Optimization of the oblique angles in the treatment of prostate cancer during six-field conformal radiotherapy

Randomised pilot study of dose escalation using conformal radiotherapy in prostate cancer: long-term follow-up

BACKGROUND

Radical three-dimensional conformal radiotherapy (CFRT) with initial androgen suppression (AS) is a standard management for localised prostate cancer (PC). This pilot study evaluated the role of dose escalation and appropriate target volume margin. Here, we report long-term follow-up.

METHODS

Eligible patients had T1b-T3b N0 M0 PC. After neoadjuvant AS, they were randomised to CFRT, giving (a) 64 Gy with either a 1.0- or 1.5-cm margin and (b) ±10 Gy boost to the prostate alone.

RESULTS

One hundred and twenty-six men were randomised and treated. Median follow-up was 13.7 years. The median age was 66.6 years at randomisation. Median presenting prostate-specific antigen (PSA) was 14 ng ml(-1). Sixty-four out of 126 patients developed PSA failure. Forty-nine out of 126 patients restarted AS, 34 out of 126 developed metastases and 28 out of 126 developed castrate-resistant prostate cancer (CRPC). Fifty-one out of 126 patients died; 19 out of 51 died of PC. Median overall survival (OS) was 14.4 years. Although escalated dose results were favourable, no statistically significant differences were seen between the randomised groups; PSA control (hazard ratio (HR): 0.77 (95% confidence interval (CI): 0.47-1.26)), development of CRPC (HR: 0.81 (95% CI: 0.40-1.65)), PC-specific survival (HR: 0.59 (95% CI:0.23-1.49)) and OS (HR: 0.81 (95% CI: 0.47-1.40)). There was no evidence of a difference in PSA control according to margin size (HR: 1.01 (95% CI: 0.61-1.66)).

INTERPRETATION

Long-term follow-up of this small pilot study is compatible with a benefit from dose escalation, but confirmation from larger trials is required. There was no obvious detriment using the smaller radiotherapy margin.

Dose distribution in 3-dimensional conformal radiotherapy for prostate cancer: comparison of femur doses for four treatment techniques

Purpose: Conformal radiotherapy of the prostate is an increasingly common technique in the treatment of prostate cancer. When using 3D conformal radiotherapy (CFRT) methods, it is desirable to protect the vital structures such as bladder, rectum, and femur. In this study, our aim was to compare the femur head doses resulting from co-planar beam arrangements in four-field (4F), five-field (5F), six-field (6F) and seven-field (7F) treatment plans, in a dose-escalated CFRT schedule.

Materials and Methods: From January 2005 to December 2006, at Istanbul University Medical Faculty of Radiation Oncology Clinic, a total of 22 patients with carcinoma of the prostate had been scanned using computed tomography (CT) (0.50 mm) in the supine position. During the CT scanning which used the Sim Pro (CMD–USA) programme, planned target volume (PTV), clinical target volume (CTV), and dose volumes received by the bladder, rectum and femur heads were recorded and dose–volume histogram (DVH) were created. The dose volume relating to prostate and seminal vesicles was termed CTV 1, and the dose volume relating to prostate alone was termed CTV 2. During the formation of PTV, into CTV 1, from the anterior-superior-inferior 8 mm, and from posterior 5 mm tolerance were taken into account. After volume determination is calculated using XiO (CMS-USA) 3D treatment planning computer, each patient 4F (45° – 25%, 135° – 25%, 225° – 25%, 315° – 25%), 5F (0° – 20%, 45° – 20%, 90° – 20%, 270° – 20%, 315° – 20%), 6F (45° – 20%, 90° – 10%, 135° 20%, 315° – 20%, 270° – 10%, 225° – 20%) and 7F (0° – 4%, 45° – 12.9%, 90° – 22.2%, 135° – 12.9%, 315° – 12.9%, 270° – 22.2%, 225° – 12.9%) was entered; 70 – 76 Gy was calculated to be given to prostate lodge. With the use of Siemes Oncor, 18 MV photons CFRT was applied. In DVH analysis, following were observed: V50, minimum and maximum doses for head of left femur and right femur total doses.

Results: Our statistical evaluation was made using SPSS software, and we found femur doses following; 4F V50 1030 cGy (minimum 58, maximum 1390), 5F V50 2425 cGy (minimum 540, maximum 3631), 6F V50 1769 cGy (minimum 1234, maximum 3912) and 7F V50 3230 cGy (minimum 2150, maximum 4137). In comparing different techniques, the greatest rectal sparing was achieved by the 5F plan. (Rectal: 5F V%25 = 59.90 ± 6.8 Gy, 4F V%25 = 62.30 ± 10.3 Gy, 6F V%25 = 69.36 ± 5.7 Gy, 7F V%25 = 61.32 ± 7.3 Gy). The greatest femoral head sparing was achieved by the 4F techniques. When paired samples t-test was made, we found considerable lower femur doses for 4F techniques (p = 0.05).

Conclusion: We concluded that, during radiotherapy to treat carcinoma of the prostate, the dose received by the rectum is the most important factor to consider, given the potential for late toxicity in this organ. However, while using lateral fields (90–270°) so as to protect the rectum, the doses received by the femur heads were observed to be higher. Especially in older patients, the critical doses of 52 Gy for TD5/5 and 65 Gy for TD 50/5 were observed to be not reached late toxicity for 4F, 5F, 6F and 7F.

