Tolerance of normal tissue to therapeutic irradiation

Normal tissue complication probabilities: dependence on choice of biological model and dose-volume histogram reduction scheme

PURPOSE

To evaluate the impact of dose-volume histogram (DVH) reduction schemes and models of normal tissue complication probability (NTCP) on ranking of radiation treatment plans.

METHODS AND MATERIALS

Data for liver complications in humans and for spinal cord in rats were used to derive input parameters of four different NTCP models. DVH reduction was performed using two schemes: "effective volume" and "preferred Lyman". DVHs for competing treatment plans were derived from a sample DVH by varying dose uniformity in a high dose region so that the obtained cumulative DVHs intersected. Treatment plans were ranked according to the calculated NTCP values.

RESULTS

Whenever the preferred Lyman scheme was used to reduce the DVH, competing plans were indistinguishable as long as the mean dose was constant. The effective volume DVH reduction scheme did allow us to distinguish between these competing treatment plans. However, plan ranking depended on the radiobiological model used and its input parameters.

CONCLUSIONS

Dose escalation will be a significant part of radiation treatment planning using new technologies, such as 3-D conformal radiotherapy and tomotherapy. Such dose escalation will depend on how the dose distributions in organs at risk are interpreted in terms of expected complication probabilities. The present study indicates considerable variability in predicted NTCP values because of the methods used for DVH reduction and radiobiological models and their input parameters. Animal studies and collection of standardized clinical data are needed to ascertain the effects of non-uniform dose distributions and to test the validity of the models currently in use.

AVS/express for the PC implementation of a 3D visualization module for radiotherapy

Treatment planning systems (TPS) are nowadays of great help in cancer radiotherapy. Basically, they allow the pair physician/physicist to simulate the beams' irradiation effects on tumors as well as healthy tissues in terms of delivered radiation doses and finally to assess the validity of a beam setup. The state of the art in TPS leads to the following evidence concerning the future of such softwares: an access to a 3D visualization at each step of the design and verification of a plan has become necessary. Moreover, the fast increasing performances of personal computers (PC) will make possible in a near future the implementation at a lower cost of a complete 3D TPS. One of the keys of such an ambition is the compatibility between the implementation tools and the needs for power and flexibility. A first implementation on Open VMS of a simple 3D visualization for Institut Curie's TPS ISIS using Advanced Visual Systems' AVS 5 has been achieved. Their next generation tool, AVS/Express, seemed to meet the needs of a wide scale development. The use of AVS/Express working together with Microsoft Visual C++ in the implementation on Windows NT of a 3D visualization module is exposed.

Immediate toxicity during fractionated total body irradiation as conditioning for bone marrow transplantation

BACKGROUND

Total body irradiation followed by bone marrow transplantation is well established as a part of the conditioning regimen in high dose therapy. The immediate tolerance of fractionated total body irradiation (FTBI) was investigated prospectively.

METHODS

From January 1995 to December 1998 162 patients received a FTBI, 6x2 Gy on 3 consecutive days, lung dose 10 Gy, for allogeneic (n=112) or autologous (n=50) bone marrow transplantation. High dose chemotherapy (mostly Cyclophosphamide) was administered after the FTBI. A standardized supportive therapy was administered. The immediate toxicity of FTBI was evaluated prospectively prior to each radiation fraction using a defined questionnaire.

RESULTS

Main symptoms distressing the patient during irradiation period were gastrointestinal symptoms like nausea and emesis. The prevalence of nausea per fraction increased to 26.1% after the 4th fraction, with a significant higher prevalence in children younger than 10 years at 1st and 2nd fractions. 42.6 and 22. 8%, respectively, of all patients complained of nausea and episodes of emesis, during FTBI. Mild xerostomia and parotiditis were observed in 29.9 and 7.1% of all patients. Further gastrointestinal side effects during FTBI were loss of appetite in 16.0%, indisposition in 25.3%, mild oesophagitis in 3.7% and diarrhoea in 3. 7% of the patients. During FTBI 41.4% of the patients developed a temporary skin irritation (mild erythema). Pruritus was registered in 3.7% of the patients. Headache was observed in 14.8% and Fatigue syndrome in 49.2% of women and 28.3% of men (P<0.005).

CONCLUSION

FTBI is a well tolerated therapeutic regimen in high dose therapy. The 162 patients investigated revealed no severe immediate side effects.

Optimization of beam orientations and weights for coplanar conformal beams in treating pancreatic cancer

In treating pancreatic cancer with external-beam radiotherapy, radiation dose given to the tumor volume is largely limited by the tolerance of the normal structures near the disease site, including the kidneys, liver, stomach, small bowel, and spinal cord. The purpose of this work was to investigate whether a coplanar conformal therapy technique with beam optimization could reduce dose to the normal tissues compared to the conventional 4-field technique; and if this was true, whether other beam arrangements were more effective than the 4-field technique in treating pancreatic cancer. In this study, 9 patients who were treated previously for T3N0 or T3N1 pancreatic cancer with external-beam therapy of 30 Gy in 10 fractions were selected. Beam orientations and weights were optimized for 4 to 6 coplanar conformal beams using a simulated annealing algorithm to minimize the kidney volume receiving more than 20 Gy. Optimized plans were compared with standard plans using a 4-field technique with respect to the isodose distributions and dose volume histograms. For the standard 4-field plans giving 30 Gy to the tumor volume, the total kidney volume above 20 Gy ranged from 10% to 35%, with a mean of 22% and a standard deviation of 7%. Optimization of the beam orientations and weights reduced this volume by approximately 2 times without a significant increase of dose to the liver, stomach, and small bowel. This indicated that the radiation toxicity to the kidneys could be reduced substantially by a careful selection of oblique beam angles and weights. Analysis of the optimized plans showed that beam arrangements which involved left and right anterior oblique beams were superior to the conventional 4-field technique for reducing the kidney dose in treating pancreatic cancer.

Preliminary report of toxicity following 3D radiation therapy for prostate cancer on 3DOG/RTOG 9406

PURPOSE

A prospective Phase I dose escalation study was conducted to determine the maximally-tolerated radiation dose in men treated with three-dimensional conformal radiation therapy (3D CRT) for localized prostate cancer. This is a preliminary report of toxicity encountered on the 3DOG/RTOG 9406 study.

METHODS AND MATERIALS

Each participating institution was required to implement data exchange with the RTOG 3D quality assurance (QA) center at Washington University in St. Louis. 3D CRT capabilities were strictly defined within the study protocol. Patients were registered according to three stratification groups: Group 1 patients had clinically organ-confined disease (T1,2) with a calculated risk of seminal vesicle invasion of < 15%. Group 2 patients had clinical T1,2 disease with risk of SV invasion > or = 15%. Group 3 (G3) patients had clinical local extension of tumor beyond the prostate capsule (T3). All patients were treated with 3D techniques with minimum doses prescribed to the planning target volume (PTV). The PTV margins were 5-10 mm around the prostate for patients in Group 1 and 5-10 mm around the prostate and SV for Group 2. After 55.8 Gy, the PTV was reduced in Group 2 patients to 5-10 mm around the prostate only. Minimum prescription dose began at 68.4 Gy (level I) and was escalated to 73.8 Gy (level II) and subsequently to 79.2 Gy (level III). This report describes the acute and late toxicity encountered in Group 1 and 2 patients treated to the first two study dose levels. Data from RTOG 7506 and 7706 allowed calculation of the expected probability of observing a > or = grade 3 late effect more than 120 days after the start of treatment. RTOG toxicity scores were used.

RESULTS

Between August 23, 1994 and July 2, 1997, 304 Group 1 and 2 cases were registered; 288 cases were analyzable for toxicity. Acute toxicity was low, with 53-54% of Group 1 patients having either no or grade 1 toxicity at dose levels I and II, respectively. Sixty-two percent of Group 2 patients had either none or grade 1 toxicity at either dose level. Few patients (0-3%) experienced a grade 3 acute bowel or bladder toxicity, and there were no grade 4 or 5 toxicities. Late toxicity was very low in all patient groups. The majority (81-85%) had either no or mild grade 1 late toxicity at dose level I and II, respectively. A single late grade 3 bladder toxicity in a Group 2 patient treated to dose level II was recorded. There were no grade 4 or 5 late effects in any patient. Compared to historical RTOG controls (studies 7506, 7706) at dose level I, no grade 3 or greater late effects were observed in Group 1 and Group 2 patients when 9.1 and 4.8 events were expected (p = 0.003 and p = 0.028), respectively. At dose level II, there were no grade 3 or greater toxicities in Group 1 patients and a single grade 3 toxicity in a Group 2 patient when 12.1 and 13.0 were expected (p = 0.0005 and p = 0.0003), respectively. Multivariate analysis demonstrated that the relative risk of developing acute bladder toxicity was 2.13 if the percentage of the bladder receiving > or = 65 Gy was more than 30% (p = 0.013) and 2.01 if patients received neoadjuvant hormonal therapy (p = 0.018). The relative risk of developing late bladder complications also increased as the percentage of the bladder receiving > or = 65 Gy increased (p = 0.026). Unexpectedly, there was a lower risk of late bladder complications as the mean dose to the bladder and prescription dose level increased. This probably reflects improvement in conformal techniques as the study matured. There was a 2.1 relative risk of developing a late bowel complication if the total rectal volume on the planning CT scan exceeded 100 cc (p = 0.019).

CONCLUSION

Tolerance to high-dose 3D CRT has been better than expected in this dose escalation trial for Stage T1,2 prostate cancer compared to low-dose RTOG historical experience. With strict quality assurance standards and review, 3D CRT can be safely studied in a co

On-line set-up corrections during radiotherapy of patients with gynecologic tumors

PURPOSE

Positioning of patients with gynecologic tumors for radiotherapy has proven to be relatively inaccurate. To improve the accuracy and reduce the margins from clinical target volume (CTV) to planning target volume (PTV), on-line set-up corrections were investigated.

