Daily Setup Variations Research Articles

SU-GG-J-30: Analysis of Daily Setup Variation with Tomotherapy Megavoltage Computed Tomography (MVCT)

Purpose: To evaluate setup variation for different sites using tomotherapy pretreatment megavoltage computed tomography (MVCT), and provide the reference margins for different anatomic sites. Method and Materials: Ninety‐two patients were positioned supinely the same as CT simulation. MVCT was used to verify patient position and target localization before each treatment. With anatomy registration tool, MVCT provided the real‐time tumor/organ shift coordinates, relative to the positions when the simulation CT was done. The thermoplastic face mask was used for H/N and brain treatment. Hip and pelvic Vac‐Lok™ cushions were used for prostate patients. There was no respiration suppression used for lung and abdomen patients. The setup variations in the inter‐fraction treatments were recorded and corrected for treatment. 2900 data points were analyzed for the 92 patients with the five different sites: head and neck, brain, prostate, lung and abdomen. Results: The mean inter‐fractional setup error for H/N and brain was smallest among the five sites analyzed. The mean setup error in the 3D translational for H/N, brain, prostate, abdomen and lung were 2.2mm, 2.3mm, 3.2mm, 4.4mm and 7.7mm respectively. The largest motion in lung was in the longitudinal direction, with mean error 6.0mm and standard deviation of 4.8mm. The mean rotational variation ranged from 0.2° to 0.5°, with the standard deviation from 0.7° to 0.9°. The system error and random error were analyzed and the suggested margin for H/N, brain, prostate, abdomen and lung in the direction of lateral, longitudinal and vertical ranged from 5.0 to 9.3 mm, 5.8 mm to 14.6 mm, and 1.7 mm to 7.8 mm respectively. Conclusion: The pre‐treatment MVCT can be used to improve the accuracy of patient positioning and to reduce the tumor margin. Results from this study could be used as a reference to determine the tumor margin for regular radiation therapy treatment.

The Effect of an Aggressive Enteral Nutritional Program on Daily Setup Variations and Planning Margins of Head and Neck Cancer Patients

The Effect of an Aggressive Enteral Nutritional Program on Daily Setup Variations and Planning Margins of Head and Neck Cancer Patients

Intra- and Interfractional Variations for Prone Breast Irradiation: An Indication for Image-Guided Radiotherapy

Intra- and interfractional errors for breast cancer patients undergoing breast irradiation in the prone position were analyzed. To assess intrafractional error resulting from respiratory motion, four-dimensional computed tomography scans were acquired for 3 prone and 3 supine patients, and the respiratory motion was compared for the two positions. To assess the interfractional error caused by daily set-up variations, daily electronic portal images of one of the treatment beams were taken for 15 prone-positioned patients. Portal images were then overlaid with images from the planning system that included the breast contour and the isocenter, treatment beam portal, and isocenter. The shift between the planned and actual isocenter was recorded for each portal image, and descriptive statistics were collected for each patient. The margins were calculated using the 2Sigma + 0.7sigma recipe, as well as 95% confidence interval based on the pooled standard deviation of the datasets. Respiratory motion of the chest wall is drastically reduced from 2.3 +/- 0.9 mm in supine position to -0.1 +/- 0.4 mm in prone position. The daily set-up errors vary in magnitude from 0.0 cm to 1.65 cm and are patient dependent. The margins were defined by considering only the standard deviation to be 1.1 cm, and 2.0 cm when the systematic errors were considered using the 2Sigma + 0.7sigma recipe. Prone positioning of patients for breast irradiation significantly reduces the uncertainty introduced by intrafractional respiratory motion. The presence of large systematic error in the interfractional variations necessitates a large clinical target volume-to-planning target volume margin and indicates the importance of image guidance for partial breast irradiation in the prone position, particularly using imaging modality capable of identifying the lumpectomy cavity.

