Beams eye view-based photon radiotherapy I

Treatment outcomes of three-dimensional conformal radiotherapy for stage III non-small cell lung cancer

PURPOSE

To evaluate the treatment outcomes of the three-dimensional conformal radiotherapy (3D-CRT), in conjunction with induction chemotherapy, for the treatment of stage III non-small cell lung cancer (NSCLC).

MATERIALS AND METHODS

Between November 1998 and March 2003, 22 patients with histologically proven, clinical stage III NSCLC, treated with induction chemotherapy, followed by 3D-CRT, were retrospectively analyzed. There were 21 males (96%) and 1 female (4%), with a median age of 68.5 (range, 42 approximately 79). The clinical cancer stages were IIIA and IIIB in 41 and 59%, respectively. The histologies were squamous cell carcinoma, adenocarcinoma and others in 73, 18 and 9%, respectively. Twenty patients (91%) received induction chemotherapy before radiation therapy. The majority of the chemotherapy regimen consisted of cisplatin and gemcitabine. Radiation was delivered with conventional anteroposterior/posteroanterior fields for 36 Gy, and then 3D-CRT was performed. The total radiation dose was 70.2 Gy. The median follow-up period was 17 months (range, 4~59 months).

RESULTS

The median overall survival was 19 months. The two and four-year overall survival rates were 37.9 and 30.3%, respectively. The median progression-free survival was 21 months. The two and four-year progression-free survival rates were 42.1 and 21%, respectively. The prognostic factors for overall survival by a univariate analysis were age, histology and T stage (p<0.05). Acute radiation toxicities, as evaluated by the RTOG toxicity criteria, included two cases of grade 3 lung toxicity and one case of grade 2 esophagus toxicity.

CONCLUSION

The radiation dose could be increased without a significant increment in the acute toxicities when using 3D-CRT. It also seems to be a safe, well-tolerated and effective treatment modality for stage III NSCLC.

Dislocation of small bowel volume within box pelvic treatment fields, using new "up down table" device

PURPOSE

To present the impact of a novel minimization device, the up down table (UDT), on the volume of small bowel included within a 4-field pelvic irradiation plan.

METHODS

A polystyrene bowel displacement standard mold was created and added to a customized vacuum cushion (Vac Lok) formed around the abdomen and legs of each patient in the prone position. Two hundred seventy-seven consecutive patients with pelvic malignancies treated with the UDT device were compared with 1 historic series (68 cases) treated at our division. Small bowel contrast dyes at the time of simulation were used in all patients.

RESULTS

The average volume of small bowel within the planning target volume (high-dose volume, calculated with Gallagher method) was 100 cm(3) (median 49 +/- 114) in the series treated with standard box technique and 23 cm(3) (median 0 +/- 64) in the series treated with the UDT (p < 0.001). The average volume of small bowel included in any isodose (any-dose volume) was 505 cm(3) (median 447 +/- 338) and 158 cm(3) (median 69 +/- 207), respectively (p < 0.001). The incidence of G1, G2, and G3 acute enteric toxicity (Radiation Therapy Oncology Group criteria) in the UDT series was 16%, 15%, and 1.5%; in the standard box technique, it was 28%, 25%, and 3%, respectively (p < 0.05). The incidence of acute enteric toxicity directly correlated with the irradiated small bowel volume. In the UDT series, the 5-year actuarial incidence of G3 chronic enteric toxicity was 1.8%. The setup procedures, analyzed in 18 cases, revealed no systematic errors and a standard deviation equal to +/-5 mm for random errors.

CONCLUSIONS

The UDT technique is comfortable, inexpensive, highly reproducible, and permits an almost full bowel displacement from standard radiotherapy fields.

Equivalent racial outcome after conformal radiotherapy for prostate cancer: a single departmental experience

PURPOSE

African-American (AA) men with prostate cancer present with advanced disease, relative to white (W) men. This report summarizes our clinical and biochemical control (bNED) rates after conformal radiotherapy (RT). In particular, we aim to characterize any race-based outcome differences seen after comparable treatment.

PATIENTS AND METHODS

We reviewed 893 patients (418 AA and 475 W) with clinically localized prostate cancer treated between 1988 and 1997. Neoadjuvant hormonal blockade was used in 22.5% of cases, and all patients received conformal RT to a median dose of 68 Gy (range, 60 to 74.8 Gy). Biochemical failure was defined according to the American Society of Therapeutic Radiology and Oncology consensus definition. Median follow-up was 24 months (range, 1 to 114 months).

RESULTS

The 5-year actuarial survival, disease-free survival, and bNED rates for the entire population were 80.5%, 70.0%, and 57.6%, respectively. When classified by prognostic risk category, the 5-year actuarial bNED rates were 78.7% for favorable, 57.7% for intermediate, and 39.8% for unfavorable category patients. AA men presented at younger ages and with more advanced disease. Controlled for prognostic risk category, AA and W men had similar 5-year actuarial bNED rates in favorable (78% v 79%, P: = .91), intermediate (52% v 62%, P: =.44), and unfavorable categories (36% v 45%, P: = .09). Race was not an independent prognostic factor (P: = .36).

CONCLUSION

Conformal RT is equally effective for AA and W patients. More research is needed in order to understand and correct the advanced presentations in AA men. These data suggest a need for early screening in AA populations.

