Prostate stereotactic body radiotherapy—first UK experience

AIMS

Stereotactic body radiotherapy (SBRT) combines image-guided radiotherapy with hypofractionation, both of which will probably result in improvements in patient outcomes in prostate cancer. Most clinical experience with this technique resides in North America. Here we present the first UK cohort to receive SBRT for prostate cancer.

MATERIALS AND METHODS

Fifty-one prostate cancer patients (10 low risk, 35 intermediate risk and 6 high risk) were treated with 36.25 Gy in five fractions over 1-2 weeks and gold seed image guidance. All patients had toxicity International Prostate Symptom score (IPSS) and Radiation Therapy Oncology Group recorded prospectively and prostate-specific antigen was measured 3-6 monthly during follow-up.

RESULTS

The median IPSS was 6, 11, 8 and 5 at baseline, 1-3 weeks, 4-6 weeks and 7-12 weeks after treatment. Radiation Therapy Oncology Group genitourinary and gastrointestinal toxicity of grade 2 was seen in 22% and 14%, respectively, at 1-3 weeks after treatment; no patient had grade 3+ toxicity at this time point, although two patients had grade 3 urinary frequency recorded during treatment. The median follow-up for the 42 patients who did not receive androgen deprivation was 14.5 months. Prostate-specific antigen at 13-18 months after treatment was 1.3 ng/ml.

CONCLUSION

Prostate SBRT is a promising treatment for organ-confined prostate cancer and is currently being investigated in a UK-led phase III trial.

Is biochemical relapse-free survival after profoundly hypofractionated radiotherapy consistent with current radiobiological models?

AIMS

The α/β ratio for prostate cancer is thought to be low and less than for the rectum, which is usually the dose-limiting organ. Hypofractionated radiotherapy should therefore improve the therapeutic ratio, increasing cure rates with less toxicity. A number of models for predicting biochemical relapse-free survival have been developed from large series of patients treated with conventional and moderately hypofractionated radiotherapy. The purpose of this study was to test these models when significant numbers of patients treated with profoundly hypofractionated radiotherapy were included.

MATERIALS AND METHODS

A systematic review of the literature with regard to hypofractionated radiotherapy for prostate cancer was conducted, focussing on data recently presented on prostate stereotactic body radiotherapy. For the work described here, we have taken published biochemical control rates for a range of moderately and profoundly fractionated schedules and plotted these together with a range of radiobiological models, which are described.

RESULTS

The data reviewed show consistency between the various radiobiological model predictions and the currently observed data.

CONCLUSION

Current radiobiological models provide accurate predictions of biochemical relapse-free survival, even when profoundly hypofractionated patients are included in the analysis.

Identification of 23 new prostate cancer susceptibility loci using the iCOGS custom genotyping array

Prostate cancer is the most frequently diagnosed cancer in males in developed countries. To identify common prostate cancer susceptibility alleles, we genotyped 211,155 SNPs on a custom Illumina array (iCOGS) in blood DNA from 25,074 prostate cancer cases and 24,272 controls from the international PRACTICAL Consortium. Twenty-three new prostate cancer susceptibility loci were identified at genome-wide significance (P < 5 × 10(-8)). More than 70 prostate cancer susceptibility loci, explaining ∼30% of the familial risk for this disease, have now been identified. On the basis of combined risks conferred by the new and previously known risk loci, the top 1% of the risk distribution has a 4.7-fold higher risk than the average of the population being profiled. These results will facilitate population risk stratification for clinical studies.

A meta-analysis of genome-wide association studies to identify prostate cancer susceptibility loci associated with aggressive and non-aggressive disease

Genome-wide association studies (GWAS) have identified multiple common genetic variants associated with an increased risk of prostate cancer (PrCa), but these explain less than one-third of the heritability. To identify further susceptibility alleles, we conducted a meta-analysis of four GWAS including 5953 cases of aggressive PrCa and 11 463 controls (men without PrCa). We computed association tests for approximately 2.6 million SNPs and followed up the most significant SNPs by genotyping 49 121 samples in 29 studies through the international PRACTICAL and BPC3 consortia. We not only confirmed the association of a PrCa susceptibility locus, rs11672691 on chromosome 19, but also showed an association with aggressive PrCa [odds ratio = 1.12 (95% confidence interval 1.03-1.21), P = 1.4 × 10(-8)]. This report describes a genetic variant which is associated with aggressive PrCa, which is a type of PrCa associated with a poorer prognosis.

Stereotactic body radiotherapy for oligometastases

The management of metastatic solid tumours has historically focused on systemic treatment given with palliative intent. However, radical surgical treatment of oligometastases is now common practice in some settings. The development of stereotactic body radiotherapy (SBRT), building on improvements in delivery achieved by intensity-modulated and image-guided radiotherapy, now allows delivery of ablative doses of radiation to extracranial sites. Many non-randomised studies have shown that SBRT for oligometastases is safe and effective, with local control rates of about 80%. Importantly, these studies also suggest that the natural history of the disease is changing, with 2-5 year progression-free survival of about 20%. Although complete cure might be possible in a few patients with oligometastases, the aim of SBRT in this setting is to achieve local control and delay progression, and thereby also postpone the need for further treatment. We review published work showing that SBRT offers durable local control and the potential for progression-free survival in non-liver, non-lung oligometastatic disease at a range of sites. However, to test whether SBRT really does improve progression-free survival, randomised trials will be essential.

Clinical trial: Efficacy of a low or modified fat diet for the prevention of gastrointestinal toxicity in patients receiving radiotherapy treatment for pelvic malignancies

BACKGROUND

Inflammatory responses to pelvic radiotherapy can result in severe changes to normal gastrointestinal function with potentially severe long-term effects. Reduced or modified fat diets may confer benefit.

METHODS

This randomised controlled trial recruited patients with gynaecological, urological or lower gastrointestinal malignancy due to receive radical radiotherapy. Patients were randomised to a low fat (20% total energy from long chain triglycerides), modified fat (20% from long chain triglycerides and 20% from medium chain triglycerides) or normal fat diet (40% total energy from long chain triglycerides). The primary outcome was a difference in change in Inflammatory Bowel Disease Questionnaire--Bowel (IBDQ-B) score, from the start to end of radiotherapy.

RESULTS

A total of 117 patients with pelvic tumours (48% urological; 32% gastrointestinal; 20% gynaecological), with mean (SD) age: 65 (11.0) years, male:female ratio: 79:38, were randomised. The mean (SE) fall in paired IBDQ-B score was -7.3 (0.9) points, indicating a worsening toxicity. Differences between groups were not significant: P = 0.914 (low versus modified fat), P = 0.793 (low versus normal fat) and P = 0.890 (modified versus normal fat). The difference in fat intake between low and normal fat groups was 29.5 g [1109 kJ (265 kcal)] amounting to 11% (of total energy intake) compared to the planned 20% differential. Full compliance with fat prescription was only 9% in the normal fat group compared to 93% in the low fat group.

CONCLUSIONS

A low or modified fat diet during pelvic radiotherapy did not improve gastrointestinal symptom scores compared to a normal fat intake. An inadequate differential in fat intake between the groups may have confounded the results.