Multibeam tomotherapy: a new treatment unit devised for multileaf collimation, intensity-modulated radiation therapy

A fully integrated system for treatment planning, application, and verification for automated multileaf collimator (MLC) based, intensity-modulated, image-guided, and adaptive radiation therapy (IMRT, IGRT and ART, respectively) is proposed. Patient comfort, which was the major development goal, will be achieved through a new unit design and short treatment times. Our device for photon beam therapy will consist of a new dual energy linac with five fixed treatment heads positioned evenly along one plane but one electron beam generator only. A minimum of moving parts increases technical reliability and reduces motion times to a minimum. Motion is allowed solely for the MLCs, the robotic patient table, and the small angle gantry rotation of +/- 36 degrees. Besides sophisticated electron beam guidance, this compact setup can be built using existing modules. The flattening-filter-free treatment heads are characterized by reduced beam-on time and contain apertures restricted in one dimension to the area of maximum primary fluence output. In the case of longer targets, this leads to a topographic intensity modulation, thanks to the combination of "step and shoot" MLC delivery and discrete patient couch motion. Owing to the limited number of beam directions, this multislice cone beam serial tomotherapy is referred to as "multibeam tomotherapy." Every patient slice is irradiated by one treatment head at any given moment but for one subfield only. The electron beam is then guided to the next head ready for delivery, while the other heads are preparing their leaves for the next segment. The "Multifocal MLC-positioning" algorithm was programmed to enable treatment planning and optimize treatment time. We developed an overlap strategy for the longitudinally adjacent fields of every beam direction, in doing so minimizing the field match problem and the effects of possible table step errors. Clinical case studies show for the same or better planning target volume coverage, better organ-at-risk sparing, and comparable mean integral dose to the normal tissue a reduction in treatment time by more than 50% to only a few minutes in comparison to high-quality 3-D conformal and IMRT treatments. As a result, it will be possible to incorporate features for better patient positioning and image guidance, while sustaining reasonable overall treatment times at the same time. The virtual multibeam tomotherapy design study TOM'5-CT contains a dedicated electron beam CT (TOM'AGE) and an objective optical topometric patient positioning system (TOPOS). Thanks to the wide gantry bore of 120 cm and slim gantry depths of 70 cm, patients can be treated very comfortably, in all cases tumor-isocentrically, as well as with noncoplanar beam arrangements as in stereotactic radiosurgery with a couch rotation of up to +/- 54 degrees. The TOM'5 treatment unit on which this theoretical concept is based has a stand-alone depth of 40 cm and an outer diameter of 245 cm; the focus-isocenter distance of the heads is 100 cm with a field size of 40 cm x 7 cm and 0.5 cm leaves, which operate perpendicular to the axis of table motion.

Forward-planning intensity-modulated radiotherapy technique for prostate cancer

In this study, we present an intensity‐modulated radiotherapy technique based on forward planning dose calculations to provide a concave dose distribution to the prostate and seminal vesicles by means of modified dynamic arc therapy (M‐DAT). Dynamic arcs (350 degrees) conforming to the beam's eye view of the prostate and seminal vesicles while shielding the rectum, combined with two lateral oblique conformal fields (15 degrees with respect to laterals) fitting the prostate only, were applied to deliver doses of 78 Gy and 61.23 Gy in 39 fractions to the prostate and seminal vesicles respectively. Dynamic wedges (45 degrees of thick end, anteriorly oriented) were used with conformal beams to adjust the dose homogeneity to the prostate, although in some cases, hard wedges (30 degrees of thick part, inferiorly oriented) were used with arcs to adjust the dose coverage to the seminal vesicles. The M‐DAT was applied to 10 patients in supine and 10 patients in prone positioning to determine the proper patient positioning for optimum protection of the rectum. The M‐DAT was compared with the simplified intensity‐modulated arc therapy (SIMAT) technique, composed of three phases of bilateral dynamic arcs. The mean rectal dose in M‐DAT for prone patients was 22.5±5.1 Gy; in M‐DAT and SIMAT for supine patients, it was 30.2±5.1 Gy and 39.4±6.0 Gy respectively. The doses to 15%, 25%, 35%, and 50% of the rectum volume in M‐DAT for prone patients were 44.5±10.2 Gy, 33.0±8.2 Gy, 25.3±6.4 Gy, and 16.3±5.6 Gy respectively. These values were lower than those in M‐DAT and in SIMAT for supine patients by 7.7%, 18.2%, 22.4%, and 28.5% and by 25.0%, 32.1%, 34.9%, and 41.9% of the prescribed dose (78 Gy) respectively. Ion chamber measurements showed good agreement of the calculated and measured isocentric dose (maximum deviation of 3.5%). Accuracy of the dose distribution calculation was evaluated by film dosimetry using a gamma index, allowing 3% dose variation and 4 mm distance to agreement as the individual acceptance criteria in prostate and seminal vesicle levels alike for all supine and prone patients. We found that fewer than 10% of the pixels in the dose distribution of the calculated area of 10×10−cm failed the acceptance criteria. These pixels were observed mainly in the low‐dose regions, particularly at the level of the seminal vesicles.

In conclusion, the single‐phase M‐DAT technique with patients in the prone position was found to provide the intended coverage of the prescribed doses to the prostate and seminal vesicles with improved protection for the rectum. Accordingly, M‐DAT has replaced non‐modulated conformal radiotherapy or SIMAT as the standard treatment for prostate cancer in our department.

PACS number: 87.53.Tf

The early toxicity of escalated versus standard dose conformal radiotherapy with neo-adjuvant androgen suppression for patients with localised prostate cancer: Results from the MRC RT01 trial (ISRCTN47772397)

BACKGROUND

Five-year disease-free survival rates for localised prostate cancer following standard doses of conventional radical external beam radiotherapy are around 80%. Conformal radiotherapy (CFRT) raises the possibility that radiotherapy doses can be increased and long-term efficacy outcomes improved, with safety an important consideration.