Dependence of linac output on the switch rate of an intensity-modulated tomotherapy collimator

The electro-mechanical, multivane intensity modulated collimator ("MIMiC") slit collimator with 40 vanes has been applied in the delivery of inversely planned sequential tomotherapy to over 4,000 patients. The collimator is binary in that each vane switches between fully open or closed status. Resulting beamlet patterns provide the intensity distributions imparting dose to the patient. The bouncing and damping of vanes at the two ends of their travel cause transient dose perturbations near and at the borders of the treatment field. These perturbations are not explicitly modeled by the planning system. Clinical beamlet profiles and output factors may then differ from those in the planning system and as a function of the vane switch period. A mechanical model of vane switching was developed to describe this dependency. Dose output and distribution of seven simple vane patterns with different switch times were measured with ionization chambers and radiographic films in polystyrene and anthropomorphic phantoms. Linac output dependence on switch time relative to vane open time was determined for four intensity modulated radiotherapy (IMRT) patients from measurements of an ionization chamber embedded in a cylindrical polystyrene phantom. Results demonstrate output dependence on switch time and, accordingly, on the servo mechanism for monitor units, arc length, dose rate, and gantry speed. In conclusion, the output dependence borders on clinical significance-improvements to collimator, dose calculation, commissioning, and quality assurance (QA) are suggested.

Results of a phase II concurrent chemoradiotherapy study using three-dimensional conformal radiotherapy with cisplatin and oral etoposide in stage III nonsmall-cell lung cancer

This phase II study was designed to utilize conformal radiation therapy with cisplatin and oral etoposide in patients with stage III or locally recurrent non-small-cell lung cancer to determine tolerance and toxicity of therapy. From April 1992-February 1996, 18 patients with pathologically confirmed stage IIIA, IIIB, or locally recurrent non-small-cell lung cancer (NSCLC) were entered on study. Metastatic workup included a CT scan of the thorax and upper abdomen as well as a bone scan. Chemotherapy consisted of IV cisplatin (100 mg/m2) with IV etoposide (25 mg/m2) on day 1; oral etoposide was given (50 mg/m2) days 2-14. Using three-dimensional planning, 40-45 Gy were delivered to the clinical target volume, followed by a boost to the gross tumor volume for a total of 70 Gy. Patients with recurrent disease received 40-50 Gy in total. Eighteen patients were enrolled: 16 patients were treated with curative intent and were evaluable for outcome. Two patients were treated for locally recurrent NSCLC and were not included in the outcome analysis. Stages included IIIA (44%) and stage IIIB (54%). Forty-four percent had T3/4 tumors, and 69% had N2/3 disease. Overall survival at 1 year was 64%, while 2-year overall survival was 50%. Distant metastasis-free survival at 1 year was 67%, and at 2 years 60%. The 1-year chest progression-free survival was 57%, and at 2 years 50%. Sixty-three percent required hospitalization for dehydration or neutropenia. Fifty-six percent developed leukopenia (<1,000 cells/microl) sometime during the therapy. We conclude that concurrent cisplatin and oral etoposide with conformal radiation therapy provide encouraging results in stage III lung cancer. The major toxicities of this therapy included leukopenia, thrombocytopenia, and mucosal esophagitis. Local progression of disease continues to be a problem with the current doses given. Future studies should evaluate dose escalation of radiation therapy with limited volumes, utilizing conformal radiation and chemotherapy to improve local control and potentially impact upon distant metastases.

Caution in interpreting biochemical control rates after treatment of prostate cancer: length of follow-up influences results

OBJECTIVES

Prostate-specific antigen (PSA) based end points are commonly used to report outcomes after treatment for prostate cancer. This study examines the influence of follow-up length on biochemical control (bNED) rates.

METHODS

We reviewed 437 patients with clinically localized prostate cancer treated with conformal radiotherapy without neoadjuvant androgen deprivation. Biochemical failure was defined as three consecutive PSA increases or an increase large enough to prompt androgen deprivation therapy. The failure date was projected back to the midpoint between the PSA nadir and the first PSA increase (or between the nadir and the initiation of androgen deprivation therapy). The analysis was performed by censoring patients with longer follow-up in a stepwise fashion, thus creating smaller subgroups with shorter follow-up intervals. Subgroup 1 (n = 191) and subgroup 2 (n = 273) were defined to include those patients monitored for up to 2 years and up to 3 years, respectively.

RESULTS

The median follow-up intervals for subgroup 1, subgroup 2, and the original study population were 1.1, 1.5, and 2.5 years. No significant differences were seen in pretreatment prognostic factors among the three groups. The 2-year bNED of subgroup 1, subgroup 2, and the original population was 86%, 77%, and 73%, respectively. Although subgroup 1 had a superior bNED compared with the original population (P = 0.04), no differences in clinical recurrence rates were seen among any of the three groups.

CONCLUSIONS

Because of projecting the biochemical failure dates back according to commonly used bNED definitions, control rates are highly dependent on the length of follow-up.

PSA-based outcome analysis after radiation therapy for prostate cancer: a new definition of biochemical failure after intervention

OBJECTIVES

To examine pretreatment variables that influence biochemical failure, and to describe and test a new definition of prostate-specific antigen (PSA)-based biochemical failure.

METHODS

We introduce and describe a new definition of biochemical failure, which is based on quadratic fitting of the logarithm of the follow-up PSA profile curve. From a data base of 449 patients with prostate cancer treated with definitive radiation therapy, 230 patients who had at least five follow-up PSA observations were chosen for analysis. The new definition of failure was applied to this cohort, as was the conventional definition of two consecutive PSA rises. Univariate and multivariate analyses were performed using established pretreatment prognostic factors as covariates. Also, the association of both definitions of failure with clinical outcome (local recurrence and any recurrence) was examined.

RESULTS

Application of the new definition of biochemical failure resulted in smoothing of the "noise" that is inherent in using definitions based on successive PSA rises. This smoothing was verified by smaller P values for the statistically significant covariates in the univariate analysis. Furthermore, the new definition correlated better with clinical outcome, as demonstrated by the statistically significant P values on regression analysis when using the quadratic fitted nadir compared with using the observed nadir.

CONCLUSIONS

We devised a new criterion based on quadratic curve fitting for PSA-based biochemical failure. This definition is based on all available PSA information, correlates with both pretreatment factors and post-treatment clinical outcome, is relatively insensitive to noise, and allows for prediction of time of failure.

