was not to modify the traditional treatment of the pelvic region.

METHODS AND MATERIALS

PET images for 4 cervical cancer patents with PALN involvement were registered with their corresponding CT scans. Positive PALNs were identified on PET images, and the surrounding critical structures were delineated on CT images. The treatment machine central axis (CAX) was placed at the level of the L4-L5 vertebral body interspace. There were two distinct treatment regions: the para-aortic bed superior to the CAX and the whole pelvis region inferior to the CAX. IMRT was used for treatment planning of PALN bed irradiation. The positive PALNs identified on PET images were defined as the gross target volume, and the para-aortic bed was defined as the clinical target volume. The radiation doses were escalated from the conventional 45 Gy to 59.4 Gy for the gross target volume and 50.4 Gy for the clinical target volume in 33 fractions. The pelvis area was treated with conventional treatment methods, AP-PA beams to 50.4 Gy in 28 fractions with a brachytherapy implant boost. The placement of the CAX allowed the two treatment regions to be abutted using the treatment machine's independent jaws.

RESULTS

Dose escalation to positive PALNs, as identified on PET images, and the PALN bed is feasible with IMRT. Treatment plans for 4 patients revealed that escalated prescription doses could be delivered to target volumes while maintaining acceptable doses to the surrounding critical structures. Strategic placement of the treatment isocenter allows the IMRT region (PALN bed) and whole pelvis fields to be treated with a relatively uniform dose distribution in the abutment region.

CONCLUSION

This study indicates that PET-guided IMRT could be used in a clinical trial in an attempt to escalate doses delivered to patients with cervical cancer who have positive PALNs.

Patient specific quality assurance for the delivery of intensity modulated radiotherapy

A patient specific quality assurance program has been developed to facilitate the clinical implementation of intensity modulated radiotherapy (IMRT) delivered using a micro-multileaf collimator. The methodology includes several dosimetric tasks that are performed prior to the treatment of each patient. Film dosimetry is performed for each individual field and for the multifield composite plan. Individual field measurements are performed at a depth of 5 cm in a water equivalent slab phantom; export of dose calculations from the treatment planning system is similarly specified. For the composite distribution, parameters from the patient plan are applied to an IMRT phantom, and film is exposed in an axial orientation. Distributions are compared with the aid of software developed for the specific tasks. The measured and calculated dose distributions can be superimposed and positioned graphically using move, rotate, and mirror tools, as well as by specifying isocenter coordinates and using fiducial marks. Horizontal and vertical profiles are available for analysis. Dose difference, distance-to-agreement, and gamma index, the minimum scaled multidimensional distance between a measurement and a calculation point determined in combined dose and physical distance space, are calculated along a specified isodose line and displayed. gamma provides an excellent measure of disagreement between measurement and calculation for complex intensity distributions. We specify 3% dose difference and 3 mm distance as our scaling acceptability criteria. Absolute dosimetry for each composite plan is performed using an ionization chamber. To date, excellent agreement between measurements and calculations has been observed.

Fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT) for small acoustic neuromas

Eight patients with acoustic neuromas were treated using a novel method developed at our institution for delivering fractionated stereotactic intensity-modulated radiotherapy (FS-IMRT). We present treatment parameters, dosimetry analysis, and preliminary clinical outcome. The method incorporates high-precision invasive fixation, obliquely-oriented tomotherapy arcs, and reduced dimension pencil beams. The delivered dose distributions for the 8 patients treated from April 1999 to May 2001 were assessed for dose conformality, homogeneity, and doses to organs at risk. Total doses prescribed were 54 Gy in daily doses of 1.8 Gy. Results show that the median planning target volume (gross tumor volume plus a safety margin of 2 mm) was 2.48 cm3 (1.64 to 16.86 cm3) and that the median conformality and homogeneity indices were 1.69 (1.56 to 2.16) and 1.12 (1.09 to 1.19), respectively. The respective average mean and maximum doses to the brain stem were 12.67 Gy and 53.86 Gy. The treatment parameters for the novel FS-IMRT method developed here document excellent dose conformality and normal tissue sparing. Preliminary short-term follow-up (mean 17, median 18.5 months) revealed a 100% local control and hearing preservation rate. No new persistent impairment of facial and trigeminal nerve was observed. Our current follow-up experience indicates a reasonable potential for achieving outcomes comparable to established stereotactic radiotherapy techniques.

Intensity-modulated radiation therapy for the spine at the University of California, Irvine

Radiation treatment of malignant diseases of the spine poses unique challenges to the radiation oncology treatment team. Intensity-modulated radiation therapy (IMRT) offers the capability of delivering high doses to targets near the spine while respecting spinal cord tolerance. At the University of California, Irvine, 8 patients received a total of 10 courses to the spine for a variety of primary and metastatic malignant conditions. This paper discusses anatomical considerations, spinal cord radiation myelopathy, and treatment planning issues as it relates to the treatment of spinal cord lesions. Between October 1997 and August 2001, a total of 8 patients received 10 courses of IMRT for primary or metastatic disease of the spine. Cancers treated included metastatic lung, renal, adrenocortical cancers, and primary sarcomas and giant cell tumor. Five cases had 6 courses given for re-irradiation of symptomatic disease and 3 cases had 4 courses of IMRT as primary management of their spinal lesions. Although 3 courses were given postoperatively, these were for grossly residual disease. For the re-irradiation patients, the mean follow-up interval was 4 months. The local control was estimated at 14%. Of the patients treated with primary intent, the mean follow-up was 9 months and the local control rate 75%. No patients developed spinal cord complications.

Intensity-modulated radiation therapy in the treatment of children

Intensity-modulated radiation therapy (IMRT) is a relatively new method of conformal radiotherapy delivery that is rapidly being incorporated in clinical practice. Of all patients treated with conformal techniques, children are the most likely to benefit as normal, developing structures can be minimized in the radiation field. The advantages of IMRT, including increased conformality and possible dose escalation, are discussed in this review. Possible disadvantages of IMRT in children are also discussed, such as lack of dose homogeneity in the target volume, increased dose to nontarget tissues, reliability of treatment setup, increased anesthesia time in younger children, and prolonged treatment planning. The issue of increased risk of second malignancy in this very young population is important, as many of these children will be long-term survivors with current multimodality therapy.