METHODS

MRC RT01 is a randomised controlled trial of 862 men with localised prostate cancer comparing Standard CFRT (64Gy/32f) versus Escalated CFRT (74Gy/37f), both administered with neo-adjuvant androgen suppression. Early toxicity was measured using physician-reported instruments (RTOG, LENT/SOM, Royal Marsden Scales) and patient-reported questionnaires (MOS SF-36, UCLA Prostate Cancer Index, FACT-P).

RESULTS

Overall early radiotherapy toxicity was similar, apart from increased bladder, bowel and sexual toxicity, in the Escalated Group during a short immediate post-radiotherapy period. Toxicity in both groups had abated by week 12. Using RTOG Acute Toxicity scores, cumulative Grade 2 bladder and bowel toxicity was 38% and 30% for Standard Group and 39% and 33% in Escalated Group, respectively. Urinary frequency (Royal Marsden Scale) improved in both groups from pre-androgen suppression to 6 months post-radiotherapy (p<0.001), but bowel and sexual functioning deteriorated. This pattern was supported by patient-completed assessments. Six months after starting radiotherapy the incidence of RTOG Grade > or = 2 side-effects was low (<1%); but there were six reports of rectal ulceration (6 Escalated Group), six haematuria (5 Escalated Group) and eight urethral stricture (6 Escalated Group).

CONCLUSIONS

The two CFRT schedules with neo-adjuvant androgen suppression have broadly similar early toxicity profiles except for the immediate post-RT period. At 6 months and compared to before hormone therapy, bladder symptoms improved, whereas bowel and sexual symptoms worsened. These assessments of early treatment safety will be complemented by further follow-up to document late side-effects and efficacy.

Automatic selection of non-coplanar beam directions for three-dimensional conformal radiotherapy

An algorithm is described, based on ray-tracing and the beam's-eye-view, that exhaustively searches all permitted beam directions. The evaluation of the search is based on a general cost function that can be adapted to the clinical objectives by means of parameters and weighting factors. The approach takes into account the constraints of the linear accelerator by discarding beam directions that are not permitted. A sensitivity analysis was carried out to determine appropriate parameters for different sized organs, and a prostate case was used to benchmark the approach. The algorithm was also applied to two clinical cases (brain and sinus) to test the benefits of the approach compared with manual angle selection. The time to perform a beam direction search was approximately 2 min for the coplanar and 12 min for the non-coplanar beam space. The angles obtained for the prostate case compared well with reports in the literature. For the brain case, the mean dose to the right and left optic nerves was reduced by 12% and 50%, respectively, whilst the target dose uniformity was improved. For the sinus case, the mean doses to the right and left parotid glands were reduced by 54% and 46%, respectively, to the right and left optic nerves by 37% and 62%, respectively, and to the optic chiasm by 39%, whilst the target dose uniformity was also improved. For the clinical cases the plans based on optimized beam directions were simpler and resulted in better sparing of critical structures compared with plans based on manual angle selection. The approach provides a practical alternative to elaborate and time consuming beam angle optimization schemes and is suitable for routine clinical usage.

Phase III pilot study of dose escalation using conformal radiotherapy in prostate cancer: PSA control and side effects

Radical radiotherapy is a standard form of management of localised prostate cancer. Conformal treatment planning spares adjacent normal tissues reducing treatment-related side effects and may permit safe dose escalation. We have tested the effects on tumour control and side effects of escalating radiotherapy dose and investigated the appropriate target volume margin. After an initial 3-6 month period of androgen suppression, 126 men were randomised and treated with radiotherapy using a 2 by 2 factorial trial design. The initial radiotherapy tumour target volume included the prostate and base of seminal vesicles (SV) or complete SV depending on SV involvement risk. Treatments were randomised to deliver a dose of 64 Gy with either a 1.0 or 1.5 cm margin around the tumour volume (1.0 and 1.5 cm margin groups) and also to treat either with or without a 10 Gy boost to the prostate alone with no additional margin (64 and 74 Gy groups). Tumour control was monitored by prostate-specific antigen (PSA) testing and clinical examination with additional tests as appropriate. Acute and late side effects of treatment were measured using the Radiation Treatment and Oncology Groups (RTOG) and LENT SOM systems. The results showed that freedom from PSA failure was higher in the 74 Gy group compared to the 64 Gy group, but this did not reach conventional levels of statistical significance with 5-year actuarial control rates of 71% (95% CI 58-81%) in the 74 Gy group vs 59% (95% CI 45-70%) in the 64 Gy group. There were 23 failures in the 74 Gy group and 33 in the 64 Gy group (Hazard ratio 0.64, 95% CI 0.38-1.10, P=0.10). No difference in disease control was seen between the 1.0 and 1.5 cm margin groups (5-year actuarial control rates 67%, 95% CI 53-77% vs 63%, 95% CI 50-74%) with 28 events in each group (Hazard ratio 0.97, 95% CI 0.50-1.86, P=0.94). Acute side effects were generally mild and 18 weeks after treatment, only four and five of the 126 men had persistent > or =Grade 1 bowel or bladder side effects, respectively. Statistically significant increases in acute bladder side effects were seen after treatment in the men receiving 74 Gy (P=0.006), and increases in both acute bowel side effects during treatment (P=0.05) and acute bladder sequelae (P=0.002) were recorded for men in the 1.5 cm margin group. While statistically significant, these differences were of short duration and of doubtful clinical importance. Late bowel side effects (RTOG> or =2) were seen more commonly in the 74 Gy and 1.5 cm margin groups (P=0.02 and P=0.05, respectively) in the first 2 years after randomisation. Similar results were found using the LENT SOM assessments. No significant differences in late bladder side effects were seen between the randomised groups using the RTOG scoring system. Using the LENT SOM instrument, a higher proportion of men treated in the 74 Gy group had Grade > or =3 urinary frequency at 6 and 12 months. Compared to baseline scores, bladder symptoms improved after 6 months or more follow-up in all groups. Sexual function deteriorated after treatment with the number of men reporting some sexual dysfunction (Grade> or =1) increasing from 38% at baseline to 66% at 6 months and 1 year and 81% by year 5. However, no consistent differences were seen between the randomised groups. In conclusion, dose escalation from 64 to 74 Gy using conformal radiotherapy may improve long-term PSA control, but a treatment margin of 1.5 cm is unnecessary and is associated with increased acute bowel and bladder reactions and more late rectal side effects. Data from this randomised pilot study informed the Data Monitoring Committee of the Medical Research Council RT 01 Trial and the two studies will be combined in subsequent meta-analysis.

