Tolerance of normal tissue to therapeutic irradiation

Musculoskeletal complications of neutron therapy for prostate cancer

The purpose of this study was to investigate the cause of hip complaints following conformal neutron therapy delivered by opposed lateral and oblique anterior ports to treat prostate cancer. Twenty-seven patients with hip complaints following neutron or mixed neutron and photon therapy for prostate cancer had 34 magnetic resonance imaging (MRI) studies 3-39 (mean 15.3) months following treatment; for comparison, 13 similarly treated patients without hip complaints were imaged 1-32 (mean 13.8) months post-treatment; 25/40 imaged patients received concurrent nonsteroidal hormone therapy. Coronal and axial images of the hips/pelvis were obtained utilizing T1 weighted spin echo and fat suppressed inversion recovery (STIR) sequences. Signal amplitude (SA) of involved muscles was measured on the STIR images and normalized to that of the psoas outside the treatment field. Hip complaints ranged from mild soreness or motion limitation to severe pain and limitation of ambulation; presence and severity of symptoms (sx) were significantly related to neutron dose (P = 0.020 and 0.0001) but not to hormone therapy (each P > 0.17). Normalized SA of the obturator muscles differed significantly with neutron dose (P = 0.013), the presence, and the severity, of sx (P = 0.0002 and 0.0007); estimated extent of abnormal muscle also differed significantly with neutron dose (P = 0.039), presence, and severity, of sx (P = 0.00004 and 0.0007); [hormone treatment had a profound effect on SA (P = 0.0001) and extent (P = 0.005) which was independent of sx (P = 0.10 and 0.14, respectively) and neutron dose (P = 0.33 and 0.32, respectively)]. Subcutaneous changes localized lateral to the greater trochanter were seen in all, and edema of the subjacent gluteus muscles in many, symptomatic hips; only 4/13 asymptomatic hips showed subcutaneous changes, 6 had mild gluteus edema. Avascular necrosis of the femoral head was seen in 5 symptomatic hips, with marked acetabular necrosis in 3 of these; small joint effusions were seen in 8 symptomatic hips; asymptomatic hips had no significant bone or joint abnormalities. Neutron therapy for prostate cancer designed to spare the rectum results in significant dose-dependent, musculoskeletal complications which are well demonstrated by MRI. SA abnormalities of irradiated muscle correlate significantly with neutron dose and both presence and severity of hip sx. Protocol modifications have been implemented to reduce these complications. MRI provides an objective means to assess both complications and the success of new protocols in ameliorating them. Concurrent hormone therapy has a profound effect on muscle changes on MRI which is independent of neutron dose and sx.

An active set algorithm for treatment planning optimization

An active set algorithm for optimization of radiation therapy dose planning by intensity modulated beams has been developed. The algorithm employs a conjugate-gradient routine for subspace minimization in order to achieve a higher rate of convergence than the widely used constrained steepest-descent method at the expense of a negligible amount of overhead calculations. The performance of the new algorithm has been compared to that of the constrained steepest-descent method for various treatment geometries and two different objectives. The active set algorithm is found to be superior to the constrained steepest descent, both in terms of its convergence properties and the residual value of the cost functions at termination. Its use can significantly accelerate the design of conformal plans with intensity modulated beams by decreasing the number of time-consuming dose calculations.

Variations of tumor control and rectum complication probabilities due to random set-up errors during conformal radiation therapy of prostate cancer

BACKGROUND AND PURPOSE

The effect of random set-up errors on tumor control probability (TCP) and rectum complication probability (NTCP) on 3D conformal treatment planning of prostate cancer has been investigated by applying the convolution method originally proposed by Leong (Leong, J. Implementation of random positioning error in computerized radiation treatment planning systems as a result of fractionation. Phys. Med. Biol. 32: 327-334, 1987).

MATERIALS AND METHODS

The combined influence of the standard deviation of the random shifts probability distribution (sigma) of the dose and of the Beam's-eye-view margin (M) between the clinical target volume (CTV) and the edge of the blocks have been investigated in two patients.

RESULTS AND CONCLUSIONS

Random set-up error has been found to decrease TCP (for a typical 70 Gy CTV mean dose) by up to 6% for a 1 cm margin (sigma = 7 mm). When M is equal to or larger than 1.5 cm, no relevant effects on TCP are obtained. Maximum acceptable TCP values (corresponding to a rectum NTCP equal to 5%) have been derived and the dependence on sigma and M has been investigated.

Proton therapy for pediatric cranial tumors: preliminary report on treatment and disease-related morbidities

PURPOSE

Accelerated protons were used in an attempt to limit treatment-related morbidity in children with tumors in or near the developing brain, by reducing the integral dose to adjacent normal tissues.

METHODS AND MATERIALS

Children treated with protons at Loma Linda University Medical Center between August 1991 and December 1994 were analyzed retrospectively. Twenty-eight children, aged 1 to 18 years, were identified as at risk for brain injury from treatment. Medical records, physical examinations, and correspondence with patients, their parents, and referring physicians were analyzed. The investigators tabulated post-treatment changes in pre-treatment signs and symptoms and made judgments as to whether improvement, no change, or worsening related to disease or treatment had supervened. Magnetic resonance images were correlated with clinical findings and radiographic impressions were tabulated.

RESULTS

Follow-up ranged from 7 to 49 months (median 25 months). Four instances of treatment-related morbidity were identified. Forty-one instances of site-specific, disease-related morbidity were identified: 15 improved or resolved and 26 remained unchanged after treatment. Four patients had radiographic evidence of local failure. Three of these patients, including two with high-grade glioma, have died.

CONCLUSION

Early treatment-related morbidity associated with proton therapy is low. Tumor progression remains a problem when treating certain histologies such as high-grade glioma. Escalating the dose delivered to target volumes may benefit children with tumors associated with poor rates of local control. Long-term follow-up, including neurocognitive testing, is in progress to assess integral-dose effects on cognitive, behavioral and developmental outcomes in children with cranial tumors.

Comparing 3-, 4- and 6-fields techniques for conformal irradiation of prostate and seminal vesicles using dose-volume histograms

BACKGROUND AND PURPOSE

Comparing some isocentric coplanar techniques for conformal irradiation of prostate and seminal vesicles.

MATERIALS AND METHODS

Five conformal techniques have been considered: (A) a 3-fields technique with an antero-posterior (AP) field and two lateral (LAT-LAT) 30 degrees wedged fields; (B) a 3-fields technique with an AP field and two oblique posterior (OBL) 15 degrees wedged fields with relative weights of 0.8, 1 and 1, respectively; (C) a 4-fields technique (AP-PA and LAT-LAT); (D) a 6-fields technique (LAT-LAT and four OBL at gantry angles 45 degrees, 135 degrees, 235 degrees and 315 degrees) with all the fields having the same weight; (E) the same 6-fields technique with lateral fields double-weighted with respect to the oblique fields. The conformal plans have been simulated on 12 consecutive patients (stages B and C) by using our 3D treatment planning system (Cadplan 2.7). The contours of the rectum, the bladder and the left femoral head were outlined together with the clinical target volume (CTV) which included the prostate and the seminal vesicles. A margin of 10 mm was added to define the planning target volume (PTV) through automatic volume expansion. Then a 7 mm margin between the PTV and block edges was added to take the beam penumbra into account. Dose distributions were normalised to the isocentre and the reference dose was considered to be 95% of the isocentre dose. Dose-volume histograms and dose statistics of the rectum, the bladder and the left femoral head were collected for all plans. For the rectum and the bladder the mean dose (Dm) and the fraction of volume receiving a dose higher than the reference dose (V95) were compared. For the femoral head, the mean dose together with the fraction of volume receiving a dose higher than 50% (V50) were compared.

RESULTS

Differences among the techniques have been found for all three considered organs at risk. When considering the rectum, technique A is better than the others both when considering Dm and V95 (P = 0.002), while technique D is the worst when considering Dm (P < 0.002) and is also worse than techniques A, E (P = 0.002) and C (P = 0.003) when considering V95. Technique E is the best when considering the bladder mean dose (P = 0.002 against A and D, P < 0.01 against B and C) and technique C is the worst (P < 0.012). No relevant differences were found for the bladder V95. In the femoral heads, techniques A and E are worse than B, C and D (P < 0.003) when considering Dm and V50. Moreover, techniques B and D are better than C (P < 0.004) when considering V50.

CONCLUSIONS

There is no technique that is absolutely better than the others. Technique A gives the best sparing of the rectum; the bladder is better spared with technique E. These results are reached with a worse sparing of the femoral heads which should be carefully taken into account.