In the radiotherapy of prostate cancer, technique determines the doses to the penile structures

For 11 consecutive prostate cancer patients undergoing three-dimensional conformal radiotherapy (3DCRT) in our institution, penile structures (PNS) were outlined in CT images obtained for treatment planning purposes. Dose-volume histograms (DVHs) were compared in order to study dose-volume relations for three techniques: 4FLD, an axial coplanar, four-field box technique; 6FLD, a six-field coplanar technique; and 4NAX, a coplanar but non-axial, four-field technique. All three techniques delivered equal doses to the planning target volumes (PTV). Our statistical analyses strongly indicate that the three techniques can be ranked as 6FLD better than 4FLD (and 4FLD better than 4NAX) as far as irradiating PNS volume during treatment of prostate cancer (PC) is concerned. For each technique, there is a "spread" owing to differences in patient anatomy and/or target size, position, and extent, but each technique has a similar "profile" or "shape" distinct from other techniques. Whether irradiating smaller volumes of PNS will influence the sexual potency outcome remains to be demonstrated. However, PNS should be considered as another critical structure in addition to rectum, bladder and femoral heads in the radiotherapy (RT) of PC, especially in 3DCRT dose escalation studies. Sexual potency outcomes can be correlated to dose-volume relations in the future and this will help refine radiotherapy techniques further.

Dosimetric verification of the dynamic intensity-modulated radiation therapy of 92 patients

PURPOSE

To verify that optimized dose distributions provided by an intensity-modulated radiation therapy (IMRT) system are delivered accurately to human patients.

METHODS AND MATERIALS

Anthropomorphic phantoms are used to measure IMRT doses. Four types of verification are developed for: I) system commissioning with beams optimized to irradiate simulated targets in phantoms, II) plans with patient-optimized beams directed to phantoms simulating the patient, III) patient-phantom hybrid plans with patient-optimized beams calculated in phantom without further optimization, and IV) in vivo measurements. Phantoms containing dosimeters are irradiated with patient-optimized beams. Films are scanned and data were analyzed with software. Percent difference between verified and planned maximum target doses is defined as "dose discrepancy" (deltavp). The frequency distribution of type II deltavp from 204 verification films of 92 IMRT patients is fit to a Gaussian. Measurements made in vivo yield discrepancies specified as deltaivp, also fit to a Gaussian.

RESULTS AND DISCUSSION

Verification methods revealed three systematic errors in plans that were corrected prior to treatment. Values of [deltavp] for verification type I are <2%. Type II verification discrepancies are characterized by a Gaussian fit with a peak 0.2% from the centroid, and 158 [deltavp] <5%. The 46 values of [deltavp] >5% arise from differences between phantom and patient geometry, and from simulation, calculation, and other errors. Values of [deltavp] for verification III are less than half of the values of [deltavp] for verification II. A Gaussian fit of deltaivp from verification IV shows more discrepancy than the fit of deltavp, attributed to dose gradients in detectors, and exacerbated by immobilization uncertainty.

CONCLUSIONS

Dosimetric verification is a critical step in the quality assurance (QA) of IMRT. Hybrid Verification III is suggested as a preliminary quality standard for IMRT.

[Conformational radiotherapy with multi-leaf collimators: one year experience at the Leon-Berard Centre]

Taking advantage of the renewal of a linear accelerator, the Radiation Therapy Department of the Centre Léon Bérard implemented, in collaboration with Philips Systèmes Médicaux, a conformal therapy set-up procedure using CT-scan for 3D treatment planning and a multileaf collimator that allows achievement of numerous irregular-shaped beams via the multileaf preparation system. The various elements of this equipment make possible well defined and structured procedures for treatment planning with different steps and essential tools used by this technique. We describe the means used and indicate future improvements that will lead to automation in order to provide good quality assurance, better security and substantial time saving. During the first year, 115 patients were treated with this new technique. They presented with central nervous system tumors (32 patients), lung cancer (29 patients), prostate cancer (20 patients), paranasal sinus tumors (14 patients) and tumors located in other sites (13 patients with soft sarcoma, hepato-bilary tumor, etc).

Potency probability following conformal megavoltage radiotherapy using conventional doses for localized prostate cancer

PURPOSE

Impotence is a familiar sequela of definitive external beam radiation therapy (EBRT) for localized prostate cancer; however, nerve-sparing radical prostatectomy (NSRP) has offered potency rates as high as 70% for selected for patients in several large series. To the authors' knowledge, age and stage-matched comparisons between the effects of EBRT and NSRP upon the normal age trend of impotence have not been performed. Herein, we report the change in potency over time in an EBRT-treated population, determine the significantly predisposing health factors affecting potency in this population, and compare age and stage-matched potency rates with those of normal males and prostatectomy patients.

METHODS AND MATERIALS

Our results are obtained from a retrospective study of 114 patients ranging in age from 52 to 85 (mean, 68) who were diagnosed with clinical stages A-C C (T1-T4N0M0) prostate cancer and then treated conformally with megavoltage x-rays to 6500-7000 cGy (180-200 cGy per fraction) using the four-field box technique. Information concerning pre-RT potency, medical and surgical history, and medications was documented for each patient as was time of post-RT change in potency during regular follow-up. The median follow-up time was 18.5 months.

RESULTS

The actuarial probability of potency for all patients gradually decreased throughout post-RT follow-up. At months 1, 12, 24, and 36, potency rates were 98, 92, 75, and 66%, respectively. For those patients who became impotent, the median time to impotence was 14 months. Factors identified from logistic regression analysis as significant predictors of post-EBRT impotence include pre-EBRT partial potency (p < 0.001), vascular disease (p < 0.001), and diabetes (p = 0.003). Next, an actuarial plot of potency probability to patient age for the EBRT-treated population was compared to that obtained from the Massachusetts Male Aging Study of normal males. The two curves were not significantly different (logrank test, p = 0.741) between ages 50 and 65. Finally, potency probability after follow-up of 1 year or more in EBRT-treated patients was stratified by age and substratified by clinical stage and then compared to similarly stratified potencies for patients treated with NSRP. The prostatectomy data were derived from the pooled data of six large (total n, 952), independent series conducted at academic centers. For patients older than 70 years, 79.1% of EBRT patients and 32.9% of NSRP patients remained potent after treatment. For patients with stage B2 disease, 75.0% of EBRT patients and 49.3% of NSRP patients remained potent after treatment. Overall EBRT patient potency was 76.1% vs. 66.2% for NSRP patients.