A risk prediction algorithm based on family history and common genetic variants: application to prostate cancer with potential clinical impact

Genome wide association studies have identified several single nucleotide polymorphisms (SNPs) that are independently associated with small increments in risk of prostate cancer, opening up the possibility for using such variants in risk prediction. Using segregation analysis of population-based samples of 4,390 families of prostate cancer patients from the UK and Australia, and assuming all familial aggregation has genetic causes, we previously found that the best model for the genetic susceptibility to prostate cancer was a mixed model of inheritance that included both a recessive major gene component and a polygenic component (P) that represents the effect of a large number of genetic variants each of small effect, where . Based on published studies of 26 SNPs that are currently known to be associated with prostate cancer, we have extended our model to incorporate these SNPs by decomposing the polygenic component into two parts: a polygenic component due to the known susceptibility SNPs, , and the residual polygenic component due to the postulated but as yet unknown genetic variants, . The resulting algorithm can be used for predicting the probability of developing prostate cancer in the future based on both SNP profiles and explicit family history information. This approach can be applied to other diseases for which population-based family data and established risk variants exist.

Prostate cancer segregation analyses using 4390 families from UK and Australian population-based studies

Familial aggregation of prostate cancer is likely to be due to multiple susceptibility loci, perhaps acting in conjunction with shared lifestyle risk factors. Models that assume a single mode of inheritance may be unrealistic. We analyzed genetic models of susceptibility to prostate cancer using segregation analysis of occurrence in families ascertained through population-based series totaling 4390 incident cases. We investigated major gene models (dominant, recessive, general, X-linked), polygenic models, and mixed models of susceptibility using the pedigree analysis software MENDEL. The hypergeometric model was used to approximate polygenic inheritance. The best-fitting model for the familial aggregation of prostate cancer was the mixed recessive model. The frequency of the susceptibility allele in the population was estimated to be 0.15 (95% confidence interval (CI) 0.11-0.20), with a relative risk for homozygote carriers of 94 (95% CI 46-192), and a polygenic standard deviation of 2.01 (95% CI 1.72-2.34). These analyses suggest that one or more genes having a strong recessively inherited effect on risk, as well as a number of genes with variants having small multiplicative effects on risk, may account for the genetic susceptibility to prostate cancer. The recessive component would predict the observed higher familial risk for siblings of cases than for fathers, but this could also be due to other factors such as shared lifestyle by siblings, targeted screening effects, and/or non-additive effects of one or more genes.

Identification of seven new prostate cancer susceptibility loci through a genome-wide association study

Prostate cancer (PrCa) is the most frequently diagnosed cancer in males in developed countries. To identify common PrCa susceptibility alleles, we previously conducted a genome-wide association study in which 541,129 SNPs were genotyped in 1,854 PrCa cases with clinically detected disease and in 1,894 controls. We have now extended the study to evaluate promising associations in a second stage in which we genotyped 43,671 SNPs in 3,650 PrCa cases and 3,940 controls and in a third stage involving an additional 16,229 cases and 14,821 controls from 21 studies. In addition to replicating previous associations, we identified seven new prostate cancer susceptibility loci on chromosomes 2, 4, 8, 11 and 22 (with P = 1.6 x 10(-8) to P = 2.7 x 10(-33)).

Identification of new genetic risk factors for prostate cancer

There is evidence that a substantial part of genetic predisposition to prostate cancer (PCa) may be due to lower penetrance genes which are found by genome-wide association studies. We have recently conducted such a study and seven new regions of the genome linked to PCa risk have been identified. Three of these loci contain candidate susceptibility genes: MSMB, LMTK2 and KLK2/3. The MSMB and KLK2/3 genes may be useful for PCa screening, and the LMTK2 gene might provide a potential therapeutic target. Together with results from other groups, there are now 23 germline genetic variants which have been reported. These results have the potential to be developed into a genetic test. However, we consider that marketing of tests to the public is premature, as PCa risk can not be evaluated fully at this stage and the appropriate screening protocols need to be developed. Follow-up validation studies, as well as studies to explore the psychological implications of genetic profile testing, will be vital prior to roll out into healthcare.

Early clinical evaluation of a novel three-dimensional structure delineation software tool (SCULPTER) for radiotherapy treatment planning

Modern radiotherapy treatment planning (RTP) necessitates increased delineation of target volumes and organs at risk. Conventional manual delineation is a laborious, time-consuming and subjective process. It is prone to inconsistency and variability, but has the potential to be improved using automated segmentation algorithms. We carried out a pilot clinical evaluation of SCULPTER (Structure Creation Using Limited Point Topology Evidence in Radiotherapy) - a novel prototype software tool designed to improve structure delineation for RTP. Anonymized MR and CT image datasets from patients who underwent radiotherapy for bladder or prostate cancer were studied. An experienced radiation oncologist used manual and SCULPTER-assisted methods to create clinically acceptable organ delineations. SCULPTER was also tested by four other RTP professionals. Resulting contours were compared by qualitative inspection and quantitatively by using the volumes of the structures delineated and the time taken for completion. The SCULPTER tool was easy to apply to both MR and CT images and diverse anatomical sites. SCULPTER delineations closely reproduced manual contours with no significant volume differences detected, but SCULPTER delineations were significantly quicker (p<0.05) in most cases. In conclusion, clinical application of SCULPTER resulted in rapid and simple organ delineations with equivalent accuracy to manual methods, demonstrating proof-of-principle of the SCULPTER system and supporting its potential utility in RTP.

A comparison of the use of bony anatomy and internal markers for offline verification and an evaluation of the potential benefit of online and offline verification protocols for prostate radiotherapy

PURPOSE

To evaluate the utility of intraprostatic markers in the treatment verification of prostate cancer radiotherapy. Specific aims were: to compare the effectiveness of offline correction protocols, either using gold markers or bony anatomy; to estimate the potential benefit of online correction protocol's using gold markers; to determine the presence and effect of intrafraction motion.

METHODS AND MATERIALS

Thirty patients with three gold markers inserted had pretreatment and posttreatment images acquired and were treated using an offline correction protocol and gold markers. Retrospectively, an offline protocol was applied using bony anatomy and an online protocol using gold markers.

RESULTS

The systematic errors were reduced from 1.3, 1.9, and 2.5 mm to 1.1, 1.1, and 1.5 mm in the right-left (RL), superoinferior (SI), and anteroposterior (AP) directions, respectively, using the offline correction protocol and gold markers instead of bony anatomy. The subsequent decrease in margins was 1.7, 3.3, and 4 mm in the RL, SI, and AP directions, respectively. An offline correction protocol combined with an online correction protocol in the first four fractions reduced random errors further to 0.9, 1.1, and 1.0 mm in the RL, SI, and AP directions, respectively. A daily online protocol reduced all errors to <1 mm. Intrafraction motion had greater impact on the effectiveness of the online protocol than the offline protocols.

CONCLUSIONS

An offline protocol using gold markers is effective in reducing the systematic error. The value of online protocols is reduced by intrafraction motion.

Adjuvant chemoradiotherapy for gastric carcinoma: dosimetric implications of conventional gastric bed irradiation and toxicity

AIMS

Recently, a survival advantage has been shown using adjuvant chemoradiotherapy after complete resection of gastric cancer. If survival advantages are to be maintained, treatment-related complications must be minimised. In this study, we explored the dosimetric implications and toxicity of conventional large field gastric bed irradiation.