Radiation therapy for ocular choroidal neovascularization (phase I/II study): preliminary report

PURPOSE/OBJECTIVE

Choroidal neovascularization (CNV) is a major cause of severe loss of visual acuity in some ocular diseases such as age-related macular degeneration (ARMD) and angioid streaks. Laser photocoagulation has been used to treat patients with subfoveal neovascular lesions with well-demarcated boundaries. However, the treatment method is usually associated with a large decrease in visual acuity. Therefore, indications for this treatment are very limited. Recently, some investigators reported the effect of low dose irradiation on the subretinal neovascular membranes in CNV. We conducted a Phase I/II study to determine the toxicity and efficacy of external photon beam radiotherapy in patients with CNV.

METHODS AND MATERIALS

Between April, 1994 and July, 1995, 36 patients with choroidal neovascularization (34 with ARMD and 2 with angioid streaks) were treated with radiation therapy. Treatment planning was performed using a CT simulator that enables real-time treatment planning from multiple CT slices. The clinical target volume that included the macula and optic disc received a dose of 10 Gy/5 fractions/1 week (first 18 eyes) or 20 Gy/10 fractions/2 weeks (last 18 eyes). All eyes were irradiated with a single lateral 6 MV photon beam, angled 10 degrees posteriorly to exclude the ipsilateral lens and the contralateral eye from the radiation field. The ipsilateral lens was irradiated with less than 10% of the total reference dose. The field size averaged 3.0 x 2.5 cm. Records of the 17 eyes with CNV referred to our hospital in 1993, which satisfied the eligibility criteria for this study, were retrospectively analyzed for comparison.

RESULTS

There was no significant acute morbidity. All patients were followed regularly by both ophthalmologists and radiation oncologists. Cataract formation after 1 year of the treatment was observed in one patient who had received a dose of 20 Gy. One patient who had received 20 Gy complained of transient dry-eye sensation 2 months after treatment, but this had disappeared spontaneously by the fourth month. The subjective symptoms, visual acuity, and size of the neovascular membrane were evaluated at 6 and 12 months after treatment in each patient. In the group of patients irradiated with 10 Gy and with 20 Gy, respectively, subjective symptoms improved in five and seven eyes, did not change in seven and four eyes, and deteriorated in six and six eyes at 12 months. Although visual acuity was significantly decreased in the control group, the patients in both irradiated groups did not show such a decrease in visual acuity. The size of the neovascular membrane in the control group progressed significantly. However, the patients in the 20 Gy group showed significant regression of the membrane, although those in the 10 Gy group showed no significant change in size.

CONCLUSION

This Phase I/II study including a dose escalation study showed that radiation therapy seems to be useful for CNV. The dose of 20 Gy in 10 fractions was more useful in treating neovascular membranes than the dose of 10 Gy in five fractions. These results have encouraged us to start a multicenter randomized prospective study of the treatment of CNV with radiation therapy.

Early vs. delayed radiotherapy in a small cohort of patients with supratentorial low grade glioma

In a cohort of 25 patients with supratentorial low grade glioma, the timing of radiotherapy made no significance difference for 10 year survival. Patients who received early radiotherapy had a 55% 10 year survival and those receiving delayed radiotherapy had a 53% 10 year survival. Radiotherapy was delayed a median of 4.8 years in those receiving delayed radiotherapy.

Dose-volume histograms for bladder and rectum

PURPOSE

A careful examination of the foundation upon which the concept of the Dose-Volume Histogram (DVH) is built, and the implications of this set of parameters on the clinical application and interpretation of the DVH concept has not been conducted since the introduction of DVHs as a tool for the quantitative evaluation of treatment plans. The purpose of the work presented herein is to illustrate problems with current methods of implementing and interpreting DVHs when applied to hollow anatomic structures such as the bladder and rectum.

METHODS AND MATERIALS

A typical treatment plan for external beam irradiation of a patient with prostate cancer was chosen to provide a data set from which DVH curves for both the bladder and rectum were calculated. The two organs share the property of being shells with contents that are of no clinical importance. DVHs for both organs were computed using a solid model and using a shell model. Typical treatment plans for prostate cancer were used to generate DVH curves for both models. The Normal Tissue Complication Probability (NTCP) for these organs is discussed in this context.

RESULTS

For an eight-field conformal treatment plan of the prostate, a bladder DVH curve generated using the shell model is higher than the corresponding curve generated using the solid model. The shell model also has a higher NTCP. A six-field conformal treatment plan also results in a higher DVH curve for the shell model. A treatment plan consisting of bilateral 120-degree arcs, results in a higher DVH curve for the shell model, as well as a higher NTCP.

CONCLUSION

The DVH concept currently used in evaluation of treatment plans is problematic because current practices of defining exactly what constitutes "bladder" and "rectum." Commonly used methods of tracing the bladder and rectum imply use of a solid structure model for DVHs. In reality, these organs are shells and the critical structure associated with NTCP is obviously and indisputably the shell, as opposed to its contents. Treatment planning algorithms for DVH computation should thus be modified to utilize the shell model for these organs.

Estimation of the spatial distribution of target cells for radiation pneumonitis in mouse lung

PURPOSE

Recent studies of Liao et al. and Travis et al. have demonstrated that irradiation of cross-sectional partial volumes contiguous to the base of mouse lung produces a higher incidence of pneumonitis than irradiation of equally sized subvolumes contiguous to the apex. One interpretation of this finding is that the critical target cells for pneumonitis are not distributed uniformly throughout the lung. The purpose of the present study was to test this interpretation by obtaining an estimate of the spatial distribution of the critical target cells for pneumonitis in mouse lung, based on the partial-volume data.

METHODS AND MATERIALS

A mathematical model was derived describing the probability of radiation pneumonitis as a function of dose, volume of lung irradiated, and location in the lung of the irradiated subvolume. The model includes a nonparametric description of the spatial target-cell distribution in lung, to be estimated from data. The model was fitted to the lethality data of Liao et al. and Travis et al. to obtain estimates of the proportion of target cells contained in each of various subvolumes of the lung.

RESULTS

The results indicate that the critical target cells in mouse lung are concentrated in the base and, to a somewhat lesser extent, in the apex of the lung, with fewer cells in the middle region. The estimated spatial distribution of target cells in mouse lung agrees well with the distribution of alveoli, whose concentration in the midlung is limited by the presence of the major conducting airways.

CONCLUSION

Heterogeneity in the spatial distribution of critical target cells in normal tissue implies that the complication probability (NTCP) depends on the location in the organ of the irradiated subvolume, as well as on radiation dose and subvolume size. Calculations using an NTCP model for mouse lung indicate that irradiation of equal subvolumes of lung with the same dose can lead to complication probabilities covering the full range from 0 to 100%, depending only on the location in the lung of the irradiated subvolume.

Spatial heterogeneity of the volume effect for radiation pneumonitis in mouse lung

PURPOSE

In a previous study to determine the effect of partial volume irradiation on damage and morbidity from pneumonitis in mouse lung, a critical determinant of the volume effect was the spatial location of the irradiated subvolume within the lung. The goals of the present study were to (a) define the dose-volume effect curves for radiation pneumonitis in mouse lung, (b) define the threshold volume, and (c) further investigate the spatial heterogeneity of the radiosensitivity of mouse lung.

METHODS AND MATERIALS

Eight fractional volumes ranging from 94% to 17% of the lungs of C3Hf/Kam mice were irradiated with single doses ranging from 12 to 22 Gy, depending on the volume irradiated. The fractional volumes irradiated were determined from computed tomographic scans of mouse lung. To determine the effect of location of irradiated subvolume, equivalent volumes in the base and the apex were irradiated by shielding the prescribed adjacent volume in the apex or base respectively. Dose-response curves of breathing rate at 22 weeks and lethality at 28 weeks were constructed for each subvolume irradiated in the apex or base and fitted by logit analysis, and ED50s and LD50s with 95% confidence limits obtained, respectively. Lungs from dead mice or mice sacrificed when moribund were examined for histologic signs of pneumonitis.

RESULTS

Irradiation of any of the eight subvolumes in the base yielded a consistently lower isoeffect dose for both assays of radiation pneumonitis than if the same irradiated subvolume was located in the apex. Plots of isoeffect dose for breathing rate as a function of subvolume irradiated in the base or apex showed that these curves were not linear but exhibited a plateau between irradiated volumes of 70% and 80% in both the apex and base. A similar curve was obtained for lethality and volume irradiated in the base. A threshold volume, i.e., irradiation of that volume that should produce no changes in breathing rate or mortality, was dependent on the location of the irradiated subvolume.