Frame-Based Immobilization and Targeting for Stereotactic Body Radiation Therapy

Frame-based stereotactic body radiation therapy (SBRT), such as that conducted with Elekta’s Stereotactic Body Frame, can provide an extra measure of precision in the delivery of radiation to extracranial targets, and facilitates secure patient immobilization. In this paper, we review the steps involved in optimal use of an extra-cranial immobilization device for SBRT treatments. Our approach to using frame-based SBRT consists of 4 steps: patient immobilization, tumor and organ motion control, treatment/planning correlation, and daily targeting with pretreatment quality assurance. Patient immobilization was achieved with the Vac-Loc bag, which uses styrofoam beads to conform to the patient’s shape comfortably within the body frame. Organ and motion control was assessed under fluoroscopy and controlled via a frame-mounted abdominal pressure plate. The compression screw was tightened until the diaphragmatic excursion range was < 1 cm. Treatment planning was performed using the Philips Pinnacle 6.2b system. In this treatment process, a 20 to 30 noncoplanar beam arrangement was initially selected and an inverse beam weight optimization algorithm was applied. Those beams with low beam weights were removed, leaving a manageable number of beams for treatment delivery. After planning, daily targeting using computed tomography (CT) to verify x-, y-, and z-coordinates of the treatment isocenter were used as a measure of quality assurance. We found our daily setup variation typically averaged < 5 mm in all directions, which is comparable to other published studies on Stereotactic Body Frame. Treatment time ranged from 30 to 45 minutes. Results demonstrate that patients have experienced high rates of local control with acceptable rates of severe side effects—by virtue of the tightly constrained treatment fields. The body frame facilitated comfortable patient positioning and quality assurance checks of the tumor, in relation to another set of independent set of coordinates defined by the body frame fiducials. The ability to impose abdominal compression proved to be a simple way to reduce target and tissue motion. SBRT with Stereotactic Body Frame enables comfortable patient immobilization and facilitates repeated registering and re-registering of the patient to the frame. With the body frame, large-dose-per fraction treatment is possible for localized tumor deposits with the aim of attaining a more therapeutic result.

Daily setup variations in the treatment of head and neck cancer patients and impact on determination of planning margins

Daily setup variations in the treatment of head and neck cancer patients and impact on determination of planning margins

SU‐FF‐J‐62: Image‐Guided Radiotherapy Feasibility Study Using Kilo‐Voltage Cone‐Beam CT Images for Patient Alignment Verification

Purpose: The objective of this work was to evaluate the feasibility to acquire the kilo‐voltage (KV) cone‐beam computer tomography (CBCT) images and to register the CBCT images with the conventional planning CT images for patient alignment verification. Method and Materials: A Varian high precision accelerator with on‐board KV imaging (OBI) system and CBCT was used in conjunction with a QA head phantom for patient setup position verification. In addition, the in‐house image registration and verification software was used for the analyses of patient alignment accuracy. First, we acquired the same reference image data sets of the QA head phantom from the CBCT and the LINAC/CT‐on‐rails unit. The conventional CT image set was used as the planning CT images. Applied the translation and/or the rotation to the QA head phantom to imitate the daily patient setup variation and then, acquired the daily CBCT images. Results: No differences were observed on the registration between the reference image sets obtained from the conventional planning CT and CBCT. Similar findings were also observed on the registration of the daily CBCT with the planning CT images when the translations were applied to the setup of the daily QA head phantom deviated from the planning QA head phantom setup. When the rotations were applied to the daily setup of the QA head phantom, the treatment target was registered well between the daily CBCT images and the planning CT images, but the difference of 1.3 mm was observed on the registration in the structure relatively far away from the target. Conclusion: Phantom studies indicated that the daily pretreatment CBCT images should be suitable to use for patient alignment verification with the planning CT images. Conflict of Interest: supported by Varian Medical Systems.

Intensity-modulated radiation therapy in the management of head and neck cancer

Intensity-modulated radiation therapy (IMRT) represents a potentially significant new advance in the radiotherapeutic treatment of head and neck cancer patients. The capacity of IMRT to produce highly conformal dose distributions affords the opportunity to decrease the spectrum of toxicities associated with head and neck radiation. This review updates recent advances regarding the use of this emerging technology. Mature clinical data demonstrating head and neck IMRT safety and efficacy remain relatively limited to date. Recent publications have sought to clarify target selection and delineation. Refinements in target design driven by clinical outcomes are beginning to emerge. Technical aspects of IMRT delivery such as the impact of daily set-up variation, planning methods, and optimal fractionation regimens are progressing. Stepwise refinement in the practice of IMRT for head and neck cancer patients is advancing worldwide. However, mature clinical data remains relatively limited and specific aspects regarding the practice of head and neck IMRT remain heterogeneous.

