A Proof-of-Concept Study on the Use of Prostate Artery Embolization Before Definitive Radiation Therapy in Prostate Cancer.

PURPOSE: Prostatic artery embolization (PAE) is an effective therapy for alleviating lower urinary tract symptoms (LUTS) in patients with benign prostatic hyperplasia; however, is not well studied in patients with concurrent prostate cancer (PCa). We demonstrate a proof of concept for PAE before definitive radiation therapy (RT) in patients with PCa. METHODS AND MATERIALS: From December 2017 to July 2019, 9 patients with PCa underwent PAE for the indication of LUTS from benign prostatic hyperplasia with concurrent PCa. Five received radiation and all follow-ups at our institution and were therefore included in the analysis. Median follow-up was 18 months from the time of PAE. Side effects during radiation were quantified using the Common Terminology Criteria for Adverse Events scoring system. Pre- and post-PAE plans were compared in the 5 patients by performing an isovolumetric expansion of the post-PAE plan (treated plan) equivalent to the measured volume reduction after PAE. Patient 1 (PT-01) and PT-02 had prostate RT alone whereas PT-03, PT-04, and PT-05 had prostate with elective nodal coverage RT. Mean doses to organs at risk were compared between the 2 plans. RESULTS: The mean International Prostate Symptom Score reduction after PAE was 13.8 (5.0-30.0; P = .02). The mean prostatic volume reduction after PAE was 23.1% (7.2%-47.7%). There were no Common Terminology Criteria for Adverse Events grade 3 (severe) or higher during radiation. Post-PAE plans in PT-01 and PT-02 had on average 23.2%, 39.8%, and 22.9% decrease in mean dose across the bladder, rectum, and penile bulb, respectively, compared with the pre-PAE plans. There were no appreciable differences in dosimetry in PT03, PT-04, and PT-05 who had nodal coverage. There was no biochemical failure in any of the patients. CONCLUSIONS: We demonstrate a proof of concept that PAE is a clinically significant adjunctive therapy for alleviating LUTS and achieving significant volume reduction before RT, resulting in decreased radiation-related toxicity from RT for PCa.

Utility of Taking Additional Margins When Performing Breast-Conserving Surgery with Intraoperative Radiation Therapy for Early Breast Cancer.

INTRODUCTION: Intraoperative radiation therapy (IORT) is an alternative to external beam radiation therapy (EBRT) after lumpectomy, in which radiation is delivered before the final margin analysis. Practices vary regarding excision of close or positive margins pre- and post-IORT. MATERIALS AND METHODS: In a retrospective cohort of women with hormone receptor-positive, clinically node-negative breast cancer undergoing lumpectomy with IORT and selective EBRT at our institution from 2011 to 2015, we compared the impact of pre- and post-IORT margin excisions on in-breast tumor recurrence. Additional pre-IORT margins were taken at surgical team discretion. Re-excisions post-IORT were performed for positive/close margins. We describe rate of invasive or in situ malignancy in additional pre-IORT and post-IORT re-excised specimens and compare IBTR using Chi-squared tests. RESULTS: There were 195 cases in 193 women (2 bilateral breast cancer). Pre-IORT, ≥1 additional margin was obtained in 139 (71%). The final margin on the initial lumpectomy was positive in 13 (9%) and ≤2 mm in 72 (52%). Additional pre-IORT margins contained in situ/invasive cancer in 16 (12%). Thirty-one patients (16%) underwent post-IORT re-excision and nine (29%) contained invasive/in situ malignancy. Twenty-three (12%) received EBRT. In 45.6-month mean follow-up, 13 had IBTR (7%) with no difference by additional pre-IORT margin excision (5 vs. 11%, p = 0.150), post-IORT margin re-excision (10 vs. 6%, p = 0.464), or EBRT (0 vs. 8%, p = 0.172). Adjuvant endocrine therapy was associated with lower IBTR (4 vs. 17%, p = 0.003). CONCLUSIONS: Taking additional pre-IORT margins and re-excising close/positive margins post-IORT improved margin clearance rates but had an unclear effect on IBTR. Adjuvant endocrine therapy significantly reduced IBTR.