CONCLUSION

The response of mouse lung to partial volume irradiation is heterogeneous and is critically dependent on the specific location of the irradiated subvolume in the lung, i.e., a given subvolume in the base is consistently more sensitive than the same subvolume in the apex using either breathing rate or lethality as assays of radiation pneumonitis. We suggest that this heterogeneity is due to the anatomy of the tracheobronchial tree, i.e., to the distribution of non-gas exchange-conducting airways in the irradiated volume. These data have implications for the modeling of dose-volume effects in the lung and the prediction of normal tissue complication probabilities for radiation pneumonitis in humans.

Promising survival with three-dimensional conformal radiation therapy for non-small cell lung cancer

PURPOSE

Local failure is a major obstacle to the cure of locally advanced non small-cell lung cancer. Three-dimensional conformal radiation therapy (3-DCRT) selects optimal treatment parameters to increase dose to tumor and reduce normal tissue dose, potentially representing an enhancement of the therapeutic ratio of radiation therapy for lung cancer. We performed this analysis of 45 non-small cell lung cancer patients treated with 3-DCRT alone, to evaluate the ability of computer derived lung dose volume histograms to predict serious pulmonary toxicity, to assess the feasibility of this approach, and to examine the resulting survival.

METHODS

There were 28 males (62%) and 17 females (38%). The median age was 65 (range: 38-82). Tumor stage was Stage I/II in 13%, IIIa in 42%, and IIIb in 44%. The histology was squamous in 44%, adenocarcinoma in 36%, and other non-small cell histologies in the others. Only 47% of patients. had combined favorable prognostic factors (i.e. KPS < or = 80, and < or = 5% wt. loss). The median dose of radiation to gross disease was 70.2 Gy (range: 52.2-72 Gy) delivered in fractions of 1.8 Gy, 5 days per week.

RESULTS

Seven patients did not complete 3-DCRT due to disease progression outside the port. Follow-up data are mature: the median follow up of the 6 survivors is 43.5 months (35-59). Thoracic progression occurred in 46%. Median survival (all 45 patients.) is 15.7 months and survival is 32% at 2 years and 12% at 59 months. Pulmonary toxicity > or = grade 3 occurred in 9% of patients. Dose volume histograms were available in 31 patients and showed a correlation between risk of pulmonary toxicity and indices of dose to lung parenchyma. Grade 3 or higher pulmonary toxicity occurred in 38% (3/8) of patients with > 30% of lung volume receiving > or = 25 Gy, versus 4% (1/23) of patients with < or = 30% lung receiving > or = 25 Gy (P = 0.04). Grade 3 or higher pulmonary toxicity occurred in 29% (4/14) of patients with a predicted pulmonary normal tissue complication probability of 12% or higher versus 0% (0/17) in patients with a predicted probability of less than 12% (P = 0.03).

CONCLUSIONS

Despite adverse prognostic criteria median survival is encouraging and may be higher than some combined modality approaches. Dose volume histogram parameters may be useful to determine the maximum dose for individual patients and thereby permit avoidance of toxicity.

Effect of irradiated volume on lung damage in pigs

BACKGROUND AND PURPOSE

The volume dependence of radiation induced lung damage is of important clinical concern. The aim of the present study was to investigate the effect of irradiated volume on radiation pneumonitis and lung fibrosis in pigs after fractionated irradiation.

MATERIALS AND METHODS

Twenty-five animals were irradiated with 10 x 14 cm2 fields to the whole right lung (about 530 cm3), while 19 animals received irradiation only to the lower part of the right lung (10 x 8 cm2 fields, about 260 cm3). The irradiations were given in five fractions over 5 days with total doses ranging from 14.3-38.0 Gy (whole lung) or 21.3-31.2 Gy (half lung) using a 60cobalt unit and an isocentric technique. Early lung damage was assessed during the first 8 weeks after the start of treatment by weekly chest radiographs and by twice weekly determinations of the breathing rate in resting animals. Fibrosis was quantified at autopsy (after 8 weeks or after 5-8 months) by histological evaluation and by determination of the hydroxyproline content of the lung tissue. Based on reference values obtained in 17 untreated control animals the experimental data were converted to quantals for probit analysis.

RESULTS

The data did not indicate any significant differences for the incidence of lung damage after half lung and whole lung irradiation when injury was assessed by radiography, histology, or hydroxyproline content. However, using an increase in breathing rate as experimental endpoint, significant differences of radiation induced morbidity were observed. While none of the animals after half lung irradiation showed pathological breathing rates even after doses of 29 Gy and 31 Gy, a clear if shallow dose-response relationship with an ED50-value of 27 +/- 11 Gy (SD) was obtained after whole lung irradiation (P < 0.01).

CONCLUSIONS

A volume effect can only be demonstrated for functional lung morbidity whereas induction of structural lung damage is independent of the volume irradiated.

[Proliferation rate and radiosensitivity. Bergonié's and Tribondeau's error]

In 1906 Bergonié and Tribondeau postulated a correlation between proliferation rate and radiosensitivity. Allowing for modern radiotherapeutic and radiobiological experience this postulate is no longer tenable.

Potential role of proton therapy in the treatment of pediatric medulloblastoma/primitive neuroectodermal tumors: reduction of the supratentorial target volume

PURPOSE

One of the components of radiotherapy (RT) in medulloblastoma/primitive neuroectodermal tumors is the prophylactic irradiation of the whole brain (WBI). With the aim of reducing late neuropsychologic morbidity a CT-scan-based dosimetric study was undertaken in which treatment was confined mainly or exclusively to supratentorial sites considered at high risk for disease recurrence.

METHODS AND MATERIALS

A comparative dosimetric study is presented in which a three field (two laterals and one posterior) proton plan (spot scanning method) is compared with a two-field conventional WBI 6 MV x-ray plan, to a 6-field "hand-made" 6 MV x-ray plan, and to a computer-optimized 9-field "inverse" 15 MV x-ray plan. For favorable patients, 30 Gy were delivered to the ventricles and main cisterns, the subfrontal and subtemporal regions, and the posterior fossa. For the unfavorable patients, 10 Gy WBI preceeded a boost to 30 Gy to the same treatment volume chosen for favorable patients. The dose distribution was evaluated with dose-volume histograms to examine the coverage of the targets as well as the dose to the nontarget brain and optical structures. In addition, the risks of radiation-related late neuropsychologic effects after WBI were collected from the literature and used to predict normal tissue complication probabilities (NTCPs) for an intelligence quotient deficit after treatment with photon or proton beams.

RESULTS

Proton beams succeeded better in reducing the dose to the brain hemispheres and eye than any of the photon plans. A 25.1% risk of an IQ score <90 was predicted after 30 Gy WBI. Almost a 10% drop in the predicted risk was observed when using proton beams in both favorable and unfavorable patients. However, predicted NTCPs for both optimized photon plans ("hand made" and "inverse") were only slightly higher (0.3-2.5%) than those of proton beams. An age-modifying factor was introduced in the predictive NTCP model to assess for IQ differences in relation with age at irradiation. Children with ages between age 4 to 8 benefitted most from the dose reduction in this exercise (similar NTCP predictions for both proton and "inverse" plans).

CONCLUSION

Modulated proton beams may help to significantly reduce the irradiation of normal brain while optimally treating the supratentorial subsites at higher risk for relapse. A decrease in morbidity can be expected from protons and both optimized proton plans compared to WBI.

Physician/patient-driven risk assignment in radiation oncology: reality or fancy?

PURPOSE

Treatment plan optimization in radiation oncology entails designing multiple x-ray beams to irradiate a tumor to a dose that will achieve locoregional control while minimizing normal tissue complications. For some anatomical sites, it is possible to estimate tumor control probabilities (TCP) and normal tissue complication probabilities (NTCP) as a function of radiation dose. Thus, treatment plan optimization can be based on biologic end points rather than on dose calculations alone. Given multiple plans with different NTCPs and TCPs, a tradeoff must be made between maximizing TCP and maintaining an acceptable NTCP. How do physicians reach these decisions? Can the process be quantified? Should patients participate in the process?

METHODS AND MATERIALS

Physicians and patients were asked to rank a series of treatment plans having different combinations of TCP and NTCP. Responses were parametrized into a figure of merit (FM) equation which quantifies predilections of TCP and NTCP.

RESULTS

Physician-based FM equations are site- and patient-specific. Variations exist among physicians, but treatment plan selection is often conservative in accordance with the primum non nocere dictum. FM equations generated from the responses of patients suggest that some patients may be willing to accept higher treatment toxicity in exchange for increased TCP.