METHODS AND MATERIALS

Anterior-posterior portal images of 14 patients were acquired using the first six monitor units (MU) of each irradiation fraction. The set-up deviation was established by matching three user-defined landmarks in portal and simulator image. If the two-dimensional deviation exceeded 4 mm, the table position was corrected. A second portal image was acquired using 30 MU of the remaining dose. This image was analyzed off-line using a semiautomatic contour match to obtain the final set-up accuracy. To verify the landmark match accuracy, the contour match was retrospectively performed on the six MU images as well.

RESULTS

The standard deviation (SD) of the distribution of systematic set-up deviations after correction was < 1 mm in left-right and cranio-caudal directions. The average random deviation was < 2 mm in these directions (1 SD). Before correction, all standard deviations were 2 to 3 mm. The landmark match procedure was sufficiently accurate and added on average 3 min to the treatment time. The application of on-line corrections justifies a CTV-to-PTV margin reduction to about 5 mm.

CONCLUSIONS

On-line set-up corrections significantly improve the positioning accuracy. The procedure increases treatment time but might be used effectively in combination with off-line corrections.

Optimization of coplanar six-field techniques for conformal radiotherapy of the prostate

PURPOSE

To determine the optimal coplanar treatment technique for six-field conformal radiotherapy of prostate only (PO) or prostate plus seminal vesicles (PSV).

METHODS AND MATERIALS

A series of 6-MV six-field coplanar treatment plans were created for PO and PSV volumes in 10 patients prescribed to both 64 and 74 Gy. All plans consisted of laterally-symmetric anterior oblique, lateral, and posterior oblique fields. The posterior oblique fields were varied through 20-45 degrees relative to the lateral fields, and for each of these angles, the anterior oblique fields were varied through 25-65 degrees relative to lateral. The plans were compared by means of rectal volumes irradiated to 80% or more of the prescribed dose (V80); normal tissue complication probability (NTCP) for rectum, bladder, and femoral heads; and tumor control probability (TCP). Femoral head tolerance was designated as 52 Gy to no more than 10% volume.

RESULTS

For the PO group, anterior oblique fields at 50 degrees from lateral and posterior oblique fields at 25 degrees from lateral produced the lowest V80, together with femoral head doses which were appropriate for most patients (V80 = 24.4+/-5.3% [1 SD]). Compared to a commonly-used six-field (reference) plan with both anterior and posterior oblique fields at 35 degrees from lateral (V80 = 26.3+/-5.9%), this represented an improvement (p = 0.001). For the PSV group, the optimal anterior and posterior oblique fields were at 65 degrees and 30 degrees from lateral, respectively (V80 = 47.5+/-6.3%). Relative to the reference plan (V80 = 49.4+/-5.6%), this was a marginal improvement (p = 0.07).

CONCLUSION

The optimized six-field plans provide increased rectal sparing at both standard and escalated doses. Moreover, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in rectal NTCP using the optimized six-field plans.

An investigation of eye lens dose for gamma knife treatments of trigeminal neuralgia

Stereotactic Gamma Knife radiosurgery has been widely used for treating trigeminal neuralgia (TN). A single large fractional dose of 7000 to 9000 cGy is commonly prescribed as the maximum dose for these treatments. For this reason, if a small percentage of the prescribed dose such as 2-3% scattered to the eye, it could reach or even exceed the tolerance dose of the lens. For several TN cases, we found that the Leksell Gamma Plan system calculates the lens dose about 0.5-2% of the maximum dose independent of the use of eye shielding. These dose values are significantly high and it motivated us to investigate the lens dose for the TN patients treated with stereotactic Gamma Knife radiosurgery. Phantom studies and in vivo dosimetry measurements were carried out for six patients treated at our institution. The average dose to the lens ipsilateral to the treated nerve was measured to be 7.7+/-0.6 cGy. Based on the biological model of Lyman and Emami [Int. J. Radiat. Oncol. Biol. Phys. 21, 109-122 (1991)], the probability of the lens complication (cataract) was determined to be 0.1%. Our findings suggest that few TN patients would develop cataracts after receiving Gamma Knife radiosurgery.

The potential for sparing of parotids and escalation of biologically effective dose with intensity-modulated radiation treatments of head and neck cancers: a treatment design study

PURPOSE

Conventional radiotherapy for cancers of the head and neck (HN) can yield acceptable locoregional tumor control rates, but toxicity of many normal tissues limits our ability to escalate dose. Xerostomia represents one of the most common complications. The purpose of this study is to investigate the potential of intensity-modulated radiotherapy (IMRT) to achieve adequate sparing of parotids and to escalate nominal and/or biologically-effective dose to achieve higher tumor control without exceeding normal tissue tolerances.

METHODS AND MATERIALS

An IMRT optimization system, developed at our institution for research and clinical purposes, and coupled to a commercial radiation treatment planning system, has been applied to a number of cases of HN carcinomas. IMRT plans were designed using dose- and dose-volume-based criteria for 4 and 6 MV coplanar but non-collinear beams ranging in number from 5 to 15 placed at equi-angular steps. Detailed analysis of one of the cases is presented, while the results of the other cases are summarized. For the first case, the IMRT plans are compared with the standard 3D conformal radiation treatment (3DCRT) plan actually used to treat the patient, and with each other. The aim of the 3DCRT plan for this particular case was to deliver 73 Gy to the tumor volume in 5 fractions of 2 Gy and 28 fractions of 2.25 Gy/fx; and 46 Gy to the nodes in 2 Gy/fx while maintaining critical normal tissues to below specified tolerances. The IMRT plans were designed to be delivered as a "simultaneous integrated boost" (SIB) using the "sweeping window" technique with a dynamic MLC. The simultaneous integrated boost strategy was chosen, partly for reasons of efficiency in planning and delivery of IMRT treatments, and partly with the assumption that dose distributions in such treatments are more conformal and spare normal tissues to a greater extent than those with sequential boost strategy. Biologically equivalent dose normalized to 2 Gy/fx, termed here as normalized total dose (NTD), for this strategy was calculated using published head and neck fractionation data.

RESULTS

IMRT plans were more conformal than the 3DCRT plans. For equivalent coverage of the tumor and the nodes, and for the dose to the spinal cord and the brainstem maintained within tolerance limits, the dose to parotids was greatly reduced. For the detailed example presented, it was shown that the tumor and the nodes in the 3DCRT plan receive NTDs of 78 and 46 Gy, respectively. For the IMRT plan, a nominal dose of 70 Gy could be delivered to the tumor in 28 fractions of 2.5 Gy each, simultaneously with 50.4 Gy to nodes with 1.8 Gy/fx. The two are biologically equivalent to 82 and 46 Gy, respectively, if delivered in 2 Gy/fx. Similar computations were carried out for other cases as well. The quality of IMRT plans was found to improve with increasing number of beams, up to 9 beams. Dose-volume-based criteria led to a modest improvement in IMRT plans and required less trial and error.

CONCLUSION

IMRT has the potential to significantly improve radiotherapy of HN cancers by reducing normal tissue dose and simultaneously allowing escalation of dose. SIB strategy is not only more efficient and yields better dose distributions, but may also be biologically more effective. Dose-volume-based criteria is better than purely dose-based criteria. The quality of plans improves with number of beams, reaching a saturation level for a certain number of beams, which for the plans studied was found to be 9.

Biologically based treatment planning

The classical way of quantifying dose-response relations for tumors and normal tissues and their dependence on the genetic make up of the patient is briefly reviewed. Response quantifiers such as quality of life and the probability of achieving a complication-free cure are helpful in solving many of the problems of radiation therapy planning. It is shown, through the use of these quantifiers, that by introducing radiobiologically optimized, intensity-modulated dose delivery, the treatment outcome can be improved by as much as 20%, and more in cases with a complex spread of the disease. The real strength of the radiobiological models is to serve as a scientific tool for the development of treatment optimization so that the models are modified when the clinical response systematically deviates from the predictions of the models. In this way, the biological models serve as a continuously updated historical database that later on may replace the control arm in clinical trials and allow all patients to benefit from the latest developments in radiobiologically optimized treatment techniques.

Critical appraisal of a conformal head and neck cancer irradiation avoiding electron beams and field matching

PURPOSE

In head and neck cancer patients, spinal chains are usually irradiated by a combination of photon and electron beams, requiring high precision in field matching. This study compares a conventional treatment approach where two lateral photon beams are combined to direct electron fields, to a conformal radiotherapy based on five photon fields, covering the whole neck.

METHODS AND MATERIALS

A comparative analysis of dose distributions and dose-volume histograms was carried out in patients with locally advanced head and neck tumors, for which planning target volumes (PTV) were outlined from the base of the skull down to the supraclavicular region. The prescribed dose to PTV (excluding booster irradiation) was 54 Gy, with spinal dose constraint not exceeding 75% of the total dose, whatever the technique.

RESULTS

For the new five-field technique, minimum and maximum point doses showed mean deviations, on five patients entered in the study, of 84% and 113% from the ICRU prescription point. In the conventional treatment, the corresponding figures were 73% and 112%, respectively. A positioning error analysis (isocenter displacement of 2 mm, in all directions) did not elicit any systematic difference in five-field treatment plans while hot spots were found with electron fields.

CONCLUSIONS

The five-field technique appears routinely feasible and compares favorably with the conventional mixed photon- and electron-therapy approach, especially in regard to its better compliance with dose homogeneity requirements and a reduced risk in dose inhomogeneity related to field matching and patient positioning.

Proton radiation therapy (PRT) for pediatric optic pathway gliomas: comparison with 3D planned conventional photons and a standard photon technique

PURPOSE

Following adequate therapy, excellent long-term survival rates can be achieved for patients with optic pathway gliomas. Therefore, avoidance of treatment-related functional long-term sequelae is of utmost importance. Optimized sparing of normal tissue is of primary concern in the development of new treatment modalities. The present study compares proton radiation therapy (PRT) with a three-dimensional (3D)-planned multiport photon and a lateral beam photon technique for localized and extensive optic pathway tumors.