Selection of beam orientations in intensity-modulated radiation therapy using single-beam indices and integer programming

While the process of IMRT planning involves optimization of the dose distribution, the procedure for selecting the beam inputs for this process continues to be largely trial-and-error. We have developed an integer programming (IP) optimization method to optimize beam orientation using mean organ-at-risk (MOD) data from single-beam plans. Two test cases were selected in which one organ-at-risk (OAR) and four OARs were simulated, respectively, along with a PTV. Beam orientation space was discretized in 10 degrees increments. For each beam orientation, a single-beam plan without intensity modulation and without constraints on OAR dose was generated and normalized to yield a mean PTV dose of 2 Gy and the corresponding MOD was calculated. The degree of OAR sparing was related to the average OAR MODs resulting from the beam orientations utilized with improvements of up to 10% at some dose levels. On the other hand, OAR DVHs in the IMRT plans were insensitive to beam numbers (in the 6-9 range) for similar average single-beam MODs. These MOD data were input to an IP optimization process, which then selected specified numbers of beam angles as inputs to a treatment planning system. Our results show that sets of beam angles with lower average single-beam MODs produce IMRT plans with better OAR sparing than manually selected beam angles. To optimize beam orientations, weights were assigned to each OAR following MOD input to the IP which was subsequently solved using the branch-and-cut algorithm. Seven-beam orientations obtained from solving the IP were applied to the test case with four OARs and the resulting plan with a dose prescription of 63 Gy was compared with an equi-spaced beam plan. The IP selected beams produced dose-volume improvements of up to 40% for OARs proximal to the PTV. Further improvement in the DVH can be obtained by increasing the weights assigned to these OARs but at the expense of the remaining OARs.

(Non)-migration of radiopaque markers used for on-line localization of the prostate with an electronic portal imaging device

PURPOSE

Radiopaque gold markers can be implanted in the prostate to visualize its position on portal images during radiation therapy. This procedure assumes that the markers do not move within the prostate. In this work we test this assumptiom.

METHODS AND MATERIALS

Three markers were implanted transrectally in the prostate of patients undergoing external radiation therapy. An orthogonal pair of portal images was acquired periodically throughout the course of radiation therapy with an a-Si electronic portal imaging device (EPID). The marker coordinates were determined, and the distances between the implanted markers were recorded. The distance time trend is used to evaluate the magnitude of marker migration.

RESULTS

The average standard deviation (SD) of the distances between markers was 1.3 mm (range 0.44 to 3.04 mm). Three of the 11 patients show a SD larger than 2 mm. For these patients, all three distances show a simultaneous reduction with time, compatible with a shrinking of the prostate. All had been treated with neoadjuvant hormone therapy. For 1 of the 3 patients, this reduction in volume was confirmed with a repeat computed tomographic scan.

CONCLUSION

None of the 33 markers studied migrated significantly. The implantation of three radiopaque gold markers enables accurate and precise on-line verification of the prostate position during external beam radiation therapy. The use of three markers provides a tool to monitor prostate position and volume changes that can occur over time due to hormone or radiation therapy.

Serum prostate-specific antigen and survival after external beam radiotherapy for carcinoma of the prostate

OBJECTIVES

To evaluate the significance of pretreatment prostate-specific antigen (pPSA) levels as a predictor of overall survival simultaneously with previously established prognostic factors. The pPSA level is a major predictor of treatment failure after radiotherapy and surgery, but to date has not been shown to predict survival.

METHODS

This analysis was based on data from 927 patients with clinically localized prostate cancer treated with radiotherapy alone between 1987 and 1998. These patients were stratified into four prognostic risk groups, and multivariate analysis was used to determine the independent impact of pPSA level on PSA failure, progression-free survival (death from any cause after PSA failure), and overall survival (death from any cause).

RESULTS

In a multivariate analysis simultaneously considering the prognostic risk group, a pPSA level greater than or equal to 20 ng/mL was associated with a higher risk of PSA failure and worse progression-free and overall survival.

CONCLUSIONS

The pPSA level is an independent predictor of survival in patients initially treated with radiotherapy alone.

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS AND CONCLUSIONS

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

Conformal photon-beam radiotherapy of prostate carcinoma

Three-dimensional conformal radiotherapy is the recommended radiation technique for localized or locally advanced prostate cancer. In the past decades, external beam irradiation procedures have evolved in the context of technical developments of radiation and imaging equipment. The article summarizes these developments and gives a definition of new techniques and their potential advantages over conventional irradiation. It is meant to provide urologists and medical and radiation oncologists with a better comprehension of modern radiation treatment of prostate cancer and its possible improvements in the future.