CONCLUSION

The term "optimized treatment plan" contains inherently subjective criteria which reflect one's willingness to accept treatment morbidity in exchange for probability of cure. These criteria may differ among patients and/or physicians. A quantifiable FM may permit the design of custom-made treatment plans that include physician and patient input.

Quantification of radiation-induced regional lung injury with perfusion imaging

PURPOSE

To better understand the dose and time dependence of radiation therapy (RT)-induced regional lung dysfunction as assessed by changes in regional lung perfusion.

METHODS AND MATERIALS

Patients who were to receive RT for tumors in and around the thorax, wherein portions of healthy lung would be incidentally irradiated, were prospectively studied. Regional function was assessed pre- and post-RT with single photon emission computed tomography (SPECT) lung perfusion scans, obtained following the intravenous administration of approximately 4 mCi of technetium-99m macroaggregated albumin. Pre-RT computed tomography (CT) scans were used to calculate the three-dimensional (3D) dose distribution, reflecting tissue density inhomogeneity corrections. Each SPECT scan was correlated with the pre-RT CT scan, and the 3D dose distribution. Changes in regional lung perfusion were correlated with regional RT dose, at various time intervals following radiation.

RESULTS

The data from 20 patients (7 breast cancer, 5 lymphoma, 1 esophagus, 1 sarcoma, and 6 lung cancer) have been analyzed. Patients with gross intrathoracic lung cancers causing obstruction of regional pulmonary arteries were not included. For most patients, there is a statistically significant dose-dependent reduction in regional blood flow at all time points following radiation. While a time dependence is suggested in the high dose range, the limited amount of data prevents meaningful statistical evaluation.

CONCLUSIONS

Radiation therapy-induced regional lung dysfunction occurs in a dose-dependent manner and develops within 3-6 months following radiation. In contrast to classical "sigmoid" dose-response curves, described mainly for changes following whole lung irradiation, these data suggest a more gradual relationship between regional dysfunction and RT dose. Retraction of irradiated lung with secondary movement of unirradiated lung into the "3D-defined irradiated volume" may have introduced inaccuracies into this analysis. Additional studies are currently underway to assess this possibility and better refine this dose-response curve. Studies are underway to determine if changes in assessments of whole lung function, such as pulmonary function tests, can be predicted by summing the regional changes observed.

Dose-volume complication analysis for visual pathway structures of patients with advanced paranasal sinus tumors

PURPOSE

The purpose of the present work was to relate dose and volume information to complication data for visual pathway structures in patients with advanced paranasal sinus tumors.

METHODS AND MATERIALS

Three-dimensional (3D) dose distributions for chiasm, optic nerve, and retina were calculated and analyzed for 20 patients with advanced paranasal sinus malignant tumors. 3D treatment planning with beam's eye view capability was used to design beam and block arrangements, striving to spare the contralateral orbit (to lessen the chance of unilateral blindness) and frequently the ipsilateral orbit (to help prevent bilateral blindness). Point doses, dose-volume histogram analysis, and normal tissue complication probability (NTCP) calculations were performed. Published tolerance doses that indicate significant risk of complications were used as guidelines for analysis of the 3D dose distributions.

RESULTS

Point doses, percent volume exceeding a specified published tolerance dose, and NTCP calculations are given in detail for patients with complications versus patients without complications. Two optic nerves receiving maximum doses below the published tolerance dose sustained damage (mild vision loss). Three patients (of 13) without optic nerve sparing and/or chiasm sparing had moderate or severe vision loss. Complication data, including individual patient analysis to estimate overall risk for loss of vision, are given.

CONCLUSION

3D treatment planning techniques were used successfully to provide bilateral sparing of the globe for most patients. It was more difficult to spare the optic nerves, especially on the ipsilateral side, when prescription dose exceeded the normal tissue tolerance doses. NTCP calculations may be useful in assessing complication risk better than point dose tolerance criteria for the chiasm, optic nerve, and retina. It is important to assess the overall risk of blindness for the patient in addition to the risk for individual visual pathway structures.

Predicting late rectal complications following prostate conformal radiotherapy using biologically effective doses and normalized dose-surface histograms

A model to predict the late normal tissue complication probability (NTCP) of the rectum following conformal therapy is described. The model evaluates the biological consequence of inhomogeneities in the physical dose by computing dose histograms of the biologically effective dose to the surface of the rectum for a given fractionation scheme. A method of normalizing the surface area of the rectum is employed so that the predicted NTCP is independent of the differing cross-sectional size of sections of the rectum, ensuring the NTCP is dependent only on the dose delivered to sensitive rectal tissues. The model has been used to assess severe late rectal complications and the milder RTOG grades 2 and 3 reactions. This model was found to predict severe toxicity levels of 1.7 +/- 0.6% for an accelerated treatment of 50 Gy in 16 fractions commonly employed at this centre. This result lies between the severe toxicities predicted for 60 and 62 Gy delivered in 2 Gy fractions. The model predicts that the average NTCP for severe late effects for nine prostate patients becomes greater than 5% with a fractionation scheme of 70 Gy in 35 fractions, for the four fields treatment. The effects of not treating all fields at each therapy session on rectal toxicity were also investigated. Biologically effective dose-surface histograms show that the dose to the lower surface of the rectum is increased by not treating all fields at each therapy session, but the predicted differences in rectal NTCP are negligible.

Inverse radiotherapy planning for a concave-convex PTV in cervical and upper mediastinal regions. Simulation of radiotherapy using an Alderson-RANDO phantom. Planning target volume

AIM

Three-dimensional inverse treatment planning with modulated beams was applied for dosimetric optimization of a lengthy (22 cm) and complex (concave-convex) shaped planning target volume (PTV) in the cervical and upper mediastinal regions.

MATERIAL AND METHOD

The planning was done for 9 coplanar beams spaced evenly at 40 intervals. Properties of 15 MV photons from a linear accelerator were simulated. The optimization of the fluence modulation profiles for each beam was based on a definition of the desired/permitted relative dose levels in the PTV and organs at risk, and a definition of the strengths of the constraints to achieve these objectives.

RESULTS

An adequate dose delivery to the PTV and protection of the spinal cord are completely achievable. The dose delivered to the lungs is clinically acceptable with respect to the risk of radiation-induced pneumonitis. For reasons of physics, no further decrease in the radiation burden on the lungs can be attained with X-rays without compromising the PTV coverage. The radiation burden on some critical part of normal tissues was effectively reduced by application of a dummy organ at risk.

CONCLUSION

The inverse planning is an effective method for conformal radiotherapy of large tumors as well. However, the power of the technique is insufficient when the tolerance dose of the neighbouring normal tissue is too low and its volume effect is high. Although requiring further operator interactions, introduction of dummy organs at risk may be of help in reducing the radiation burden on normal tissues.

Dose escalation for non-small cell lung cancer using conformal radiation therapy

PURPOSE

Improved local control of non-small cell lung cancer (NSCLC) may be possible with an increased dose of radiation. Three-dimensional radiation treatment planning (3D RTP) was used to design a radiation therapy (RT) dose escalation trial, where the dose was determined by (a) the effective volume of normal lung irradiated, and (b) the estimated risk of a complication. Preliminary results of this trial were reviewed.

METHODS AND MATERIALS

A graph of the iso-normal tissue complication probability (NTCP) levels associated with a dose and effective volume (V(eff)) was derived, using normal tissue parameters derived from the literature. This led to a dose escalation schema, where patients were sorted into 1 of 5 treatment bins, determined by the V(eff) of the best possible treatment plan. The starting doses ranged from 63 to 84 Gy. Each treatment bin was then escalated separately, as in Phase I dose escalation fashion, with Grade > or = 3 radiation pneumonitis defined as dose limiting. To allow for dose escalation, we required patient follow-up to be > or = 6 months for at least three patients. 3D treatment planning was used to irradiate only the radiographically abnormal areas, with 2.1 Gy (corrected for lung inhomogeneity)/day. Clinically uninvolved lymph nodes were not treated prophylactically.

RESULTS

A total of 48 NSCLC patients have been treated (Stage I/II: 18 patients; Stage III: 28 patients; mediastinal recurrence postsurgery: 2 patients). No radiation pneumonitis has been observed in the 30 patients currently evaluable beyond the 6-month time point. All treatment bins have been escalated at least once. Current doses in the five treatment bins are 69.3, 69.3, 75.6, 84, and 92.4 Gy. None of the 15 evaluable patients in any bin with > or = 30% NTCP experienced clinical radiation pneumonitis, implying that the actual risk is < 20% (beta error rate 5%). Despite the observation of the clinically negative lymph nodes at high risk, there has been no failure in the untreated mediastinum as the sole site of first failure. Three of 10 patients receiving > or = 84 Gy have had biopsy proven residual or locally recurrent disease.