CONCLUSIONS

1) By 36 months after completion of EBRT for localized prostate cancer, fully one-third of all patients becomes impotent; however, for patients younger than 70 years, the probability of impotence does not depart significantly from that for normal males. 2) In the EBRT-treated population, pre-EBRT partial potency, vascular disease, and diabetes are the most significant predispositions to the development of impotence. Patients with these predispositions, though, do not become impotent significantly earlier than other patients. 3) When comparing age and stage-stratified potency rates for EBRT and NSRP patients, potency is roughly equal for both modalities for most age and stage groups; however, for patients older than 70 years or with stage B2 disease, EBRT offers notably higher posttreatment potency rates than NSRP. Thus, for the treatment of localized prostate cancer, EBRT may not affect the normal age trend of impotence in younger patients and may induce impotence less frequently than NSRP in older patients or in patients with later stage disease.

Three dimensional comparison of blocked arcs vs. four and six field conformal treatment of the prostate

PURPOSE

The purpose of this study is to compare five different techniques for treatment the prostate without seminal vesicles. Dose volume histograms and a time survey are the tools that were used for this analysis.

METHODS AND MATERIALS

For this study we compared 3D techniques using four and six field conformal treatments, to open and blocked 8 x 8 cm2 120 degrees bilateral arcs. All the plans were normalized to deliver 100% to the central axis, and full 3D calculations were performed. Blocked arcs were created using the 'average beam's eye view' (A-BEV) technique.

RESULTS

Analysis of the dose volume histograms revealed: (1) Arcs with blocks result in an improved dose distribution compared to standard arcs and four field 3DCRT techniques, (2) The DVH associated with blocked arcs, using block margins of 1.3 cm, resulted in a somewhat lower dose to the rectum but a 'tighter' margin around the prostate compared to the DVH generated using the six field 3DCRT technique.

CONCLUSION

This technique is for treatment of the prostate only, when treatment of the seminal vesicle is not required. The use of blocked arcs significantly improved the dose distribution compared to using standard arcs and 4-field conformal techniques. The DVHs associated with using blocked arcs is comparable to the SFC technique. It is likely to be less expensive, faster to set-up and may allow for safe dose escalation when only the prostate is receiving treatment.

Localization of the prostatic apex for radiotherapy planning: a comparison of two techniques

Autopsy and pathology studies have shown that the caudal portion of the prostate gland harbors tumour in 64-75% of specimens examined. Accurate localization of the prostatic apex may be important in improving local control with external beam radiation therapy. We compared the location of the apex obtained with CT based treatment planning versus localization using retrograde urethrography in 32 consecutive patients. The prostatic apex, localized by CT and retrograde urethrography, was compared relative to the ischial tuberosities and the symphysis pubis. Discordance between the location of the prostatic apex as defined on CT scan and retrograde urethrography was found in 50% of patients evaluated. There was 31% discordance between the location of the prostatic apex as defined on CT and retrograde urethrography when data were analysed with the location of the prostatic apex 1 cm above the narrowing on urethrography, a definition others have suggested. The urethrogram defined prostatic apex, as compared with the CT definition, necessitated the treatment of more of the surrounding normal tissues in 31% of our cases, with four-field techniques. Comparison of dose-volume histograms of the bladder, rectum and penis irradiated for target volumes defined by CT versus retrograde urethrography showed that more penis was irradiated in some patients with the urethrogram defined prostatic apex; irradiation of the base of the penis could be relatively avoided by using a six-field treatment plan instead of the standard four-field box. There is discordance between the CT and urethrogram defined prostatic apex. Dose-volume histogram information suggests that differences in apex localization can significantly affect doses to normal adjacent prostatic tissues. Combining CT localization with the urethrogram localization of the prostatic apex optimizes radiotherapy planning and dose delivery.

The "critical volume tolerance method" for estimating the limits of dose escalation during three-dimensional conformal radiotherapy for prostate cancer

PURPOSE

To describe the "Critical Volume Tolerance" (CVT) method for defining normal tissue tolerance during 3D-based dose escalation studies for prostate cancer.

METHODS AND MATERIALS

The CVT method predicts the tolerance to radiation for "in series"-type functional units based on the assumption that tolerance depends on a critical threshold "low-volume high-dose region." The data used for describing this model were generated from 3D analysis of randomly selected patients with prostate cancer. Commonly used coplanar four-and six-field conformal (SFC) techniques were chosen as the comparison techniques. For purposes of comparison, rectal tolerance was assumed to be reached following whole pelvic irradiation using a four-field box technique to 50 Gy, followed by a conedown boost to 70 Gy using bilateral 9 x 9 cm 120 degree arcs as popularized by investigators from Stanford University (SUH).

RESULTS

Based on the average dose volume histograms for the patients studied, the maximum safe increase in dose for the SFC technique compared to the SUH technique, would be 10% if 30% of the rectal volume was the critical dose limiting volume (CVT = 30%), 5% if the CVT = 10%, or greater than 20% if the CVT = 40%. Commonly used four-field conformal techniques would not be expected to allow significant escalation of the dose without increasing the risk of complications.

CONCLUSIONS

The CVT method is relatively simple, and data generated based on it can be used to support normal tissue complication probability equations. The CVT method can be verified or modified as partial tolerance data become available. Based on the CVT model, sophisticated treatment techniques should allow a modest increase in the total dose of radiation delivered to the prostate without an increase in late complications.