Optically guided intensity modulated radiotherapy

BACKGROUND AND PURPOSE

Previously, we reported on development of an optically guided system for 3D conformal intracranial radiotherapy using multiple noncoplanar fixed fields. In this paper we report on the extension of our system for stereotactic fractionated radiotherapy to include intensity modulated static ports.

METHODS AND MATERIALS

A 3D treatment plan with maximum beam separation is developed in the stereotactic space established by an optically guided system. Gantry angles are chosen such that each beam has a unique entrance and exit pathway, avoids the critical structures, and has a minimal beam's eye view projection. Once, a satisfactory treatment plan is found using this geometric approach an inverse treatment plan is developed using the beam portals established previously. The purpose of adding inverse planing is two fold, on the one hand it allows further reduction of margins around the PTV, while on the other hand it affords the possibility of conformal avoidance of critical structures that are close to or abut the PTV.

RESULTS

The use of the optically guided system in conjunction with intensity modulated noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit smaller 90, 70, and 50% of prescription dose isodose volumes, improved PITV ratios, comparable or improved EUD, smaller NTD(mean) for the critical structures, and an inhomogeneity index that is within generally accepted limits.

CONCLUSION

Because optically guided technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, the planning target volume needs to be corrected only for the limitations of image resolution. Intensity modulated static beam radiotherapy planning then provides the user the ability to further reduce margins on the PTV and to conform very closely to this smaller target volume, and enhances the normal tissue sparing, and high degree of conformality possible with 3D conformal radiotherapy. In addition, since optically guided technology affords improved patient localization and online monitoring of patient position during treatment delivery it allows for safe and efficient delivery of intensity modulated radiotherapy.

Toxicity following high-dose three-dimensional conformal and intensity-modulated radiation therapy for clinically localized prostate cancer

OBJECTIVES

To report the toxicity profile of patients treated with three-dimensional conformal radiation therapy (3D-CRT) or intensity-modulated radiation therapy (IMRT) receiving doses of 82 Gy or more to portions of their prostate.

METHODS

Forty-four patients treated with radiation therapy for prostate cancer between June 1992 and August 1998 at the University of California, San Francisco received a maximal dose within the target volume (Dmax) of 82 Gy or more. Eighteen patients were boosted selectively to a limited portion of their prostate using IMRT, whereas 26 patients were treated with 3D-CRT and had unselected "hot spots" within their prostate. The Radiation Therapy Oncology Group (RTOG) acute and late toxicity scales were used to score gastrointestinal (GI) and genitourinary (GU) morbidity.

RESULTS

Median follow-up and Dmax were 23.1 months (range 10.0 to 84.7) and 84.5 Gy (range 82.0 to 96.7), respectively. Of the patients, 59.1% and 34.1% developed some level of acute GU and GI toxicity, respectively. One patient experienced grade 3 acute GI toxicity. No other grade 3 or greater acute toxicity was observed. The 2-year actuarial rates for freedom from late GI and GU morbidity were 77.1% (95% confidence interval [CI] 60.4% to 87.5%) and 79.5% (95% CI 62.7% to 89.3%), respectively. Although no grade 3 or greater late GU morbidity has been observed to date, 3 patients experienced grade 3 late GI morbidity. However, these cases involved rectal bleeding and were effectively managed with laser coagulation/fulguration.

CONCLUSIONS

Doses of 82 Gy or more to a portion of the prostate gland can be tolerated with acceptable morbidity. This observation supports the continued investigation of IMRT as a means for improving disease control in prostate cancer.

Potency preservation after three-dimensional conformal radiotherapy for prostate cancer: preliminary results

We sought to assess potency preservation after three-dimensional conformal radiotherapy (3D-CRT) in prostate cancer patients eligible for radical prostatectomy, conventional radiotherapy, 3D-CRT, or transperineal prostate implantation. Patients with more advanced disease are commonly treated with hormonal therapy, which can cause impotence, and were consequently excluded from the analysis. Between December 1991 and June 1998, 198 prostate cancer patients were treated with 3D-CRT at the University of California, Davis Medical Center. Fifty-two of these patients had a pretreatment prostate-specific antigen (PSA) level of 10.0 ng/ml or less, a Gleason score of 6 or less, and a 1997 AJCC clinical stage T1bN0M0 to T2bN0M0. One patient was not evaluable. None of the 51 evaluable patients had diabetes mellitus. In 40 patients, the prostate gland only was irradiated to a total dose of 66 to 79.2 Gy by using daily 1.8-Gy fractions. In 11 patients, the prostate and seminal vesicles were treated to 44 to 55.8 Gy. Lymph nodes were not included in the clinical target volume. The median age was 68 years, and the median length of follow-up was 15 months. Potency in this study is defined as an erection sufficient for vaginal penetration. Kaplan-Meier analysis was used to describe potency as a function of time after 3D-CRT. Of the 51 evaluable patients, 35 (69%) were potent, 15 were impotent, and 1 was sexually inactive before 3D-CRT. Kaplan-Meier estimates of the potency preservation rates 1, 2, and 3 years after 3D-CRT are 100%, 83%, and 63%, respectively. On multivariate analysis, age, total radiation dose, and a history of transurethral resection of the prostate did not significantly affect potency preservation rates. Three (43%) of 7 patients who became impotent after 3D-CRT and used sildenafil were subsequently able to achieve erections sufficient for vaginal penetration. The preliminary results reported herein suggest that approximately two thirds of prostate cancer patients will retain their potency 3 years after 3D-CRT. Further follow-up is necessary to assess long-term potency after 3D-CRT. Sildenafil should be considered in patients who develop radiation-induced impotence.