CONCLUSION

Successful dose escalation in a volume-dependent organ can be performed using this technique. By incorporating the effective volume of irradiated tissue, some patients have been treated to a total dose of radiation over 50% higher than traditional doses. The literature-derived parameters appear to overestimate pneumonitis risk with higher volumes. There has been no obvious negative effect due to exclusion of elective lymph node radiation. When completed, this trial will have determined the maximum tolerable dose of RT as a single agent for NSCLC and the appropriate dose for Phase II investigation.

Tumor control probability of nasopharyngeal carcinoma: a comparison of different mathematical models

PURPOSE

Radiation dose and tumor volume are factors known to affect the local control of a given type of tumor. Local tumor control is a major factor to consider when a treatment plan is evaluated. This article reports the correlation between tumor control probability, dose, and volume in a retrospective study of 142 patients with nasopharyngeal carcinoma (NPC).

METHODS AND MATERIALS

The tumor volume was outlined and calculated from a computed tomographic scan. Patients were categorized according to tumor volume and radiation dose received in treatment. Local control rate was calculated for each category by the Kaplan-Meier method. Mathematical models were fitted to correlate the local control rate, dose, and volume. Both empirical and mechanistic approaches were attempted; the former included logistic models with two and three parameters, and the latter, the formulation from Brenner and Bentzen with a radiobiological basis.

RESULTS

Brenner's model estimated alpha at 0.041 Gy(-1) with 95% confidence limits (-0.032, 0.113) Gy(-1). The volume dependent constant h was estimated at 0.160 cm(-3) with 95% confidence limits (-0.729, 1.048) cm(-3). The Pearson correlation coefficient was 0.64. The magnitude and sign of the fitted parameters were reasonable and consistent with reported clinical experience. The other models were fitted with slightly better goodness of fit (r = 0.65 - 0.68), but with less interpretable parameters.

CONCLUSION

Brenner's model is considered appropriate for a description of the dose and volume effect on the local control of the NPC. It could be used in combination with normal tissue complication probability for treatment plan evaluation to optimize treatment results.

Advances in prevention of radiation damage to visceral and solid organs in patients requiring radiation therapy of the trunk

BACKGROUND

As a part of multimodality therapy, many patients with tumors of the trunk receive radiation therapy. The major morbidity of this therapy is often secondary to incidental radiation damage to tissues adjacent to treatment areas.

METHODS

We detail our use of saline breast implants placed in polyglycolic acid mesh sheets to displace visceral and solid organs away from the radiation field.

RESULTS

Analysis of CT scans and dose volume histograms reveal that this technique successfully displaces uninvolved organs away from the radiation fields, thereby minimizing the radiation dose to such organs and tissues.

CONCLUSION

We believe this is a safe and efficacious method to prevent radiation damage to visceral and solid organs adjacent to trunk tumor sites.

Number and orientations of beams in intensity-modulated radiation treatments

The fundamental question of how many equispaced coplanar intensity-modulated photon beams are required to obtain an optimum treatment plan is investigated in a dose escalation study for a typical prostate tumor. Furthermore, optimization of beam orientations to improve dose distributions is explored. A dose-based objective function and a fast gradient technique are employed for optimizing the intensity profiles (inverse planning). An exhaustive search and fast simulated annealing techniques (FSA) are used to optimize beam orientations. However, to keep computation times reasonable, the intensity profiles for each beam arrangement are still optimized using inverse planning. A pencil beam convolution algorithm is employed for dose calculation. All calculations are performed in three-dimensional (3D) geometry for 15 MV photons. DVHs, dose displays, TCP, NTCP, and biological score functions are used for evaluation of treatment plans. It is shown that for the prostate case presented here, the minimum required number of equiangular beams depends on the prescription dose level and ranges from three beams for 70 Gy plans to seven to nine beams for 81 Gy plans. For the highest dose level (81 Gy), beam orientations are optimized and compared to equiangular spaced arrangements. It is shown that (1) optimizing beam orientations is most valuable for a small numbers of beams (< or = 5) and the gain diminishes rapidly for higher numbers of beams; (2) if sensitive structures (for example rectum) are partially enclosed by the target volume, beams coming from their direction tend to be preferable, since they allow greater control over dose distributions; (3) while FSA and an exhaustive search lead to the same results, computation times using FSA are reduced by two orders of magnitude to clinically acceptable values. Moreover, characteristics of and demands on biology-based and dose-based objective functions for optimization of intensity-modulated treatments are discussed.

Changes in plasma transforming growth factor beta during radiotherapy and the risk of symptomatic radiation-induced pneumonitis

PURPOSE

To determine whether changes in the plasma Transforming Growth Factor beta1 (TGF beta1) concentration during radiotherapy could identify patients at risk for developing symptomatic radiation pneumonitis.

METHODS AND MATERIALS

Thirty-six patients who received radiation therapy with curative intent for lung cancer (n = 31), Hodgkin's disease (n = 4), or thymoma (n = 1) were evaluated prospectively. All patients had serial plasma TGF beta1 measurements obtained before, during, and after treatment. Plasma TGF beta1 was quantified using an enzyme-linked immunosorbent assay. Pneumonitis was defined clinically. Plasma TGF beta1 levels were considered to have normalized if the following occurred: the last on-treatment TGF beta1 level was both <7.5 ng/ml and lower than the pretreatment level.

RESULTS

Thirteen of these 36 patients developed pneumonitis. Significant changes in plasma TGF beta1 levels during treatment were seen only in the subset of patients whose TGF beta1 levels were >7.5 ng/ml at baseline (n = 22). Failure of plasma TGF beta1 to normalize by the end of treatment, as defined above, much more accurately identified patients at risk for symptomatic pneumonitis if their baseline TGF beta1 was >7.5 ng/ml than if it was <7.5 ng/ml.

CONCLUSIONS

Changes in plasma TGF beta1 levels during radiotherapy appears to be a useful means by which to identify patients at risk for the development of symptomatic radiation pneumonitis, particularly in the subset of patients whose pretreatment TGF beta1 levels are >7.5 ng/ml.

A phase I pilot study of pelvic radiation and alpha-2A interferon in patients with locally advanced or recurrent rectal cancer

PURPOSE

The purpose of this pilot study was to determine the maximum tolerated dose of alpha-2a interferon given by subcutaneous injection and combined with high dose pelvic radiation for locally advanced or recurrent rectal cancer.

METHODS AND MATERIALS

In this Phase I pilot study, patients with locally advanced, unresectable, or recurrent rectal cancer with or without distant metastases received external beam pelvic radiotherapy over 5 to 6 weeks combined with escalating doses of alpha-2a interferon. Interferon was escalated in increments of 3 million units for each patient cohort, starting at 3 million units subcutaneously 3 days weekly during pelvic radiation. Radiotherapy consisted of 44 Gy (2 Gy fractions) to the pelvis followed by a boost of 6 Gy or 16 Gy to gross pelvic tumor, depending on the presence or absence of small bowel in the boost field, respectively. Between 1991 and 1993, 10 patients were treated on this study, five with locally advanced and five with locally recurrent rectal cancer.

RESULTS

At 6 million units of interferon, Grade 3 (WHO criteria) toxicities were as follows: diarrhea (one), leukopenia (one), and neutropenia (one). One patient died of a massive GI bleed at this dose level. Death was not felt to be treatment related. The maximum tolerated dose of interferon was 3 million units three times weekly with radiation. Three patients had unusual complications at 4, 6, and 6 months possibly related to treatment. The first had a right distal ureteric stricture with a right urinoma. The second had a sudden left foot drop that has remained stable. The third had sudden onset of bilateral lower extremity paraplegia with spontaneous resolution.

CONCLUSIONS

The maximally tolerated dose of interferon alpha-2a given three times weekly during pelvic radiation was 3 million units based on acute side effects. Nevertheless, even at this dose level there were three unusual subacute complications possibly related to treatment. Caution is advised when combining interferon alpha-2a with high dose pelvic radiation, especially in patients with predisposing conditions (such as diabetes) for radiotherapy complications.