MATERIALS AND METHODS

Between 2000 and 2002, 16 patients received adjuvant 5-fluorouracil (5-FU) chemoradiotherapy after complete resection of gastric cancer. Radiotherapy was simulator planned using anterior-posterior parallel opposed fields to 45 Gy in 25 daily fractions over 5 weeks.

RESULTS

Thirteen patients (81%) completed radiotherapy and eight patients (50%) completed chemotherapy as planned. Toxicity was the main factor for discontinuation. Substantial dose inhomogeneities were shown using retrospective computed tomography recreation of dose-volume histograms (DVHs) of the organs at risk.

CONCLUSIONS

Although the delivery of chemoradiotherapy using conventional two-dimensional simulator planning is a feasible technique, significant under-appreciation of dose inhomogeneity exists. Conformal computed tomography planning is vital to document doses received by organs at risk, especially the spinal cord and kidneys, which may receive high doses, and prospectively correlate these with acute and long-term toxicity in order to redefine organ at risk tolerances in the setting of chemoradiation.

New developments in MRI for target volume delineation in radiotherapy

MRI is being increasingly used in oncology for staging, assessing tumour response and also for treatment planning in radiotherapy. Both conformal and intensity-modulated radiotherapy requires improved means of defining target volumes for treatment planning in order to achieve its intended benefits. MRI can add to the radiotherapy treatment planning (RTP) process by providing excellent and improved characterization of soft tissues compared with CT. Together with its multiplanar capability and increased imaging functionality, these advantages for target volume delineation outweigh its drawbacks of lacking electron density information and potential image distortion. Efficient MR distortion assessment and correction algorithms together with image co-registration and fusion programs can overcome these limitations and permit its use for RTP. MRI developments using new contrast media, such as ultrasmall superparamagnetic iron oxide particles for abnormal lymph node identification, techniques such as dynamic contrast enhanced MRI and diffusion MRI to better characterize tissue and tumour regions as well as ultrafast volumetric or cine MR sequences to define temporal patterns of target and organ at risk deformity and variations in spatial location have all increased the scope and utility of MRI for RTP. Information from these MR developments may permit treatment individualization, strategies of dose escalation and image-guided radiotherapy. These developments will be reviewed to assess their current and potential use for RTP and precision high dose radiotherapy.

Evaluating the relationship between erectile dysfunction and dose received by the penile bulb: Using data from a randomised controlled trial of conformal radiotherapy in prostate cancer (MRC RT01, ISRCTN47772397)

AIM

To evaluate the relationship between erectile function and the radiation dose to the penile bulb and other proximal penile structures in men receiving conformal radiotherapy (CFRT) for prostate cancer (PCa).

METHODS

The Medical Research Council (MRC) RT01 trial randomised 843 men who had localised PCa to receive either 64 or 74 Gy after 3 - 6 months neoadjuvant hormonal treatment. Fifty-one men were selected who were potent prior to hormonal treatment, having completed both pre-hormone and 2-year post-CFRT Quality of Life assessments, and on whom dose volume data were available for analysis. The men were divided into three groups according to 2-year follow-up: potent, reduced potency, and impotent. The bulb of the penis together with the crura, were outlined on restored treatment plans. Dose - volume histograms were generated and compared between the three groups. An ordered logistic regression model was used to calculate the odds ratio of a range of dose - volume parameters to the penile bulb and effect on erectile dysfunction. The dose to the penile bulb was correlated to the dose received by the crura.

RESULTS

Of the 51 patients, 12 remained potent, 22 had reduced potency, and 17 were impotent at 2 years. No differences were seen in mean dose to the penile bulb by allocated treatment (t test = 1.61, p = 0.11). The mean doses to the penile bulb received by the potent, reduced potency, and impotent groups were 45.5 Gy (SD 17.1), 48 Gy (SD 16.1), and 59.2 Gy (SD 13.8), respectively. There was a strong correlation between the mean dose received by the penile bulb and dose to the crura (r = 0.82, p < 0.0001). 83.3% of impotent patients received a D90 > or = 50 Gy to the penile bulb compared with 29.4% of patients who maintained potency at 2 years (p = 0.006).

CONCLUSION

There is evidence from this study to suggest a dose volume effect on the penile bulb and erectile dysfunction. A D90 > or = 50 Gy is associated with a significant risk of erectile dysfunction and this should form a basis for selecting dose constraints in future dose escalation studies.

A modified inflammatory bowel disease questionnaire and the Vaizey Incontinence questionnaire are more sensitive measures of acute gastrointestinal toxicity during pelvic radiotherapy than RTOG grading

PURPOSE

Simple scales with greater sensitivity than Radiation Therapy Oncology Group (RTOG) grading to detect acute gastrointestinal toxicity during pelvic radiotherapy, could be clinically useful.

METHODS AND MATERIALS

Do questionnaires used in benign gastrointestinal diseases detect toxicity in patients undergoing radiotherapy? The patient-completed Inflammatory Bowel Disease (IBDQ) and Vaizey Incontinence questionnaires were compared prospectively at baseline and at Week 5 to physician-completed RTOG grading.

RESULTS

A total of 107 patients, median age 63 years, were recruited. After 5 weeks of treatment, patients with gynecologic and gastrointestinal cancer were more symptomatic than urologic patients (p = 0.012; p = 0.014). Overall, 94% had altered bowel habits, 80% loose stool, 74% frequency, 65% difficult gas, 60% pain, >48% distress, 44% tenesmus, >40% restrictions in daily activity, 39% urgency, 37% fecal incontinence, and 40% required antidiarrheal medication. The median RTOG score was 1 (range, 0-2), median IBDQ score 204.5 (range, 74-224), and median Vaizey score 5 (range, 0-20). Chemotherapy preceding radiotherapy increased fecal incontinence (p = 0.002). RTOG scores stabilized after 3 weeks, IBDQ scores peaked at Week 4, and Vaizey scores worsened throughout treatment. IBDQ and Vaizey scores distinguished between groups with different RTOG scores.

CONCLUSION

The IBDQ and Vaizey questionnaires are reliable and sensitive, offering greater insight into the severity and range of symptoms compared with RTOG grading.

X-ray volume imaging in bladder radiotherapy verification

PURPOSE

To assess the clinical utility of X-ray volume imaging (XVI) for verification of bladder radiotherapy and to quantify geometric error in bladder radiotherapy delivery.

METHODS AND MATERIALS

Twenty subjects undergoing conformal bladder radiotherapy were recruited. X-ray volume images and electronic portal images (EPIs) were acquired for the first 5 fractions and then once weekly. X-ray volume images were co-registered with the planning computed tomography scan and clinical target volume coverage assessed in three dimensions (3D). Interfraction bladder volume change was described by quantifying changes in bladder volume with time. Bony setup errors were compared from both XVI and EPI.

RESULTS

The bladder boundary was clearly visible on coronal XVI views in nearly all images, allowing accurate 3D treatment verification. In 93.5% of imaged fractions, the clinical target volume was within the planning target volume. Most subjects displayed consistent bladder volumes, but 25% displayed changes that could be predicted from the first three XVIs. Bony setup errors were similar whether calculated from XVI or EPI.

CONCLUSIONS

Coronal XVI can be used to verify 3D bladder radiotherapy delivery. Image-guided interventions to reduce geographic miss and normal tissue toxicity are feasible with this technology.