Treatment of pancreatic cancer tumors with intensity-modulated radiation therapy (IMRT) using the volume at risk approach (VARA): employing dose-volume histogram (DVH) and normal tissue complication probability (NTCP) to evaluate small bowel toxicity

The emergent use of a combined modality approach (chemotherapy and radiation) in pancreatic cancer is associated with increased gastrointestinal toxicity. Intensity-modulated radiation therapy (IMRT) has the potential to deliver adequate dose to the tumor volume while decreasing the dose to critical structures such as the small bowel. We evaluated the influence of IMRT with inverse treatment planning on the dose-volume histograms (DVHs) of normal tissue compared to standard 3-dimensional conformal radiation treatment (3D-CRT) in patients with pancreatic cancer. Between July 1999 and May 2001, 10 randomly selected patients with adenocarcinoma of the pancreatic head were planned simultaneously with 3D-CRT and inverse-planned IMRT using the volume at risk approach (VaRA) and compared for various dosimetric parameters. DVH and normal tissue complication probability (NTCP) were calculated using IMRT and 3D-CRT plans. The aim of the treatment plan was to deliver 61.2 Gy to the gross tumor volume (GTV) and 45 Gy to the clinical treatment volume (CTV) while maintaining critical normal tissues to below specified tolerances. IMRT plans were more conformal than 3D-CRT plans. The average dose delivered to one third of the small bowel was lower with the IMRT plan compared to 3D-CRT. The IMRT plan resulted in one third of the small bowel receiving 30.2+/-12.9 Gy vs. 38.5+/-14.2 Gy with 3D-CRT (p = 0.006). The median volume of small bowel that received greater than either 50 or 60 Gy was reduced with IMRT. The median volume of small bowel exceeding 50 Gy was 19.2+/-11.2% (range 3% to 45%) compared to 31.4+/-21.3 (range 7% to 70%) for 3D-CRT (p = 0.048). The median volume of small bowel that received greater than 60 Gy was 12.5+/-4.8% for IMRT compared to 19.8+/-18.6% for 3D-CRT (p = 0.034). The VaRA approach employing IMRT techniques resulted in a lower dose per volume of small bowel that exceeded 60 Gy. We used the Lyman-Kutcher models to compare the probability of small bowel injury employing IMRT compared to 3D-CRT. The BIOPLAN model predicted a small bowel complication probability of 9.3+/-6% with IMRT compared to 24.4+/-18.9% with 3D-CRT delivery of dose (p = 0.021). IMRT with an inverse treatment plan has the potential to significantly improve radiation therapy of pancreatic cancers by reducing normal tissue dose, and simultaneously allow escalation of dose to further enhance locoregional control.

[Target-volume and critical-organ delineation for conformal radiotherapy of prostate cancer: experience of French dose-escalation trials]

The delineation of target volume and organs at risk depends on the organs definition, and on the modalities for the CT-scan acquisition. Inter-observer variability in the delineation may be large, especially when patient's anatomy is unusual. During the two french multicentric studies of conformal radiotherapy for localized prostate cancer, it was made an effort to harmonize the delineation of the target volumes and organs at risk. Two cases were proposed for delineation during two workshops. In the first case, the mean prostate volume was 46.5 mL (extreme: 31.7-61.3), the mean prostate and seminal vesicles volume was 74.7 mL (extreme: 59.6-80.3), the rectal and bladder walls varied respectively in proportion from 1 to 1.45 and from 1 to 1.16; in the second case, the mean prostate volume was 53.1 mL (extreme: 40.8-73.1), the volume of prostate plus seminal vesicles was 65.1 mL (extreme: 53.2-89), the rectal wall varied proportionally from 1 to 1, 24 and the vesical wall varied from 1 to 1.67. For participating centers to the french studies of dose escalation, a quality control of contours was performed to decrease the inter-observer variability. The ways to reduce the discrepancies of volumes delineation, between different observers, are discussed. A better quality of the CT images, use of urethral opacification, and consensual definition of clinical target volumes and organs at risk may contribute to that improvement.

Dose-response curves for late functional changes in the normal rat brain after single carbon-on doses evaluated by magnetic resonance imaging: influence of follow-up time and calculation of relative biological effectiveness

This study investigated late effects in the brain after irradiation with carbon ions using a rat model. Thirty-six animals were irradiated stereotactically at the right frontal lobe using an extended Bragg peak with maximum doses between 15.2 and 29.2 Gy. Dose-response curves for late changes in the normal brain were measured using T1- and T2-weighted magnetic resonance imaging (MRI). Tolerance doses were calculated at several effect probability levels and times after irradiation. The MRI changes were progressive in time up to 17 months and remained stationary after that time. At 20 months the tolerance doses at the 50% effect probability level were 20.3 +/- 2.0 Gy and 22.6 +/- 2.0 Gy for changes in T1- and T2-weighted MRI, respectively. The relative biological effectiveness (RBE) was calculated on the basis of a previous animal study with photons. Using tolerance doses at the 50% effect probability level, RBE values of 1.95 +/- 0.20 and 1.88 +/- 0.18 were obtained for T1- and T2-weighted MRI. A comparison with data in the literature for the spinal cord yielded good agreement, indicating that the RBE values for single-dose irradiations of the brain and the spinal cord are the same within the experimental uncertainty.

188Re-labeled anti-CD66 monoclonal antibody in stem cell transplantation for patients with high-risk acute myeloid leukemia

We have intensified the conditioning regimen prior to stem cell transplantation in 57 patients with high-risk AML and MDS by treating patients with a 188Re-labeled anti-CD66 monoclonal antibody. Dosimetry was performed prior to therapy and a favorable dosimetry was observed in all cases. Radioimmunotherapy with the labeled antibody provided a mean of 15.5 Gy of additional radiation to the marrow, the kidney was the normal organ receiving the highest dose of supplemental radiation (mean 7.4 Gy): Radioimmunotherapy was followed by standard full-dose conditioning with total body irradiation (12 Gy) (n = 30) or busulfan (n = 27) and high-dose cyclophosphamide +/- thiotepa. Patients subsequently received a T cell depleted allogeneic graft from a HLA-compatible family donor (n = 24), a matched unrelated donor (n = 23) or a haploidentical family donor (n = 6). In four patients, an unmanipulated autologous graft was used. Infusion-related toxicity due to the labeled antibody was minimal and no increase in treatment-related mortality due to the radioimmunoconjugate was observed. Day +30 and day +100 mortalities were 3 and 7%, respectively, and after a median follow-up of 26 months treatment-related mortality was 30%. Late renal toxicity was observed in 14% of patients. The disease-free survival rate for 44 patients in 1 or 2 CR or in very good PR (< 15% blasts in the marrow at transplant) is 64% with only 8% disease-free survival for those with > 15% blasts in the marrow at transplant.

