SU-E-T-561: A Comparative Study of Single Verses Two Field Daily Fraction for Treatment of Prostate Cancer Using IMPT, Double-Scattered, and SUFD Delivery Technique.

PURPOSE: We conducted an investigation to evaluate the robustness of different proton therapy delivery technique for treatment of prostate cancer. Three commonly used delivery techniques; intensity modulated, double-scattered, and single field uniform dose delivery was investigated for one field verses two field daily fraction. METHOD: Computer tomography (CT) for a patient was deformed based on acquired daily MVCTs obtained during the course of treatment by a Tomotherapy unit. The deformed CTs were used for proton planning retrorespectively using intensity modulated (IMPT), double-scattered (DSPT), and single field uniform dose (SFUD) delivery technique. The plans were evaluated for single-field versus two-field per fraction for each technique. The plans robustness was evaluated for each technique by comparing the maximum dose to rectum, bladder, prostate and CTV as well as the minimum dose to prostate and CTV. In addition, 95% coverage to prostate and CTV compared for each plan. RESULTS: The average and STD for deformed prostate volume was 22.4 ±0.5 (1s) for the course of treatment. On average the maximum dose delivered to rectum and bladder with single-field verses two-field IMPT were higher by 2.5%. With same respect, the single-field verses two-field for DSPT were 0.5% higher for rectum but the same for bladder. Single-field SFUD delivered 1% higher dose to both rectum and bladder compare to two-field delivery. Table 1 summarizes the results. CONCLUSION: Single-field IMPT delivered higher dose to rectum, bladder, prostate, and CTV than any other technique. But two-file IMPT delivered most homogenous and consistent dose to prostate and CTV with much lower dose to rectum and bladder compare to DSPT and SFUD. With same respect two-field SFUD delivery produced better dose coverage to prostate and CTV compare to DSPT. The two-field IMPT with conjunction of daily cone beam CT can be considered a better dose delivery technique.

A quality assurance device for the accuracy of the isocentres of teletherapy and simulation machines.

A new quality assurance device has been designed to measure the location and wobble of the radiation isocentre of linacs and simulation machines as a function of gantry rotation. The radiation isocentre is the intersection in space of the central x rays of a linac or simulation machine at different gantry angles. Six radio-opaque markers 1 mm in size are embedded in a radio-transparent calibration object (specifically, a hollowed cube) in such a way that the markers are non-coplanar and uniquely identifiable in radiographic projections. The projective radiographs are obtained on the films held by the film holder attached to the gantry during the QA procedure. The marker positions of the calibration object define a known 3D reference frame, and their image positions on each radiograph determine the projective (3D to 2D matrix) transformation for that radiograph. Once the transformation is found, a 3D ray from the radiation source to any radiograph pixel becomes known. The radiographic pixels are coordinated (positioned and scaled) with respect to the projected image of radio-opaque fiducial cross-hairs fixed to a block tray and thus to the gantry. We select the central ray to correspond to the radiographic pixel whose rays at different gantry angles intersect in the smallest spatial domain. That pixel is found by a spiral search in the radiograph outward from the image of the radio-opaque cross-hair intersection. The wobble of the isocentre is defined by the set of points (on the central rays) at closest approach to the isocentre. The device was tested and compared with commercially available QA devices. It is able to locate the isocentre to within 0.5 mm. The offset of this derived radiation isocentre from the intersection of the positioning lasers can be found. To do this, the calibration object is initially placed so that the laser intersection point falls on a seventh radio-opaque marker near the centre of the hollow cube calibration object. The seventh marker is embedded in a thin radio-transparent rod that diagonally spans the hollowed space.

Neoadjuvant androgen deprivation prior to transperineal prostate brachytherapy: smaller volumes, less morbidity.

PURPOSE: Prostate brachytherapy is becoming increasingly utilized in the definitive treatment of men with early-stage prostate cancer. Others have reported a close relation between total dose to the gland and genitourinary and gastrointestinal toxicity. We tested the hypothesis that 3 months of hormone deprivation would decrease gland size and decrease radioactivity implanted, which would result in less morbidity. Here, we report the toxicity associated with this novel treatment strategy. METHODS: One hundred fifty-five prostate cancer patients underwent ultrasound-guided transperineal implantation of palladium-103 at the Hospital of the University of Pennsylvania between January 1994 and July 1998. All men received at least 3 months of neoadjuvant luteinizing hormone-releasing hormone (LHRH) agonist therapy and were registered in the study. This group of men were compared with 55 men treated at the Hospital of the University of Pennsylvania with brachytherapy alone between December 1991 and December 1993. RESULTS: Compared with men treated with implant alone, men who received LHRH agonist therapy had significantly smaller glands at the time of implant (27.7 cm3 vs 36.3 cm3), required fewer seeds (47.9 vs 83.2), and had significantly less radioactivity implanted (76.3 mCi vs 117 mCi). The genitourinary and gastrointestinal morbidity in the men receiving hormone deprivation was minimal, with long-term side effects occurring in only three patients. In addition, potency was preserved in 83% of men. DISCUSSION: Three months or more of neoadjuvant LHRH agonist therapy before transperineal brachytherapy is safe, significantly reduces the amount of radioactivity implanted, and is associated with very low rates of genitourinary and gastrointestinal toxicity. In addition, potency preservation after combined-modality therapy is excellent and is similar to that of implantation alone. Further studies of this treatment approach are warranted.

The effect of androgen deprivation on the early changes in prostate volume following transperineal ultrasound guided interstitial therapy for localized carcinoma of the prostate.

PURPOSE: To determine the change in volume of the prostate as a result of neoadjuvant androgen deprivation prior to prostate implant and in the early postimplant period following transperineal ultrasound guided palladium-103 brachytherapy for early-stage prostate cancer. METHODS AND MATERIALS: Sixty-nine men received 3 to 6 months of androgen deprivation therapy followed by treatment planning ultrasound followed 4 to 8 weeks later by palladium-103 implant of the prostate. All patients had clinical and radiographic stage T1c-T2b adenocarcinoma of the prostate. A second ultrasound study was carried out 11 to 13 days following the implant to determine the change in volume of the prostate as a result of the implant. The prehormonal and preimplant volumes were compared to the postimplant volume to determine the effect of hormones and brachytherapy on prostate volume. RESULTS: The median decrease in prostate volume as a result of androgen deprivation was 33% among the 54 patients with prostate volume determinations prior to hormonal therapy. The reduction in volume was greatest in the quartile of men with the largest initial gland volume (59%) and least in the quartile of men with smallest glands (10%). The median reduction in prostate volume between the treatment planning ultrasound and the follow-up study after implant was 3%, but 23 (33%) patients had an increase in prostate volume, including 16 (23%) who had an increase in volume >20%; 11 of these patients (16%) had an increase in volume >30%. The time course of development and resolution of this edema is not known. The severity of the edema was not related to initial or preimplant prostate volume or duration of hormonal therapy. CONCLUSIONS: Prostate edema may significantly affect the dose delivered to the prostate following transperineal ultrasound guided brachytherapy. The effect on the actual delivered dose will be greater when shorter lived isotopes are used. It remains to be observed whether this edema will affect outcome.

Characterization of optical coatings with backscattering spectrometry.

We present three examples to illustrate the use of backscattering spectrometry to determine film stoichiometry, areal density, and impurity levels in optical coatings. Helium-ion beams with energies in the 1.5-5.0-MeV range were used to analyze (1) a magnesium fluoride coating, (2) a tungsten/silicon multilayer soft x-ray mirror, and (3) a trilayer optical data storage film.