X-ray volumetric imaging in image-guided radiotherapy: The new standard in on-treatment imaging

PURPOSE

X-ray volumetric imaging (XVI) for the first time allows for the on-treatment acquisition of three-dimensional (3D) kV cone beam computed tomography (CT) images. Clinical imaging using the Synergy System (Elekta, Crawley, UK) commenced in July 2003. This study evaluated image quality and dose delivered and assessed clinical utility for treatment verification at a range of anatomic sites.

METHODS AND MATERIALS

Single XVIs were acquired from 30 patients undergoing radiotherapy for tumors at 10 different anatomic sites. Patients were imaged in their setup position. Radiation doses received were measured using TLDs on the skin surface. The utility of XVI in verifying target volume coverage was qualitatively assessed by experienced clinicians.

RESULTS

X-ray volumetric imaging acquisition was completed in the treatment position at all anatomic sites. At sites where a full gantry rotation was not possible, XVIs were reconstructed from projection images acquired from partial rotations. Soft-tissue definition of organ boundaries allowed direct assessment of 3D target volume coverage at all sites. Individual image quality depended on both imaging parameters and patient characteristics. Radiation dose ranged from 0.003 Gy in the head to 0.03 Gy in the pelvis.

CONCLUSIONS

On-treatment XVI provided 3D verification images with soft-tissue definition at all anatomic sites at acceptably low radiation doses. This technology sets a new standard in treatment verification and will facilitate novel adaptive radiotherapy techniques.

Radiotherapeutic techniques for prostate cancer, dose escalation and brachytherapy

There is evidence to confirm a dose-response relationship in prostate cancer. The relative benefit is dependent on the clinical prognostic risk factors (T stage, Gleason score and presenting prostate-specific antigen [PSA]) being more favourable for intermediate-risk patients. Refinement of prognostic groups and clinical threshold parameters is ongoing. Escalation of dose in prostate radiotherapy using conventional techniques is limited by rectal tolerance. Substantial advances have been made in radiotherapy practice, such as the development of conformal radiotherapy (CFRT) and intensity-modulated radiotherapy (IMRT). Randomised data support the value of CFRT in reducing rectal toxicity. IMRT can permit higher-dose escalation while still respecting known rectal tolerance thresholds. Brachytherapy is a recognised alternative for low-risk prostate cancer subgroups. New radiotherapeutic strategies for prostate cancer include pelvic nodal irradiation, exploiting the presumed low alpha/beta ratio in prostate cancer for hypofractionation and combining external beam with high-dose-rate brachytherapy boosts. New image-guided methodologies will enhance the therapeutic ratio of any radiotherapy technique or dose escalation programme by enabling more reliable and accurate treatment delivery for improved patient outcomes.

An assessment of clinically optimal gold marker length and diameter for pelvic radiotherapy verification using an amorphous silicon flat panel electronic portal imaging device

Verification of target organ position is essential for the accurate delivery of conformal radiotherapy. Megavoltage electronic portal imaging with flat panel amorphous silicon detectors delivers high quality images that can be used for verification of bony landmark position. Gold markers implanted into the target organ can be visualized and used as a surrogate of actual organ position. On-line compensation for marker displacement, by adjusting patient position, can reduce geometric errors associated with radiation delivery. This study assesses the optimal marker length and diameter to be used with an amorphous silicon (a-Si) flat panel detector and electronic portal images (EPIs), prior to implementation of a clinical programme of gold marker insertion in prostate cancer patients. Seven marker sizes varying from 3 mm to 8 mm in length and 0.8 mm to 1.1 mm in diameter were investigated in a group of patients undergoing pelvic radiotherapy using an 8 MV Elekta SL20 linear accelerator. Markers were placed on the skin entry and exit sites of the treatment beam and EPIs in both lateral and anterior pelvic views were acquired. Three observers independently assessed visibility success and failure using a subjective scoring system. Markers less than 5 mm in length or 0.9 mm in diameter were poorly visualized (<70% visualization success in lateral EPIs). The marker measuring 0.9 mm x 5 mm appears to be clinically optimal in pelvic radiotherapy patients (80% visualization success in lateral EPIs) and will be used for actual organ implantation.

Treatment planning evaluation of non-coplanar techniques for conformal radiotherapy of the prostate

BACKGROUND AND PURPOSE

To evaluate the benefit of using non-coplanar treatment plans for irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV).

MATERIAL AND METHODS

An inverse planning algorithm was used to produce three-field, four-field, five-field and six-field non-coplanar treatment plans without intensity-modulation in ten patients. These were compared against a three-field coplanar plan. A dose of 74 Gy was prescribed to the isocentre. Plans were compared using the minimum dose to the planning target volume (PTV), maximum dose to the small bowel, and irradiated volumes of rectum, bladder and femoral head. Biological indices were also evaluated.

RESULTS

For the PO group, volume of rectum irradiated to 60 Gy (V(60)) was 22.5+/-3.7% for the coplanar plan, and 21.5+/-5.3% for the five-field non-coplanar plan, which was the most beneficial (p=0.3). For the PSV group, the five-field non-coplanar plan was again the most beneficial. Rectal V(60) was in this case reduced from 41.5+/-10.4% for the coplanar plan to 35.2+/-9.3% for the non-coplanar plan (p=0.02).

CONCLUSIONS

The use of non-coplanar beams in conformal prostate radiotherapy provides a small increase in rectal sparing, more significantly with PSV volumes than for PO volumes.

Technological advances in radiotherapy for the treatment of localised prostate cancer

There is good evidence that radiation dose escalation in localised prostate cancer is associated with increased cell kill. The traditional two-dimensional (2D) technique of treatment planning and delivery is limited by normal tissue toxicity, such that the dose that can be safely delivered to the prostate by external beam radiotherapy is 65-70 Gy. Several technological advances over the last 20 years have enhanced the precision of external beam radiotherapy (EBRT), and have resulted in improved outcomes. The three-dimensional conformal radiotherapy (3D-CRT) approach reduces the dose-limiting late side-effect of proctitis and has allowed for dose escalation to the whole prostate to 78 Gy. More recently, intensity modulated radiotherapy (IMRT), an advanced form of conformal therapy, has resulted in reduced rectal toxicity when using doses greater than 80 Gy. In addition, IMRT can potentially escalate the dose to specific parts of the prostate where there are resistant subpopulations of tumour clonogens, or can be used to extend the high-dose region to pelvic lymph nodes. The addition of androgen deprivation to conventional radiotherapy has an impact on survival and local control. Initial hormone therapy causes cytoreduction of the prostate cancer allowing for a reduction in radiotherapy volume as well as an additive effect on cell kill. Long-term adjuvant androgen deprivation has been shown to improve overall survival in more advanced tumours. Prostate brachytherapy is now a recognised treatment for those with low-risk disease. It achieves similar long-term outcome to other treatment modalities. Brachytherapy can be used as monotherapy for localised disease, or as boost treatment following conventional EBRT for locally advanced disease. New techniques are available to improve the precision of both target definition and treatment verification. This so-called image-guided radiotherapy will help to enhance the accuracy of dose delivery by correcting both for inter-fraction positional variation and for intra-fraction movement of the prostate in real-time and will allow for tighter tumour margins and avoidance of normal tissues, thereby enhancing the safety of treatment.