Prostate volumes defined by magnetic resonance imaging and computerized tomographic scans for three-dimensional conformal radiotherapy

PURPOSE

To compare the prostate volumes defined on magnetic resonance imaging (MRI), and noncontrast computerized tomographic (CT) scans used for three-dimensional (3D) treatment planning.

METHODS AND MATERIALS

Ten patients were simulated for treatment using immobilization and a retrograde urethrogram. 3D images were used to compare prostate volumes defined by MRI (4-6 mm thick slices) and CT images (5 mm thick slices). Prostate volumes were calculated in cm(3) using the Scanditronix 3D planning system. MRI/CT images were merged using bony anatomy to define the regions of discrepancy in prostate volumes.

RESULTS

The mean prostate volume was 32% larger (range-5-63%) when defined by noncontrast CT compared to MRI. The areas of nonagreement tended to occur in four distinct regions of discrepancy: (a) the posterior portion of the prostate, (b) the posterior-inferior-apical portion of the prostate, (c) the apex due to disagreement between a urethrogram based definition and the location defined by MRI, (d) regions corresponding to the neurovascular bundle.

CONCLUSION

There is a tendency to overestimate the prostate volume by noncontrast CT compared to MRI. Awareness of this tendency should allow us to be to more accurately define the prostate during 3-D treatment planning.

A comparison of four patient immobilization devices in the treatment of prostate cancer patients with three dimensional conformal radiotherapy

PURPOSE

To determine the variability of patient positioning during three-dimensional conformal radiotherapy (3D-CRT) for prostate cancer treated with no immobilization or one of four immunobilization devices, and to determine the effects of patient body habitus and pelvic circumference on patient movement with each individual inmobilization technique.

METHODS AND MATERIALS

To see whether our immobilization techniques have improved day-to-day patient movement, a retrospective analysis was carried out. A total of 62 patients treated at one facility on a single machine with 3D-CRT via a four-field box technique (anterior-posterior and opposed laterals) in the supine position with either no immobilization or one of four immobilization devices. Five groups of patients were compared: (a) group 1-no immobilization; (b) group 2-alpha cradle from the waist to upper thigh; (c) group 3-alpha cradle from waist to below the knees; (d) group 4-styrofoam leg immobilizer (below knees); and (e) group 5-aquaplast cast encompassing the entire abdomen and pelvis to midthigh with alpha cradle immobilization to their lower legs and feet. Prior to starting radiotherapy, portal films of all four treatment fields were obtained 1 day before treatment. Subsequently, portal films were then obtained at least once a week. Portal films were compared with the simulation films and appropriate changes were made and verified on the next day prior to treatment. A deviation of greater than 0.5 cm or greater was considered to be clincally significant in our analysis. We studied the difference among the types of immobilization and no immobilization by looking at the frequency of movements (overall, and on each of the three axes) that a patient had during the course of his treatment. Using a logistic regression model, the probability of overall and individual directional movement for each group was obtained. In addition, the effects of patient body habitus and pelvic circumference on movement were analyzed.

RESULTS

The maximum deviation was 2 cm and the median deviation was 1.2 cm. For each patient, the probability of movement ranged from 0 to 76%, with a mean of 39%. There was no significant difference seen in overall movement with any of the immobilzation devices compared to no immobilization, but there was less vertical (9 vs. 18%; p = 0.03) and AP (6 vs. 15%; p = 0.14) movement with the aquaplast than any other group. However, when examining the lateral direction, the aquaplast had significantly more movement (32 vs. 9%; p < 0.001). When accounting for body habitus and pelvic circumference, no immobilization device was effective in reducing movement in obese patients or in patients with pelvic circumference greater than 105 cm. The aquaplast group had a significantly increased amount of lateral movement with obesity (42 vs. 23%; p < 0.05), and with pelvic circumference >105 cm (33 vs. 29%; p < 0.05).

CONCLUSIONS

There was no significant reduction in overall patient movement noted with any of the immobilization devices compared to no immobilization. The aquaplast group had reduced vertical and AP movement of greater than 0.5 cm. There was significantly more lateral movement with aquaplast appreciated in obese patients or patients with pelvic circumferences greater than 105 cm. The aquaplast immobilization appears to be useful in reducing movement in two very clinicaly important dimensions (AP and vertical). Despite our findings, other immobilization may still be useful especially in the treatment of nonobese patients. It is clear that the optimal immobilization technique and patient positioning are yet to be determined.

Head and neck cancer

This synthesis of the literature on radiotherapy for head and neck cancer is based on 424 scientific articles, including 3 meta-analyses, 38 randomized studies, 45 prospective studies, and 246 retrospective studies. These studies involve 79174 patients. The literature review shows that radiotherapy, either alone or in combination with surgery, plays an essential role in treating head and neck cancers. When tumors are localized, many tumor patients can be cured by radiotherapy alone and thereby maintain full organ function (1, 2). Current technical advancements in radiotherapy offer the potential for better local tumor control with lower morbidity (3). This, however, will require more sophisticated dose planning resources. To further improve treatment results for advanced tumors, other fractionation schedules, mainly hyperfractionation, should be introduced (5). This mainly increases the demands on staff resources for radiotherapy. The combination of radiotherapy and chemotherapy should be subjected to further controlled studies involving a sufficiently large number of patients (4, 5). Interstitial treatment (in the hands of experienced radiotherapists) yields good results for selected cancers. The method should be more generally accessible in Sweden. Intraoperative radiotherapy should be targeted for further study and development.

Advanced interactive planning techniques for conformal therapy: high level beam descriptions and volumetric mapping techniques

PURPOSE

To aid in design of conformal radiation therapy treatment plans involving many conformally shaped fields, this work investigates the use of two methodologies to enhance the ease of interactive treatment planning: high-level beam constructs and beam's-eye view volumetric mapping.