A dosimetric comparison of volumetric modulated arc therapy with step-and-shoot intensity modulated radiation therapy for prostate cancer.

PURPOSE: To compare variable dose-rate volumetric modulated arc therapy (VMAT) with 7-field, step-and-shoot intensity modulated radiation therapy (IMRT) in prostate cancer patients treated with a consistent planning target volume (PTV) to a uniform total radiation therapy dose. METHODS AND MATERIALS: We studied 32 patients who received 8100 cGy in 45 daily fractions to their prostate and proximal 1 cm of the seminal vesicles using variable dose rate VMAT (n = 22) or 7-field, step-and-shoot IMRT (n = 10) for intermediate-risk or high-risk prostate cancer between July 2010 and April 2013. In 90% of patients, VMAT was delivered with 2 arcs. To have an unbiased comparison of plan quality, patients who were treated with VMAT were also planned with IMRT and vice versa. Each patient served as his own control for the comparison. RESULTS: VMAT reduced median radiation beam-on time from 4.3 to 3.4 minutes (P = .03). There was no statistically significant difference in PTV volumes between the VMAT and step-and-shoot IMRT groups (P = .76). VMAT dose distributions were more homogeneous (P = .003). There was no difference between groups with regard to rectal V60, V65, V70, V75, bladder V65, V70, V75, V80, or femoral heads V33. CONCLUSIONS: Two-arc VMAT resulted in shorter beam-on times and more homogenous dose distributions than 7-field, step-and-shoot IMRT for prostate cancer. With decreased beam-on time, the intrafraction motion during irradiation is reduced, thus improving confidence that the delivered dose distribution agrees with the plan.

Monte Carlo comparison of superficial dose between flattening filter free and flattened beams.

This study investigates the superficial dose from FFF beams in comparison with the conventional flattened ones using a Monte Carlo (MC) method. Published phase-space files which incorporated real geometry of a TrueBeam accelerator were used for the dose calculation in phantom and clinical cases. The photon fluence on the central axis is 3 times that of a flattened beam for a 6 MV FFF beam and 5 times for a 10 MV beam. The mean energy across the field in air at the phantom surface is 0.92-0.95 MeV for the 6 MV FFF beam and 1.18-1.30 MeV for the corresponding flattened beam. At 10 MV, the values are 1.52-1.72 and 2.15-2.87 MeV for the FFF and flattened beams, respectively. The phantom dose at the depth of 1 mm in the 6 MV FFF beam is 6% ± 2.5% (of the maximum dose) higher compared to the flattened beam for a 25 × 25 cm(2) field and 14.6% ± 1.9% for the 2 × 2 cm(2) field. For the 10 MV beam, the corresponding differences are 3.4% ± 1.5% and 10.7% ± 0.6%. The skin dose difference at selected points on the patient's surface between the plans using FFF and flattened beams in the head-and-neck case was 6.5% ± 2.3% (1SD), and for the breast case it was 6.4% ± 2.3%. The Monte Carlo simulations showed that due to the lower mean energy in the FFF beam, the clinical superficial dose is higher without the flattening filter compared to the flattened beam.

Comparing dose in the build-up region between compensator- and MLC-based IMRT.

The build-up dose in the megavoltage photon beams can be a limiting factor in intensity-modulated radiation therapy (IMRT) treatments. Excessive surface dose can cause patient discomfort and treatment interruptions, while underdosing may lead to tumor repopulation and local failure. Dose in the build-up region was investigated for IMRT delivery with solid brass compensator technique(compensator-based IMRT) and compared with that of multileaf collimator (MLC)-based IMRT. A Varian Trilogy linear accelerator equipped with an MLC was used for beam delivery. A special solid brass step-wise compensator was designed and built for testing purposes. Two step-and-shoot MLC fields were programmed to produce a similar modulated step-wise dose profile. The MLC and compensator dose profiles were measured and adjusted to match at the isocenter depth of 10 cm. Build-up dose in the 1-5 mm depth range was measured with an ultrathin window, fixed volume parallel plate ionization chamber. Monte Carlo simulations were used to model the brass compensator and step-and-shoot MLC fields. The measured and simulated profiles for the two IMRT techniques were matched at the isocenter depth of 10 cm. Different component contributions to the shallow dose, including the MLC scatter, were quantified. Mean spectral energies for the open and filtered beams were calculated. The compensator and MLC profiles at 10 cm depth were matched better than ± 1.5%. The build-up dose was up to 7% lower for compensator IMRT compared to MLC IMRT due to beam hardening in the brass. Low-energy electrons contribute 22% and 15% dose at 1 mm depth for compensator and MLC modalities, respectively. Compensator-based IMRT delivers less dose in the build-up region than MLC-based IMRT does, even though a compensator is closer to the skin than the MLC.