A high-precision system for conformal intracranial radiotherapy

PURPOSE

Currently, optimally precise delivery of intracranial radiotherapy is possible with stereotactic radiosurgery and fractionated stereotactic radiotherapy. We report on an optimally precise optically guided system for three-dimensional (3D) conformal radiotherapy using multiple noncoplanar fixed fields.

METHODS AND MATERIALS

The optically guided system detects infrared light emitting diodes (IRLEDs) attached to a custom bite plate linked to the patient's maxillary dentition. The IRLEDs are monitored by a commercially available stereo camera system, which is interfaced to a personal computer. An IRLED reference is established with the patient at the selected stereotactic isocenter, and the computer reports the patient's current position based on the location of the IRLEDs relative to this reference position. Using this readout from the computer, the patient may be dialed directly to the desired position in stereotactic space. The patient is localized on the first day and a reference file is established for 5 different couch positions. The patient's image data are then imported into a commercial convolution-based 3D radiotherapy planning system. The previously established isocenter and couch positions are then used as a template upon which to design a conformal 3D plan with maximum beam separation.

RESULTS

The use of the optically guided system in conjunction with noncoplanar radiotherapy treatment planning using fixed fields allows the generation of highly conformal treatment plans that exhibit a high degree of dose homogeneity and a steep dose gradient. To date, this approach has been used to treat 28 patients.

CONCLUSION

Because IRLED technology improves the accuracy of patient localization relative to the linac isocenter and allows real-time monitoring of patient position, one can choose treatment-field margins that only account for beam penumbra and image resolution without adding margin to account for larger and poorly defined setup uncertainty. This approach enhances the normal tissue sparing, high degree of conformality, and homogeneity characteristics possible with 3D conformal radiotherapy.

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.

Preliminary results of three-dimensional conformal radiotherapy as salvage treatment for a rising prostate-specific antigen level postprostatectomy

The purpose of this study is to determine the effectiveness of three-dimensional conformal radiotherapy delivered to the fossa of the prostate and seminal vesicles as salvage treatment for a prostate-specific antigen (PSA) level that becomes undetectable and subsequently begins to rise postprostatectomy. Between August 1994 and December 1997, 14 patients with prostate cancer whose PSA became undetectable after a radical prostatectomy subsequently developed a rising PSA, had no evidence of metastatic disease, and were treated with three-dimensional conformal radiotherapy at the University of California, Davis Cancer Center. Gleason scores ranged from 4 to 9 (29% of the patients had a Gleason score > or =8). The seminal vesicles were involved in three (21%) cases and the surgical margins were involved in seven (50%) cases. PSA values ranged from 0.3 to 6.7 (median: 0.7) ng/ml at the start of radiotherapy. Daily 1.8-2.0-Gy fractions were administered to total doses at isocenter ranging from 60.6 to 74.2 (median: 64.9) Gy. None of the patients received hormonal therapy. Follow-up ranged from 13 to 36 (median: 22) months. For patients with a preradiotherapy Hybritech PSA < or = 1.0 ng/ml, the Kaplan-Meier estimate of the 2-year biochemical disease-free survival rate is 67%, whereas for patients with a preradiotherapy PSA more than 1.0 ng/ml, the 2-year biochemical disease-free survival rate is 20% (p = 0.17). Because of the small number of patients, the difference is not statistically significant. A positive microscopic margin had no impact on the results obtained with salvage radiotherapy. Only one of four patients with a poorly differentiated adenocarcinoma remains free of disease. Acute toxicity was mild and did not require medication (Radiation Therapy Oncology Group grade I): four (29%) patients experienced genitourinary morbidity and three (21%) patients experienced gastrointestinal morbidity. With regard to late toxicity, one (7%) patient developed a urethral stricture requiring dilatation (Radiation Therapy Oncology Group grade III). All five patients who were potent at the start of radiotherapy remain potent. Medicare's median reimbursement for salvage three-dimensional conformal radiotherapy in this study ($7,512 in 1999 U.S. dollars) is equivalent to its reimbursement for a 17-month course of goserelin hormonal therapy. Patients with prostate cancer who develop an undetectable followed by a rising PSA postprostatectomy should be referred for salvage treatment with radiotherapy when their PSA is still less than or equal to 1.0 ng/ml. Salvage three-dimensional conformal radiotherapy is well tolerated and is less expensive than more than 17 months of goserelin.

Acute toxicity of three-dimensional conformal radiotherapy in prostate cancer patients eligible for implant monotherapy

PURPOSE

To assess the acute toxicity of three-dimensional conformal radiotherapy (3D-CRT) in prostate cancer patients eligible for implant monotherapy.

METHODS AND MATERIALS

Between December 1991 and June 1998, 198 prostate cancer patients were treated with 3D-CRT at the University of California Davis Medical Center. Fifty-two of these patients had a prostate-specific antigen (PSA) level </= 10.0 ng/ml, Gleason score </= 6, and a 1997 AJCC clinical stage T1bN0-T2bN0. Eleven (21%) patients received radiotherapy to the prostate and seminal vesicles; the remaining patients were treated to the prostate only. The 3D-CRT treatment planning guidelines in Radiation Therapy Oncology Group (RTOG) 9406 were followed after 1994 (similar treatment planning was used before the protocol became available). Typically, 4 oblique and 2 lateral fields were treated. All patients were seen at least weekly while under treatment, 1 month postirradiation and then every 3 months. Total radiation doses ranged from 66.0-79.2 Gy, with a median dose of 73.8 Gy in 41 fractions over 8 weeks. Acute toxicity is described according to the RTOG acute toxicity scoring system.