Do differences in target volume definition in prostate cancer lead to clinically relevant differences in normal tissue toxicity?

PURPOSE

Many studies have described the quantitated differences between clinicians in target volume definition in prostate cancer. However, few studies have looked at the clinical effects of this. We aimed to assess the relevance and sequelae of such differences.

METHODS AND MATERIALS

Five experienced radiation oncologists were given the clinical details of 5 patients with early-stage prostate cancer and asked to define the clinical target volume, consisting of the prostate and seminal vesicles (CTV1) and the prostate alone (CTV2), on specified planning CT scans of the pelvis. Planning target volumes (PTV1) were generated by automatic expansion of the CTV1 by a 1-cm margin. The PTV2 was defined as the CTV2. The rectum and bladder were defined by a single experienced clinician for each plan without knowledge of the involved clinician marking the CTVs. The Pinnacle planning system was used to generate the plans, using four-field conformal radiotherapy, to deliver 64 Gy in 32 fractions to the PTV1 followed by a boost of 10 Gy to the PTV2 (Medical Research Council RT01 trial protocol). Dose-volume histograms were generated for the whole bladder and rectum for each plan and the volume receiving a specific percentage of the dose (e.g., V(90)) calculated for 74 Gy, followed by estimates of normal tissue complication probabilities (NTCPs) for the bladder and rectum.

RESULTS

Statistically significant differences were found in the CTV1 and CTV2 and, consequently, the PTV1 among the 5 clinicians (p < 0.0005). Most of the discrepancies occurred at the delineation of the prostatic apex and seminal vesicles, with the smallest variance noted at the rectum-prostate and bladder-prostate interfaces. No statistically significant differences were found among clinicians for the rectal V(90), V(85), V(80), V(70), or V(50) or for the bladder V(85), V(80), V(70), or V(50). A difference was noted among consultants for the bladder V(90) (p = 0.015), although no correlation was found between the bladder V(90) and the size of the outlined volumes. No statistically significant differences were found between the estimates of bladder (p = 0.1) and rectal (p = 0.09) NTCPs.

CONCLUSION

The statistically significant difference in outlined volumes of the CTV1, CTV2, and PTV1 among the 5 clinicians is in keeping with the findings of previous studies. However, the interclinician variability did not result in clinically relevant outcomes with respect to the irradiated volume of rectum and bladder or NTCP. This may have been because the outlined areas in which interclinician differences were smallest (the rectal-prostate and prostate-bladder interfaces) are the areas that have the greatest effect on normal tissue toxicity. For the areas in which the interclinician correlation was lowest (the prostatic apex and distal seminal vesicles), the effects on normal tissue toxicity are smallest. The results of this study suggest that interclinician outlining differences in prostate cancer may have less clinical relevance than was previously thought.

Trans-perineal implantation of radio-opaque treatment verification markers into the prostate: an assessment of procedure related morbidity, patient acceptability and accuracy

On-line imaging of prostate markers can be used to compensate for errors in radiation delivery. This study assessed the patient acceptability and morbidity associated with the trans-perineal route of implantation. A minority experienced acute pain or bleeding. Placement was accurate in all but one subject. An operator related learning curve exists. Although this is an invasive procedure most patients found it acceptable. Implementation for routine clinical practice is feasible.

Radiotherapy for muscle-invasive carcinoma of the bladder: results of a randomized trial comparing conventional whole bladder with dose-escalated partial bladder radiotherapy

PURPOSE

To investigate whether delivering an increased radiation dose to the tumor-bearing region of the bladder alone would improve local disease control without increasing treatment toxicity.

METHODS AND MATERIALS

A total of 149 patients with unifocal T2-T3N0M0 bladder carcinoma were randomized between whole bladder conformal radiotherapy (WBRT, 52.5 Gy in 20 fractions, n = 60) and partial bladder conformal RT (PBRT) to tumor alone with 1.5-cm margins within either 4 weeks (PBRT4, 57.5 Gy in 20 fractions, n = 44) or 3 weeks (PBRT3, 55 Gy in 16 fractions, n = 45). The response was assessed cystoscopically after 4 months.

RESULTS

The 5-year overall and CFS rate was 58% and 47%, respectively, for the whole population. The CR rate was 75% for WBRT, 80% for PBRT4, and 71% for PBRT3 (p = 0.6), with a 5-year local control rate of 58%, 59%, and 34%, respectively (p = 0.18). Solitary new tumors arose within the bladder, outside the irradiated volume, in 6 (7%) of 89 patients who underwent PBRT. The 5-year overall survival and cystectomy-free survival rate was 61% and 49% for WBRT, 60% and 50% for PBRT4, and 51% and 41% for PBRT3 (p = 0.81 and p = 0.59). The treatment toxicity was mild and equivalent across the three trial arms.

CONCLUSION

The reduction in treatment volume allowed delivery of an increased radiation dose without a reduction in local tumor control or the development of excess toxicity. However, this dose-escalated partial bladder approach did not result in significantly improved overall survival.

Controversies in the radiotherapeutic management of poor prognosis locally advanced prostate cancer

The Grand Round was held at the Christie Hospital, Manchester, U.K., on 30 November 2002. It followed a presentation by Dr David Dearnaley from the Royal Marsden Hospital in Sutton on 'Novel approaches and trials in prostate cancer'. Controversies in the management of locally advanced prostate cancer were illustrated by a case presentation and followed by a discussion on the evaluation of disease extent, and the roles of radiotherapy and hormone ablation.

Anal Canal Cancer and Chemoradiation Treatment in Two Patients with Systemic Lupus Erythematosus treated by Chronic Therapeutic Immunosuppression

Two case reports of anal cancer developing during chronic therapeutic immunosuppression for systemic lupus erythematosus (SLE) and their cancer management are presented. The complex issues of delivery of curative chemoradiation treatment for anal cancer in the context of co-existing autoimmune connective tissue disease (AICD) are discussed. These two cases show that combined chemotherapy and radiation regimens are possible in patients with SLE. However, frequent, careful assessment with judicious and prompt management of haematological and other complications during treatment is important.

Hypofractionated conformal radiotherapy in carcinoma of the prostate: five-year outcome analysis

PURPOSE

Recent publications have indicated that the alpha/beta ratios for carcinoma of the prostate are much lower than had originally been thought, suggesting that prostate cancer may be highly sensitive to fraction size. We have reviewed our unique experience of the use of 3.13 Gy fractions in a large cohort of men treated homogeneously in a single institute.

MATERIALS AND METHODS

The outcome for 705 men with T1-T4, N0, M0 prostate cancer who received conformal radiotherapy between 1995 and 1998 at this center was analyzed. No patient received hormonal manipulation. Mean age was 68 years (range: 49-84 years). Median pretreatment PSA was 13 ng/mL (range: 0.6-270 ng/mL). Disease characteristics were as follows: Stage T1, 125 (18%); T2, 365 (52%); T3/4, 215 (30%); Gleason 2-6, 463 (66%); Gleason 7-10, 242 (34%); pretreatment PSA < or =10 ng/mL, 291 (41%); 10 to < or =20, 228 (32%); >20, 186 (27%). Median follow-up was 48 months (range: 1-82 months). Biochemical-free survival (bNED) was defined by the American Society for Therapeutic Radiology and Oncology consensus definition. Radiotherapy was delivered to a planning target volume (prostate plus all/base of the seminal vesicles dependent on risk criteria with a 1-cm margin) with a 4-field conformal technique to a dose of 50 Gy in 16 daily fractions over 22 days.