METHODS AND MATERIALS

Between February 1992 and November 1997, seven children with optic pathway gliomas underwent PRT. For this study, we computed proton, 3D photon, and lateral photon plans based on the same CT data sets, and using the same treatment planning software for all plans. Radiation exposure for normal tissue and discrete organs at risk was quantified based on dose-volume histograms.

RESULTS

Gross tumor volume (GTV) ranged from 3.9 cm3 to 127.2 cm3. Conformity index (relation of encompassing isodose to GTV volume) was 2.3 for protons, 2.9 for 3D photons, and 7.3 for lateral photons. The relative increase of normal tissue (NT) encompassed at several isodose levels in relation to NT encompassed by the 95% proton isodose volume was computed. Relative NT volume of proton plan isodoses at the 95%, 90%, 80%, 50%, and 25% isodose level increased from 1 to 1.6, 2.8, 6.4, to a maximum of 13.3. Relative volumes for 3D photons were 1.6, 2.4, 3.8, 11.5, and 34.8. Lateral plan relative values were 6, 8.3, 11.5, 19.2, and 26.8. Analysis for small (<20 cm3) and larger (> 80 cm3) tumors showed that protons encompassed the smallest volumes of NT at all isodose levels. Comparable conformity and high-dose gradient were achieved for proton and 3D photon plans in small tumors. However, with increasing tumor volume and complexity, differences became larger. At the 50% isodose level, 3D photons were superior to lateral photons for small tumors; this advantage was equalized for larger tumors. At the lowest isodose level, 3D photons encompassed the highest amount of NT. Analysis of organs at risk showed that PRT reduced doses to the contralateral optic nerve by 47% and 77% compared to 3D photons and lateral photons, respectively. Reductions were also seen for the chiasm (11% and 16%) and pituitary gland (13% and 16%), with differences at clinically relevant tolerance levels. Furthermore, reduced dose exposure of both temporal lobes (sparing 39% and 54%) and frontal lobes was achieved with PRT.

CONCLUSION

PRT offered a high degree of conformity to target volumes and steep dose gradients, thus leading to substantial normal tissue sparing in high- and low-dose areas. It is expected that this will result in decreased long-term toxicity in the maturing child. Advantages of proton versus 3D photon plans became increasingly apparent with increasing target size and tumor complexity. Even in small tumors, conformity of 3D photon irradiation came at the expense of a larger amount of NT receiving moderate to low radiation doses. Lateral photons resulted in inferior dose distribution with high radiation exposure of clinically relevant normal tissues.

Influence of patient positioning on dose-volume histogram and normal tissue complication probability for small bowel and bladder in patients receiving pelvic irradiation: a prospective study using a 3D planning system and a radiobiological model

PURPOSE

A prospective study was undertaken to evaluate the influence of patient positioning (prone position using a belly board vs. supine position) on the dose-volume histograms (DVHs) of organs of risk, and to analyze its possible clinical relevance using radiobiological models.

METHODS AND MATERIALS

From November 1996 to August 1997 a computed tomography (CT) scan was done in the prone position using a belly board and in supine position in 20 consecutive patients receiving postoperative pelvic irradiation because of rectal cancer. Using a three-dimensional (3D) planning system (Helax, TMS) the DVH for small bowel, bladder, a standard planning target volume (PTV) of postoperative irradiation of rectal cancer, the intersection of volume of PTV and small bowel (PTV intersection V(SB), respectively, of PTV and bladder (PTV intersection V(B)) were defined in each axial CT slice. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami. For evaluation of late toxicity alpha/beta ratio was 2.5; for evaluation of acute toxicity, it was 10. Total dose was 50.4 Gy (1.8 Gy/fraction) (ICRU 50).

RESULTS

Using the prone position compared to the supine position, the median volume of PTV intersection V(B) was reduced by 18.5 cm3 (62%). Median dose (related to the reference dose) to the bladder was 44.5% (22.4 Gy) in prone and 66.05% (33.3 Gy) in supine position (p<0.001). Median V(B) within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose was significantly lower in the prone position when compared to the supine position. Using the radiobiological models, however, there was no difference of NTCP between prone position or supine position. In the prone position, median volume of PTV intersection V(SB) was reduced by 32.5 cm3 (54%). The median dose to small bowel was 30.85% (15.4 Gy) in the prone position and 47.35% (23.9Gy) in the supine position (p<0.001). Significant differences between prone and supine position were found for median V(SB) within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose. According to the method of Lyman, median NTCP of small bowel was significant lower in prone than in supine position.

CONCLUSION

The prone position with a standard belly board should be the standard positioning technique for patients receiving adjuvant postoperative radiation therapy following surgery of rectal cancer. Both irradiated volume and total dose to the organs of risk can be reduced significantly. As a consequence of this, radiation induced toxicity will be minimized.

The rationale and use of three-dimensional radiation treatment planning for lung cancer

Treatment of lung cancer with conventional radiation therapy is associated with suboptimal local tumor control and poor long-term survival. Poor local tumor control may result from inaccurate tumor targeting, failure to satisfactorily conform to dose distribution with the target volume, and/or inadequate radiation doses. Three-dimensional treatment planning is a radiotherapy technique that provides more accurate dose targeting via the direct transfer of three-dimensional anatomic information from diagnostic scans into the planning process. This technology can assist treatment planning by providing dose-volume histograms, an estimation of normal tissue complication probabilities, and facilitate dose escalation. Preliminary clinical studies suggest that this is a feasible approach worthy of additional study. The three-dimensional tools provide new opportunities to better understand radiation-induced changes in pulmonary function.

Radiotherapy: the last 25 years

Some of the major changes in radiotherapy over the last years are reviewed in this paper. Radiotherapy has played a role in the changes in oncological practice including an increase in organ-sparing treatment and achieving good local control and improving survival. About half of all breast cancer patients are now treated with breast conserving therapy. Organ preservation, usually with multimodality therapy, has also been further developed in the treatment of cancers in the head and neck, anus, bladder and soft tissue sarcomas. Developments in radiobiology have led to the development of new fractionation schedules. Hyperfractionation allows an increase in the tumour dose whilst sparing normal tissues and accelerated fractionation combats accelerated tumour proliferation during treatment. Advances in accelerator technology and computerized treatment planning have enabled the development of three-dimensional conformal radiotherapy. This gives the oportunity to spare normal tissues and escalate the dose to the tumour. Quality control and standardization of dosimetry and treatment delivery at departmental and international level has also improved treatment results.

Radiation-induced hearing impairment in patients treated for malignant parotid tumor

Radiation-induced hearing loss was evaluated in 21 patients with unilateral malignant parotid tumors treated with surgery and radiotherapy. The contralateral ear was used as a control. Eight patients (38%) were found to have a reduction in static compliance of the tympanic membrane (type B tympanogram) in the irradiated ear. By audiometry, significant hearing loss was found in 9 patients (43%). These hearing losses were mainly sensorineural, as shown by a similar reduction in both air and bone conduction, although mixed-type hearing loss existed in some patients. A statistically significant difference in incidence of 67% versus 0% (p = .0085) was noted for patients with a cochlear dose of greater than or equal to 60 Gy, in comparison to those receiving doses of less than 60 Gy. A type B tympanogram was also found to be a prognostic factor for significant sensorineural hearing loss. Patients with type B tympanograms had a much higher incidence of significant sensorineural hearing loss than those with type A tympanograms (88% versus 15%, p = .02). This study clearly shows that radiotherapy can induce significant hearing impairment, especially when the cochlear doses are higher than 60 Gy.

Late complications after a combined pre and postoperative (sandwich) radiotherapy for rectal cancer

BACKGROUND AND PURPOSE

The purpose of this study was to analyse the treatment related side effects, the outcome and the prognostic significance of clinical parameters in two groups of patients with rectal cancer receiving either preoperative or pre and postoperative radiotherapy after radical resection. The authors of this study were not involved in the radiation treatments.

PATIENTS AND METHODS

From 1986 to 1990, 63 patients received a combined pre and postoperative (sandwich) radiotherapy. Preoperative irradiation was given in four fractions of 5 Gy each applied within 2 or 3 days. Postoperative irradiation consisted mostly of 15 x 2 Gy (31 patients) but the range was 20-40 Gy. The results were compared with those on 73 patients who only received preoperative radiotherapy in the same time period. The distribution of prognostic factors was not very different between treatment groups. Out of 63 patients in the sandwich group, 22 received concurrent chemotherapy and 18 also received radiotherapy to the liver. Radical surgery usually followed on the day after the last preoperative radiotherapy session. Median follow-up of survivors was 6 years.

RESULTS

Local tumour control was 88% after 5 years and 84% after 8 years in the sandwich group, and 90 and 85%, respectively, in the preoperative radiotherapy group. Thus, tumour control was similar for the two radiotherapy regimens applied. However, the percentage of patients suffering from one or more complications after 5 years was 84% in the sandwich and 17% in the preoperative radiotherapy group. The incidence of severe late complications (grade > or = 3) was recorded as a function of time after start of treatment. In the sandwich group the actuarial rates of late complications at 5 years (and the median time to diagnosis) were 53% (27 months) for anorectum, 43% (37 months) for bladder, 28% (51 months) for bone, 19% (36 months) for dermis, 47% (48 months) for ileum, 41% (32 months) for lymphatic and soft tissue, and 44% (53 months) for ureters.

CONCLUSIONS

Severe late reactions did not occur within a certain period of time, but continued to appear for at least 10 years after radiotherapy. Sandwich therapy, as given in this series, did not appear to give a greater tumour control than preoperative radiotherapy alone, whereas the rate of complications was drastically enhanced. Thus, the rationale of a sandwich therapy with a long time interval between surgery and postoperative irradiation appears questionable.