Analysis of interfraction and intrafraction variation during tangential breast irradiation with an electronic portal imaging device

To evaluate the daily setup variation and the anatomic movement of the heart and lungs during breast irradiation with tangential photon beams, as measured with an electronic portal imaging device. Analysis of 1,709 portal images determined changes in the radiation field during a treatment course in 8 patients. Values obtained for every image included central lung distance (CLD) and area of lung and heart within the irradiated field. The data from these measurements were used to evaluate variation from setup between treatment days and motion due to respiration and/or patient movement during treatment delivery. The effect of respiratory motion and movement during treatment was minimal: the maximum range in CLD for any patient on any day was 0.25 cm. The variation caused by day-to-day setup variation was greater, with CLD values for patients ranging from 0.59 cm to 2.94 cm. Similar findings were found for heart and lung areas. There is very little change in CLD and corresponding lung and heart area during individual radiation treatment fractions in breast tangential fields, compared with a relatively greater amount of variation that occurs between days.

The impact of daily setup variations on head-and-neck intensity-modulated radiation therapy

Intensity-modulated radiation therapy (IMRT) in the treatment of head-and-neck (H&N) cancer provides the opportunity to diminish normal tissue toxicity profiles and thereby enhance patient quality of life. However, highly conformal treatment techniques commonly establish steep dose gradients between tumor and avoidance structures. Daily setup variations can therefore significantly compromise the ultimate precision of idealized H&N IMRT delivery. This study provides a detailed analysis regarding the potential impact of daily setup variations on the overall integrity of H&N IMRT. A series of 10 patients with advanced H&N cancer were prospectively enrolled in a clinical trial to examine daily H&N radiation setup accuracy. These patients were treated with conventional shrinking field design using three-dimensional treatment planning techniques (not IMRT). Immobilization and alignment were performed using modern H&N practice techniques including conventional thermoplastic masking, baseplate fixation to the treatment couch, three-point laser alignment, and weekly portal film evaluation. After traditional laser alignment, setup accuracy was assessed daily for each patient by measuring 3 Cartesian and 3 angular deviations from the specified isocenter using a high-precision, optically guided patient localization system, which affords submillimeter setup accuracy. These positional errors were then applied to a distinct series of 10 H&N IMRT plans for detailed analysis regarding the impact of daily setup variation (without optical guidance) on the ultimate integrity of IMRT plans over a 30-day treatment course. Dose-volume histogram (DVH), equivalent uniform dose (EUD), mean total dose (mTd), and maximal total dose (MTD) for normal structures were analyzed for IMRT plans with and without incorporation of daily setup variation. Using conventional H&N masking and laser alignment for daily positioning, the mean setup error in any single dimension averaged 3.33 mm. However, when all six degrees of freedom were accounted for, using the optically guided patient localization system, the mean composite vector offset was 6.97 mm with a standard deviation of 3.63 mm. Superimposition of mean offset vectors on idealized H&N IMRT treatment plans enabled evaluation of resultant shifts in DVH, EUD, mTd, and MTD calculations. Partial geographic tumor miss (GTV underdosing) and normal tissue overdosing was common when these mean positional offsets were incorporated. The decrease in EUD for defined tumor volumes ranged up to 21% when the largest offset histories were applied, and 3-14% for plans when the least and median offset histories were applied. The successful implementation of H&N IMRT requires accurate and reproducible treatment delivery over a 6- to 7-week treatment course. The adverse impact of daily setup variation, which occurs routinely with conventional H&N masking techniques, may be considerably greater than recognized. Isocenter verification checks on two-dimensional orthogonal films may not sufficiently alert the clinician to the magnitude of three-dimensional offset vectors and the resultant impact on the quality of overall IMRT delivery. Unrecognized geographic miss and resultant target underdose may occur. Similarly, selected normal structures such as parotid glands may receive higher doses than intended. The results of this study suggest that more rigorous immobilization techniques than conventional masking and routine patient setup tracking methodologies are important for the accurate monitoring and successful delivery of high-quality IMRT for H&N cancer.