Effect of concurrent radiation therapy and chemotherapy on pulmonary function in patients with esophageal cancer: dose-volume histogram analysis

PURPOSE

The pulmonary effects of concurrent radiation therapy and chemotherapy were studied in patients enrolled in a phase I trial for esophageal cancer.

MATERIALS AND METHODS

Pulmonary function tests were performed prospectively before and after combined-modality therapy (oxaliplatin, 5-fluorouracil, and radiation therapy) in 20 patients with esophageal cancer. Cumulative and differential lung DVH analysis from 0 to 5400 cGy in 25-cGy intervals was performed for the last 15 patients. Correlation between radiation exposure in various dose ranges and percent reduction in pulmonary function tests was calculated as an exploratory analysis.

RESULTS

Significant reductions in carbon monoxide diffusion capacity corrected for hemoglobin (12.3%) and total lung capacity (2.5%) were evident at a median of 15.5 days after radiation therapy. DVH analysis revealed that the single dose of maximum correlation between lung volume radiation exposure and lung function reduction was less than 1000 cGy for all pulmonary functions. The percent lung volume that received a total dose between 700 and 1000 cGy maximally correlated with the percent reductions in total lung capacity and vital capacity, and the absolute lung volume that received a total dose between 700 and 1000 cGy maximally correlated with the percent reductions in total lung capacity, vital capacity, and carbon monoxide diffusion capacity.

DISCUSSION

Significant declines in carbon monoxide diffusion capacity and total lung capacity are evident immediately after the administration of conformal radiation therapy, oxaliplatin, and 5-fluorouracil for esophageal cancer. Other lung functions remain statistically unchanged. The percent or absolute lung volume that received a total dose between 700 and 1000 cGy may be significantly correlated with the percent decline of carbon monoxide diffusion capacity, total lung capacity, and vital capacity. These associations will be evaluated further in a follow-up study.

[Probabilities of controlling tumors and complications (TCP/NTCP) after radiotherapy: methodologic, physical, and biological aspects]

Radiotherapy is aimed at getting the best possible therapeutic ratio (tumor local control versus morbidity). Physicists and radiation oncologists have to evaluate explicitly or implicitly the probability of induced complications to normal surrounding tissues. This is based on published data and clinician's experience. Quantitative methods have been introduced with different models in order to predict the impact of partial or global irradiation on a normal organ. These models correspond to the Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP). These biological models may be useful to evaluate the quality of a treatment planning or for the optimization process. The methodologies used and the clinical data are developed and discussed.

Estimating risks of radiotherapy complications as part of informed consent: the high degree of variability between radiation oncologists may be related to experience

PURPOSE

Estimating the risks of radiotherapy (RT) toxicity is important for informed consent; however, the consistency in estimates has not been studied. This study aimed to explore the variability and factors affecting risk estimates (REs).

METHODS AND MATERIALS

A survey was mailed to Australian radiation oncologists, who were asked to estimate risks of RT complications given 49 clinical scenarios. The REs were assessed for association with oncologist experience, subspecialization, and private practice.

RESULTS

The REs were extremely variable, with a 50-fold median variability. The least variability (sevenfold) was for estimates of late, small intestinal perforation/obstruction after a one-third volume received 50 Gy with concurrent 5-fluorouracil (RE range 5-35%). The variation between the smallest and largest REs in 17 scenarios was >or=100-fold. The years of experience was significantly associated with REs of soft/connective-tissue toxicity (p = 0.01) but inversely associated with estimates of neurologic/central nervous system toxicity (p = 0.08). Ninety-six percent of respondents believed REs were important to RT practice; only 24% rated evidence to support their estimates as good. Sixty-seven percent believed national/international groups should pursue the issue further.

CONCLUSION

Enormous variability exists in REs for normal tissue complications due to RT that is influenced by the years of experience. Risk estimation is perceived as an important issue without a good evidence base. Additional studies are strongly recommended.

On-line correction of beam portals in the treatment of prostate cancer using an endorectal balloon device

BACKGROUND

Reproducible target volume assessment is required in order to optimize portal field margins in the treatment of prostate cancer. The benefits of an endorectal balloon on target volume assessment remain unclear.

MATERIAL AND METHODS

Nine patients were treated with a daily placed air filled rectal balloon. Portal films and computer-associated tomography during the treatment were used to determine the position of the structures of interest. Comparative planning with or without a balloon was performed in order to determine rectal wall exposure to radiation.

RESULTS

The range of movements during treatment predicting the position of the prostate in relation to the symphysis was 0.05-0.59 cm in the lateral direction, 0.27-2.2 cm in the antero-posterior direction, and 0.33-1.8 cm in the crano-caudal direction, as compared to the position of the prostate predicted by the balloon ranging from 0.18 to 0.76 cm in the lateral direction, 0.22-1.68 cm in the antero-posterior direction, and 0.58-2.99 cm in the crano-caudal direction. Planning target volumes (PTV) margins as defined by the position of the balloon were 10 mm in the antero-posterior direction, 6 mm in the lateral direction, and 16 mm in the crano-caudal direction. The volume of rectal wall exposed to radiation was reduced from 40 (+/- 12%) to 25% (+/- 19%) with an endorectal balloon (P < 0.05).

CONCLUSIONS

Daily online correction with portal vision for external beam set-up is improved by an endorectal balloon device, leading to improved PTV margins and reduced radiation exposure of the rectal wall.

Dose-volume factors contributing to the incidence of radiation pneumonitis in non-small-cell lung cancer patients treated with three-dimensional conformal radiation therapy

PURPOSE

To analyze acute lung toxicity data of non-small-cell lung cancer patients treated with three-dimensional conformal radiation therapy in terms of dosimetric variables, location of dose within subvolumes of the lungs, and models of normal-tissue complication probability (NTCP).

METHODS AND MATERIALS

Dose distributions of 49 non-small-cell lung cancer patients treated in a dose escalation protocol between 1992 and 1999 were analyzed (dose range: 57.6-81 Gy). Nine patients had RTOG Grade 3 or higher acute lung toxicity. Correlation with dosimetric and physical variables, as well as Lyman and parallel NTCP models, was assessed. Lungs were evaluated as a single structure, as superior and inferior halves (to assess significance of dose to upper and lower lungs), and as ipsilateral and contralateral lungs.