Bone marrow doses and leukaemia risk in radiotherapy of prostate cancer

BACKGROUND AND PURPOSE

As more and more patients with prostate cancer are cured and survive with only minor chronic morbidity, other potentially treatment related morbidity, in particular second cancers, becomes an urgent problem which may influence decisions on treatment strategy and treatment plan optimisation. Epidemiological data suggest a radiotherapy associated risk of AML in prostate cancer patients of approximately 0.1% in 10 years. The aim of the study was to determine the range of bone marrow doses from different treatment plans and in different patients in order to develop criteria for optimisation of treatment plans in conformal radiotherapy of prostate cancer to further minimise the small risk of secondary leukaemia.

MATERIALS AND METHODS

Doses to the pelvic bone marrow were calculated for eight different plans used in radiotherapy of prostate cancer to determine the variability of bone marrow doses in radiotherapy of prostate cancer. Computer tomography (CT) slices of the entire pelvic region of an Alderson phantom were acquired and transferred to the TPS. Critical bone marrow structures were outlined in each slice. Different treatment plans were evaluated on this phantom and dose-volume histograms (DVH) for the pelvic bone marrow were obtained. Similarly, the DVH for the bone marrow of 14 patients who received conformal radiotherapy for prostate cancer was determined.

RESULTS

Mean total bone marrow doses ranged from 3.4 to 5.6 Gy in the phantom study. Approximately 99% of the mean dose to the total bone marrow comes from the dose to bone marrow located in the pelvic bones and lumbar vertebrae. Mean bone marrow doses of 14 patients given the same conformal radiotherapy plan ranged from 3.5 to 7.7 Gy.

CONCLUSIONS

No correlation was found between the rectum normal tissue complication probability (NTCP) and the mean bone marrow dose. This means that in the process of treatment planning, exposure to both critical organs, the rectum as well as the bone marrow, should be minimised independently to arrive at the optimal treatment plan.

[Radiotherapy using a combination of photons and protons for locally aggressive intracranial tumors. Preliminary results of protocol CPO 94-C1]

PURPOSE

From October 1993 through July 1998, 48 assessable adult patients with non-resectable aggressive intracranial tumors were treated by a combination of high dose photon + proton therapy at the Centre de Protonthérapie d'Orsay.

PATIENTS AND METHODS

Grade 1 and 4 gliomas were excluded. Patients benefited from a 3D dose calculation based on high-definition CT and MRI, a stereotactic positioning using implanted fiducial markers and a thermoplastic mask. Mean tumor dose ranged between 63 and 67 Gy delivered in five weekly sessions of 1.8 Gy in most patients, according to the histological types (doses in Co Gy Equivalent, with a mean proton-RBE of 1.1).

RESULTS

With a median 18-month follow-up (range: four-58 months), local control in tumors located in the envelopes and in the skull base was 97% (33/34), and in parenchymal tumors, 43% (6/14) only. Two patients (5%) presented with a clinically severe radiation-induced necrosis (temporal lobe and chiasm).

CONCLUSION

In our experience, high-dose radiation combining photons and protons is a safe and highly efficient procedure in selected malignancies of the skull base and envelopes.

Optimization of the dose level for a given treatment plan to maximize the complication-free tumor cure

During the past decade, tumor and normal tissue reactions after radiotherapy have been increasingly quantified in radiobiological terms. For this purpose, response models describing the dependence of tumor and normal tissue reactions on the irradiated volume, heterogeneity of the delivered dose distribution and cell sensitivity variations can be taken into account. The probability of achieving a good treatment outcome can be increased by using an objective function such as P+, the probability of complication-free tumor control. A new procedure is presented, which quantifies P+ from the dose delivery on 2D surfaces and 3D volumes and helps the user of any treatment planning system (TPS) to select the best beam orientations, the best beam modalities and the most suitable beam energies. The final step of selecting the prescribed dose level is made by a renormalization of the entire dose plan until the value of P+ is maximized. The index P+ makes use of clinically established dose-response parameters, for tumors and normal tissues of interest, in order to improve its clinical relevance. The results, using P+, are compared against the assessments of experienced medical physicists and radiation oncologists for two clinical cases. It is observed that when the absorbed dose level for a given treatment plan is increased, the treatment outcome first improves rapidly. As the dose approaches the tolerance of normal tissues the complication-free cure begins to drop. The optimal dose level is often just below this point and it depends on the geometry of each patient and target volume. Furthermore, a more conformal dose delivery to the target results in a higher control rate for the same complication level. This effect can be quantified by the increased value of the P+ parameter.

Effect of radiotherapy and chemotherapy on pulmonary function after treatment for breast cancer and lymphoma: A follow-up study

PURPOSE

To determine the changes in pulmonary function tests (PFTs) 0 to 48 months after treatment for breast cancer and lymphoma.

PATIENTS AND METHODS

The alveolar volume (V(A)), vital capacity, forced expiratory volume in 1 second, and corrected transfer factor of carbon monoxide (T(L,COc)) were measured in 69 breast cancer and 41 lymphoma patients before treatment and 3, 18, and 48 months after treatment with radiotherapy alone or radiotherapy in combination with chemotherapy (mechlorethamine, vincristine, procarbazine, prednisone, doxorubicin, bleomycin, vinblastine; cyclophosphamide, epidoxorubicin, fluorouracil; cyclophosphamide, thiotepa, carboplatin; cyclophosphamide, methotrexate, fluorouracil). The three-dimensional dose distribution in the lung of each patient was converted to the mean lung dose. Statistical analysis was used to evaluate the changes in PFT values over time in relation to age, sex, smoking, chemotherapy, and the mean lung dose.

RESULTS

After an initial reduction in PFT values at 3 months, significant recovery was seen at 18 months for all patients. Thereafter, no further improvement could be demonstrated. Reductions in spirometry values and V(A) were related to the mean lung dose only (0.9% per Gy at 3 months and 0.4% per Gy mean dose at 18 months). T(L,COc) decreased 1. 1% per Gy mean dose and additionally decreased 6% when chemotherapy was given after radiotherapy. Chemotherapy administered before radiotherapy reduced baseline T(L,COc) values by 8% to 21%. All patients showed an improvement of 5% at 18 months.

CONCLUSION

On the basis of the mean lung dose and the chemotherapy regimen, the changes in PFT values can be estimated before treatment within 10% of the values actually observed in 72% to 85% of our patients with healthy lungs.

Deep inspiration breath-hold technique for lung tumors: the potential value of target immobilization and reduced lung density in dose escalation

PURPOSE/OBJECTIVE

This study evaluates the dosimetric benefits and feasibility of a deep inspiration breath-hold (DIBH) technique in the treatment of lung tumors. The technique has two distinct features--deep inspiration, which reduces lung density, and breath-hold, which immobilizes lung tumors, thereby allowing for reduced margins. Both of these properties can potentially reduce the amount of normal lung tissue in the high-dose region, thus reducing morbidity and improving the possibility of dose escalation.

METHODS AND MATERIALS

Five patients treated for non-small cell lung carcinoma (Stage IIA-IIIB) received computed tomography (CT) scans under 4 respiration conditions: free-breathing, DIBH, shallow inspiration breath-hold, and shallow expiration breath-hold. The free-breathing and DIBH scans were used to generate 3-dimensional conformal treatment plans for comparison, while the shallow inspiration and expiration scans determined the extent of tumor motion under free-breathing conditions. To acquire the breath-hold scans, the patients are brought to reproducible respiration levels using spirometry, and for DIBH, modified slow vital capacity maneuvers. Planning target volumes (PTVs) for free-breathing plans included a margin for setup error (0.75 cm) plus a margin equal to the extent of tumor motion due to respiration (1-2 cm). Planning target volumes for DIBH plans included the same margin for setup error, with a reduced margin for residual uncertainty in tumor position (0.2-0.5 cm) as determined from repeat fluoroscopic movies. To simulate the effects of respiration-gated treatments and estimate the role of target immobilization alone (i.e., without the benefit of reduced lung density), a third plan is generated from the free-breathing scan using a PTV with the same margins as for DIBH plans.

RESULTS

The treatment plan comparison suggests that, on average, the DIBH technique can reduce the volume of lung receiving more than 25 Gy by 30% compared to free-breathing plans, while respiration gating can reduce the volume by 18%. The DIBH maneuver was found to be highly reproducible, with intra breath-hold reproducibility of 1.0 (+/- 0.9) mm and inter breath-hold reproducibility of 2.5 (+/- 1.6) mm, as determined from diaphragm position. Patients were able to perform 10-13 breath-holds in one session, with a comfortable breath-hold duration of 12-16 s.

CONCLUSION

Patients tolerate DIBH maneuvers well and can perform them in a highly reproducible fashion. Compared to conventional free-breathing treatment, the DIBH technique benefits from reduced margins, as a result of the suppressed target motion, as well as a decreased lung density; both contribute to moving normal lung tissue out of the high-dose region. Because less normal lung tissue is irradiated to high dose, the possibility for dose escalation is significantly improved.

Dose, volume, and function relationships in parotid salivary glands following conformal and intensity-modulated irradiation of head and neck cancer

PURPOSE

To determine the relationships between the three-dimensional dose distributions in parotid glands and their saliva production, and to find the doses and irradiated volumes that permit preservation of the salivary flow following irradiation (RT).

METHODS AND MATERIALS

Eighty-eight patients with head and neck cancer irradiated with parotid-sparing conformal and multisegmental intensity modulation techniques between March 1994 and August 1997 participated in the study. The mean dose and the partial volumes receiving specified doses were determined for each gland from dose-volume histograms (DVHs). Nonstimulated and stimulated saliva flow rates were selectively measured from each parotid gland before RT and at 1, 3, 6, and 12 months after the completion of RT. The data were fit using a generalized linear model and the normal tissue complication probability (NTCP) model of Lyman-Kutcher. In the latter model, a "severe complication" was defined as salivary flow rate reduced to < or =25% pre-RT flow at 12 months.