Respiratory gating and 4‐D tomotherapy

Helical tomotherapy is a new intensity‐modulated radiotherapy (IMRT) delivery process developed at the University of Wisconsin and TomoTherapy Inc. Tomotherapy may be of advantage in lung cancer treatment due to its rotational delivery mode. As with conventional IMRT delivery, however, intrafraction respiratory motion during a tomotherapy treatment causes unnecessary radiation to the healthy tissue. Possible solutions to these problems associated with intrafraction motion have been studied in this thesis. A spirometer is useful for monitoring breathing because of its direct correlation with lung volume changes. However, its inherent drift prevents its application in long‐term breathing monitoring. With calibration and stabilization algorithms, a spirometer is able to provide accurate, long‐term lung volume change measurements. Such a spirometer system is most suited for deep inspiration breath‐hold (DIBH) treatments. An improved laser‐spirometer combined system has also been developed for target tracking in 4‐D treatment. Spirometer signals are used to calibrate the displacement measurements into lung volume changes, thereby eliminating scaling errors from daily setup variations. The laser displacement signals may also be used to correct spirometer drifts during operation. A new 4‐D treatment technique has been developed to account for intrafraction motion in treatment planning. The patient's breathing and the beam delivery are synchronized, and the target motion/deformation is incorporated into treatment plan optimization. Results show that this new 4D treatment technique significantly reduces motion effects and provides improved patient tolerance.

Optimized radiation of pelvic volumes in the clinical setting by using a novel bellyboard with integrated gonadal shielding

The purpose of this study was to determine the feasibility of a custom-made, modified bellyboard to reduce radiotherapy side effects on small bowel, bladder, skin, and male gonads. Two groups of 10 consecutive patients each were treated from January 2003 through April 2003 with neoadjuvant (45 Gy) or adjuvant (54 Gy) radio(chemo)therapy in single fractions of 5 days a week 1.8 Gy for rectal carcinoma, using a photon energy of 15 MV. One group was positioned in a prone position without an immobilization device, the other group was positioned on our bellyboard. Treatment planning was calculated by using a 4- and a 3-field box technique. Differences in the dose of organs of risk were calculated. For 1 male patient, a gonadal shielding was developed and integrated. All patients examined with the bellyboard demonstrated an anterior and cranial dislocation of the small bowel. Using a 4-field box, the mean dose to the small bowel of patients treated on our bellyboard was 56.5% as compared to 63.1% when treated without the bellyboard. When a 3-field box was used, the mean dose to the small bowel was 52.4% when the bellyboard was used, as compared to a mean dose of 63.1% without the bellyboard. Regarding the dose volume effects to the bladder, the mean dose for patients treated with a 4-field box was about 14.5% higher as compared to patients treated with a 3-field box. The mean dose to the hip joints and skin also depended on the radiation technique. The patient who received gonadal shielding received a maximal total gonadal dose of about 75.0 cGy in single fractions of maximal 3.0 cGy (TL-dosimeters). Daily setup variations evaluated by a beam’s-eye view were similar in both groups and ranged from 0.5 cm 1.0 cm. For daily use, our bellyboard appears to be an ideal compromise due to effectiveness, its easy handling, and reproductive positioning; moreover, it can also be used in combination with gonadal shielding.

Quantification of volumetric and geometric changes occurring during fractionated radiotherapy for head-and-neck cancer using an integrated CT/linear accelerator system

