Accelerated partial-breast irradiation using intensity-modulated proton radiotherapy: do uncertainties outweigh potential benefits?

OBJECTIVE

Passive scattering proton beam (PSPB) radiotherapy for accelerated partial-breast irradiation (APBI) provides superior dosimetry for APBI three-dimensional conformal photon radiotherapy (3DCRT). Here we examine the potential incremental benefit of intensity-modulated proton radiotherapy (IMPT) for APBI and compare its dosimetry with PSPB and 3DCRT.

METHODS

Two theoretical IMPT plans, TANGENT_PAIR and TANGENT_ENFACE, were created for 11 patients previously treated with 3DCRT APBI and were compared with PSPB and 3DCRT plans for the same CT data sets. The impact of range, motion and set-up uncertainties as well as scanned spot mismatching between fields of IMPT plans was evaluated.

RESULTS

IMPT plans for APBI were significantly better regarding breast skin sparing (p<0.005) and other normal tissue sparing than 3DCRT plans (p<0.01) with comparable target coverage (p=ns). IMPT plans were statistically better than PSPB plans regarding breast skin (p<0.002) and non-target breast (p<0.007) in higher dose regions but worse or comparable in lower dose regions. IMPT plans using TANGENT_ENFACE were superior to that using TANGENT_PAIR in terms of target coverage (p<0.003) and normal tissue sparing (p<0.05) in low-dose regions. IMPT uncertainties were demonstrated for multiple causes. Qualitative comparison of dose-volume histogram confidence intervals for IMPT suggests that numeric gains may be offset by IMPT uncertainties.

CONCLUSION

Using current clinical dosimetry, PSPB provides excellent dosimetry compared with 3DCRT with fewer uncertainties compared with IMPT.

ADVANCES IN KNOWLEDGE

As currently delivered in the clinic, PSPB planning for APBI provides as good or better dosimetry than IMPT with less uncertainty.

Preliminary evaluation of implantable MOSFET radiation dosimeters

In this paper, we report on measurements performed on a new prototype implantable radiation detector that uses metal-oxide semiconductor field effect transistors (MOSFETs) designed for in vivo dosimetry. The dosimeters, which are encapsulated in hermetically sealed glass cylinders, are used in an unbiased mode during irradiation, unlike other MOSFET detectors previously used in radiotherapy applications. They are powered by radio frequency telemetry for dose measurements, obviating the need for a power supply within each capsule. We have studied the dosimetric characteristics of these MOSFET detectors in vitro under irradiation from a 60Co source. The detectors show a dose reproducibility generally within 5% or better, with the main sources of error being temperature fluctuations occurring between the pre- and post-irradiation measurements as well as detector orientation. A better temperature-controlled environment leads to a reproducibility within 2%. Our preliminary in vitro results show clearly that true non-invasive in vivo dosimetry measurements are feasible and can be performed remotely using telemetric technology.

Prognosis for papillary serous carcinoma of the endometrium after surgical staging

BACKGROUND

To investigate the pattern of failure and the prognosis following pathological staging for uterine papillary serous carcinoma (UPSC).

PATIENTS AND METHODS

A retrospective review was conducted of 22 patients with UPSC, treated between 1989 and 1998 at a single institution. All patients were surgically staged. Two patients with advanced disease received chemotherapy only. Two patients with early-stage disease were followed without further treatment. Eighteen patients received postoperative irradiation; eight patients received whole abdominal irradiation (WART), and the remaining 10 patients, pelvic irradiation (PRT). In addition, seven of these patients received vaginal cuff irradiation with low-dose-rate or high-dose-rate brachytherapy. Toxicity, pattern of failure, and survival were evaluated and compared to the literature.

RESULTS

Seven patients (32%) developed distant metastases, three out of seven (42%) after WART. Four out of seven patients who had distant metastases died from disease progression during subsequent chemotherapy. All patients with distant metastases had locally advanced-stage disease at presentation (six stage III, one stage IV). Four patients with pelvic recurrences developed concurrent (2) and subsequent (2) distant metastases. Three patients had isolated distant metastases. No patient with early stage-disease (stage I and II) died from disease progression.

CONCLUSION

Pathological staging should be performed for all patients with UPSC to determine the prognosis as well as to tailor the treatment. The role of abdominal irradiation in the treatment of UPSC is yet to be determined; however, such an approach may not be necessary for the control of disease for patients with early-stage (I and II) disease. Patients with locally advanced-stage (stage III) disease are at risk of local regional failures and distant metastases despite WART. Therefore, the benefit of WART for advanced-stage disease is also questionable. Paclitaxel-based chemotherapy is currently being investigated in this setting.