METHODS AND MATERIALS

High-performance computer graphics running on various workstations using a graphical visualization system (AVS) have been used in this work. Software specific to this application has been written in standard FORTRAN and C languages. A new methodology is introduced by defining radiation therapy "fields" to be composed of multiple beam "segments." Fields can then be defined as higher-level entities such as arcs, cones, and other shapes. A "segmental cone" field, for example, is defined by a symmetry axis and a cone angle, and can be used to rapidly place a series of beam segments that converge at the target volume, while reducing the degree of overlap elsewhere. A new beam's-eye view (BEV) volumetric mapping technique is presented to aid in selecting the placement of conformal radiation fields. With this technique, the relative average dose within an organ of interest is calculated for a sampling of isocentric, conformally shaped beams and displayed either as a "globe," which can be combined with the display of anatomical surfaces, or as a two-dimensionally mapped projection. The dose maps from multiple organs can be generated, stacked, or composited with relative weightings to aid in the placement of fields that minimize overlap with critical structures.

RESULTS

The use of these new methodologies is demonstrated for prostate and lung treatment sites and compared to conventional planning techniques.

DISCUSSION

The use of many beams for conformal treatment delivery is difficult with current interactive planning. The use of high-level beam constructs provides a means to quickly specify, place, and configure multiple beam arrangements. The BEV volumetrics aids in the placing of fields, which minimize involvement with critical normal tissues.

CONCLUSIONS

Early experience with the new methodologies suggest that the new methods help to enhance (or at least speed up) the ability of a treatment planner to create optimal radiation treatment field arrangements.

The treatment of stage III nonsmall cell lung cancer using high dose conformal radiotherapy

PURPOSE

To review our experience using conformal treatment planning and high-dose radiotherapy for Stage IIIa and IIIb nonsmall cell lung cancer (NSCLC), and to identify a subset of patients best suited for this approach by analyzing multiple pretreatment patient and tumor characteristics.

METHODS AND MATERIALS

Between December 1987 and June 1992, 37 patients with Stage III NSCLC treated with high-dose radiotherapy using conformal radiotherapy were reviewed. The patient characteristics were as follows: Stage IIIa (18 patients), IIIb [19]; T1-2 [13], T3-4 [24]; N0-1 [8], N2-3 [29]; and median age 63. All patients were treated with 1.8-2.0 Gy fractions to a median dose of 66 Gy (range 60-70 Gy). Outcome was analyzed by multiple pretreatment variables including age, sex, Karnofsky performance score, pretreatment symptoms, stage group, T and N stage, tumor volume (calculated from computed tomography (CT) contours), presence of atelectasis, and tumor histology. Outcome was also analyzed by total radiotherapy dose.

RESULTS

The median, 1-year and 2-year survival rates for the entire group were 19.5 months, 75 and 37%, respectively. The median, 1-year, and 2-year local progression-free survival rates are 15.6 months, 62 and 23%. There was no difference in survival by stage group (IIIa vs. IIIb) or by T or N stage. Tumor volumes ranged from 47-511 cc in the patients without atelectasis and were not a significant prognostic factor. Histology was found to be a significant prognostic factor, with squamous cell carcinoma having a better overall survival and local progression-free survival than other histologies. No other patient characteristic was found to be significant by either univariate or multivariate analysis. When outcome was analyzed by radiotherapy dose, no dose response was evident in the narrow dose range studied (60-70 Gy). Toxicity included two cases of pneumonitis, which resolved with conservative therapy.

CONCLUSION

High-dose conformal radiotherapy, in our experience, results in overall survival rates that compare favorably with trials of chemoradiotherapy or conventional radiotherapy with a low treatment-associated morbidity. However, local progression remains a significant problem despite median radiotherapy doses of 66 Gy. Future trials using escalating radiotherapy doses with conformal radiotherapy are therefore, indicated.

Implementation of three dimensional conformal radiation therapy: prospects, opportunities, and challenges

PURPOSE

To briefly review scientific rationale of 3D conformal radiation therapy (3DCRT) and discuss the prospects, opportunities, and challenges in the implementation of 3DCRT. Some of these ideas were discussed during a workshop on "Implementation of Three-Dimensional Conformal Radiation Therapy" in April 1994 at Bethesda, MD, and others have been discussed elsewhere in the literature.

METHODS AND MATERIALS

Local-regional control of cancer is an important component in the overall treatment strategy in any patient with cancer. It has been shown that failure to achieve local-regional control can lead to (a) an increase in chances of distant metastases, and (b) a decrease in the survival. In many disease sites, the doses delivered currently are inadequate to achieve satisfactory local tumor control rates; this is because in many sites, only limited doses of radiotherapy can be delivered due to the proximity of cancer to radiosensitive normal tissues. By conforming the radiotherapy beams to the tumor, doses to the tumors can be enhanced and doses to the normal tissues can be reduced. With the advances in 3DCRT, such conformation is possible now and is the rationale for using 3DCRT. However, a number of questions do remain that are not limited to the following: (a) What are the implications in terms of target volume definitions when implementing 3DCRT? (b) Are there some sites where research efforts can be focused to document the efficacy and cost effectiveness of 3DCRT? (c) How do we implement day-to-day 3DCRT treatment efficiently? (d) How do we transfer the technology from the university centers to the community without compromising quality? (e) What are all the quality assurance/quality improvement questions that need to be addressed and how do we ascertain quality assurance of 3DCRT? (f) Have we looked at cost-benefit ratios and quality of life (QOL) issues closely?