RESULTS

Saliva flow rates data were available for 152 parotid glands. Glands receiving a mean dose below or equal to a threshold (24 Gy for the unstimulated and 26 Gy for the stimulated saliva) showed substantial preservation of the flow rates following RT and continued to improve over time (to median 76% and 114% of pre-RT for the unstimulated and stimulated flow rates, respectively, at 12 months). In contrast, most glands receiving a mean dose higher than the threshold produced little saliva with no recovery over time. The output was not found to decrease as mean dose increased, as long as the threshold dose was not reached. Similarly, partial volume thresholds were found: 67%, 45%, and 24% gland volumes receiving more than 15 Gy, 30 Gy, and 45 Gy, respectively. The partial volume thresholds correlated highly with the mean dose and did not add significantly to a model predicting the saliva flow rate from the mean dose and the time since RT. The NTCP model parameters were found to be TD50 (the tolerance dose for 50% complications rate for whole organ irradiated uniformly) = 28.4 Gy, n (volume dependence parameter) = 1, and m (the slope of the dose/response relationship) = 0.18. Clinical factors including age, gender, pre-RT surgery, chemotherapy, and certain medical conditions were not found to be significantly associated with the salivary flow rates. Medications (diuretics, antidepressants, and narcotics) were found to adversely affect the unstimulated but not the stimulated flow rates.

CONCLUSIONS

Dose/volume/function relationships in the parotid glands are characterized by dose and volume thresholds, steep dose/response relationships when the thresholds are reached, and a maximal volume dependence parameter in the NTCP model. A parotid gland mean dose of < or =26 Gy should be a planning goal if substantial sparing of the gland function is desired.

Clinical dose-volume histogram analysis for pneumonitis after 3D treatment for non-small cell lung cancer (NSCLC)

PURPOSE

To identify a clinically relevant and available parameter upon which to identify non-small cell lung cancer (NSCLC) patients at risk for pneumonitis when treated with three-dimensional (3D) radiation therapy.

METHODS AND MATERIALS

Between January 1991 and October 1995, 99 patients were treated definitively for inoperable NSCLC. Patients were selected for good performance status (96%) and absence of weight loss (82%). All patients had full 3D treatment planning (including total lung dose-volume histograms [DVHs]) prior to treatment delivery. The total lung DVH parameters were compared with the incidence and grade of pneumonitis after treatment.

RESULTS

Univariate analysis revealed the percent of the total lung volume exceeding 20 Gy (V20), the effective volume (Veff) and the total lung volume mean dose, and location of the tumor primary (upper versus lower lobes) to be statistically significant relative to the development of > or = Grade 2 pneumonitis. Multivariate analysis revealed the V20 to be the single independent predictor of pneumonitis.

CONCLUSIONS

The V20 from the total lung DVH is a useful parameter easily obtained from most 3D treatment planning systems. The V20 may be useful in comparing competing treatment plans to evaluate the risk of pneumonitis for our individual patient treatment and may also be a useful parameter upon which to stratify patients or prospective dose escalation trials.

The effect of patient-specific factors on radiation-induced regional lung injury

PURPOSE

To assess the impact of patient-specific factors on radiation (RT)-induced reductions in regional lung perfusion.

METHODS

Fifty patients (32 lung carcinoma, 7 Hodgkin's disease, 9 breast carcinoma and 2 other thoracic tumors) had pre-RT and > or = 24-week post-RT single photon emission computed tomography (SPECT) perfusion images to assess the dose dependence of RT-induced reductions in regional lung perfusion. The SPECT data were analyzed using a normalized and non-normalized approach. Furthermore, two different mathematical methods were used to assess the impact of patient-specific factors on the dose-response curve (DRC). First, DRCs for different patient subgroups were generated and compared. Second, in a more formal statistical approach, individual DRCs for regional lung injury for each patient were fit to a linear-quadratic model (reduction = coefficient 1 x dose + coefficient 2 x dose2). Multiple patient-specific factors including tobacco history, pre-RT diffusion capacity to carbon monoxide (DLCO), transforming growth factor-beta (TGF-beta), chemotherapy exposure, disease type, and mean lung dose were explored in a multivariate analysis to assess their impact on the coefficients.

RESULTS

None of the variables tested had a consistent impact on the radiation sensitivity of regional lung (i.e., the slope of the DRC). In the formal statistical analysis, there was a suggestion of a slight increase in radiation sensitivity in the dose range >40 Gy for nonsmokers (vs. smokers) and in those receiving chemotherapy (vs. no chemotherapy). However, this finding was very dependent on the specific statistical and normalization method used.

CONCLUSION

Patient-specific factors do not have a dramatic effect on RT-induced reduction in regional lung perfusion. Additional studies are underway to better clarify this issue. We continue to postulate that patient-specific factors will impact on how the summation of regional injury translates into whole organ injury. Refinements in our methods to generate and compare SPECT scans are needed.

Optimization of stereotactically-guided conformal treatment planning of sellar and parasellar tumors, based on normal brain dose volume histograms

PURPOSE

To investigate the optimal treatment plan for stereotactically-guided conformal radiotherapy (SCRT) of sellar and parasellar lesions, with respect to sparing normal brain tissue, in the context of routine treatment delivery, based on dose volume histogram analysis.

METHODS AND MATERIALS

Computed tomography (CT) data sets for 8 patients with sellar- and parasellar-based tumors (6 pituitary adenomas and 2 meningiomas) have been used in this study. Treatment plans were prepared for 3-coplanar and 3-, 4-, 6-, and 30-noncoplanar-field arrangements to obtain 95% isodose coverage of the planning target volume (PTV) for each plan. Conformal shaping was achieved by customized blocks generated with the beams eye view (BEV) facility. Dose volume histograms (DVH) were calculated for the normal brain (excluding the PTV), and comparisons made for normal tissue sparing for all treatment plans at > or =80%, > or =60%, and > or =40% of the prescribed dose.

RESULTS

The mean volume of normal brain receiving > or =80% and > or =60% of the prescribed dose decreased by 22.3% (range 14.8-35.1%, standard deviation sigma = 7.5%) and 47.6% (range 25.8-69.1%, sigma = 13.2%), respectively, with a 4-field noncoplanar technique when compared with a conventional 3-field coplanar technique. Adding 2 further fields, from 4-noncoplanar to 6-noncoplanar fields reduced the mean normal brain volume receiving > or =80% of the prescribed dose by a further 4.1% (range -6.5-11.8%, sigma = 6.4%), and the volume receiving > or =60% by 3.3% (range -5.5-12.2%, sigma = 5.4%), neither of which were statistically significant. Each case must be considered individually however, as a wide range is seen in the volume spared when increasing the number of fields from 4 to 6. Comparing the 4- and 6-field noncoplanar techniques to a 30-field conformal field approach (simulating a dynamic arc plan) revealed near-equivalent normal tissue sparing.

CONCLUSION

Four to six widely spaced, fixed-conformal fields provide the optimum class solution for the treatment of sellar and parasellar lesions, both in terms of normal brain tissue sparing and providing a relatively straightforward patient setup. Increasing the number of fields did not result in further significant sparing, with no clear benefit from techniques approaching dynamic conformal radiotherapy in the cases examined.

Comparison of intensity-modulated tomotherapy with stereotactically guided conformal radiotherapy for brain tumors

PURPOSE

Intensity-modulated radiotherapy (IMRT) offers the potential to more closely conform dose distributions to the target, and spare organs at risk (OAR). Its clinical value is still being defined. The present study aims to compare IMRT with stereotactically guided conformal radiotherapy (SCRT) for patients with medium size convex-shaped brain tumors.

METHODS AND MATERIALS

Five patients planned with SCRT were replanned with the IMRT-tomotherapy method using the Peacock system (Nomos Corporation). The planning target volume (PTV) and relevant OAR were assessed, and compared relative to SCRT plans using dose statistics, dose-volume histograms (DVH), and the Radiation Therapy Oncology Group (RTOG) stereotactic radiosurgery criteria.

RESULTS

The median and mean PTV were 78 cm3 and 85 cm3 respectively (range 62-119 cm3). The differences in PTV doses for the whole group (Peacock-SCRT +/-1 SD) were 2%+/-1.8 (minimum PTV), and 0.1%+/-1.9 (maximum PTV). The PTV homogeneity achieved by Peacock was 12.1%+/-1.7 compared to 13.9%+/-1.3 with SCRT. Using RTOG guidelines, Peacock plans provided acceptable PTV coverage for all 5/5 plans compared to minor coverage deviations in 4/5 SCRT plans; acceptable homogeneity index for both plans (Peacock = 1.1 vs. SCRT = 1.2); and comparable conformity index (1.4 each). As a consequence of the transaxial method of arc delivery, the optic nerves received mean and maximum doses that were 11.1 to 11.6%, and 10.3 to 15.2% higher respectively with Peacock plan. The maximum optic lens, and brainstem dose were 3.1 to 4.8% higher, and 0.6% lower respectively with Peacock plan. However, all doses remained below the tolerance threshold (5 Gy for lens, and 50 Gy for optic nerves) and were clinically acceptable.

CONCLUSIONS

The Peacock method provided improved PTV coverage, albeit small, in this group of convex tumors. Although the OAR doses were higher using the Peacock plans, all doses remained within the clinically defined threshold and were clinically acceptable. Further improvements may be expected using other methods of IMRT planning that do not limit the treatment delivery to transaxial arcs. Each IMRT system needs to be individually assessed as the paradigm utilized may provide different outcomes.