RESULTS

The 5-year bNED survival was significantly associated (p < 0.001) with pretreatment PSA, stage, and Gleason score. Five-year bNED rates with respect to pretreatment characteristics were as follows: 73% (PSA < or =10), 52% (>10-20), 35% (>20), 64% (Stage T1/2), 38% (T3/4), 61% (Gleason score 2-6), and 46% (Gleason > or =7). When patients were grouped into good (Stage T1/2, PSA < or =10 ng/mL, and Gleason score <7) (n = 181), intermediate (1 raised value) (n = 247), or poor (2 or more raised values) (n = 277) prognostic groups, the bNED was, respectively, 82%, 56%, and 39%. Radiation Therapy Oncology Group Grade > or =2 bowel toxicity was 5% and bladder 9%.

CONCLUSIONS

These data indicate that the delivery of a relatively low total dose using a hypofractionated regime results in similar tumor control and normal-tissue toxicity to 65-70 Gy delivered in 1.8-2 Gy fractions. These data suggest that this is an acceptable regime for good-prognosis patients. However, because of the evidence for a dose effect at doses above 70 Gy with "conventional fractionation," we are now treating intermediate- and poor-risk patients within a hypofractionated dose escalation trial to 60 Gy in 20 fractions using intensity- modulated radiotherapy.

Evaluation of the LENT-SOMA scales for the prospective assessment of treatment morbidity in cervical carcinoma

PURPOSE

To examine the Late Effects Normal Tissue Task Force (LENT)-Subjective, Objective, Management, Analytic (SOMA) scales prospectively in carcinoma of the cervix treated curatively with radiotherapy (RT) using interviews and postal questionnaires and to test the sensitivity of the scales in assessing the radiation effects.

METHODS AND MATERIALS

A consecutive series of 100 patients completed questionnaires to score the subjective part of the published LENT-SOMA scales. Assessments were made before RT and at approximately 21, 70, 200, 400, 600, and 800 days after the start of treatment. The acceptability and feasibility of using the scales was examined using compliance in completion of the questionnaires. The scales were validated by evaluating the concordance of data obtained by two independent scorers and by examining the ability of the scales to measure radiation-related symptoms.

RESULTS

Questionnaires were completed for 89 patients before RT. The level of noncompliance was 11%. The concordance between scores when two people completed the questionnaires independently was excellent. Subjective subsite scores were highest 21 days after treatment but generally fell by 70 days. The average baseline overall LENT-SOMA subjective scores increased with advancing stage (p = 0.008) and were higher for patients treated with RT alone (p = 0.044).

CONCLUSION

In cervical carcinoma, the LENT-SOMA scales were acceptable and feasible to administer in the clinic and appropriate in the measurement of early subjective morbidity from RT.

Class solutions for conformal external beam prostate radiotherapy

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSION

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

Ki-67 staining is an independent correlate of biochemical failure in prostate cancer treated with radiotherapy

PURPOSE

To determine the significance of Ki-67/MIB1 staining as a marker of patient outcome for prostate cancer patients treated with radiotherapy.

EXPERIMENTAL DESIGN

Pretreatment archival prostate biopsy tumor tissue was available from 106 stage T1-T4 prostate cancer patients treated with external beam radiotherapy between 1987 and 1993 at M. D. Anderson Cancer Center. Diagnosis was made from prostate needle biopsy in 64 cases and from transurethral resection of the prostate (TURP) in 42 cases. All patients had a pretreatment prostate-specific antigen (PSA), and no patient had evidence of metastasis. Immunohistochemical staining for MIB1 was used to determine the percentage of Ki-67-positive tumor cells, the Ki-67 labeling index (Ki67-LI). Biochemical failure after radiotherapy was defined as three rises in PSA on follow-up. Median follow-up was 62 months.

RESULTS

The mean and median Ki67-LI for the entire cohort was 3.2 and 2.3. The mean and median Ki67-LIs for those diagnosed by needle biopsy were 3.2 and 2.3, and by TURP were 3.1 and 2.4. For all patients, mean Ki67-LI levels were significantly higher with stage T3/T4 disease, Gleason 7-10 disease, and in those that developed treatment failure. Similar relationships were observed when the Ki67-LI was dichotomized into low (< or =3.5%) and high (>3.5%) groups. Actuarial freedom from biochemical failure (bNED) when Ki67-LI was low and high was 76 and 33% at 5 years (P < 0.0001, log rank). Similar statistically significant differences were observed when the TURP and needle biopsy groups were analyzed separately. Cox proportional hazards regression showed that dichotomized Ki67-LI was an independent correlate of bNED, along with pretreatment PSA, Gleason score, and clinical stage.

CONCLUSIONS

The Ki67-LI obtained from pretreatment prostate cancer tissue is a strong independent predictor of failure after radiotherapy using biochemical criteria. This prognostic factor was equally valuable for patients diagnosed by TURP or needle biopsy.

Stereotactically guided conformal radiotherapy for progressive low-grade gliomas of childhood

PURPOSE

To describe the rationale, technique, and early results of stereotactically guided conformal radiotherapy (SCRT) in the treatment of progressive or inoperable low-grade gliomas (LGGs) of childhood.

METHODS AND MATERIALS

Between September 1994 and May 1999, 14 children (median age 6 years, range 5-16) with LGG were treated with SCRT at the Royal Marsden NHS Trust. Tumors were located at the optic chiasm (n = 9), third ventricle (n = 2), hypothalamus, craniocervical junction, and pineal region (each n = 1). Four patients received chemotherapy before SCRT. Immobilization was in a Gill-Thomas-Cosman frame (n = 12) and subsequently in a specially designed pediatric version of the frame (n = 2). Stereotactic coordinates and the tumor were defined by CT scanning with a fiducial system and MRI fusion. The median tumor volume was 19.5 cm(3) (range 7.5-180). The planning target volume was defined as the area of enhancing tumor plus a 5-10-mm margin. The treatment technique consisted of 4 isocentric, noncoplanar, conformal, fixed fields. Treatment was delivered in 30-33 daily fractions to a total dose of 50-55 Gy.

RESULTS

SCRT was well tolerated, with transient hair loss the only acute toxicity. The median follow-up was 33 months (range 2-53). At 6 months after SCRT, 4 of 12 children with neurologic deficits improved and 5 remained stable. Twelve children were available for MRI evaluation. Two had a complete response, 6 a partial response, and 4 stable disease. One child with optic chiasm glioma had local progression at 25 months, and 1 developed diffuse leptomeningeal disease without local progression at 27 months. The 3-year local progression-free survival and overall survival rate after SCRT was 87% and 100%, respectively, compared with 89% and 98% for an historic control treated with conventional RT. New endocrine deficiencies were noted in 2 children after a follow-up of 20 and 23 months.

CONCLUSION

SCRT is a feasible, high-precision technique of RT for children with LGGs for whom RT is considered appropriate. The local control and acute toxicity of SCRT are comparable to a historic control of patients with conventionally delivered RT. The frequency of delayed hypothalamic-pituitary axis dysfunction reflects tumor location adjacent to the hypothalamus and pituitary. Additional follow-up is required to demonstrate that SCRT contributes to a reduction in treatment-related late toxicity, while maintaining the local control achieved with conventionally delivered RT in children with progressive LGGs.