RESULTS

There is a need for defining multiple target volumes: gross tumor volume, clinical target volume(s), and planning target volume(s). Such definitions should make implementation of 3DCRT more complex, yet will make high-dose delivery a possibility. There are many sites in which single and multiinstitutional studies are ongoing that include prostate, lung, head and neck, and brain. In other areas, cooperative group trials are required because of the inability of single institutions to accrue enough patients to answer clinically relevant questions with statistical validity. Although implementation of 3DCRT will require multiple steps, these multiple steps can be brought into clinical practice gradually and one does not have to wait until all steps required for implementation of 3DCRT are available. In this respect, "3DCRT" should be used in a very broad sense, from beam's eye view blocking, use of multibeam dose distribution, use of dose-volume histograms in choosing alternative plans, noncoplanar beam arrangements, intensity modulation, inverse planning, to totally automated implementation of 3DCRT. To transfer the 3DCRT capabilities to the community from the University Centers, there is a necessity to develop quality assurance programs. RTOG and the Three-Dimensional Oncology Group are spearheading these efforts. Three-dimensional conformal radiation therapy has potential not only to improve local control and decrease toxicity, but also to improve the cost benefit ratio in the use of radiotherapy as well as in improving quality of life in patients with cancer.

CONCLUSIONS

Achieving many potential benefits of 3DCRT (improvement in local control, decreasing toxicity, organs-function preservation, improvement in cost effectiveness) will require further physics-related and clinical research in carefully conceived and successfully completed future clinical trials.

The value of nonuniform margins for six-field conformal irradiation of localized prostate cancer

PURPOSE

Evaluate the hypothesis that by combining nonuniform margins with a technique for limiting the possible extent of posterior motion of the prostate during the delivery of six-field conformal radiotherapy (SFCRT) of the prostate, it is possible to adequately treat the clinical target volume (CTV) and minimize dose to normal structures.

METHODS AND MATERIALS

Serial computed tomography (CT) scans of prostate patients were taken at 0.5 cm intervals for treatment planning purposes. The initial treatment planning scans were performed with the rectum empty and the bladder full. Subsequent scans were taken at the end of the first week of treatment with the bladder full, but with no attempt to empty the rectum, to mimic the typical treatment situation. The gross tumor volume (GTV), consisting of the prostate and seminal vesicles, as well as the CTV, were defined on the CT images with the aid of a urethrogram to define the inferior border (apex) of the prostate. Variable blocking margins were designed around the CTV using the University of Michigan three dimensional (3D) treatment planning system (UM-PLAN). Isodose distributions displayed on axial, sagittal, coronal, and oblique slices were used to evaluate the adequacy of the various margins applied. Nonuniform margins varying from 0.75 cm posteriorly to 2.0 cm anteriorly and inferiorly were compared to uniform margins of 1.0, 1.5, and 2.0 cm for each patient. Dose volume histograms (DVH) were used to compare doses to the GTV, CTV, rectum, and bladder.

RESULTS

In a series of 10 patients scanned with the above protocol, treatment plans with nonuniform margins were compared with uniform margins of 1.0, 1.5, and 2.0 cm. Dose-volume histograms showed that nonuniform and 1.0 cm uniform margins deliver the lowest doses to the rectum and bladder, but the use of 1.0 cm uniform margins resulted in inadequate coverage of the CTV in 40% of the cases. The 1.5 and 2.0 cm uniform margins adequately covered the CTV but resulted in significantly higher doses to the bladder and rectum.

CONCLUSIONS

The use of nonuniform margins, when combined with CT scans performed with the rectum empty and bladder full, can improve tumor control probability while minimizing the risk of morbidity to adjacent critical structures.

Bilateral arcs using "averaged beam's eye views": a simplified technique for delivering 3-D based conformal radiotherapy

The purpose of this study is to describe a conformal radiotherapy technique for treating only the prostate with bilateral 120 degrees arcs using "averaged beams-eye-views" (A-BEV). For this study a CT scan from a patient with a large prostate but with a low risk for seminal vesicle involvement was chosen for comparing several different treatment techniques. Dose volume histograms (DVHs) of the prostate, femoral heads, bladder, and rectum were compared for plans using "standard" bilateral 120 degree unblocked arcs (8 x 8 and 9 x 9 cm), similar sized arcs with "generic" (small corner) blocks applied, arcs using hand drawn "semi-conformal" blocks added, and arcs using the A-BEV. The A-BEV was generated by averaging the shapes of fixed lateral and oblique BEVs from a six-field plan. These arc techniques were compared to four-field conformal (4-FC) and six-field conformal (6-FC) techniques. The addition of generic corner blocks to a 9 x 9 field resulted in a more favorable dose distribution than using open unblocked 9 x 9 arcs. The technique employing the A-BEV resulted in an improvement in the DVHs compared to other arc techniques and to 4-FC techniques. The dose volume histograms associated with using this technique approached those associated with using a 6-FC technique. Treating only the prostate with blocked arcs generated using an A-BEV results in an improved dose distribution compared to unblocked arcs and 4-FC techniques. This blocked arc technique also results in a DVH that is comparable to using a more complex 6-FC technique. Blocks that are drawn on manually reduce the dose to the surrounding normal tissues but are associated with a greater risk of underdosing the target volume. This problem is diminished when computer generated conformal blocks are used.

Defining treatment margins for six field conformal irradiation of localized prostate cancer

PURPOSE

To define the "ideal margins" to be used for the delivery of six-field conformal radiotherapy for localized prostate cancer.

METHODS AND MATERIALS

For a typical patient, 3-D based 6-field conformal treatment plans were generated using uniform margins ranging from 0.5-2.5 cm (in 0.25 cm increments). In a step-wise fashion the minimum margins required to encompass the gross tumor volume within the 90% isodose shell were identified. Additional margins were then added to account for extracapsular penetration, setup and patients movement error as well as for organ movement. Assumptions about the relative tolerance of surrounding normal tissues were also incorporated into the final decisions regarding margins.

RESULTS

For the various areas of interface, between the prostate and surrounding normal tissues "ideal margins" varied from 0.75-2.25 cm.

CONCLUSION

The use of nonuniform "ideal margins" appears to insure adequate coverage of the tumor, while minimizing the volume of surrounding dose limiting normal tissues irradiated. This approach should in theory improve the tumor control and complication probabilities compared to using conventional treatment techniques and to using a 6-field conformal technique with uniform margins.