RESULTS

For the whole lung, Grade 3 or higher pneumonitis was significantly correlated (p <or= 0.05) with mean dose and Lyman and parallel model indices (d(eff) and f(dam)). It was significantly correlated with these indices and with V20 for the ipsilateral lung and with mean dose and d(eff) for the inferior half of the lungs. Dosimetric and NTCP model quantities for the superior half of the lungs and contralateral lung were not significantly correlated (p > 0.5 for superior lung indices, and >0.1 for contralateral lung indices studied).

CONCLUSIONS

For these patients, commonly used dosimetric and NTCP models are significantly correlated with >or= Grade 3 pneumonitis. Equivalently strong correlations are found in the lower portion of the lungs and the ipsilateral lung, but not in the upper portion or contralateral lung.

Small-volume image-guided radiotherapy using hypofractionated, coplanar, and noncoplanar multiple fields for patients with inoperable Stage I nonsmall cell lung carcinomas

BACKGROUND

Occasionally, medically compromised and/or elderly patients with nonsmall cell lung carcinomas (NSCLCs) cannot be treated surgically. We investigated small-volume hypofractionated image-guided radiotherapy (IGRT) without the need for breath control in patients with inoperable Stage I NSCLCs.

METHODS

Between September 1996 and September 1999, 22 patients with Stage I NSCLCs, including 19 males and 3 females, were treated with IGRT. Among these patients, there were 13 Stage IA and 9 Stage IB tumors. The tumors ranged in size from 14.2 to 58.5 mm, with a median size of 26.7 mm. Of the 22 patients, 19 were unfit for surgical treatment due to poor pulmonary function, complications, and/or advanced age and 3 refused surgery. Computed tomographic scans (CT) of the primary tumor were taken during three respiratory phases and they were analyzed to determine the planning target volume, which included only the primary tumor with allowances for respiratory movement. The radiation doses administered at the edge of the moving tumor during normal breathing were 80% of the prescribed dose, either 48 or 60 Gy given in eight fractions over 2 weeks. Clinical evaluation, chest CT scan, and pulmonary function tests were performed before irradiation and at regular intervals for the post-IGRT follow-up. The median follow-up period was 24 months (range, 2-44 months; mean, 21.8 months) (at least 24 months for survivors).

RESULTS

Of 17 tumors assessed at the initial follow-up 2-6 months after treatment (5 complete responses, 11 partial responses, and 1 progressive disease), 16 (94%) were controlled locally. One local recurrence was observed during the follow-up. The lung carcinoma-specific survival rate at 1 year was 94% and the 1-year actuarial recurrence-free survival rate was 71%. The lung carcinoma-specific survival rate at 2 years was 73% and the 2-year actuarial recurrence-free survival rate was 67%. The treatment was well tolerated and no major side effects were observed. Localized radiation pneumonitis was observed in all patients who were examined by CT scan, but the patients were asymptomatic. Parameters of pulmonary function, including vital capacity, total lung capacity, and diffusion capacity for carbon monoxide, decreased very little or not at all, indicating that IGRT rarely deteriorated pulmonary functions.

CONCLUSIONS

Small-volume hypofractionated IGRT without breath control is a feasible and beneficial method for the curative treatment of patients with Stage I NSCLCs. It has the potential of a high local tumor control rate and low morbidity.

Pelvic insufficiency fracture after pelvic irradiation in uterine cervix cancer

OBJECTIVES

Pelvic insufficiency fractures (IF) are well known but uncommon and are frequently misinterpreted sequelae. The clinical features were investigated.

METHODS

Four hundred sixty-three patients, who were treated between 1994 and 2000 for uterine cervix cancer, were clinically examined. All patients had been treated with 10 or 15 MV photons, with 50.4-55.8 Gy in 28 fractions with adjuvant intent (n = 235) in addition to high-dose-rate brachytherapy 24 Gy in 6 fractions for curative treatment (n = 228). The median follow-up was 38 months.

RESULTS

Eight patients (8/463, 1.7%) developed pelvic IF 7-19 months (median, 12 months) after the treatment. Among these, seven patients (7/228, 3.1%) were treated with curative intent and one (1/235, 0.4%) was treated with adjuvant intent. All patients were postmenopausal and complained of moderate to severe pelvic pain, which resolved after 1-11 months with conservative therapy in all patients. Two of these patients also had radiation proctitis.

CONCLUSION

In women who present with pelvic pain after radiotherapy for cervical cancer, bony destruction and fractures may be indicative of a late radiation effect rather than osseous metastasis. IF are more common in the curative treatment group than in the postoperative adjuvant group.

A review of intensity modulated radiation therapy: incorporating a report on the seventh education workshop of the ACPSEM--ACT/NSW branch. Australasian College of Physical Scientists and Engineers in Medicine

Intensity modulated radiation therapy (IMRT) is an evolving treatment technique that has become a clinical treatment option in several radiotherapy centres around the world. In August 2001 the ACT/NSW branch of the ACPSEM held its seventh education workshop, the subject was IMRT. This review considers the current use of IMRT and reports on the proceedings of the workshop. The workshop provided some of the theory behind IMRT, discussion of the practical issues associated with IMRT, and also involved presentations from Australian centres that had clinically implemented IMRT. The main topics of discussion were patient selection, plan assessment, multi-disciplinary approach, quality assurance and delivery of IMRT. Key points that were emphasised were the need for a balanced multi-disciplinary approach to IMRT, in both the establishment and maintenance of an IMRT program; the importance of the accuracy of the final dose distribution as compared to the minor in-field fluctuations of individual beams; and that IMRT is an emerging treatment technique, undergoing continuing development and refinement.

Radiation-induced liver disease after three-dimensional conformal radiotherapy for patients with hepatocellular carcinoma: dosimetric analysis and implication

PURPOSE

To analyze the correlation of radiation-induced liver disease (RILD) with patient-related and treatment-related dose-volume factors and to describe the probability of RILD by a normal tissue complication probability (NTCP) model for patients with hepatocellular carcinoma (HCC) treated with three-dimensional conformal radiotherapy (3D-CRT).