RESULTS

Overall, 3D-CRT was well-tolerated: 29% of patients experienced RTOG Grade 1 and 27% experienced Grade 2 acute lower gastrointestinal (GI) toxicity. Forty percent and 33% of patients experienced Grade 1 and 2 acute genitourinary (GU) toxicity, respectively. As expected, more acute morbidity, especially GI, was observed with a larger clinical target volume (prostate and seminal vesicles versus prostate only; p = 0. 05). Neoadjuvant hormonal therapy did not increase the incidence or severity of radiation-induced side effects. No acute toxicity >/= Grade 3, e.g., hourly nocturia, gross hematuria, diarrhea requiring parenteral support, narcotics for pain control, or catheterization for acute urinary retention, was observed.

CONCLUSION

Although relatively high doses of radiation are delivered to prostate cancers with 3D-CRT compared with conventional radiotherapy, 3D-CRT is surprisingly well-tolerated. No patients in the cohort eligible for implant monotherapy experienced acute toxicity >/= Grade 3.

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.

The effect of patient position and treatment technique in conformal treatment of prostate cancer

PURPOSE

The relative value of prone versus supine positioning and axial versus nonaxial beam arrangements in the treatment of prostate cancer remains controversial. Two critical issues in comparing techniques are: 1) dose to critical normal tissues, and 2) prostate stabilization.

METHODS AND MATERIALS

Ten patients underwent pretreatment CT scans in one supine and two prone positions (flat and angled). To evaluate normal tissue exposure, prostate/seminal vesicle volumes or prostate volumes were expanded 8 mm and covered by the 95% isodose surface by both 6-field axial and 4-field nonaxial techniques. A total of 280 dose-volume histograms (DVHs) were analyzed to evaluate dose to rectal wall and bladder relative to patient position and beam arrangement. A CT scan was repeated in each patient after 5 weeks of treatment. Prostate motion was assessed by comparing early to late scans by three methods: 1) center of mass shift, 2) superior pubic symphysis to anterior prostate distance, and 3) deviation of the posterior surface of the prostate.

RESULTS

For prostate (P) or prostate/seminal vesicle (P/SV) treatments, prone flat was advantageous or equivalent to other positions with regard to rectal sparing. The mechanism of rectal sparing in the prone position may be related to a paradoxical retraction of the rectum against the sacrum, away from the P/SV. Although there was no clear overall preference for beam arrangement, substantial improvements in rectal sparing could be realized for individual patients. In this limited number of patients, there was no convincing evidence prostate position was stabilized by prone relative to supine position.

CONCLUSIONS

Prone flat positioning was advantageous over other positions and beam arrangements in rectal sparing. This study suggests that patient position is a more critical a factor in conformal therapy than beam arrangement, and may improve the safety of dose escalation.

Impact of collimator leaf width on stereotactic radiosurgery and 3D conformal radiotherapy treatment plans

PURPOSE

The authors undertook a study to analyze the impact of collimator leaf width on stereotactic radiosurgery and 3D conformal radiotherapy treatment plans.

METHODS AND MATERIALS

Twelve cases involving primary brain tumors, metastases, or arteriovenous malformations that had been planned with BrainLAB's conventional circular collimator-based radiosurgery system were re-planned using a beta-version of BrainLAB's treatment planning software that is compatible with MRC Systems' and BrainLAB's micro-multileaf collimators. These collimators have a minimum leaf width of 1.7 mm and 3.0 mm, respectively, at isocenter. The clinical target volumes ranged from 2.7-26.1 cc and the number of static fields ranged from 3-5. In addition, for 4 prostate cancer cases, 2 separate clinical target volumes were planned using MRC Systems' and BrainLAB's micro-multileaf collimators and Varian's multileaf collimator: the smaller clinical target volume consisted of the prostate gland and the larger clinical target volume consisted of the prostate and seminal vesicles. For the prostate cancer cases, treatment plans were generated using either 6 or 7 static fields. A "PITV ratio," which the Radiation Therapy Oncology Group defines as the volume encompassed by the prescription isodose surface divided by the clinical target volume, was used as a measure of the quality of treatment plans (a PITV ratio of 1.0-2.0 is desirable). Bladder and rectal volumes encompassed by the prescription isodose surface, isodose distributions and dose volume histograms were also analyzed for the prostate cancer patients.

RESULTS

In 75% of the cases treated with radiosurgery, a PITV ratio between 1.0-2.0 could be achieved using a micro-multileaf collimator with a leaf width of 1.7-3.0 mm at isocenter and 3-5 static fields. When the clinical target volume consisted of the prostate gland, the micro-multileaf collimator with a minimum leaf width of 3.0 mm allowed one to decrease the median volume of bladder and rectum within the prescription isodose surface by 26% and 17%, respectively, compared to the multileaf collimator with a leaf width of 10 mm. Use of the 1.7 mm leaf width micro-multileaf collimator allowed one to decrease the median volume of bladder and rectum within the prescription isodose surface by 48% and 39%, respectively, compared to the multileaf collimator with a leaf width of 10 mm.

CONCLUSIONS

For most lesions treated with radiosurgery, the use of a micro-multileaf collimator with a leaf width of 1.7-3.0 mm at isocenter and 3-5 static fields allows one to meet the Radiation Therapy Oncology Group guidelines for treatment planning. Both planning and treatment are relatively straightforward with a micro-multileaf collimator, allowing for efficient treatment of non-spherical targets with either stereotactic radiosurgery or fractionated stereotactic radiotherapy. When the clinical target volume consists of the prostate gland, micro-multileaf collimators with a minimum leaf width of 1.7-3.0 mm allow one to spare more bladder and rectum than one can with a multileaf collimator that has a 10-mm leaf width based on an analysis of PITV ratios, isodose distributions, and dose volume histograms.