Simultaneous optimization of beam orientations and beam weights in conformal radiotherapy

A methodology for the concurrent optimization of beam orientations and beam weights in conformal radiotherapy treatment planning has been developed and tested on a cohort of five patients. The algorithm is based on a beam-weight optimization scheme with a downhill simplex optimization engine. The use of random voxels in the dose calculation provides much of the required speed up in the optimization process, and allows the simultaneous optimization of beam orientations and beam weights in a reasonable time. In the implementation of the beam-weight optimization algorithm just 10% of the original patient voxels are used for the dose calculation and cost function evaluation. A fast simulated annealing algorithm controls the optimization of the beam arrangement. The optimization algorithm was able to produce clinically acceptable plans for the five patients in the cohort study. The algorithm equalized the dose to the optic nerves compared to the standard plans and reduced the mean dose to the brain stem by an average of 4.4% (+/- 1.9, 1 SD), p value = 0.007. The dose distribution to the PTV was not compromised by developing beam arrangements via the optimization algorithm. In conclusion, the simultaneous optimization of beam orientations and beam weights has been developed to be routinely used in a realistic time. The results of optimization in a small cohort study show that the optimization can reliably produce clinically acceptable dose distributions and may be able to improve dose distributions compared to those from a human planner.

A comparison of multileaf collimator with conformal blocks for the boost phase of dose-escalated conformal prostate radiotherapy

A multileaf collimator (MLC) is compared with conformal blocks for delivering the boost phase of dose-escalated conformal prostate radiotherapy. When using conformal blocks, the volume of rectum irradiated to 90% (V90) is lower (1.4+/-1.3%, 1 SD) for a three-field plan with gantry angles 0 degree, 90 degrees, 270 degrees than for a six-field plan with gantry angles 50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees (2.1 +/- 1.3%, P = 0.002). However, when using an MLC in which the leaves and wedge are oriented at right angles, V90 is higher (4.7 +/- 3.0%) for a three-field plan than for a six-field plan (2.7 +/- 1.6%, P=0.05). The larger increase in V90 for the three-field plan when changing from conformal blocks to MLC is mainly due to the limitation imposed upon the MLC orientation by the use of wedges.

Evaluation of the optimal co-planar field arrangement for use in the boost phase of dose escalated conformal radiotherapy for localized prostate cancer

The aim of this study was to determine the optimal co-planar beam arrangement from a variety of three-field (3F), four-field (4F) and six-field (6F) plans for the boost phase of a dose escalated conformal radiotherapy schedule. Three selected plans (3F 0 degrees, 90 degrees, 270 degrees plan, 4F 45 degrees, 90 degrees, 270 degrees, 315 degrees plan and 6F 40 degrees, 90 degrees, 115 degrees, 245 degrees, 270 degrees, 320 degrees plan) were compared with reference plans (3F 0 degrees, 120 degrees, 240 degrees plan, 4F 0 degrees, 90 degrees, 180 degrees, 270 degrees plan, 6F 55 degrees, 90 degrees, 125 degrees, 235 degrees, 270 degrees, 305 degrees plan and 6F 50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees plan) in 10 patients. Doses of 64 Gy and 74 Gy were prescribed to the isocentre using 6 MV photons. The boost planning target volume comprised the prostate gland alone without a margin. Plans were compared by means of rectal volumes irradiated to >50% (V50), >80% (V80) and >90% (V90) of the prescribed dose. Irradiated volumes were also measured for the bladder (V90) and the femoral heads (V70). All optimal 3F, 4F and 6F plans gave lower irradiated rectal V80 and V90 levels than their corresponding reference plan. The 3F (0 degrees, 90 degrees, 270 degrees) plan consistently provided lower irradiated rectal levels at V50 to V90, with acceptable bladder and femoral head doses compared with the other plans in the study. When the 6F (50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees) plan used at our institution for the boost phase was compared with the 3F (0 degrees, 90 degrees, 270 degrees) plan, the rectal V50 was reduced from 20.8+/-5.2%, to 12.6+/-5.1%, the rectal V80 was reduced from 8.7+/-2.9% to 6.5+/-3.1% and the rectal V90 was reduced from 5.5+/-2.1% to 3.9+/-2.0% (all p<0.001). The bladder V90 and the femoral heads V70 levels were equivalent. For the boost phase when escalating the dose from 64 Gy to 74 Gy, the co-planar plan that allowed optimal rectal sparing was a 3F beam arrangement using gantry angles of 0 degrees, 90 degrees and 270 degrees. This 3F plan provided improved rectal sparing compared with the 6F (50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees) beam arrangement currently used at our institution, with equivalent and acceptable bladder and femoral head doses.

Correlations between dose-surface histograms and the incidence of long-term rectal bleeding following conformal or conventional radiotherapy treatment of prostate cancer

BACKGROUND AND PURPOSE

In a randomized trial, the incidence of rectal bleeding among patients treated for prostate cancer using conformal radiotherapy was significantly lower (p = 0.002) than that among those treated conventionally. Here the relationship between rectal dose distributions and incidences of bleeding is assessed.

METHODS AND MATERIALS

Rectal dose-surface histograms (DSHs) have been calculated for 79 trial patients. The relationship between the DSHs and incidences of Grade 1-3 bleeding has been explored using both semiempiric and biologic (parallel) model-based approaches.

RESULTS

Semiempiric analysis of the trial data suggests that it is more useful to work with DSH fractional surface areas multiplied by outlined rectal lengths than with either raw DSH fractional areas or fractional areas multiplied by absolute total outlined rectal surface area. Fitting the parallel model to length-multiplied rectal DSHs and complication data reveals the existence of a significant volume effect, the rate of Grade 1-3 bleeding falling by 1.1% (95% confidence interval [0.04, 2.2]%) for each 1% decrease in the fraction of rectal wall (outlined over an 11-cm length) receiving a dose of more than 57 Gy.

CONCLUSION

The existence of this volume effect suggests that dose escalation can be achieved using conformal techniques, although the extent to which doses may be safely escalated cannot be reliably estimated from the trial data.

Radiotherapy planning of the pelvis using distortion corrected MR images: the removal of system distortions

Image distortion is an important consideration in the use of magnetic resonance (MR) images for radiotherapy planning. The distortion is a consequence of system distortion (arising from main magnetic field inhomogeneity and nonlinearities in the applied magnetic field gradients) and of effects arising from the object/patient being imaged. A two stage protocol has been developed to correct both system and object-induced distortion in pelvic images which incorporates measures to maintain the quality, accuracy and consistency of the imaging and correction procedures. The first stage of the correction procedure is described here and involves the removal of system distortion. Object- (patient-) induced effects will be described in a subsequent work. Images are acquired with the patient lying on a flat rigid bed, which reproduces treatment conditions. A frame of marker tubes surrounding the patient and attached to the bed provides quality assurance data in each image. System distortions in the three orthogonal planes are mapped using a separate phantom, which fits closely within the quality control frame. Software has been written which automates the measurement and checking of the many marker positions which the test objects generate and which ensures that patient data are acquired using a consistent imaging protocol. Results are presented which show that the scanner and the phantoms used in measuring distortion give highly reproducible results with mean changes of the order of 0.1 mm between repeated measurements of marker positions in the same imaging session. Effective correction for in plane components of system distortion is demonstrated.