METHODS AND MATERIALS

Between November 1993 and December 1999, 93 patients with intrahepatic malignancies were treated with 3D-CRT at our institution. Sixty-eight patients who were diagnosed with HCC and had complete 3D dose-volume data were included in this study. Of the 68 patients, 50 had chronic viral hepatitis before treatment, either type B or type C. According to the Child-Pugh classification for liver cirrhosis, 53 patients were in class A and 15 in class B. Fifty-two patients underwent transcatheter arterial chemoembolization with an interval of at least 1 month between transcatheter arterial chemoembolization and 3D-CRT to allow adequate recovery of hepatic function. The mean dose of radiation to the isocenter was 50.2 +/- 5.9 Gy, in daily fractions of 1.8-2Gy. No patient received whole liver irradiation. RILD was defined as Grade 3 or 4 hepatic toxicity according to the Common Toxicity Criteria of the National Cancer Institute. All patients were evaluated for RILD within 4 months of RT completion. Three-dimensional treatment planning with dose-volume histogram analysis of the normal liver was used to compare the dosimetric difference between patients with and without RILD. Maximal likelihood analysis was conducted to obtain the best estimates of parameters of the Lyman NTCP model. Confidence intervals of the fitted parameters were estimated by the profile likelihood method.

RESULTS

Twelve of the 68 patients developed RILD after 3D-CRT. None of the patient-related variables were significantly associated with RILD. No difference was found in tumor volume (780 cm(3) vs. 737 cm(3), p = 0.86), normal liver volume (1210 cm(3) vs. 1153 cm(3), p = 0.64), percentage of normal liver volume with radiation dose >30 Gy (V(30 Gy); 42% vs. 33%, p = 0.05), and percentage of normal liver volume with >50% of the isocenter dose (V(50%); 45% vs. 36%, p = 0.06) between patients with and without RILD. The mean hepatic dose was significantly higher in patients with RILD (2504 cGy vs. 1965 cGy, p = 0.02). The probability of RILD in patients could be expressed as follows: probability = 1/[1 + exp(-(0.12 x mean dose - 4.29))], with coefficients significantly different from 0. The best estimates of the parameters in the Lyman NTCP model were the volume effect parameter of 0.40, curve steepness parameter of 0.26, and 50% tolerance dose for uniform irradiation of whole liver [TD(50)(1)] of 43 Gy. Patients with RILD had a significantly higher NTCP than did those with no RILD (26.2% vs. 15.8%; p = 0.006), using the best-estimated parameters.

CONCLUSION

Dose-volume histogram analysis can be effectively used to quantify the tolerance of the liver to RT. Patients with RILD had received a significantly higher mean dose to the liver and a significantly higher NTCP. The fitted volume effect parameter of the Lyman NTCP model was close to that from the literature, but much lower in our patients with HCC and prevalent chronic viral hepatitis than that reported in other series with patients with normal liver function. Additional efforts should be made to test other models to describe the radiation tolerance of the liver for Asian patients with HCC and preexisting compromised hepatic reserve.

A comparison of normal tissue complication probability of brain for proton and photon therapy of canine nasal tumors

This study compared the calculated normal tissue complication probability of brain in dogs with a nasal tumor, which had both photon and proton treatment planning. Nine dogs diagnosed with a variety of histologies, but all with large, caudally located nasal tumors were studied. Three-dimensional (3-D) photon dose distribution, and a proton dose distribution was calculated for each dog. To calculate the normal tissue complication probability (NTCP) for brain, the partial brain volume irradiated with the prescribed dose was determined, then a mathematic model relating complications to partial volume and radiation dose was used. The NTCP was always smaller for proton plans as compared to photon plans, indicating conformation of the dose to the target allows a higher dose to be given. If a 5% NTCP were accepted, the mean applicable dose for this group of dogs was 50.2 Gy for photons, but 58.3 Gy for protons. Not all dogs would benefit the same from proton irradiation. If a large partial brain volume has to be irradiated, the advantage becomes minimal. There is also a minimal advantage if the planning target volume (PTV) includes a small, superficial brain volume. However, for a complex PTV shape the degree of conformation is clearly superior for protons and results in smaller calculated NTCPs.

Dose-response relationship in local radiotherapy for hepatocellular carcinoma

PURPOSE

Dose escalation using three-dimensional conformal radiotherapy (3D-CRT) is based on the hypothesis that increasing the dose can enhance tumor control. This study aimed to determine whether a dose-response relationship exists in local radiotherapy for primary hepatocellular carcinoma (HCC).

METHODS AND MATERIALS

One hundred fifty-eight patients were enrolled in the present study between January 1992 and March 2000. The exclusion criteria included the presence of an extrahepatic metastasis, liver cirrhosis of Child class C, tumors occupying more than two-thirds of the entire liver, and a performance status on the Eastern Cooperative Oncology Group scale of more than 3. Radiotherapy was given to the field, including the tumor, with generous margin using 6- or 10-MV X-rays. The mean radiation dose was 48.2 +/- 7.9 Gy in daily 1.8-Gy fractions. The tumor response was assessed based on diagnostic radiologic examinations, including a computed tomography scan, magnetic resonance imaging, and hepatic artery angiography 4-8 weeks after the completion of treatment. Liver toxicity and gastrointestinal complications were evaluated.

RESULTS

An objective response was observed in 106 of 158 (67.1%) patients. Statistical analysis revealed that the total dose was the most significant factor associated with the tumor response. The response rates in patients treated with doses <40 Gy, 40-50 Gy, and >50 Gy were 29.2%, 68.6%, and 77.1%, respectively. Survivals at 1 and 2 years after radiotherapy were 41.8% and 19.9%, respectively, with a median survival time of 10 months. The rate of liver toxicity according to the doses <40 Gy, 40-50 Gy, and >50 Gy was 4.2%, 5.9%, and 8.4%, respectively, and the rate of gastrointestinal complications was 4.2%, 9.9%, and 13.2%, respectively.

CONCLUSIONS

The present study showed the existence of a dose-response relationship in local radiotherapy for primary HCC. Only the radiation dose was a significant factor for predicting an objective response. The results of this study showed that 3D-CRT can theoretically be used for treating primary HCC.