Purpose Many patients receiving fractionated radiotherapy (RT) for head-and-neck cancer have marked anatomic changes during their course of treatment, including shrinking of the primary tumor or nodal masses, resolving postoperative changes/edema, and changes in overall body habitus/weight loss. We conducted a pilot study to quantify the magnitude of these anatomic changes with systematic CT imaging. Methods and materials Fourteen assessable patients were enrolled in this pilot study. Eligible patients had to have a pathologic diagnosis of head-and-neck cancer, be treated with definitive external beam RT, and had have gross primary and/or cervical nodal disease measuring at least 4 cm in maximal diameter. All patients were treated using a new commercial integrated CT-linear accelerator system (EXaCT) that allows CT imaging at the daily RT sessions while the patient remains immobilized in the treatment position. CT scans were acquired three times weekly during the entire course of RT, and both gross tumor volumes (GTVs: primary tumor and involved lymph nodes) and normal tissues (parotid glands, spinal canal, mandible, and external contour) were manually contoured on every axial slice. Volumetric and positional changes relative to a central bony reference (the center of mass of the C2 vertebral body) were determined for each structure. Results Gross tumor volumes decreased throughout the course of fractionated RT, at a median rate of 0.2 cm 3 per treatment day (range, 0.01–1.95 cm 3/d). In terms of the percentage of the initial volume, the GTVs decreased at a median rate of 1.8%/treatment day (range, 0.2–3.1%/d). On the last day of treatment, this corresponded to a median total relative loss of 69.5% of the initial GTV (range, 9.9–91.9%). In addition, the center of the mass of shrinking tumors changed position with time, indicating that GTV loss was frequently asymmetric. At treatment completion, the median center of the mass displacement (after corrections for daily setup variation) was 3.3 mm (range, 0–17.3 mm). Parotid glands also decreased in volume (median, 0.19 cm 3/d range, 0.04–0.84 cm 3/d), and generally shifted medially (median, 3.1 mm; range, 0–9.9 mm) with time. This medial displacement of the parotid glands correlated highly with the weight loss that occurred during treatment. Conclusion Measurable anatomic changes occurred throughout fractionated external beam RT for head-and-neck cancers. These changes in the external contour, shape, and location of the target and critical structures appeared to be significant during the second half of treatment (after 3–4 weeks of treatment) and could have potential dosimetric impact when highly conformal treatment techniques are used. These data may, therefore, be useful in the development of an adaptive RT scheme (periodic adjustment of the conformal treatment plan) that takes into account such treatment-related anatomic changes. In theory, such a strategy would maximize the therapeutic ratio of RT.

Reduction of irradiated small bowel volume and accurate patient positioning by use of a bellyboard device in pelvic radiotherapy of gynecological cancer patients

Purpose: To reduce the volume of small bowel within pelvic treatment fields for gynecological cancer using a bellyboard device and to determine the accuracy of the prone treatment position. Materials and methods: Fifteen consecutive patients with a gynecologic malignancy who were treated with postoperative pelvic radiotherapy were selected for this study. The volume of small bowel within the treatment fields was calculated for both the supine and prone treatment positions. The patients were treated in the prone position in a so-called bellyboard device. During treatment sessions electronic portal images were obtained. An off-line setup verification and correction protocol was used and the setup accuracy of the positioning in the bellyboard was determined. Results: The average volume of small bowel within the treatment fields was 229 cm 3 and 66 cm 3 in the supine and prone treatment, respectively, which means an average volume reduction in the prone position of 64% (95% CI 56–72%), as compared with the supine position. For the position of the patient in the field, the systematic error defined by the standard deviation (SD) of the mean difference per patient between simulation and treatment images was 1.7 mm in the lateral direction, 2.1 mm in the craniocaudal direction and 1.7 mm in the ventrodorsal direction. On average, only 0.4 setup correction per patient was required to achieve this accuracy. The random day-to-day variations were 1.9 (1SD), 2.6 and 2.3 mm, respectively. Standard deviations of the systematic differences between patient positioning relative to the bellyboard were 6.2 mm in lateral direction and 9.1 mm in craniocaudal direction. Conclusions: Treatment of gynecological cancer patients in the prone position using a bellyboard reduces the volume of irradiated small bowel. An off-line verification and correction protocol ensures accurate patient positioning. Daily setup variations using the bellyboard were small (1 SD<3 mm). Therefore for pelvic radiotherapy in patients with a gynecological malignancy, the use of a bellyboard is recommended.