[Conformal radiotherapy of non-small-cell lung cancer]

About one third of lung cancers initially present with a localised disease, without any curative surgery potential, because of local spread or comorbidity. Definitive radiation, alone or combined with chemotherapy, then represents the treatment of choice for these patients. The results, however, are disappointing, with a biopsy-proven local control of 10% at two years and a 5-10% five-year survival rate. These poor results may be partially explained by the difficulties in delineating the tumour volume as well as the dose limitations due to poor tolerance of surrounding normal organs. Lung parenchyma sequelae remain daily worrying events for the oncologist. The advent of 3D conformal radiation therapy (3DRT) allows progress and innovations, including the use of modern imaging techniques, sophisticated dosimetry and treatment planning, efficient immobilisation devices and on-line verification procedures. With more precise (and time-consuming) procedures, 3DRT will allow a better tumour volume delineation, an increased tumour dose and a dose limitation in normal tissues. These improvements may help increase local control and survival results. 3DRT, which has been used for several years for prostate cancer and benefits from recent imaging improvements, will now allow treatment of other locations, such as lung cancer, with conformal therapy. The few preliminary results are encouraging. This work reviews the current data and remaining questions regarding lung cancer treated with 3DRT, and presents and discusses the literature before discussing future trends in this area.

[Conformal radiotherapy in cancer of the upper aerodigestive tract]

The outcome of head and neck malignancies is closely related to the achievement of local tumor control. The occurrence of severe late complications is the consequence of the anatomic vicinity between dose-limiting normal tissues and the tumor, thus reducing the curative potential of radiotherapy. Conformal radiotherapy is presently actively investigated as a way to improve the dose distribution in head and neck malignancies (especially when originating from the nasopharynx or the sinuses) while protecting healthy organs. Such an approach requires a chain of sophisticated procedures, including efficient quality assurance programs, in order to achieve the proper degree of safety. The relatively limited clinical studies published to-date have already confirmed the advantage of conformal radiotherapy in terms of dose delivery. The development of beam intensity modulation is likely to further contribute to the improvement of the therapeutic ratio.

Clinical and dosimetric predictors of radiation-induced esophageal toxicity

PURPOSE

To evaluate the incidence, severity, and clinical/dosimetric predictors of acute and chronic esophageal toxicities in patients with non-small cell lung cancer (NSCLC) treated with high-dose conformal thoracic radiation.

METHODS AND MATERIALS

Ninety-one patients with localized NSCLC treated definitively with high-dose conformal radiation therapy (RT) at Duke University Medical Center (DUMC) were reviewed. Patient characteristics were as follows: 53 males and 38 females; median age 64 yr (range 46-82); stage I--16, II--3, IIIa--40, IIIb--30, X--2; dysphagia pre-RT--6 (7%). Treatment parameters included: median corrected dose-78.8 Gy (range 64.2-85.6); BID fractionation-58 (64%); chemotherapy-43 (47%). Acute and late esophageal toxicities were graded by RTOG criteria. Using 3D treatment planning tools, the esophagus was contoured in a uniform fashion, the 3D dose distribution calculated (with lung density correction), and the dose-volume (DVH) and dose-surface histograms (DSH) generated. At each axial level, the percentage of the esophageal circumference at each dose level was calculated. The length of circumferential esophagus and the maximum circumference treated to doses >50 Gy were assessed. Patient and treatment factors were correlated with acute and chronic esophageal dysfunction using univariate and multivariate logistic regression analyses.

RESULTS

There were no acute or late grade 4 or 5 esophageal toxicities. Ten of 91 patients (11%) developed grade 3 acute toxicity. On univariate analysis of clinical parameters, both dysphagia pre-RT (p = 0.10) and BID fractionation (p = 0.11) tended toward significantly predicting grade 3 acute esophagitis. None of the dosimetric parameters analyzed significantly predicted for grade 3 acute esophagitis. Twelve of 66 assessable patients (18%) developed late esophageal toxicity. Of the clinical parameters analyzed, only dysphagia pre-RT (p = 0.06) tended toward significantly predicting late esophageal toxicity. On univariate analyses, the effects of percent organ volume treated >50 Gy (p = 0.05), percent surface area treated >50 Gy (p = 0.05), length of 100% circumference treated >50 Gy (p = 0.04), and maximum percent of circumference treated >80 Gy (p = 0.01) significantly predicted for late toxicity of all grades. On multivariate analysis, percent organ volume treated >50 Gy (p = 0.02) and maximum percent of circumference treated >80 Gy (p = 0.02) predicted for late toxicity.

CONCLUSIONS

Late esophageal toxicity following aggressive, high-dose conformal radiotherapy is common but rarely severe. Dosimetric variables addressing the longitudinal and circumferential character of the esophagus have biologic rationale and are predictive of late toxicity. Further studies are needed to assess whether these parameters are better predictors than those derived from traditional DVHs.

Impact of the filling status of the bladder and rectum on their integral dose distribution and the movement of the uterus in the treatment planning of gynaecological cancer

PURPOSE

Determination of the impact of the filling status of the organs at risk (bladder and rectum) on the uterus mobility and on their integral dose distribution in radiotherapy of gynaecological cancer.

METHODS

In 29 women suffering from cervical or endometrial cancer two CT scans were carried out for treatment planning, one with an empty bladder and rectum, the second one with bladder and rectum filled. The volumes of the organs at risk were calculated and in 14 patients, receiving a definitive radiotherapy, the position of the uterus within the pelvis was shown using multiplanar reconstructions. After generation of a 3D treatment plan the dose volume histograms were compared for empty and filled organs at risk.

RESULTS

The mobility for the corpus uteri with/without bladder and rectum filling was in median 7 mm (95%-confidence interval: 3-15 mm) in cranial/caudal direction and 4 mm (0-9 mm) in posterior/anterior direction. Likewise, cervical mobility was observed to be 4 mm (-1-6 mm) mm in cranial/caudal direction. A full bladder led to a mean reduction in organ dose in median from 94-87% calculated for 50% of the bladder volume (P < 0.05, Wilcoxon's matched-pairs signed-ranks test). For 66% of the bladder volume the dose could be reduced in median from 78 to 61% (P < 0.005) and for the whole bladder from 42 to 39% (P < 0.005), respectively. No significant contribution of the filling status of the rectum to its integral dose burden was noticed.

CONCLUSIONS

Due to the mobility of the uterus increased margins between CTV and PTV superiorly, inferiorly, anteriorly and posteriorly of 15, 6 and 9 mm each, respectively, should be used. A full bladder is the prerequisite for an integral dose reduction.

Theoretical assessment of late cardiac complication from endovascular brachytherapy for restenosis prevention

PURPOSE

In this study, a theoretical assessment of late cardiac complication from endovascular brachytherapy is performed using the integrated logistic model.

MATERIALS AND METHODS

Calculation were performed for various lengths of Ir-192 sources using alpha/beta = 3.2 for the endpoint of chronic ischemia, TD50/5 = 7,000 cGy, and TD5/5 = 5,000 cGy. The dose distribution over a standard heart was divided into volume elements with uniform dose (dose-volume histogram). Using linear-quadratic equation, the dose in each of the volume elements was converted into dose equivalent to standard fractionation external beam irradiation. The normal tissue complication probability (NTCP) for each volume element was calculated and combined together to arrive at the cumulative risk of late cardiac complication. The NTCP was plotted against the dose prescribed at 2-mm radial distance for four treatment lengths.

RESULTS

(1) The overall risk of late cardiac toxicity (chronic ischemia within 5 years) was estimated to be less than 1% for current clinical trials using Ir-192. (2) There is a volume effect with higher risk for larger irradiated volume, which can come from longer treatment time, the same dose prescribed at a greater radial distance, and a longer source train. (3) The NTCP vs. dose demonstrates a sigmoidal relationship. There is a threshold dose (about 500 cGy), below which the risk is minimal; the gradient of the curve is greater for longer treatment length.

CONCLUSION

If the prediction from this model is validated with clinical data, it will contribute to guidelines for dose prescription, dose escalation, evaluation of new source design, and multivessel treatment.

A comparison of coplanar four-field techniques for conformal radiotherapy of the prostate

BACKGROUND AND PURPOSE

Conformal radiotherapy of the prostate is an increasingly common technique, but the optimal choice of beam configuration remains unclear. This study systematically compares a number of coplanar treatment plans for four-field irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV).

MATERIALS AND METHODS

A variety of four-field coplanar treatment plans were created for PO and PSV volumes in each of ten patients. Plans included a four-field 'box' plan, a symmetric plan having bilateral anterior and posterior oblique fields, a plan with anterior oblique and lateral fields, a series of asymmetric plans, and a three-field plan having anterior and bilateral fields for comparison. Doses of 64 and 74 Gy were prescribed to the isocentre. Plans were compared using the volume of rectum irradiated to greater than 50% (V50), 80% (V80) and 90% (V90) of the prescribed dose. Tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) for the rectum, bladder and femoral heads were also evaluated. Femoral head dose was limited such that less than 10% of each femoral head received 70% of the prescribed dose.

RESULTS

For the PO group, the optimal plan consisted of anterior oblique and lateral fields (Rectal V80 = 23.8+/-5.0% (1 SD)), while the box technique (V80 = 26.0+/-5.8%) was less advantageous in terms of rectal sparing (P = 0.001). Similar results were obtained for the PSV group (Rectal V80 = 43.9+/-5.0% and 47.3+/-5.5% for the two plan types, respectively, P = 0.001). The three-field plan was comparable to the optimal four-field plan but gave higher superficial body dose. With dose escalation from 64 to 74 Gy, the mean TCP for the optimal plan rose from 52.0+/-2.8% to 74.1+/-2.0%. Meanwhile, rectal NTCP for the optimal plan rose by 3.5% (PO) or 8.4% (PSV), compared to 4.7% (PO) or 10.1% (PSV) for the box plan.

CONCLUSIONS

For PO volumes, a plan with gantry angles of 35 degrees, 90 degrees, 270 degrees and 325 degrees offers a high level of rectal sparing and acceptable dose to the femoral heads for all patients, while for PSV volumes, the corresponding plan has gantry angles of 20 degrees, 90 degrees , 270 degrees and 340 degrees. Using these plans, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in anticipated rectal NTCP.