Methodological issues in radiation dose-volume outcome analyses: summary of a joint AAPM/NIH workshop

This report represents a summary of presentations at a joint workshop of the National Institutes of Health and the American Association of Physicists in Medicine (AAPM). Current methodological issues in dose-volume modeling are addressed here from several different perspectives. Areas of emphasis include (a) basic modeling issues including the equivalent uniform dose framework and the bootstrap method, (b) issues in the valid use of statistics, including the need for meta-analysis, (c) issues in dealing with organ deformation and its effects on treatment response, (d) evidence for volume effects for rectal complications, (e) the use of volume effect data in liver and lung as a basis for dose escalation studies, and (f) implications of uncertainties in volume effect knowledge on optimized treatment planning. Taken together, these approaches to studying volume effects describe many implications for the development and use of this information in radiation oncology practice. Areas of significant interest for further research include the meta-analysis of clinical data; interinstitutional pooled data analyses of volume effects; analyses of the uncertainties in outcome prediction models, minimal parameter number outcome models for ranking treatment plans (e.g., equivalent uniform dose); incorporation of the effect of motion in the outcome prediction; dose-escalation/isorisk protocols based on outcome models; the use of functional imaging to study radioresponse; and the need for further small animal tumor control probability/normal tissue complication probability studies.

Acute radiation-induced toxicity of heavy ion radiotherapy delivered with intensity modulated pencil beam scanning in patients with base of skull tumors

PURPOSE

The purpose of this paper is to evaluate acute radiation-induced toxicity of carbon ion therapy.

MATERIAL AND METHODS

From December 1997 to November 2000, 37 patients with chordomas and low-grade chondrosarcomas of the skull base have been treated with carbon ions at the heavy ion synchrotron (SIS) at GSI, Darmstadt. Tumor-conformal application of carbon beams was realized by intensity-controlled raster scanning in combination with pulse-to-pulse energy variation. The treatment planning procedure included a biological plan optimization. We applied a cobalt-Gray equivalent dose of 60GyE. Acute toxicity was assessed according to the common toxicity criteria (CTC).

RESULTS

Acute toxicity included skin reactions ( degrees I+ degrees II) in four patients, mucositis ( degrees I- degrees III) in eight patients, otitis and middle ear effusion in four, sinusitis in four, nausea/weight loss in one and edema of the temporal lobes in one patient. In two patients, preexisting neurological symptoms worsened. We did not observe acute morbidity > degrees III of normal tissues.

CONCLUSION

Scanning beam delivery of heavy charged particles is safe and reliable. No unexpected acute dose limiting toxicity was observed. With regard to toxicity, a substantial improvement compared to passive beam shaping technology is achieved.

Early skin and lung reactions in breast cancer patients after radiotherapy: prospective study

PURPOSE

The association between early radiological lung reactions consequent upon radiotherapy and patients' symptoms is not well established. This prospective study examined the association between symptoms experienced by the patient, clinical findings observed by the physician and reactions visible in chest X-ray as interpreted by a radiologist, as well as the association between skin or breast symptoms and lung symptoms induced by radiotherapy after different methods of surgery.

METHODS

Altogether 207 consecutive breast cancer patients entered the trial between 1st October 1997 and 31st December 1998. Chest X-rays were taken at entry and 3, 6 and 12 months after radiotherapy. The frequency and intensity of symptoms as well as clinical and chest X-ray findings were assessed over time.

RESULTS

Skin and breast symptoms were common after radiotherapy but seldom severe (9%). Lung reactions were seen in chest X-ray in 47% of patients in re-evaluation by a radiologist at 3 months. The frequency of lung or skin symptoms did not correlate with chest X-ray findings, but there was a significant correlation between skin and lung symptoms. Radiotherapy after conservative surgery for node-positive breast cancer caused lung reactions seen in chest X-ray more often than after mastectomy when using other techniques. The reactions were most common at the 6 month evaluation (P=0.01). Concomitant adjuvant chemo- or endocrine therapy did not significantly increase the incidence of lung reactions.

CONCLUSIONS

Skin, breast and lung symptoms were frequent after radiotherapy, but there was no real association between lung or skin symptoms and chest X-ray findings. The only correlation noted was between skin or breast symptoms and lung symptoms experienced by patients. Radiotherapy after conservative surgery was more frequently linked to chest X-ray findings than radiotherapy after mastectomy. We conclude that routine chest X-ray after radiotherapy gives no more clinically relevant information than the symptoms of the patient and we do not recommend routine chest X-rays for that reason.

Determination and delineation of nodal target volumes for head-and-neck cancer based on patterns of failure in patients receiving definitive and postoperative IMRT

PURPOSE

We present the guidelines for target volume determination and delineation of head-and-neck lymph nodes based on the analysis of the patterns of nodal failure in patients treated with intensity-modulated radiotherapy (IMRT).

METHODS AND MATERIALS

Data pertaining to the natural course of nodal metastasis for each head-and-neck cancer subsite were reviewed. A system was established to provide guidance for nodal target volume determination and delineation. Following these guidelines, 126 patients (52 definitive, 74 postoperative) were treated between February 1997 and December 2000 with IMRT for head-and-neck cancer. The median follow-up was 26 months (range 12-55), and the patterns of nodal failure were analyzed.

RESULTS

These guidelines define the nodal target volume based on the location of the primary tumor and the probability of microscopic metastasis to the ipsilateral and contralateral (Level I-V) nodal regions. Following these guidelines, persistent or recurrent nodal disease was found in 6 (12%) of 52 patients receiving definitive IMRT, and 7 (9%) of 74 patients receiving postoperative IMRT had failure in the nodal region.

CONCLUSION

On the basis of our clinical experience in implementing inverse-planning IMRT for head-and-neck cancer, we present guidelines using a simplified, but clinically relevant, method for nodal target volume determination and delineation. The intention was to provide a foundation that enables different institutions to exchange clinical experiences in head-and-neck IMRT. These guidelines will be subject to future refinement when the clinical experience in head-and-neck IMRT advances.

Modelling normal tissue isoeffect distribution in conformal radiotherapy of glioblastoma provides an alternative dose escalation pattern through hypofractionation without reducing the total dose

The purpose of this study was to prove that by using conformal external beam radiotherapy (RT) normal brain structures can be protected even when applying an alternative approach of biological dose escalation: hypofractionation (HOF) without total dose reduction (TDR). Traditional 2-dimensional (2D) and conformal 3-dimensional (3D) treatment plans were prepared for 10 gliomas representing the subanatomical sites of the supratentorial brain. Isoeffect distributions were generated by the biologically effective dose (BED) formula to analyse the effect of conventionally fractionated (CF) and HOF schedules on both the spatial biological dose distribution and biological dose-volume histograms. A comparison was made between 2D-CF (2.0 Gy/day) and 3D-HOF (2.5 Gy/day) regimens, applying the same 60 Gy total doses. Integral biologically effective dose (IBED) and volumes received biologically equivalent to a dose of 54 Gy or more (V-BED54) were calculated for the lower and upper brain stem as organs of risk. The IBED values were lower with the 3D-HOF than with the 2D-CF schedule in each tumour location, means 22.7+/-17.1 and 40.4+/-16.9 in Gy, respectively (p < 0.0001). The V-BED54 values were also smaller or equal in 90% of the cases favouring the 3D-HOF scheme. The means were 2.7+/-4.8 ccm for 3D-HOF and 10.7+/-12.7 ccm for 2D-CF (p = 0.0006). Our results suggest that with conformal RT, fraction size can gradually be increased. HOF radiotherapy regimens without TDR shorten the treatment time and seem to be an alternative way of dose escalation in the treatment of glioblastoma.

