Assessment of target dose delivery in anal cancer using in vivo thermoluminescent dosimetry

Estimating dose delivery accuracy in stereotactic body radiation therapy: A review of in-vivo measurement methods

Stereotactic body radiation therapy (SBRT) has been recognized as a standard treatment option for many anatomical sites. Sophisticated radiation therapy techniques have been developed for carrying out these treatments and new quality assurance (QA) programs are therefore required to guarantee high geometrical and dosimetric accuracy. This paper focuses on recent advances on in-vivo measurements methods (IVM) for SBRT treatment. More specifically, all of the online QA methods for estimating the effective dose delivered to patients were compared. Determining the optimal IVM for performing SBRT treatments would reduce the risk of errors that could jeopardize treatment outcome. A total of 89 papers were included. The papers were subdivided into the following topics: point dosimeters (PD), transmission detectors (TD), log file analysis (LFA), electronic portal imaging device dosimetry (EPID), dose accumulation methods (DAM). The detectability capability of the main IVM detectors/devices were evaluated. All of the systems have some limitations: PD has no spatial data, EPID has limited sensitivity towards set-up errors and intra-fraction motion in some anatomical sites, TD is insensitive towards patient related errors, LFA is not an independent measure, DAMs are not always based on measures. In order to minimize errors in SBRT dose delivery, we recommend using synergic combinations of two or more of the systems described in our review: on-line tumor position and patient information should be combined with MLC position and linac output detection accuracy. In this way the effects of SBRT dose delivery errors will be reduced.

Prospective phase II study of tomotherapy based chemoradiation treatment for locally advanced anal cancer

BACKGROUND AND PURPOSE

To evaluate toxicity, local control, and survival of anal cancer patients treated with helical tomotherapy (HT) and concurrent 5-fluorouracil and mitomycin-C (5FU/MMC).

MATERIALS AND METHODS

Fifty-seven patients were treated with HT and concurrent 5FU/MMC. The planning objectives were to deliver 54 Gy to the tumor (PTV54) and 45 Gy to the nodes at risk (PTV45) in 30 fractions. Patients were reviewed for toxicity weekly during HT, every 6 weeks for 3 months, and then every 3-4 months for 5 years.

RESULTS

The median follow-up was 40 months. The median age was 58 years (range: 37-83). Stage distribution: stage II-48%, IIIA-18%, IIIB-34%. The majority of patients developed ⩽ grade 2 acute toxicity scores. The most common ⩾ grade 3 acute toxicity was neutropenia (40%). Common late toxicities were grade 2 anal incontinence (16%) and telangiectasia (12%). The 3 year colostomy-free survival rate was 77% (95% CI: 61-87%), 3 year disease-free survival rate was 80% (CI: 66-89%), and 3 year overall survival was 91% (CI: 77-96%).

CONCLUSIONS

Incorporation of HT with concurrent 5FU/MMC had low treatment-related acute and late morbidity with few treatment breaks. However, the expected dosimetric benefit for hematological toxicity was not experienced clinically.

Investigation into the use of a MOSFET dosimeter as an implantable fiducial marker

It may be possible to use a single device to measure the in vivo dose delivered during radiotherapy, as well as to localize the target volume. This potential, as well as the detectors' ability to relate dosimetry and localization, were evaluated using two implantable MOSFET dosimeters placed inside an acrylic pelvic phantom. A wedged-field photon plan and an eight-field prostate treatment plan were developed. For each plan, conditions were simulated so that detectors were in their correct positions or slightly displaced to represent patient setup error and/or organ motion. Doses measured by the two detectors after irradiation were compared to those calculated by the treatment planning software. Additionally, using localization software and kilovoltage images of each setup, the displacement of the detectors from their correct locations was calculated and compared to the induced physical displacement. For all alignments and detector positions, measured and calculated doses showed an average disagreement of 2.7%. The detectors were easily visualized radiographically and the induced detector displacements were typically recognized by the localization software to within 0.1 cm. The implantable detector functioned well as both an internal dosimeter and as an internal fiducial marker, and thus may be useful as a clinical tool to localize the target volume and verify dose delivery in vivo.