Skin dose study of chest wall treatment with tomotherapy.

PURPOSE: The tangential-beam technique frequently presents challenges in homogeneity of radiation dose to the target. To ensure an adequate dose to the skin, a bolus is often used. Tomotherapy has already been shown to improve target conformity and homogeneity in other disease sites. Because of the tangential delivery technique and lack of flattening filter in TomoTherapy accelerators, we hypothesize that during chest wall irradiation using tomotherapy, the skin dose will be adequate without bolus. MATERIALS AND METHODS: This study compares the dosimetric differences between tomotherapy chest wall irradiation and traditional linear accelerator-based tangential-beam technique. Tomotherapy treatment plans with and without bolus were compared with tangentialbeam plans. Plans were also generated for phantom studies, and point doses were measured using MOSFET dosimetry to verify the adequate skin dose. Monte Carlo simulations of static beams of both techniques were performed, and dosimetry was compared. RESULTS: Monte Carlo simulations and measurements confirmed that beams from tomotherapy deliver a higher skin dose than a standard linear accelerator. Skin dose also increases with the incident angle of the beams. CONCLUSION: Because of the characteristics of the tomotherapy beam and delivery technique, chest wall treatment plans from tomotherapy showed adequate skin dose [more than 75% of prescribed planning target volume (PTV) dose] even without bolus.

Compensator-based intensity-modulated radiation therapy for malignant pleural mesothelioma post extrapleural pneumonectomy.

The present work investigated the potential of compensator-based intensity-modulated radiation therapy (CB-IMRT) as an alternative to multileaf collimator (MLC)-based intensity-modulated radiation therapy (IMRT) to treat malignant pleural mesothelioma (MPM) post extrapleural pneumonectomy. Treatment plans for 4 right-sided and 1 left-sided MPM post-surgery cases were generated using a commercial treatment planning system, XIO/CMS (Computerized Medical Systems, St. Louis, MO). We used a 7-gantry-angle arrangement with 6 MV beams to generate these plans. The maximum required field size was 30 x 40 cm. We evaluated IMRT plans with brass compensators (.Decimal, Sanford, FL) by examining isodose distributions, dose-volume histograms, metrics to quantify conformal plan quality, and homogeneity. Quality assurance was performed for one of the compensator plans. Conformal dose distributions were achieved with CB-IMRT for all 5 cases, the average planning target volume (PTV) coverage being 95.1% of the PTV volume receiving the full prescription dose. The average lung V20 (volume of lung receiving 20 Gy) was 1.8%, the mean lung dose was 6.7 Gy, and the average contralateral kidney V15 was 0.6%. The average liver dose V30 was 34.0% for the right-sided cases and 10% for the left-sided case. The average monitor units (MUs) per fraction were 980 MUs for the 45-Gy prescriptions (mean: 50 Gy) and 1083 MUs for the 50-Gy prescriptions (mean: 54 Gy). Post surgery, CB-IMRT for MPM is a feasible IMRT technique for treatment with a single isocenter. Compensator plans achieved dose objectives and were safely delivered on a Siemens Oncor machine (Siemens Medical Solutions, Malvern, PA). These plans showed acceptably conformal dose distributions as confirmed by multiple measurement techniques. Not all linear accelerators can deliver large-field MLC-based IMRT, but most can deliver a maximum conformal field of 40 x 40 cm. It is possible and reasonable to deliver IMRT with compensators for fields this size with most conventional linear accelerators.