Respiration-induced motion of the kidneys in whole abdominal radiotherapy: implications for treatment planning and late toxicity

PURPOSE

Whole abdominal radiotherapy (WAR) has potential utility in the management of several malignancies. The limited radiation tolerance of the kidneys is an important consideration in the design of WAR fields. Although renal blocking is standard for WAR, few guidelines exist in the literature to factor respiration-induced kidney motion into the design of these blocks.

METHODS

Radiographs were obtained to measure kidney excursion under forced respiratory conditions in eight patients (14 visualized kidneys). Intravenous contrast was administered and AP films were obtained at maximum inspiration and expiration. Renal excursion was measured relative to a horizontal reference line at the bottom of the L3 vertebral body. The kidney position on the actual treatment simulation film was also determined using this technique. Treatment isodose distributions through the kidneys were obtained for a sample patient using phantom measurements and two blocking schemes: AP/PA and PA only. These provided quantification of the actual dose received by the kidney in a typical WAR treatment.

RESULTS

In the worst case scenario, the left kidney block required an additional 10 mm above and 15 mm below the renal silhouette on the simulation film in order to account for all phases of respiration. The corresponding values for the right kidney were 2 mm and 19 mm, respectively. The dose received by the kidney under the center of the block was 20% of prescribed using AP/PA blocks and 50% of prescribed using PA blocks only. However, portions of 'blocked' kidney received up to 90% of the prescribed dose with either technique.

CONCLUSIONS

Although kidney motion under forced respiratory conditions is not representative of typical treatment conditions, the data highlight the possibility of renal movement during treatment. This is particularly important in light of the significant dose (20 to 50%) delivered to the kidney under the center of the kidney block of typical treatments. Given the potential for overdosage of this critical organ, careful prospective documentation of renal function is warranted in patients receiving WAR.

Specification of the dose to organs at risk in external beam radiotherapy

Reporting of the clinical relevant dose to organs at risk (OR) and other normal tissues is crucial in trials and protocols where the aim is to assess late complications and to increase the therapeutic ratio for external beam radiotherapy. The dose distribution in normal tissues and ORs are, however, most often heterogeneous, at least when more than two opposing beams are applied. To decide the most clinical relevant dose with respect to late occurring complications is therefore not a straight forward problem. In this work we discuss what parameters characterise the dose-volume-histogram (DVH) best by calculating normal tissue complication probabilities (NTCPs) by using the Lyman model and various sets of statistical parameters drawn out from the DVHs. These NTCPs are compared to NTCPs calculated from the full DVHs, when the sets of parameters are evaluated. Our calculations indicate that the NTCP based on the Lyman model is best correlated to the Dmax value for serially organised tissues such as the spinal cord. For organs, described largely as tissues organised in parallel, the Dmedian or Dmean of the DVH may be applied. Our calculations reveal that Dmean is the parameter of choice when Dmedian is quite small, but when the two parameters approach each other. Dmedian will be a better choice, using a unity volume fraction. For ORs characterised by a mixed serial and parallel functional structure, as the heart, neither Dmax, Dmedian nor Dmean may predict the actual NTCP.

Comparative treatment planning between proton and X-ray therapy in locally advanced rectal cancer

BACKGROUND AND PURPOSE

Conformal treatment planning with megavoltage X-rays and protons for medically inoperable patients with a large rectal cancer has been studied in an attempt to determine if there are advantages of using protons instead of X-rays.

MATERIAL AND METHODS

Three dose plans were made for each of the six patients: one proton plan, including three beams covering the primary tumour and adjacent lymph nodes and three boost beams covering the primary tumour: one X-ray plan, eight beams including a boost with four beams and one mixed plan with four X-ray beams and a boost with three proton beams. A three dimensional treatment-planning systems, TMS, was used. The evaluation of the different plans was made by applying the biological models TCP and NTCP on the dose distributions in terms of dose-volume histograms.

RESULTS

The comparison shows advantages of using protons instead of X-rays for all six patients, but in three of them, the advantage is only marginal. The dose-limiting organ at risk is the small bowel, but the proton plan and the mixed plan also spare the bladder and the femoral heads better. At 5% NTCP in any risk organ, the calculated mean TCP value for the six patients is increased by 14%-units with the proton plan and 8%-units with the mixed plan compared to X-rays only.

CONCLUSIONS

Proton beam therapy has potential advantages when treating medically inoperable patients with a large rectal cancer over conventional X-ray therapy. Since the benefits are comparatively small, although clinically worthwhile, large randomised studies are needed.

Treatment planning for radio-immunotherapy

To foster the success of clinical trials in radio-immunotherapy (RIT), one needs to determine (i) the quantity and spatial distribution of the administered radionuclide carrier in the patient over time, (ii) the absorbed dose in the tumour sites and critical organs based on this distribution and (iii) the volume of tumour mass(es) and normal organs from computerized tomography or magnetic resonance imaging and appropriately correlated with nuclear medicine imaging techniques (such as planar, single-photon emission computerized tomography or positron-emission tomography). Treatment planning for RIT has become an important tool in predicting the relative benefit of therapy based on individualized dosimetry as derived from diagnostic, pre-therapy administration of the radiolabelled antibody. This allows the investigator to pre-select those patients who have 'favorable' dosimetry characteristics (high time-averaged target: non-target ratios) so that the chances for treatment success may be more accurately quantified before placing the patient at risk for treatment-related organ toxicities. The future prospects for RIT treatment planning may yield a more accurate correlation of response and critical organ toxicity with computed absorbed dose, and the compilation of dose-volume histogram information for tumour(s) and normal organ(s) such that computing tumour control probabilities and normal tissue complication probabilities becomes possible for heterogeneous distributions of the radiolabelled antibody. Additionally, radiobiological consequences of depositing absorbed doses from exponentially decaying sources must be factored into the interpretation when trying to compute the effects of standard external beam isodose display patterns combined with those associated with RIT.

Long-term cardiac mortality after radiotherapy of breast cancer--application of the relative seriality model

Effects on the heart constitute a potentially significant and serious clinical problem in primary radiation therapy of early breast cancer. Increased cardiac mortality among irradiated patients may offset the potential benefit in terms of a reduced risk of recurrence or of death from breast cancer. Clinical data on long-term cardiac mortality among breast cancer patients included in two randomized trials (the Stockholm and Oslo studies) of radiation therapy as an adjunct to primary surgery were analysed using the relative seriality model of radiation response. Five different radiation therapy techniques were used in the trials. The original treatment plans were recalculated on a group of model patients using a three-dimensional treatment planning system. A mean dose-volume histogram (DVH) was calculated for each treatment technique. Both heart and myocardium, i.e. excluding circulating blood within the heart, were separately investigated as risk organs. Model parameters, (D50, i.e. the dose giving 50% complication probability; gamma, i.e. the maximum relative slope of the dose-response curve; s, describing the organ relative seriality) were determined by a chi 2 fitting of the calculated probability of excess cardiac mortality, based on the DVHs, to the incidence data. Computed complication probabilities for each treatment technique were modelled within the 95% confidence interval (CI) of the clinical incidence data. It was shown that the relative seriality model, assuming a homogeneous radiation sensitivity within the volume of the heart/myocardium can be used to describe the incidence data. A small dependence on the volume was found. The results do not, however, exclude the possibility that more sensitive structures within the myocardium are the main target for radiation.

Reduction of the rectal dose in gynecological brachytherapy: modification to the Fletcher-Suit applicator

The dose to the anterior rectal wall is a known limiting factor for the delivery of radical doses of radiation to the uterine cervix with brachytherapy. We developed a modification to the Fletcher-Suit afterloading applicator, consisting of two small inflatable balloons attached to the posterior end of each colpostat. The balloons are connected to catheters that emerge from the vagina attached to the colpostat's handles. The balloons were affixed to the colpostats with a plastic adaptor and are inserted empty. After an anterior radiograph is taken, the balloons are filled with radiological contrast material and a lateral orthogonal film is made. This lateral film taken with the balloons filled with contrast typically shows a significant posterior displacement of the anterior rectal wall away from the vaginal sources. The International Commission on Radiation Units (ICRU) rectal point is then determined 5 mm beyond the posterior boundary of the opacified balloons. We have performed 90 applications using this device, including brachytherapy applications for cervical cancer, as well as vaginal applications for endometrial carcinoma following TAH-BSO. On average, the ICRU rectal point was displaced 14 mm away from the colpostats, thus reducing the dose rate by 60% and resulting in an average dose sparing of about 1000 cGy to the anterior rectal wall.

Reirradiation of primary CNS tumors

PURPOSE

Primary central nervous system (CNS) tumors are seldom reirradiated due to toxicity concerns and sparse clinical data regarding efficacy.