A comparison of multileaf-collimator and alloy-block field shaping

Purpose : The purpose of this report was to compare distribution at a field edge defined with divergent alloy blocks to the distribution obtained with a multileaf collimator (MLC). The comparison is made for simple block replacement situations. Methods and Materials : A tertiary multileaf collimator mounted on a linear accelerator operating at 6 MV was compared to divergent alloy blocks positioned at the level of the blocking tray. The leaves of the MLC were positioned to give maximum stepping (leaf displacement equals leaf width), and the blocking produced the same field shape. Three different treatment plans were compared: single field, opposed fields, and a four-field “box.” Dose distributions were determined using radiographic film scanned with a lase densitometer with a 0.45-mm spot size. One experiment was repeated using radiochromic film with reduced energy dependence. Dose distributions were examined on the isocenter plane, and on planes displaced by 1.0 and 2.5 cm. The effect of daily setup variations was also studied by comparing a single fraction treatment with a fractioned treatment consisting of 15 fields slightly displaced relative to each other. The magnitude of these displacemnts was determined using available literature on treatment reproducibility. Results : For a single plan, maximum stepping of an MLC-defined edge produces an obvious undulating dose pattern compared to an alloy block edge. At the isocenter plane, this pattern is unchanged when parallel opposed fields are used. However, blurring occurs for both MLC and block edges when planes displaced from the isocenter are examined. The gradient for the block edge is 8%/mm for opposed fields and a plane 2.5 cm from the isocenter, compared to 15%/mm for the isocenter plane. Adding two additional fields does not change the dose pattern in the isocenter plane, but does reduce the gradient across the steepest portion of the penumbra to 8%/mm, and shifts the isodose line with the most pronounced stepping to higher values (from 50 to 80%). Introducing daily setup variations results in a reduction of the sharp dose gradient along the sides of a single field, and around the periphery of the beam at the isocenter plane of opposed fields. Smaller changes are found for edges around the periphery of the beam at the isocenter plane of opposed fields. Smaller changes are found for edges already blurred by other factors. Radiochromic film was generally noiser than radiographic film, but comparisons of the two films did not show a significant difference, indicating that the energy dependence of the radiographic film was not a problem. Conclusions : The obvious dose stepping seen a portal image of a single fields with MLC shaping is shown to be partially erased by the addition of other fields, and for planes away from the isocenter. However, the effects of daily setup variations must be included to more effectively blur dose stepping along the external envelope of a single field or near the isocenter plane of opposed fields. This result conflicts with attemps to improve immobilization. the

Effects of treatment setup variation on beam's eye view dosimetry for radiation therapy using the multileaf collimator vs. the cerrobend block

The purpose of this study is to quantify and compare retrospectively the effects of treatment setup variation on beam's eye view (BEV) dosimetry for radiation therapy using a multileaf collimator (MLC) vs. cerrobend block. A study was performed on a group of 18 patients with cancer of the head and neck, lung, and pelvis who were treated with irregularly shaped fields. The BEV dosimetry of the fields shaped with cerrobend blocks and the MLC was measured with films at the depth of dose prescription in a solid water phantom. A "one-half-leaf" insertion convention was used to shape the MLC. In addition, an average of 15 sequential daily port films was taken per patient during the course of radiotherapy. The port films were aligned with the prescription film for each patient. Systematic error and random error of treatment setup for each patient were calculated. The effects of setup variation were incorporated by convolving the patient portal imaging data with the corresponding BEV film dosimetry. Two parameters were used to quantify the BEV dosimetry. First, the field penumbra width was calculated, which represented the average of the normal separations between 20 and 80% isodose lines along the prescription outline. Second, the ratio of areas covered by the 90 and 20% isodose lines, A90/20, was determined. The BEV dosimetry was then characterized with and without the effects of treatment setup variation. In addition, the difference in BEV dosimetry between the cerrobend block and the MLC was used to estimate the corresponding changes in tumor control probability (TCP). These changes were also compared to the changes in TCP for the treatment with or without the effects of random setup variation. With or without daily setup variation, the use of cerrobend block was more favorable than the MLC in terms of the field penumbra width and A90/20 for all treatment sites. In the absence of daily variation, the MLC field penumbra width was on average 1.3 mm larger than that of the cerrobend block, and 0.9 mm larger in the presence of daily setup variation. Similarly, the ratio A90/20 of the cerrobend block was on average 0.03 larger than that of MLC without daily setup variation, and 0.02 with daily setup variation. The difference in field penumbra width and A90/20 between the MLC and the cerrobend block was slightly reduced due to the effects of daily setup variation. For both the cerrobend block and the MLC, daily setup variation produced a significant increase in the field penumbra width, 2.3 mm for the cerrobend block and 1.9 mm for the MLC, and a decrease in the A90/20, 0.06 for the former and 0.05 for the latter. The change due to the daily setup variation was about a factor of 2 larger than the changes due to replacing the cerrobend block with the MLC. Using the TCP model, the change in TCP due to the daily setup variation was more than a factor of 3 larger than the change in TCP due to replacing the cerrobend block with the MLC. It was noted that the average changes in the penumbra, the A90/20 and the TCP calculated for the patient population did not adequately describe the changes for the individual patient. Our results do not show significant dosimetric differences between the MLC and the cerrobend block in conventional radiation treatment, whether or not daily setup variation was taken into consideration. The effects of daily setup variation alone produced a larger dosimetric change. The same results were obtained when the data were applied to calculate changes in TCP. For optimal radiation therapy, efforts should be concentrated on reducing daily setup variation. Our results also demonstrate the importance of frequent evaluation of MLC treatment using electronic portal imaging devices.