Prognosis for papillary serous carcinoma of the endometrium after surgical staging

Abstract.

Nguyen NP, Sallah S, Karlsson U, Vos P, Ludin A, Semer D, Tait D, Salehpour M, Jendrasiak G, Robiou C. for papillary serous carcinoma of the endometrium after surgical staging.

Background: To investigate the pattern of failure and the prognosis following pathological staging for uterine papillary serous carcinoma (UPSC).

Patients and methods: A retrospective review was conducted of 22 patients with UPSC, treated between 1989 and 1998 at a single institution. All patients were surgically staged. Two patients with advanced disease received chemotherapy only. Two patients with early-stage disease were followed without further treatment. Eighteen patients received postoperative irradiation; eight patients received whole abdominal irradiation (WART), and the remaining 10 patients, pelvic irradiation (PRT). In addition, seven of these patients received vaginal cuff irradiation with low-dose-rate or high-dose-rate brachytherapy. Toxicity, pattern of failure, and survival were evaluated and compared to the literature.

Results: Seven patients (32%) developed distant metastases, three out of seven (42%) after WART. Four out of seven patients who had distant metastases died from disease progression during subsequent chemotherapy. All patients with distant metastases had locally advanced-stage disease at presentation (six stage III, one stage IV). Four patients with pelvic recurrences developed concurrent (2) and subsequent (2) distant metastases. Three patients had isolated distant metastases. No patient with early stage-disease (stage I and II) died from disease progression.

Conclusion: Pathological staging should be performed for all patients with UPSC to determine the prognosis as well as to tailor the treatment. The role of abdominal irradiation in the treatment of UPSC is yet to be determined; however, such an approach may not be necessary for the control of disease for patients with early-stage (I and II) disease. Patients with locally advanced-stage (stage III) disease are at risk of local regional failures and distant metastases despite WART. Therefore, the benefit of WART for advanced-stage disease is also questionable. Paclitaxel-based chemotherapy is currently being investigated in this setting.

Combined preoperative chemotherapy and radiation for locally advanced rectal carcinoma

To determine the efficacy of combined preoperative chemotherapy and radiation therapy for locally advanced rectal carcinoma and the rate of sphincter conservation, a retrospective survey of 39 patients with locally advanced rectal carcinoma treated with various 5-fluorouracil- and leukovorin-based chemotherapy regimens and radiation prior to surgery in a single institution was reviewed. Toxicity, local control and survival were evaluated and compared to previous studies with similarly staged patients. Long-term follow-up was available on 35 patients. The actuarial local failure was 5.7% while the actuarial 5-year survival was 87%. The mortality rate was low (2.5%) and the rate of long-term serious complications acceptable (11.4%). Combined preoperative chemotherapy and radiation provided excellent local regional control despite the poor prognostic factors associated with size, fixation, and the initial advanced tumor stage with acceptable morbidity. In addition, patients with tumors located in the lower third of the rectum may be able to undergo sphincter-sparing surgery. Although the median follow-up is relatively short (32.4 months), the results are in accordance with previous studies of neoadjuvant combined chemotherapy and radiation for locally advanced rectal carcinoma in terms of local and distant control.

Comparison of CT-based treatment planning and retrograde urethrography in determining the prostatic apex at simulation

In 20 consecutive patients who underwent treatment planning, localization of the prostatic apex with CT-based techniques at simulation was compared to location of the apex as defined by retrograde urethrography. In addition, the location of the urethrogram-defined prostatic apex was compared with the bottom of the ischial tuberosities, which is often recommended as the inferior margin of the field. In 15% of the patients there was agreement between the CT-defined apex and the urethrogram-defined apex; in 85% there was discordance. In a majority of patients with discordance, the urethrogram apex was located caudad to the CT-defined apex (71%) with a median difference of .65 cm. In 29% of the patients the urethrogram apex was located superior to the CT-defined apex. Overall, 75% of the patients had discordance between the urethrogram apex and the CT apex of 0.5 cm or greater; 30% had an absolute difference of 1.0 cm or greater. Comparing the location of the prostatic apex with the bottom of the ischial tuberosities revealed that in 15% of the patients the apex was 1.0 cm or less from the bottom of the tuberosities and in 45% it was less than 1.5 cm. This would place the apex of the prostate in the penumbra region of the field and risk undertreatment of the prostate if the bottom of the ischial tuberosities was the inferior margin of the field. Measuring the location of the prostatic apex from the top of the symphysis pubis revealed that a distance of 4.9 cm encompassed the apex in all 20 patients.(ABSTRACT TRUNCATED AT 250 WORDS)