METHODS AND MATERIALS

We retrospectively reviewed 34 patients with primary brain tumors retreated with fractionated external beam irradiation at the University of California, San Francisco from 1977-1993. Tumors included 15 medulloblastomas, 10 high-grade gliomas, 7 low-grade gliomas, and 2 meningiomas.

RESULTS

Initial course of radiation was radical in intent for all patients. Median age at initial diagnosis was 19.8 years (range: 3.6-67). Median interval between radiation courses was 16.3 months (range: 3.8-166). Median Karnofsky Performance Status (KPS) prior to reirradiation was 80 (range: 40-100). Reirradiation volumes overlapped previous treatment in 30 patients and were nonoverlapping in 4 patients. Fractionation schemes used were hyperfractionated in 17, conventionally fractionated in 9, and hypofractionated in 8. Cumulative maximum overlap dose within the CNS ranged from 43.2-111 Gy (median: 79.7 Gy). Retreatment was completed as planned in 27 out of 34 patients and modified or aborted in 7 (four tumor progression on retreatment, three patient request). As measured from the time of retreatment median progression free and overall survival was 3.3 and 8.3 months. Clinical and radiographic indices were stabilized or improved in about half of patients evaluable at a median of 3 months postretreatment. Complications (early or late) potentially attributable to retreatment were noted in 10 of 34 (29%) of patients. Overt necrosis was noted in 3 of 34 (9%) of patients and the actuarial risk of necrosis was 22% at 1 year following retreatment.

CONCLUSIONS

Reirradiation of primary central nervous system tumors was associated with only modest palliative and survival benefits in this retrospective review. Difficulties separating toxicity due to retreatment vs. tumor progression and limited patient survival following retreatment preclude definite conclusions regarding the safety of this practice.

Primary bone lymphoma (osteolymphoma)

Seventeen patients with primary lymphoma of bone are reviewed. In 15 patients treated with radical radiotherapy, local progression or recurrence occurred in four. The results support the use of radiotherapy alone, using doses of 45-50 Gy. Although small numbers prevent firm conclusions, the inclusion of the whole bone or regional nodes in the irradiated volume did not appear to improve results. Eight patients received systemic chemotherapy with no apparent improvement in rates of relapse. Two patients suffered pathological fractures after radiotherapy in the absence of recurrence at the fracture site; however, osteomyelitis, older age, Paget's disease, high-dose prednisolone and whole-bone radiotherapy may have added to the risk of fracture. Because of the many complex names and selection criteria applied to this condition, literature searching and comparison between studies was difficult. The simple term osteolymphoma is proposed, consistent with other primary bone conditions.

Combined error of patient positioning variability and prostate motion uncertainty in 3D conformal radiotherapy of localized prostate cancer

PURPOSE

To measure the patient positioning and prostate motion variability and to estimate its influence on the calculated 3D dose distribution in 3D conformal radiotherapy of patients with localized prostate carcinoma.

METHODS AND MATERIALS

Patient positioning variability was determined retrospectively by comparing 54 orthogonal simulator films with 125 corresponding portal films from 27 patients. Prostate motion variability was determined by 107 computed tomography (CT) examinations with a CT simulator in 28 patients during radiotherapy.

RESULTS

In each observed direction, the patient positioning variability and prostate motion showed a normal distribution. This observation enabled the calculation of a combined error of both components. The standard deviation (1 SD) of the patient positioning error in three directions ranged from 3.1 to 5.4 mm; the prostate motion variability was significantly greater in the anterior-posterior direction (1 SD = 2.8 mm) than in the mediolateral direction (1 SD = 1.4 mm). The 1 SD of the estimated combined error was in the anterior-posterior direction 6.1 mm and in mediolateral direction 3.6 mm.

CONCLUSION

The range of patient positioning variability and prostate motion were statistically predictable under the patient setup conditions used. Dose-volume histograms demonstrating the influence of the combined error of both components on the calculated dose distribution are presented.

Preoperative radiotherapy in rectal carcinoma--aspects of acute adverse effects and radiation technique

PURPOSE

To explain a possible association between treatment technique and postoperative mortality after preoperative radiotherapy of rectal carcinoma, the dose distributions were compared in model experiments.

METHODS AND MATERIALS

Preoperative radiotherapy with a three-beam technique delivered in five fractions to 25 Gy (5 Gy/daily for 5 or 7 days) was given to patients with primary resectable rectal carcinoma. The adverse effects of this treatment, both acute and late, have been low. In a parallel trial using an identical fractionation schedule and total dose but with a two-beam technique, the postoperative mortality was higher. Two-, three-, and four-beam techniques were analyzed in 20 patients with computed tomography based, three-dimensional dose planning. Dose distributions and dose-volume histograms in the planning target volume (PTV) and in the organs at risk were considered. A numerical "biological" model was used to compare the techniques.

RESULTS

The two-beam and the four-beam box techniques give the most homogeneous dose distributions in the PTV, although all techniques result in dose distributions that would be considered adequate, provided 16 MV or higher photon energies are used. Three- and four-beam techniques show advantages over the two-beam technique with respect to organs at risk, particularly the small bowel. With the two-beam technique and the upper beam limit at mid-L4, the volume of the bowel that receives > 95% of the prescribed dose, and hence, is included in the treated volume (TV), is more than twice as large as that with three- and four-beam techniques, and that of the total body between 1.5 and 2 times as large. The results of the analyses using the biological model indicate that the three- and four-beam techniques result in less small bowel complication rates than the two-beam technique. The integral energy to the total body is similar for all treatment modalities compared.

CONCLUSIONS

The volume of bowel included in the TV, rather than the energy imparted to the body, influences postoperative mortality, and emphasizes the importance of precise radiotherapy planning to minimize normal tissue toxicity.

Hip stiffness following mixed conformal neutron and photon radiotherapy: a dose-volume relationship

PURPOSE

To determine the relationship between dose, volume, and the incidence of hip stiffness in patients who received conformal neutron irradiation for prostate cancer.

METHODS AND MATERIALS

A series of dose-searching studies using neutron irradiation for prostate cancer were performed to determine the optimal dose, fraction size, field size, technique, and proportions of photon and neutron dose. Neutron doses ranged from 9 to 20 Gy and photon doses ranged from 0 to 38 Gy. Data were analyzed by using a hip stiffness grading scale.

RESULTS

Hip stiffness was recorded on follow-up examination in 30% of patients (40 out of 132) treated with fast neutrons or mixtures of fast neutron and photon radiation for prostate cancer. Hip stiffness was categorized as none (Grade 0, 92 patients), mild (Grade 1, 24 patients), moderate (Grade 2, 10 patients), or severe (Grade 3, 6 patients). The incidence of hip stiffness differed significantly by dose and volume in the five dose levels studied (p < 0.001).

CONCLUSIONS

By using a mixture of conformal neutron and photon irradiation and limiting the total neutron dose to less than 13 Gy, hip stiffness toxicity could be reduced to acceptable levels.

Radiation therapy tolerance limits. For one or for all?--Janeway Lecture

BACKGROUND

The optimal use of radiation therapy for cancer treatment is hampered by the application of tolerance limits of normal tissues derived empirically from population averages. Such limits do not reflect the considerable differences from patient to patient in susceptibility to late radiation sequelae. Assays that accurately predict normal tissue tolerance in individual patients would permit real application of the concept of treatment to tolerance thereby increasing the probability of an uncomplicated cure for the population as a whole.

METHODS

A summary of laboratory research is presented to test the hypothesis that the cellular radiosensitivity of normal skin fibroblasts can predict the severity of late connective tissue damage that develops following radiotherapy. The pathogenesis of radiation reactions and the possible role of radiation induced cellular senescence in the development of clinical late effects are briefly reviewed.

RESULTS

Although the pathogenesis of radiation injury is highly complex, several clinical studies have demonstrated a significant correlation between fibroblast radiosensitivity and the severity of late sequelae from treatment. However, the precision and reproducibility of fibroblast cell survival assays are inadequate for routine clinical use. Newer assays incorporating insights into the effects of radiation on cellular senescence and cytokine production are being developed. Such assays may, in the future, be complemented or replaced by molecular and/or cytogenetic probes to derive robust estimates of individual tolerance.

CONCLUSIONS

The principle of prediction of tolerance to radiotherapy has been established. Although current assays lack the precision required for clinical use, the goal of individualized treatment to tolerance ultimately should be achieved.