Prediction of AVM obliteration after stereotactic radiotherapy using radiobiological modelling

This study was carried out in order to derive the radiobiological parameters of the dose-response relation for the obliteration of arteriovenous malformation (AVM) following single fraction stereotactic radiotherapy. Furthermore, the accuracy by which the linear Poisson model predicts the probability of obliteration and how the haemorrhage history, location and volume of the AVM influence its radiosensitivity are investigated. The study patient material consists of 85 patients who received radiation for AVM therapy. Radiation-induced AVM obliterations were assessed on the basis of post-irradiation angiographies and other radiological findings. For each patient the dose delivered to the clinical target volume and the clinical treatment outcome were available. These data were used in a maximum likelihood analysis to calculate the best estimates of the parameters of the linear Poisson model. The uncertainties of these parameters were also calculated and their individual influence on the dose-response curve was studied. AVM radiosensitivity was assumed to be the same for all the patients. The radiobiological model used was proved suitable for predicting the treatment outcome pattern of the studied patient material. The radiobiological parameters of the model were calculated for different AVM locations, bleeding histories and AVM sizes. The range of parameter variability had considerable effect on the dose-response curve of AVM. The correlation between the dosimetric data and their corresponding clinical effect could be accurately modelled using the linear Poisson model. The derived response parameters can be introduced into the clinical routine with the calculated accuracy assuming the same methodology in target definition and delineation. The known volume dependence of AVM radiosensitivity was confirmed. Moreover, a trend relating AVM location with its radiosensitivity was observed.

Analysis of radiation-induced liver disease using the Lyman NTCP model

PURPOSE

To describe the dose-volume tolerance for radiation-induced liver disease (RILD) using the Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model.

METHODS AND MATERIALS

A total of 203 patients treated with conformal liver radiotherapy and concurrent hepatic arterial chemotherapy were prospectively followed for RILD. Normal liver dose-volume histograms and RILD status for these patients were used as input data for determination of LKB model parameters. A complication was defined as Radiation Therapy Oncology Group Grade 3 or higher RILD < o r =4 months after completion of radiotherapy. A maximal likelihood analysis yielded best estimates for the LKB NTCP model parameters for the liver for the entire patient population. A multivariate analysis of the potential factors associated with RILD was also completed, and refined LKB model parameters were obtained for patient subgroups with different risks of RILD.

RESULTS

Of 203 patients treated with focal liver irradiation, 19 developed RILD. The LKB NTCP model fit the complication data for the entire group. The "n" parameter was larger than previously described, suggesting a strong volume effect for RILD and a correlation of NTCP with the mean liver dose. No cases of RILD were observed when the mean liver dose was <31 Gy. Multivariate analysis demonstrated that in addition to NTCP and the mean liver dose, a primary hepatobiliary cancer diagnosis (vs. liver metastases), bromodeoxyuridine hepatic artery chemotherapy (vs. fluorodeoxyuridine chemotherapy), and male gender were associated with RILD. For 169 patients treated with fluorodeoxyuridine, the refined LKB model parameters were n = 0.97, m = 0.12, tolerance dose for 50% complication risk for whole organ irradiated uniformly [TD50(1)] = 45.8 Gy for patients with liver metastases, and TD50(1) = 39.8 Gy for patients with primary hepatobiliary cancer.

CONCLUSION

These data demonstrate that the liver exhibits a large volume effect for RILD, suggesting that the mean liver dose may be useful in ranking radiation plans. The inclusion of clinical factors, especially the diagnosis of primary hepatobiliary cancer vs. liver metastases, improves the estimation of NTCP over that obtained solely by the use of dose-volume data. These findings should facilitate the application of focal liver irradiation in future clinical trials.

Modeling volume effects of experimental brachytherapy in the rat rectum: uncovering the limitations of a radiobiologic concept

PURPOSE

To analyze the significance of volume effects in experimental brachytherapy, based on modeling normal tissue complication probability.

METHODS AND MATERIALS

Experimental brachytherapy in the rat rectum was based on an eight-step 2.5-mm step size source configuration for 192Ir, afterloaded into an unshielded polystyrene applicator. Volume effects were studied using a half-circumferential lead-shielded applicator and a shorter (two-step) source configuration. The main end point was rectal stenosis.

RESULTS

Rectal stenosis was always caused by a radiation ulcer. With the shielded configuration, single-dose ED50 (50% incidence of rectal stenosis) increased from 23 Gy to 36.5 Gy. Single-dose ED50 for the short configuration was 77.9 Gy. The data showed a reasonable fit to a three-parameter version of the biophysical model described by Jackson et al. (1995). This model assumes that organs consist of a large number of radiobiologically independent subunits and that radiation causes a complication if the fraction of the organ damaged is greater than its functional reserve. The fraction of the organ damaged is calculated summing over fractions of the organ damaged at each dose level. The calculated mean functional reserve (nu50) of the rat rectum, assuming a cumulative functional reserve distribution in the group of experimental rats, was 0.53.

CONCLUSIONS

The volume effect observed within small brachytherapy volumes agreed well with clinical experience of large tolerance doses in contact X-ray therapy. However, the nu50 value was comparable to the high functional reserve value reported for liver. Experimental volume effects probably reflect repair processes originating in the areas adjacent to small radiation fields of brachytherapy more than the radiobiologic characteristics of the cells in the irradiated volume.

Skin toxicity due to intensity-modulated radiotherapy for head-and-neck carcinoma

PURPOSE

To investigate the cause of acute skin toxicity observed in the treatment of head-and-neck cancer with extended-field intensity-modulated radiotherapy (EF-IMRT).