Long-term evolution of renal function in patients with ovarian cancer after whole abdominal irradiation with or without preceding cisplatin

BACKGROUND

The upper limit of the natural decline in creatinine clearance is 1 ml/min/year. To define the loss of renal function, we started a long-term assessment of patients with ovarian cancer treated by whole abdominal irradiation (WAI) with preceding cisplatin chemotherapy (CDDP) and second-look laparotomy (SLL).

PATIENTS AND METHODS

We analyzed the creatinine clearance over time of 56 patients treated from 1982 to 1988 for ovarian cancer. Thirty-one of 56 patients had received WAI after their initial surgery, and 25 of 56 patients had undergone CDDP therapy followed by SLL, and then WAI after their initial surgery. Median follow-up was 99 months (7-156). Twenty of 56 patients accepted our invitation for additional assessment of tubular function, nine of the 31 patients without CDDP therapy and SLL, and 11 of the 25 patients with CDDP followed by SLL and WAI. Ten of twenty patients had received four to six cycles CDDP, 80 mg/m2/cycle, and one patient nine cycles. The median total dose for each kidney was 1450 cGy (480-1690).

RESULTS

The mean creatinine clearance decreased from 84 ml/min to 66 ml/min. Seventy-six percent of the 25 patients who had undergone CDDP therapy, SLL and WAI had declines of more than 1 ml/min/year, 64% of these patients of more than 2 ml/min/year. For the 31 patients who had received WAI after their initial surgery, the corresponding numbers were 71% and 55%, respectively. The tubular function of the 20 patients who had undergone the additional investigations was not impaired.

CONCLUSION

The decline in renal function after WAI is more pronounced than in healthy subjects. The treatment with cisplatin and SLL prior to WAI does not seem to contribute to this loss of kidney function.

A treatment planning inter-comparison of proton and intensity modulated photon radiotherapy

PURPOSE

A comparative treatment planning study has been undertaken between standard photon delivery techniques,b intensity modulated photon methods and spot scanned protons in order to investigate the merits and limitations of each of these treatment approaches.

METHODS

Plans for each modality were performed using CT scans and planning information for nine patients with varying indications and lesion sites and the results have been analysed using a variety of dose and volume based parameters.

RESULTS

Over all cases, it is predicted that the use of protons could lead to a reduction of the total integral dose by a factor three compared to standard photon techniques and a factor two compared to IM photon plans. In addition, in all but one Organ at Risk (OAR) for one case, protons are predicted to reduce both mean OAR dose and the irradiated volume at the 50% mean target dose level compared to both photon methods. However, when considering the volume of an OAR irradiated to 70% or more of the target dose, little difference could be shown between proton and intensity modulated photon plans. On comparing the magnitude of dose hot spots in OARs resulting from the proton and IM photon plans, more variation was observed, and the ranking of the plans was then found to be case and OAR dependent.

CONCLUSIONS

The use of protons has been found to reduce the medium to low dose load (below about 70% of the target dose) to OARs and all non-target tissues compared to both standard and inversely planned photons, but that the use of intensity modulated photons can result in similar levels of high dose conformation to that afforded by protons. However, the introduction of inverse planning methods for protons is necessary before general conclusions on the relative efficacy of photons and protons can be drawn.

Practical considerations in using calculated healthy-tissue complication probabilities for treatment-plan optimization

PURPOSE

Healthy and neoplastic tissues are generally exposed nonuniformly to ionizing radiation. It is thus useful to develop algorithms that predict the probability of tumor control or normal tissue complication probability (NTCP) for any given spatial pattern of dose delivery. The questions addressed here concern: (a) the sensitivity of the NTCP predictions to the actual model used for extrapolation from uniform irradiation (where some clinical data exist) to nonuniform exposures, (b) its dependence on tissue type, and (c) consequences for treatment-plan optimization.

METHODS AND MATERIALS

Two (of several possible) NTCP formulations are used here: the Lyman model and a binomial equation. The effective volume-reduction scheme of Kutcher and Burman is used to obtain the NTCP for an arbitrary distribution of dose. NTCP was calculated for seven organs by postulating a dose distribution of maximum nonuniformity.

RESULTS

Both models fit available NTCP data well, but have very different extrapolations for exposures of small tissue volumes and very low values of NTCP (e.g., < 5%) where no data exist. Organs with pronounced volume effects (lung, kidneys) show substantial NTCP differences between the two models. Even in organs where the volume effect is small (e.g., spinal cord, brain), differences in NTCP due to the model selected may still have serious clinical consequences, as an actual example (for the spinal cord) indicates.

CONCLUSIONS

NTCP calculations based on extrapolations to volume fractions and/or NTCP levels for which reliable data do not exist depend on the model used to fit the data and the degree of dose nonuniformity. If NTCP is to be used in treatment-plan optimization, the prudent approach is to design plans that reproduce the conditions under which available dose-volume data were taken (e. g., uniform dose distributions).

Radiotherapy for lung cancer: target splitting by asymmetric collimation enables reduction of radiation doses to normal tissues and dose escalation

PURPOSE

This study was performed to develop a method of reducing the radiation doses to normal thoracic tissues, increasing the target dose, especially in the primary radiotherapy of non-small cell lung cancer (NSCLC), and to evaluate acute/subacute toxicity of dose escalation.

METHODS AND MATERIALS

From December 1195 to March 1998, the technique of target splitting has been applied to 58 patients. In this period, 30 patients were treated with doses > 80 Gy (ICRU-specification, mean 85.1 Gy, range 80. 1-90.2 Gy). The target volume is split into a cranial part (e.g., upper mediastinum) and a caudal part (e.g., primary tumor and middle mediastinum). Both volumes are planned and treated independently, using conformal irradiation techniques for both parts with half-collimated fields to prevent over- or underdosage in the junction plane. After fine-adjustment of the jaws, a verification film, exposed in a polymethylmethacrylate (PMMA) phantom, demonstrates the homogeneity of dose in the entire target volume. For comparison with conventional techniques, planning to identical doses is performed for 5 patients. Dose-volume histograms (DHVs) for normal lung tissue are presented for both methods.

RESULTS

The irradiated volume of normal tissue of the ipsilateral lung can be lowered at dose levels > or = 65, > or =45 Gy, and > or = 20 Gy to values of 37% (range 25-54%), 49% (range 46-54%), and 86% (range 55-117%), respectively. Other organs at risk, such as heart or esophagus, can also be spared significantly. Only 1 patient showed a transient grade 3 toxicity (pneumonitis), and there where no grade 4 acute/subacute side-effects. Two patients with Stage III A central tumors in close proximity to the large vessels died due to a pulmonary hemorrhage 2 and 4 months after therapy, respectively. No patient developed esophagitis. Antimycotic prophylaxis for esophagitis and posttherapeutic steroid prophylaxis for pneumonitis for several weeks were routinely used.

CONCLUSION

The technique of target splitting by asymmetric collimation helps to increase conformation, and thus enhances the sparing of normal tissues. It can be used whenever there is a marked difference in the shape of the planning target volume (PTV) in a cranio-caudal direction. This technique can principally be handled with 2D-planning systems, because it is coplanar. We consider target splitting as an important tool for dose escalation in the primary radiotherapy of NSCLC, that should also be used for other lung cancer patients necessitating moderate doses only.

[Inverse radiotherapy planning]

BACKGROUND

In clinical practice it sometimes happens that with currently available conformal radiotherapy techniques no satisfactory dose distribution can be achieved. In these cases inverse radiotherapy planning and intensity modulated radiotherapy may give better solutions.

METHOD

Inverse planning is a technique using a computer program to automatically achieve a treatment plan which has an optimal merit. This merit may either depend on dose or dose-volume constraints like minimum and maximum doses in the target region or critical organs, respectively, or biological indices like the complication free tumor control rate. As the result of inverse planning the inhomogeneous intensity fluence of the beams is calculated. These fluence distributions may be generated by beam compensators or multi-leaf collimation.

RESULTS

Clinical studies to prove the advantage of inverse planning are already on the way. It has been shown that this technology is safe and that the dose distributions which can be achieved are superior to conventional methods.

CONCLUSIONS

Inverse treatment planning and intensity modulated radiation therapy will almost certainly come to be the technique of choice for selected clinical cases.

Early detection of radiation-induced liver injury in rat by superparamagnetic iron oxide-enhanced MR imaging

The detectability of early liver injury induced by irradiation was studied using magnetic resonance (MR) imaging enhanced with superparamagnetic iron oxide (SPIO), a tissue-specific contrast agent against the reticuloendothelial system (RES). In rat, 3 days after focal irradiation (0-10 Gy), MR imaging was performed and specimens were obtained to observe the phagocytic function of RES. The irradiated portion of the liver was visualized with a clear demarcation from the nonirradiated part by SPIO-enhanced MR images as a decrease in negative enhancement reflecting the function of RES (P < 0.05), whereas this was impossible with nonenhanced MR images. Significant regression was observed as a dose-related change of the signal intensity in the irradiated portion on SPIO-enhanced MR images (R = 0.867, P < 0.0001). SPIO-enhanced MR imaging was reliable for detecting the range and extent of liver injury a few days after low-dose irradiation, and it may be a useful procedure for verifying the target area in clinical cases of radiation therapy.

Ischemic heart disease after mantlefield irradiation for Hodgkin's disease in long-term follow-up

BACKGROUND AND PURPOSE

In patients with Hodgkin's disease treated by radiotherapy with a moderate total dose and a low (mean) fraction dose to the heart, the risk of ischemic heart disease was investigated during long-term follow-up.

MATERIALS AND METHODS

The medical records of 258 patients treated in the period 1965-1980 with radiotherapy alone as the primary treatment were reviewed. The median follow-up was 14.2 years (range 0.7-26.2). The mean total dose and fraction dose to the heart were 37.2 Gy (SD 2.9) and 1.64 Gy (SD 0.09), respectively. The impact on the development of ischemic heart disease of treatment-related parameters, such as the applied (fraction) dose, irradiation technique (one or two fields per day), and chemotherapy in case of a relapse, was investigated. The incidence of ischemic heart disease in this patient population was compared with the expected incidence based on gender, age and calendar period-specific data for the Dutch population.