Successful treatment of radiation-induced fibrosis using Cu/Zn-SOD and Mn-SOD: an experimental study

PURPOSE

To establish how far liposomal copper/zinc superoxide dismutase (Cu/Zn-SOD) and manganese superoxide dismutase (Mn-SOD), respectively, reduce radiation-induced fibrosis (RIF), using a well-characterized pig model of RIF permitting the design of a controlled laboratory experiment.

METHODS AND MATERIALS

In this model of acute localized gamma irradiation simulating accidental overexposure in humans, three groups of five large white pigs were irradiated using a collimated 192Ir source to deliver a single dose of 160 Gy onto the skin surface (100%) of the outer side of the thigh. A well-defined block of subcutaneous fibrosis involving skin and skeletal muscle developed 6 months after irradiation. One experimental group of five pigs was then injected i.m. with 10 mg/10 kg b.wt. of Cu/Zn-SOD, twice a week for 3 weeks, and another experimental group of five was injected with 10 mg/10 kg b.wt. of Mn-SOD, three times a week for 3 weeks. Five irradiated control pigs were injected with physiological serum. Animals were assessed for changes in the density of the palpated fibrotic block and in the dimensions of the projected cutaneous surface. Block depth was determined by ultrasound. Physical and sonographic findings were confirmed by autopsy 12-14 weeks after completing SOD injections. The density, length, width, and depth of the fibrotic block, and the areas and volume of its projected cutaneous surface were compared before treatment, 1, 3, and 6 weeks thereafter, and at autopsy, 12-14 weeks after treatment ended.

RESULTS

The experimental animals exhibited no change in behavior and no abnormal clinical or anatomic signs. Whether they were given Cu/Zn- or Mn-SOD, significant and roughly equivalent softening and shrinking of the fibrotic block were noted in all treated animals between the first week after treatment ended and autopsy, when mean regression was 45% for length and width, 30% for depth, and 70% for area and volume. Histologic examination showed completely normal muscle and subcutaneous tissue surrounding the residual scar. This replacement of scar tissue by normal tissue in experimental animals and the 50% decrease in the linear dimensions of the scar were comparable to the results obtained in previous clinical studies and highly significant compared to the clinical and autopsy results for the control animals.

CONCLUSIONS

Our results are striking and comparable to the results obtained in our previous clinical study after liposomal Cu/Zn-SOD treatment. To our knowledge, this is the first time that two agents have been shown to reverse the radiation-induced fibrotic process in experimental animals and to permit the regeneration of normal tissue in a zone of well-established postirradiation fibrosis.

Radiotherapy for atypical or malignant intracranial meningioma

PURPOSE

To study the natural history of intracranial atypical and malignant meningiomas, and the role of radiotherapy in the treatment of these tumors.

METHODS AND MATERIALS

The records of the 59 patients who were treated at the Princess Margaret Hospital between 1966 and 1990 with histologically confirmed intracranial atypical or malignant meningiomas were retrospectively reviewed. The median age was 58 years. Twenty-four patients were referred for radiation immediately after diagnosis and the remainder after at least one recurrence. The extent of the most recent surgery prior to radiation was gross total excision in 17, subtotal excision in 35, biopsy in 3, and none or unknown in 4. Seventeen had atypical meningiomas, defined as the presence of mitoses, nuclear atypia, or necrosis. Forty-two had malignant meningiomas on the basis of brain invasion (60%) or a pathologist's designation of malignant or hemangiopericytic meningioma. All patients received megavoltage radiation to a median dose of 50 Gy.

RESULTS

Disease progressed in 39 patients (66%) after radiation. Of these, 36 died of meningioma and 3 were alive after further surgery. The 5-year actuarial overall and cause-specific survivals were 28 and 34%, respectively. Age less than 58, treatment after 1975, and a radiation dose of 50 Gy or more were independently associated with higher cause-specific survival by multivariate analysis.

CONCLUSIONS

Young age, modern imaging and treatment planning techniques, and a postoperative radiation dose of at least 50 Gy contribute to improved outcome in patients with atypical or malignant meningiomas. We recommend that all patients receive radiotherapy immediately after initial surgery.

Acute lumbosacral plexopathy during and after preoperative radiotherapy of rectal adenocarcinoma

The benefit of preoperative radiotherapy of adenocarcinoma of the rectum with respect to a reduced local recurrence rate and an improved survival should be weighed against adverse effects. For 14 years a three-beam, isocentric technique was employed at our hospital to deliver five fractions (5.0 or 5.1 Gy), over 5 or 7 days preoperatively, to patients with rectal cancer which was considered primarily resectable. The adverse effects of the radiotherapy were few, but acute pain and subacute neurological symptoms and signs did occur. An apparent increase in the frequency of these symptoms/signs was noted during 1993. The pain and neurological symptoms are described in case reports and the individual treatments are reviewed. The three-beam technique was analyzed in detail with individual, CT-based, three-dimensional dose-planning and dose distributions in the vicinity of the lumbar nerve plexus are presented. The major result of this analysis showed that technical errors could be excluded, that human errors were unlikely, and that the culprit probably was an unexpected sensitivity to marginal changes in the daily dose and unknown or unexpected radiosensitizing effects of concurrent diseases or medication.

Evaluation of an objective plan-evaluation model in the three dimensional treatment of nonsmall cell lung cancer

PURPOSE

Evaluation of three dimensional (3D) radiotherapy plans is difficult because it requires the review of vast amounts of data. Selecting the optimal plan from a set of competing plans involves making trade-offs among the doses delivered to the target volumes and normal tissues. The purpose of this study was to test an objective plan-evaluation model and evaluate its clinical usefulness in 3D treatment planning for nonsmall cell lung cancer.

METHODS AND MATERIALS

Twenty patients with inoperable nonsmall cell lung cancer treated with definitive radiotherapy were studied using full 3D techniques for treatment design and implementation. For each patient, the evaluator (the treating radiation oncologist) initially ranked three plans using room-view dose-surface displays and dose-volume histograms, and identified the issues that needed to be improved. The three plans were then ranked by the objective plan-evaluation model. A figure of merit (FOM) was computed for each plan by combining the numerical score (utility in decision-theoretic terms) for each clinical issue. The utility was computed from a probability of occurrence of the issue and a physician-specific weight indicating its clinical relevance. The FOM was used to rank the competing plans for a patient, and the utility was used to identify issues that needed to be improved. These were compared with the initial evaluations of the physician and discrepancies were analyzed. The issues identified in the best treatment plan were then used to attempt further manual optimization of this plan.

RESULTS

For the 20 patients (60 plans) in the study, the final plan ranking produced by the plan-evaluation model had an initial 73% agreement with the ranking provided by the evaluator. After discrepant cases were reviewed by the physician, the model was usually judged more objective or "correct." In most cases the model was also able to correctly identify the issues that needed improvement in each plan. Subsequent replanning confirmed that further manual plan optimization could be achieved in 17 patients.

CONCLUSION

The objective plan-evaluation model was able to rank lung cancer radiotherapy plans from best to worst. It was useful in improving plans and may be useful to physicians in defining goals for patients based on the ability to effectively and safely treat their tumors.

A method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy

PURPOSE

To develop a method of analyzing rectal surface area irradiated and rectal complications in prostate conformal radiotherapy.

METHODS AND MATERIALS

Dose-surface histograms of the rectum, which state the rectal surface area irradiated to any given dose, were calculated for a group of 27 patients treated with a four-field box technique to a total (tumor minimum) dose ranging from 68 to 70 Gy. Occurrences of rectal toxicities as defined by the Radiation Therapy Oncology Group (RTOG) were recorded and examined in terms of dose and rectal surface area irradiated. For a specified end point of rectal complication, the complication probability was analyzed as a function of dose irradiated to a fixed rectal area, and as a function of area receiving a fixed dose. Lyman's model of normal tissue complication probability (NTCP) was used to fit the data.

RESULTS

The observed occurrences of rectal complications appear to depend on the rectal surface area irradiated to a given dose level. The patient distribution of each toxicity grade exhibits a maximum as a function of percentage surface area irradiated, and the maximum moves to higher values of percentage surface area as the toxicity grade increases. The dependence of the NTCP for the specified end point on dose and percentage surface area irradiated was fitted to Lyman's NTCP model with a set of parameters. The curvature of the NTCP as a function of the surface area suggests that the rectum is a parallel structured organ.

CONCLUSIONS

The described method of analyzing rectal surface area irradiated yields interesting insight into understanding rectal complications in prostate conformal radiotherapy. Application of the method to a larger patient data set has the potential to facilitate the construction of a full dose-surface-complication relationship, which would be most useful in guiding clinical practice.

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.

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.