METHODS AND MATERIALS

EF-IMRT was used to treat head-and-neck cancer, with the gross target volume receiving 70 Gy and the clinical target volume 60 Gy. A thermoplastic mask covering the head, neck, and shoulder was used for immobilization. Dosimetric studies were conducted to investigate the possible causes of the skin reactions, such as the bolus effect of the mask, the use of multiple tangential beams with IMRT plans, and the way in which the physicians contoured the lymph nodes. The dose-volume histograms of conventional opposed-lateral fields were compared with that of the multiple tangential EF-IMRT fields. IMRT plans with neck nodes contoured up to and including the skin surface were compared with plans that contoured the neck nodes 5 mm away from the skin surface. In addition, IMRT plans defining the skin as a sensitive structure were compared with plans that did not define the skin as a sensitive structure. All plans were created using an anthropomorphic Rando phantom, and the skin doses were measured with and without the mask. In each measurement, 6 thermoluminescent dosimeters (TLDs) were placed at the lateral and medial surfaces of the neck.

RESULTS

For all four plans, the measured skin doses with the mask were consistently higher than those without the mask. The average dose increase was about 18% owing to the bolus effect of the mask. Multiple tangential fields used in IMRT plans contributed to an increase in skin dose by about 19% and 27%, with and without the mask, respectively. If the skin of the neck was contoured as a sensitive structure for dose optimization, the volume of skin that received >45 Gy was further reduced by about 20%. Five patients immobilized with head and shoulder masks were treated with EF-IMRT plans with the neck nodes carefully delineated away from the skin surface. The neck skin was identified as a sensitive structure for dose optimization. Grade 1 toxicity was observed in 3 patients, Grade 2 in 1 patient, and Grade 3 in 1 patient toward the end of treatment.

CONCLUSION

Multiple factors contributed to the observed acute skin reaction for head-and-neck cancer patients treated with EF-IMRT. By taking into consideration the skin as a sensitive structure during inverse planning, it was possible to reduce the skin dose to a tolerable level without compromising tumor target coverage.

Radiobiological indices that consider volume: a review

Understanding and predicting the impact of any radiotherapy treatment is critical if patients are to receive treatment with a high likelihood of eliminating the tumour and low likelihood of complications. One of the major contributing factors in determining these effects is the volume treated. This review assesses the current use and accuracy of a series of models which consider volume, building on a previous review which investigated the impact of fractionation particularly with respect to the linear quadratic model. Volume is particularly important in assessing the overall effect with respect to destroying the clonogenic cells and preventing damage to the normal tissues. Dose volume histograms are one of the simplest and most useful forms of representing volume information, however it is difficult to correlate plans based only on DVHs. For this reason various reduction schemes have been introduced and tumour control probability and normal tissues complication probability models adjusted to use this information. Many of these models have proved quite useful in the clinic although they are limited by the available radiobiological data.

Gemcitabine-induced radiation recall

PURPOSE

To study and report 6 patients with radiation recall in unique sites, secondary to gemcitabine chemotherapy.

METHODS AND MATERIALS

The clinical presentations and outcomes of 6 patients with radiation recall secondary to gemcitabine chemotherapy were retrospectively analyzed over the course of a 1-year period.

RESULTS

Radiation recall reactions were seen in the central nervous system, skin, gastrointestinal tract, and in the lymphatic and musculoskeletal systems. The time between initiation of radiation and recall of the radiation phenomenon ranged from 3 weeks to 8 months from the time gemcitabine was initiated. The usual dosage of gemcitabine in these cases was 1000 mg/m(2) given on a weekly basis. No radiation therapy was given concomitantly with gemcitabine. Treatment of the recall reaction consisted of discontinuing gemcitabine and initiating steroid therapy, supportive therapy, and/or nonsteroidal anti-inflammatory agents. Minimal improvement was seen in 3 out of 6 patients, and resolution of the radiation recall was seen in 3 out of 6 patients. A comprehensive review of the literature revealed that radiation recall with gemcitabine has been related to skin reactions only; no previous cases of radiation recall occurring in the central nervous system have been reported with any chemotherapy agent.

CONCLUSION

Radiation recall from gemcitabine chemotherapy is rare, but can potentially arise in any site that has been previously irradiated. Treating physicians must be aware of this potential toxicity from gemcitabine and radiation and discontinue the gemcitabine if radiation recall is observed.

Dose-response curves and tolerance doses for late functional changes in the normal rat brain after stereotactic radiosurgery evaluated by magnetic resonance imaging: influence of end points and follow-up time

Late reaction of normal tissue is still a limiting factor in radiotherapy and radiosurgery of patients with brain tumors. Few quantitative data in terms of dose-response curves are available. In the present study, 99 animals were irradiated stereotactically at the right frontal lobe using a linear accelerator and single doses between 26 and 50 Gy. The diameter of the spherical dose distribution was 4.7 mm (80% isodose). Dose-response curves for late changes in the normal brain at 20 months were measured using T1- and T2-weighted magnetic resonance imaging (MRI). The dependence of the dose-response curves on the follow-up time and the definition of the biological end point were determined. Tolerance doses were calculated at several effect probability levels and times after irradiation. The MRI changes were found to be dependent on dose and progressive in time. At 20 months, the tolerance doses at a 50% effect probability level were 39.6 +/- 1.0 Gy and 42.4 +/- 1.4 Gy for changes in T1- and T2-weighted images, respectively. These dose-response curves can be used for further quantitative investigations on the influence of various treatment parameters, such as the application of charged particles, radiopharmaceuticals or the variation of tissue oxygenation.

Treatment planning for molecular targeted radionuclide therapy

Molecular targeted radionuclide therapy promises to expand the usefulness of radiation to successfully treat widespread cancer. The unique properties of radioactive tags make it possible to plan treatments by predicting the radiation absorbed dose to both tumors and normal organs, using a pre-treatment test dose of radiopharmaceutical. This requires a combination of quantitative, high-resolution, radiation-detection hardware and computerized dose-estimation software, and would ideally include biological dose-response data in order to translate radiation absorbed dose into biological effects. Data derived from conventional (external beam) radiation therapy suggests that accurate assessment of the radiation absorbed dose in dose-limiting normal organs could substantially improve the observed clinical response for current agents used in a myeloablative regimen, enabling higher levels of tumor control at lower tumor-to-normal tissue therapeutic indices. Treatment planning based on current radiation detection and simulations technology is sufficient to impact on clinical response. The incorporation of new imaging methods, combined with patient-specific radiation transport simulations, promises to provide unprecedented levels of resolution and quantitative accuracy, which are likely to increase the impact of treatment planning in targeted radionuclide therapy.