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.

Comparison of three-dimensional conformal radiation therapy and intensity-modulated radiation therapy systems

The use of three-dimensional conformal radiation therapy (3DCRT) has now become common practice in radiation oncology departments around the world. Using beam's eye viewing of volumes defined on a treatment planning computed tomography scan, beam directions and beam shapes can be selected to conform to the shape of the projected target and minimize dose to critical normal structures. Intensity-modulated radiation therapy (IMRT) can yield dose distributions that conform closely to the three-dimensional shape of the target volume while still minimizing dose to normal structures by allowing the beam intensity to vary across those shaped fields. Predicted dose distributions for patients with tumors of the prostate, nasopharynx, and paraspinal region are compared between plans made with 3DCRT programs and those with inverse-planned IMRT programs. The IMRT plans are calculated for either static or dynamic beam delivery methods using multileaf collimators. Results of these comparisons indicate that IMRT can yield significantly better dose distributions in some situations at the expense of additional time and resources. New technologies are being developed that should significantly reduce the time needed to plan, implement, and verify these treatments. Current research should help define the future role of IMRT in clinical practice.

A three-field arc technique (3-FAT) for treating prostate cancer

PURPOSE

We have previously designed two external beam radiotherapy techniques for treating prostate cancer. The seven-field, coplanar fixed beam technique resulted in dose distributions that were superior to other coplanar plans studied. The other technique using bilateral blocked arcs produced slightly higher doses to normal tissues but was far simpler to execute. We combined aspects of both these plans to produce a technique that was less complicated yet resulted in an improved dose distribution, i.e., to improve dose delivery to the clinical target volume (CTV) while minimizing doses to the rectum, bladder, and femoral heads.

METHODS AND MATERIALS

Twenty patients, previously treated at the University of California, San Francisco (UCSF) with radiotherapy for adenocarcinoma of the prostate, were studied. Each patient was treated with an immobilizer, urethrogram, and a preplanning CT scan. A previously employed, seven-field, coplanar, fixed beam technique was compared with a newly designed three-field, arc technique (3-FAT). This 3-FAT was designed using two equally weighted rotational beams, with nonuniform blocks, beginning in the lateral gantry position and spanning anteriorly 35 degrees. The two beams became noncoplanar by turning the table 20 degrees, bringing the patient's feet toward the gantry (inferior oblique arcs). An anterior inferior oblique (AIO), angled 20 degrees to the inferior of anterior was included for 10% of the daily treatment. Dose-volume histograms (DVH) were used to evaluate doses to adjacent critical structures. The dose to each critical structure was averaged and tabulated for the 20 patients. In addition, we compared normalized doses to adjacent structures using 3-FAT and seven-coplanar, fixed beams vs. a technique using four noncoplanar, fixed beams.

RESULTS

The three-field arc technique produced favorable dose distributions for the rectum, bladder, and femoral heads. Compared to the seven-field plan, employing the 3-FAT resulted in a 13% lower dose to 40% of the rectum, and 25% lower dose to 40% of the bladder. Compared to the four-field plan, employing the 3-FAT resulted in a 23% lower dose to 40% of the rectum, and 1% decrease in dose to 40% of the bladder. The three-field arc technique reduced the dose delivered to 40% of the femoral heads by approximately 45% when compared to the other techniques. Compared to other standard treatment techniques, the improvement in dose distribution was even greater.

CONCLUSIONS

The 3-FAT represents a technical improvement in the treatment of cancer of the prostate and seminal vesicles by minimizing the dose delivered to adjacent critical structures. The 3-FAT can incorporate the advances of multileaf collimation and digitally reconstructed radiographs to deliver treatment with cost effectiveness and technological efficiency.

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

BACKGROUND AND PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSION

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

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSIONS

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

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSION

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

The impact of isocenter placement errors associated with dose distributions used in irradiating prostate cancer

Historically, four perpendicular treatment fields or bilateral arcs have been used in the treatment of prostate cancer. "New techniques" including four conformal fields, seven conformal fields, 120 degrees bilateral conformal coplanar, and non-coplanar arc'ed beam arrangements, are replacing the "older" approaches. These techniques result in a reduction in doses to adjacent critical structures while covering the clinical target volume (CTV). This study, analyzes the impact of random or systematic isocenter displacement errors (IDE) associated with the delivery of radiotherapy, using the best of these "newer techniques". Dose Volume Histograms (DVH) were used to evaluate the dose to the prostate and surrounding normal tissues with 0.3 cm, 0.5 cm and 0.8 cm IDE. It was determined that IDE associated with fixed coplanar treatment techniques could reduced the prescribed dose to the prostate by 0-8%, the coplanar are technique reduced the prescribed prostate dose by 3-10%, and the noncoplanar conformal arc technique could lower the prescribed prostate dose by 0-5%. Predictably, 0.3 cm IDE found in the posterior and inferior direction increase the dose to the rectum by 5-12% and lowered the dose to the bladder by 4-8%. Errors in the superior and anterior direction increased the dose to the bladder by 4-8% and decreased the dose to the rectum by 8-10%. Errors in the right to left direction slightly increased the dose to the ipsilateral femoral head. Doses to the rectum and bladder associated with 0.5 cm and 0.8 cm IDE are significantly larger. The frequency and magnitude of IDE must be accounted for before higher doses can be delivered safety. Recognizing the impact of IDE on our ability to deliver the prescribed dose to the planning target volumes (PTV) could incorporate the impact of IDE during the planning process.

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

PURPOSE

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

METHODS AND MATERIALS

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

RESULTS

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

CONCLUSIONS

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