Acquired immunodeficiency syndrome-related primary cerebral lymphoma: response to irradiation

Acquired immunodeficiency syndrome-related primary cerebral lymphoma (AIDS-PCL) is uncommon. Fourteen cases of presumed AIDS-PCL between 1986 and 1995 were reviewed retrospectively in order to characterize the natural history, and the response to radiotherapy. The median age was 38 years (range 24-65). The median interval between seropositive diagnosis of HIV and AIDS-PCL was 28 months (range 5-113). The median duration of symptoms was 2 weeks (range 0.2-12). At presentation, the Eastern Cooperative Oncology Group performance status (PS) was PS1 (2/14 patients), PS2 (6/14) and PS3 (6/14). The symptoms and signs were non-specific and depended on the site and extent of cerebral involvement. There was no characteristic pattern of brain imaging in terms of size, number, location or pattern of contrast enhancement of the cerebral lesions. Nine patients received various fractionation-dose schedules (range 8-50 Gy). Complete and partial responses were seen in 2/9 and 3/9 cases, respectively. Clinical stabilization of neurological symptoms was noted in 3/9 cases and disease progression in 1/9. The median survival times (MST) from presentation for irradiated and non-irradiated patients were 9.3 and 2.1 weeks, respectively (range 0.9-43.1). Although patient selection introduced bias, there appears to be a modest improvement in MST for treated patients. The MST with radiotherapy alone remains poor, but radiotherapy may provide palliation. For some selected patients, a prolonged response is possible.

An evaluation of three-field coplanar plans for conformal radiotherapy of prostate cancer

BACKGROUND AND PURPOSE

A series of coplanar three-field configurations for two different clinical treatment volumes, prostate only (PO) and prostate plus seminal vesicles (PSV) were studied to determine the optimal three-field plan arrangement for prostate radiotherapy.

MATERIALS AND METHODS

A variety of conformal three-field 6 MV plans prescribed to both 64 and 74 Gy were created for PO and PSV volumes in each of ten patients. For description, the orientation of each sequential beam was named in a clockwise fashion. Plans included series with arrangements of 0 degrees, 60-150 degrees, 210-300 degrees; 0 degrees, 90 degrees, 225-255 degrees; 90 degrees, 210-240 degrees, 300-330 degrees and a four-field (4F) box plan for comparison. Six-hundred and eighty plans were compared using the rectal volume irradiated to greater than 50% (V(50)), 80% (V(80)), and 90% (V(90)) of the prescribed dose, normal tissue complications (NTCP) for rectum, bladder, and femoral heads (FH), and tumour control probabilities (TCP). FH tolerance was set at 52 Gy to 10% volume.

RESULTS

In comparing the 34 different three-field configurations for each of the PO and PSV groups, the greatest rectal sparing was achieved by a three-field plan with gantry angles of 0 degrees, 90 degrees, 270 degrees (PO: rectal V(80)=22.8+/-5.5% (1S.D.), V(90)=18.4+/-5.7%, and PSV: rectal V(80)=41.9+/-5.8%, V(90)=35.5+/-5.9%). This also improved on the 4F-box plan (PO: rectal V(80)=26.0+/-5.8%, V(90)=21.4+/-5.2%, P<0.001; and PSV: rectal V(80)=47.3+/-5.5%, V(90)=41.6+/-5.1%, P<0.001). The worst rectal sparing was seen with the 0 degrees, 120 degrees, 240 degrees plan (PO: rectal V(80)=35.2+/-8.0%, V(90)=30.3+/-7.1%, P<0.001; and PSV: rectal V(80)=65.7+/-9.0%, V(90)=58.8+/-8.8%, P<0.001). In the PO group, the increase in predicted rectal NTCP with dose escalation from 64 to 74 Gy was 3.3% using the 0 degrees, 90 degrees, 270 degrees plan, 4.7% with the 4F-box plan, and 6.9% with the 0 degrees, 120 degrees, 240 degrees plan. In the PSV group, dose escalation increased the predicted rectal NTCP by 7.9, 10.1 and 15.7% for the 0 degrees, 90 degrees, 270 degrees plan, 4F-box plan, and 0 degrees, 120 degrees, 240 degrees plan, respectively.

CONCLUSIONS

For both PO and PSV volumes, the three-field plan which afforded the greatest rectal sparing with acceptable bladder and femoral head doses was the 0 degrees, 90 degrees, 270 degrees plan. This plan also improved on the 4F-box. The increase in predicted rectal NTCP when escalating dose from 64 to 74 Gy was smaller using this plan compared to either the three-field 0 degrees, 120 degrees, 240 degrees plan or the 4F-box plan.

A Comparison of clinical target volumes determined by CT and MRI for the radiotherapy planning of base of skull meningiomas

PURPOSE

To assess the utility of image registration and to compare the localization of clinical target volumes (CTV) using CT and MRI for patients with base of skull meningiomas undergoing radiotherapy.

METHODS AND MATERIALS

Seven patients were imaged using CT and a T1-weighted MR volumetric sequence. Following image registration using a chamfer-matching algorithm, transaxial MR slices were reconstructed to match the planning CT slices. The accuracy of the image fusion was assessed in a preliminary study with matching accuracy better than 1.5 mm. The CTV in each patient was separately segmented by two independent observers for both CT and reconstructed MR image sets. Scalar and vector assessments were made of the difference in radial extent between the two outlines on each transaxial plane for all patients. A positive vector value corresponded to a greater extension of the tumor on MR compared to CT and vice versa. Scalar measurements compared the modulus of the differences between MR and CT, regardless of which volume was more extensive. Qualitative comparisons were also performed.

RESULTS

Interobserver difference was small with a mean (+/- 1SD) volume difference of 1.5 +/- 1.5 cm(3) for CT and 0.5 +/- 1.0 cm(3) for MRI. The mean CT- and MR- CTVs were 17.6 +/-10.8 and 19.6 +/-14.2 cm(3) respectively. The mean overlap and composite volumes were 13.8 +/-10. 1 and 23.3 +/-14.8 cm(3) respectively. Average scalar differences in the left, right, anterior, and posterior directions were 6.0 +/- 7.0, 3.3 +/- 2.5, 4.9 +/- 3.9, and 4.5 +/- 5.0 mm respectively. The average vector differences were 3.3 +/- 8.5, -0.3 +/- 3.8, 1.1 +/- 5. 8, 1.5 +/- 6.4 mm (for left, right, anterior, and posterior directions respectively). Qualitatively, MR appeared to discern more tumor involvement in soft tissue regions adjacent to the skull base whereas CT appeared to provide larger target volumes within bony regions.

CONCLUSIONS

MRI appeared to define CTVs that were larger but not inclusive of CT-defined CTVs. Although the average vector differences were small, the differences on individual borders could be large. In some instances, the CT or MR volumes were vastly different, each providing separate information. Therefore, the use of MRI and CT is complementary. Until accurate histological confirmation of disease extent is available, it is prudent to consider composite CT/MR volumes for the radiotherapy planning of base of skull meningiomas.