The observed variance between predicted and measured radiation dose in breast and prostate patients utilizing an in vivo dosimeter

PURPOSE

Report the results of using a permanently implantable dosimeter in radiation therapy: determine specific adverse events, degree of migration, and acquire dose measurements during treatment to determine difference between expected and measured dose.

METHODS AND MATERIALS

The Dose Verification System is a wireless, permanently implantable metal-oxide semiconductor field-effect transistor dosimeter using a bidirectional antenna for power and data transfer. The study cohort includes 36 breast (33 patients received two devices) and 29 prostate (21 patients received two devices) cancer patients. A total of 1,783 and 1,749 daily dose measurements were obtained on breast and prostate patients, respectively. The measurements were compared with the planned expected dose. Biweekly computed tomography scans were obtained to evaluate migration and the National Cancer Institute's Common Toxicity Criteria, version 3, was used to evaluate adverse events.

RESULTS

Only Grade I/II adverse events of pain and bleeding were noted. There were only four instances of dosimeter migration of >5 mm from known factors. A deviation of > or =7% in cumulative dose was noted in 7 of 36 (19%) for breast cancer patients. In prostate cancer patients, a > or =7% deviation was noted in 6 of 29 (21%) and 8 of 19 (42%) during initial and boost irradiation, respectively. The two patterns of dose deviation were random and systematic. Some causes for these differences could involve organ movement, patient movement, or treatment plan considerations.

CONCLUSIONS

The Dose Verification System was not associated with significant adverse events or migration. The dosimeter can measure dose in situ on a daily basis. The accuracy and utility of the dose verification system complements current image-guided radiation therapy and intensity-modulated radiation therapy techniques.

Image-guided in vivo dosimetry for quality assurance of IMRT treatment for prostate cancer

PURPOSE

In external beam radiotherapy (EBRT) and especially in intensity-modulated radiotherapy (IMRT), the accuracy of the dose distribution in the patient is of utmost importance. It was investigated whether image guided in vivo dosimetry in the rectum is a reliable method for online dose verification.

METHODS AND MATERIALS

Twenty-one dose measurements were performed with an ionization chamber in the rectum of 7 patients undergoing IMRT for prostate cancer. The position of the probe was determined with cone beam computed tomography (CBCT). The point of measurement was determined relative to the isocenter and relative to an anatomic reference point. The dose deviations relative to the corresponding doses in the treatment plan were calculated. With an offline CT soft-tissue match, patient positioning after ultrasound was verified.

RESULTS

The mean magnitude +/- standard deviation (SD) of patient positioning errors was 3.0 +/- 2.5 mm, 5.1 +/- 4.9 mm, and 4.3 +/- 2.4 mm in the left-right, anteroposterior and craniocaudal direction. The dose deviations in points at corresponding positions relative to the isocenter were -1.4 +/- 4.9% (mean +/- SD). The mean dose deviation at corresponding anatomic positions was 6.5 +/- 21.6%. In the rare event of insufficient patient positioning, dose deviations could be >30% because of the close proximity of the probe and the posterior dose gradient.

CONCLUSIONS

Image-guided dosimetry in the rectum during IMRT of the prostate is a feasible and reliable direct method for dose verification when probe position is effectively controlled.

Distal cT2N0 rectal cancer: is there an alternative to abdominoperineal resection?

PURPOSE

Patients with cT2N0 distal rectal cancer do not require adjuvant therapy. However, when a patient refuses an abdominoperineal resection (APR), is there an alternative? The purpose of this trial is to determine whether preoperative external-beam radiation therapy can increase the rate of sphincter preservation for patients with distal cT2N0 adenocarcinoma of the rectum.