Conformal static field therapy for low volume low grade prostate cancer with rigid immobilization

The ability to improve existing standards of treating prostate cancer was investigated. To deliver a homogeneous dose to the prostate with as little normal tissue margin as practical, seven patients with low volume carcinoma of the prostate were immobilized with alpha cradle body casts prior to using a CT-based 3D treatment planning system and beam's eye view (BEV) template. All patients had clinical Stage B-1 prostate cancer of favorable histologic differentiation (Gleason Score 2–5). A four field box technique was used, each beam having a single customized cerrobend block cut-out conforming to the exact contour of the prostate. To assess the accuracy of this process, daily port films were taken for 5 consecutive days and compared to a matched control group who were treated in a similar fashion, but were not casted. Dose volume histograms illustrate an average of 14% of bladder dose and 14% of rectal dose that can be eliminated using this technique when compared to field sizes and block placement in our previous technique. Daily setup variation was markedly improved using the cast, with a median daily variation of 1 mm as compared to 3 mm without the cast. The average range of movement for each of the seven tasted patients was 3.3 mm as compared to 8 mm for the seven uncasted patients. Immobilization eliminated the worst 10% of all daily positioning errors. Using CT treatment planning with the patient tasted and BEV allows for precise block placement with the prostate gland in its proper orientation during daily treatment. With improved immobilization and precise localization of the prostate gland, margins around the target can be made significantly smaller, and this may translate into a decrease in acute and/or late complications.

Conformal Static Field Therapy for Low Volume Low Grade Prostate Cancer with Rigid Immobilization: International Journal of Radiation Oncology, Biology, Physics, Vol. 20, January 1991, pp. 141–146

The ability to improve existing standards of treating prostate cancer was investigated. To deliver a homogenous dose to the prostate with as little normal tissue margin as practical, seven patients with low volume carcinoma of the prostate were immobilized with alpha cradle body casts prior to using a CT-based 3D treatment planning system and beam's eye view (BEV) template. All patients had clinical Stage B-1 prostate cancer of favorable histologic differentiation (Gleason Score 2-5). A four field box technique was used, each beam having a single customized cerrobend block cut-out conforming to the exact contour of the prostate. To assess the accuracy of this process, daily port films were taken for 5 consecutive days and compared to a matched control group who were treated in a similar fashion, but were not casted. Dose volume histograms illustrate an average of 14% of bladder dose and 14% of rectal dose that can be eliminated using this technique when compared to field sizes and block placement in our previous technique. Daily setup variation was markedly improved using the cast, with a median daily variation of 1 mm as compared to 3 mm without the cast. The average range of movement for each of the seven casted patients was 3.3 mm as compared to 8 mm for the seven uncasted patients. Immobilization eliminated the worst 10% of all daily positioning errors. Using CT treatment planning with the patient casted and BEV allows for precise block placement with the prostate gland in its proper orientation during daily treatment. With improved immobilization and precise localization of the prostate gland, margins around the target can be made significantly smaller, and this may translate into a decrease in acute and/or late complications.