RESULTS

Thirty-one patients (12%) experienced ischemic heart disease (actuarial risk at 20-25 years: 21.2% (95% C.I. 15-30). Twenty-five of them were hospitalized. When compared with the expected incidence, the relative risk (RR) of hospital admission for ischemic heart disease was 2.7 (95% C.I. 1.7-4.0). There were 12 deaths (4.7%) due to ischemic myocardial or sudden death (actuarial risk at 25 years: 10.2% (95% C.I. 5.3-19), compared to 2.3 cases that were expected to have died from these causes, yielding a standardized mortality ratio (SMR) of 5.3 (95% C.I. 2.7-9.3). Gender (male), pretreatment cardiac medical history and increasing age appeared to be the only significant factors for the development of ischemic heart disease.

CONCLUSIONS

Despite the moderate total dose and the low (mean) fraction dose to the heart, the observed incidence of ischemic heart disease is high, especially after long follow-up periods. Treatment related cardiac disease in patients treated for Hodgkin's disease has only been reported for doses above 30 Gy. Although the optimum curative dose is still under debate, some studies recommend a dose as low as 32.5 Gy. The observed high rate of severe heart complications in this study advocates a dose reduction to this level, particularly in the regions where the coronary arteries are located.

Radiation-induced esophageal carcinoma 30 years after mediastinal irradiation: case report and review of the literature

A 54-year-old man who had been irradiated in 1964 for cervical involvement by Hodgkin's disease was admitted in December 1994 to our clinic with strong complaints of dysphagia. The reason was a moderately differentiated squamous cell carcinoma of the proximal esophagus in the previously irradiated region. The patient had no risk factors (abuse of nicotine or alcohol) for the developement of esophageal carcinoma. A reirradiation was performed, but the disease progressed locally and two weeks after the beginning of the therapy the patient developed two tracheoesophagocutaneous fistulae. The radiation therapy was discontinued and the tumor stenosis was bridged by a tube closing the fistulae. A retrospective dose analysis to evaluate the applied doses will be performed. Furthermore, an overview of 66 cases of the literature with radiation-induced esophageal carcinoma analysed concerning applied dose and latent interval will be given. In conclusion the reported case fits the criteria for radiation-induced malignancies (Chudecki Br J Radiol 1972;45:303-4) known from literature: (1) a history of previous irradiation, (2) a cancer occurring within the irradiated area, (3) gross tissue damage due to an excessive dose of radiation, and (4) a long latent interval between irradiation and development of cancer. Esophageal carcinomas belong to the rare secondary malignancies after the therapeutic use of ionizing radiation. Nevertheless in patients with dysphagia they should be suspected as a differential diagnosis even many years after mediastinal irradiation. The treatment of these tumors is very difficult and is associated with a poor prognosis.

Reirradiation and lomustine in patients with relapsed high-grade gliomas

PURPOSE

The aim of this study was to evaluate the toxicity, response, and survival of patients with relapsed high-grade gliomas after radiation therapy (RT) combined with lomustine (CCNU).

METHODS AND MATERIALS

Thirty-one patients with relapsed gliomas at least 6 months after completion of RT were reirradiated. Twenty-four patients had a pathological diagnosis of high-grade gliomas, whereas 7 had a radiological diagnosis of relapsed malignant gliomas. The study focused on patients with high-grade relapsed gliomas. A total dose of 34.5 Gy was delivered in 23 fractions over 4.5 weeks. Oral administration of CCNU (130 mg/m2) was begun at the same time as RT, and was repeated every 6 weeks until disease progression, or up to 12 courses.

RESULTS

Twelve of 24 patients had surgery before RT plus CCNU treatment. Median interval between RT courses was 14 months (range 6-73). All patients received a complete course of RT, and 22 of 24 patients received at least one course of CCNU. Objective responses were seen in 14 evaluable patients: 3 with partial response, 5 with stable disease, and 6 with progressive disease. Duration of partial response was 20, 9, and 8 months. Median time to progression and overall survival from the onset of retreatment were 8.4 months (range 1-22) and 13.7 months (range 1-63+), respectively. One case of G4 thrombocytopenia was observed. Five patients had G1 or G2 leucopenia and 3 patients had G3 leucopenia. Moderate nausea and vomiting were reported in 4 patients. One patient, after one course of CCNU, refused further chemotherapy. No significant difference in survival from relapse was found between patients who underwent surgery before RT plus CCNU and those who received only RT plus CCNU (p = 0.74).

CONCLUSION

Overall, the acute toxicity was moderate, and patient compliance was good. Reirradiation of high-grade glioma was associated with modest subjective and objective response rates. It is remarkable that median overall survival from relapse was 13.7 months.

An objective function for radiation treatment optimization based on local biological measures

The implementation of biological optimization of radiation treatment plans is impeded by both computational and modelling problems. We derive an objective function from basic model assumptions which includes the normal tissue constraints as interior penalty functions. For organs that are composed of parallel subunits, a mean response model is proposed which leads to constraints similar to dose-volume constraints. This objective function is convex in the case when no parallel organs lie in the treatment volume. Otherwise, an argument is given to show that a number of local minima may exist which are near degenerate to the global minimum. Thus, together with the measure quality of the objective function, highly efficient gradient algorithms can be used. The number of essential biological model parameters could be reduced to a minimum. However, if the optimization constraints are given as TCP/NTCP values, Lagrange multiplier updates have to be performed by invoking comprehensive biological models.

Incorporation of functional status into dose-volume analysis

The dose-volume histogram (DVH) has gained wide acceptance as a mechanism for reducing the voluminous data of a three-dimensional dose distribution into a two-dimensional graph. These graphs are often converted to a single figure of merit. This data reduction technique is used both for clinical treatment plan evaluation and as part of proposed systems for estimating control and complication probabilities. It has long been recognized that a major shortcoming of the DVH as an analysis tool is that all spatial information is discarded. A subtler problem, which is addressed in this work, is that the DVH also implies homogeneity of biological consequence of irradiation in what may be a functionally heterogeneous volume of tissue. An extension to the DVH, the functional dose-volume histogram, or dose-function histogram (DFH), is proposed, that explicitly includes quantitative three-dimensional functional information. The concept is illustrated by the use of SPECT imaging to assess the functional status of irradiated lung.

Computerized design of target margins for treatment uncertainties in conformal radiotherapy

PURPOSE

We describe a computerized method of determining target margins for beam aperture design in conformal radiotherapy plans.

MATERIALS AND METHODS

The method uses previously measured data from a population of patients to simulate setup error and organ motion in the patient currently being planned. Starting with a clinical target volume (CTV) and nontarget organs from the patient's planning CT scan, the simulation is repeated many times to produce a spatial probability distribution for each organ in the treatment machine coordinate system. This is used to determine a prescribed dose volume (PDV), defined as the volume to receive the prescribed dose, which encompasses the CTV while restricting the volume of nontarget organs within it, according to planner-specified values. The PDV is used to design beam apertures using a conventional margin for beam penumbra.

RESULTS

The method is applied to 6-field prostate conformal treatment plans, in which the PDV encloses the prostate and seminal vesicles while limiting the enclosed rectal wall volume. The effect of organ motion is assessed by applying the plans on subsequent CT scans of the same patients, calculating probabilities for tumor control (TCP) and normal tissue complication (NTCP), and comparing with plans designed from a physician-drawn planning target volume (PTV). Although prostate TCP and rectal wall NTCP are found to be similar in the two sets of plans, TCP for the seminal vesicles is significantly higher in the PDV-based plans.

CONCLUSIONS

The method can improve the dose conformality of treatment plans by incorporating population-based measurements of treatment uncertainties and consideration of nontarget tissues in the design of nonuniform target margins.

Normal tissue complication probabilities correlated with late effects in the rectum after prostate conformal radiotherapy

PURPOSE

Radiation therapy of deep-sited tumours will always result in normal tissue doses to some extent. The aim of this study was to calculate different risk estimates of late effects in the rectum for a group of cancer prostate patients treated with conformal radiation therapy (CRT) and correlate these estimates with the occurrences of late effects. Since the rectum is a hollow organ, several ways of generating dose-volume distributions over the organ are possible, and we wanted to investigate two of them.

METHODS AND MATERIALS

A mathematical model, known as the Lyman-Kutcher model, conventionally used to estimate normal tissue complication probabilities (NTCP) associated with radiation therapy, was applied to a material of 52 cancer prostate patients. The patients were treated with a four field box technique, with the rectum as organ at risk. Dose-volume histograms (DVH) were generated for the whole rectum (including the cavity) and of the rectum wall. One to two years after the treatment, the patients completed a questionnaire concerning bowel (rectum) related morbidity quantifying the extent of late effects.

RESULTS

A correlation analysis using Spearman's rank correlation coefficient, for NTCP values calculated from the DVHs and the patients' scores, gave correlation coefficients which were not statistically significant at the p<0.01 level. The correlation coefficients based on histograms of the whole rectum were larger than those derived from histograms of the rectum wall. Also, simpler descriptive measures as Dmax, of the whole rectum, correlated better to observed late toxicity than Dmax derived from histograms of the rectum wall. Correlation coefficients from "high-dose" measures were larger than those calculated from the NTCP values. Accordingly, as the volume parameter of the Lyman-Kutcher model was reduced, raising the impact of small high-dose volumes on the NTCP values, the correlation between observed effects and NTCP values became significant at p<0.01 level.

CONCLUSIONS

1) High-dose levels corresponding to small volume fractions of the cumulative dose-volume histograms were best correlated with the occurrences of late effects in the rectum as measured with questionnaires. This is compatible with a more serial organisation of the rectal tissue architecture than previously reported. 2) Reducing the Lyman-Kutcher model's volume parameter, thus allowing small high-dose regions to determine the NTCP, improved the correlation, but not beyond that of high-dose levels corresponding to small volume fractions of the cumulative dose-volume histograms.