PATIENTS AND METHODS

Between April 1988 and October 2003, 27 patients with distal rectal adenocarcinoma staged T2 by clinical and/or endorectal ultrasound who were judged by the operating surgeon to require an APR were treated with preoperative pelvic radiation alone (50.4 Gy). Surgery was performed 4 to 7 weeks later. If pathologic positive pelvic nodes were identified, postoperative adjuvant chemotherapy was recommended. The median follow-up was 55 months (range, 9 to 140 months).

RESULTS

The pathologic complete response rate was 15% and 78% of patients underwent a sphincter-sparing procedure. The crude incidence of local failure for patients undergoing a sphincter sparing procedure was 10% and the 5-year actuarial incidence was 13%. The actuarial 5-year survival for patients undergoing sphincter preservation was as follows: disease-free, 77%; colostomy-free, 100%; and overall, 85%. Using the Memorial Sloan-Kettering Cancer Center sphincter function score, 54% of those undergoing a sphincter-sparing procedure had good/excellent bowel function at 12 to 24 months after surgery, and 77% had good/excellent function at 24 to 36 months after surgery.

CONCLUSION

Our data suggest that for patients with cT2N0 distal rectal cancer who require an APR, preoperative pelvic radiation improves sphincter preservation without an apparent compromise in local control or survival.

Initial clinical results of an in vivo dosimeter during external beam radiation therapy

PURPOSE

An implantable radiation dosimeter has been developed to monitor dose delivered at depth in patients undergoing external beam therapy. A clinical pilot study was conducted to test the safety, efficacy, and utility of the device.

METHODS AND MATERIALS

Ten patients, all with unresectable malignant disease, were enrolled to assess implantation risk and movement of the device in the body and to compare the in vivo measured dose to the value predicted by the treatment planning system software.

RESULTS

Migration of the sensor away from the point of original placement was noted in only 1 patient (due to unconsolidated host tissue) and no adverse events were recorded during the implantation procedure or thereafter. Daily dose measurements were recorded successfully for all sensors in all patients. Variance between measured and predicted dose values was reported as a frequency of error at the > or =5% and > or =8% levels. The error frequency at the > or =8% level was as high as 47%, 29%, and 21% for lung, prostate, and rectal tumors, respectively.

CONCLUSIONS

The implantable dosimeter was found to be safe and effective in measuring dose at depth. There are many factors that can influence delivered dose, and the implantable dosimeter measures the net effect of these factors. The daily sensor readings provide a new tool for rigorous treatment quality assurance.

An implantable radiation dosimeter for use in external beam radiation therapy

An implantable radiation dosimeter for use with external beam therapy has been developed and tested both in vitro and in canines. The device uses a MOSFET dosimeter and is polled telemetrically every day during the course of therapy. The device is designed for permanent implantation and also acts as a radiographic fiducial marker. Ten dogs (companion animals) that presented with spontaneous, malignant tumors were enrolled in the study and received an implant in the tumor CTV. Three dogs received an additional implant in collateral normal tissue. Radiation therapy plans were created for the animals and they were treated with roughly 300 cGy daily fractions until completion of the prescribed cumulative dose. The primary endpoints of the study were to record any adverse events due to sensor placement and to monitor any movement away from the point of placement. No adverse events were recorded. Unacceptable device migration was experienced in two subjects and a retention mechanism was developed to prevent movement in the future. Daily dose readings were successfully acquired in all subjects. A rigorous in vitro calibration methodology has been developed to ensure that the implanted devices maintain an accuracy of +/-3.5% relative to an ionization chamber standard. The authors believe that an implantable radiation dosimeter is a practical and powerful tool that fosters individualized patient QA on a daily basis.

Thin sintered Al2O3 pellets as thermoluminescent dosimeters for the therapeutic dose range

Thermoluminescent properties of sintered alumina pellets were investigated with the aim of using them as radiation dosimeters. Peak temperatures, signal reproducibility, fading, curves of the response to X-radiation, as well as energy and angular dependences were studied. The results show that the pellets can be used in quality control programs in the therapeutic dose range.