Acute toxicity during external-beam radiotherapy for localized prostate cancer: comparison of different techniques

PURPOSE

The chronic and acute toxicities associated with conventional radiotherapy of localized prostate cancer are well documented. However, the degree and incidence of toxicities with conformal techniques are not known. Studying side effects associated with modern radiotherapeutic techniques is more important now since there has been a general trend to use computerized tomography-based techniques in recent years; beam's eye view-based conformal techniques are also becoming more commonplace. It is possible that the local disease control can be improved with the delivery of higher doses than currently used. Conformation of the treatment volume to the target volume may facilitate such dose-escalation. However, prior to such dose-escalation, it is important to know the toxicities associated with such techniques with conventional doses.

METHODS AND MATERIALS

We have compared week-by-week acute toxicities associated with conventional (Group A, 16 patients), computerized tomography-based, manual (Group B, 57 patients) and beam's eye view-based (Group C, 43 patients) techniques during 7 weeks of radiotherapy. Group B and C patients were treated contemporaneously (1988-1990).

RESULTS

Acute side effects gradually increased from week 1 through weeks 4-5 and generally declined or plateaued after that. The incidence of acute toxicities was significantly less with the beam's eye view/based technique than with the other two methods. For instance, the percentages of Grade 2 acute genitourinary toxicities for Groups A, B, and C were as follows: Week 1-0, 0, 0; Week 2-6, 0, 0; Week 3-6, 9, 2; Week 4-12, 14, 9; Week 5-35, 14, 9; Week 6-31, 16, 7; Week 7-33, 8, 8, respectively. The p values associated with differences in acute genitourinary toxicities for Weeks 1-7 using chi-square test were 0.072, 0.627, 0.389, 0.538, 0.123, 0.06, and 0.012; the p values for acute gastrointestinal toxicities were 0.512, 0.09, 0.031, 0.031, 0.003, < 0.0001, and 0.004, respectively. Pairwise comparison (Wilcoxon rank-sum test) showed statistically significant lower acute toxicity in Group C than Group B (e.g., p values, Weeks 1-7 for gastrointestinal toxicity: 0.633, 0.056, 0.010, 0.014, < 0.0001, < 0.0001, and < 0.0001, respectively) in the latter part of the treatment course. No correlation was found between the extent of toxicity and the patient age or the overall treatment time. Also, no correlation was found between the degree of toxicity and the radiation dose and fraction size, within the narrow ranges used (65-70 Gy and 180-200 cGy, respectively). A trend suggesting increased severity of toxicity with increase in the volume of treatment was seen.

CONCLUSION

The findings in this retrospective study need to be confirmed by other prospective studies.

An analysis of image segmentation time in beam's-eye-view treatment planning

In this work we tabulate and histogram the image segmentation time for beam's eye view (BEV) treatment planning in our center. The average time needed to generate contours on CT images delineating normal structures and treatment target volumes is calculated using a data base containing over 500 patients' BEV plans. The average number of contours and total image segmentation time needed for BEV plans in three common treatment sites, namely, head/neck, lung/chest, and prostate, were estimated.

Comparison of CT-based treatment planning and retrograde urethrography in determining the prostatic apex at simulation

In 20 consecutive patients who underwent treatment planning, localization of the prostatic apex with CT-based techniques at simulation was compared to location of the apex as defined by retrograde urethrography. In addition, the location of the urethrogram-defined prostatic apex was compared with the bottom of the ischial tuberosities, which is often recommended as the inferior margin of the field. In 15% of the patients there was agreement between the CT-defined apex and the urethrogram-defined apex; in 85% there was discordance. In a majority of patients with discordance, the urethrogram apex was located caudad to the CT-defined apex (71%) with a median difference of .65 cm. In 29% of the patients the urethrogram apex was located superior to the CT-defined apex. Overall, 75% of the patients had discordance between the urethrogram apex and the CT apex of 0.5 cm or greater; 30% had an absolute difference of 1.0 cm or greater. Comparing the location of the prostatic apex with the bottom of the ischial tuberosities revealed that in 15% of the patients the apex was 1.0 cm or less from the bottom of the tuberosities and in 45% it was less than 1.5 cm. This would place the apex of the prostate in the penumbra region of the field and risk undertreatment of the prostate if the bottom of the ischial tuberosities was the inferior margin of the field. Measuring the location of the prostatic apex from the top of the symphysis pubis revealed that a distance of 4.9 cm encompassed the apex in all 20 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Beam's eye view volumetrics: an aid in rapid treatment plan development and evaluation

A well-designed treatment plan fully irradiates the target to the prescribed dose while minimizing radiation to adjacent critical structures. Beam's eye view is an important component of treatment planning systems because it provides the operator with tools needed to achieve this goal. Through interactive manipulation of displays, the planner uses beam's eye view to adequately cover the target volume while geometrically avoiding certain critical, normal structures. A factor not considered in current beam's eye view programs is the fractional volume of each structure irradiated given a specified beam direction. We have incorporated a rapid volume calculation capability in our beam's eye view program, and have applied it to provide a quantitative aid to treatment planning development and evaluation. Treatment planning of lung tumors has been studied using this tool. Volumes of lung and spinal cord treated as a function of portal angle may be calculated much more rapidly than dose volume histograms and yet provide quantitative indices which follow the trends of dose volume histograms as a function of field angle. Plots of normal tissue volume irradiated as a function of field angle identify the optimal angle to minimize irradiated volume of a structure at a glance. For multiple field plans, a bitmap approach identifies areas treated by various combinations of beams. Volumetrics combined with beam's eye view are useful in treatment planning because they (a) provide quantitative information needed in choosing and optimizing portal entry angle (b) provide an interactive approach to understanding the relative merits of different multiple field plans and (c) complement the information provided by the more time consuming generation of dose volume histograms. The clinical application of this tool in treatment planning is presented.