M. Mathai

University of California, Davis, Davis, California, United States

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Publications (25)33 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Purpose This investigation details the time and teamwork required for CT-guided tandem and ring high-dose-rate brachytherapy. Methods and Materials From 2010 to 2012, 217 consecutive implantations were identified on 52 patients. We gathered key workflow times: preoperative, applicator insertion, CT image, treatment planning, treatment, patient recovery, and total time in clinic. Linear fixed-effects models were used, and key workflow times were the outcome variables and factors including age, body mass index, stage, outside referral, number of implant per patient, number of implants per day, and year of implantation were examined as fixed effects. Results Of the 52 patients, 62% of the patients were Fédération Internationale de Gynécologie et d'Obstétrique Stage 2B, 88% were treated with concurrent chemotherapy, and 23% were treated at an outside facility and referred for the procedure. The mean times (minutes) for each step were as follows: preoperative evaluation, 93; insertion, 23; imaging, 45; treatment planning, 137; treatment, removal, and recovery, 115; total clinic time, 401. For the insertion time, the greater implant number per patient was significantly associated with a decreased total insertion time, with and without adjusting for other covariates, p = 0.002 and p = 0.0005, respectively. Treatment planning time was expedited with increasing number of implant per patient and comparing treatment times in 2012 with those in 2010, p = 0.01 and p < 0.0001, respectively. Conclusions Gynecologic brachytherapy requires a skillfully coordinated and efficient team approach. Identifying critical components and the time required for each step in the process is needed to improve the safety and efficiency of brachytherapy. Continuous efforts should be made to enhance the optimal treatment delivery in high-dose-rate gynecologic brachytherapy.
    Brachytherapy 01/2014; · 1.22 Impact Factor
  • The British journal of radiology 10/2013; · 2.11 Impact Factor
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    ABSTRACT: Purpose: To determine the effect of adaptive re-planning on clinical outcome among patients treated by intensity-modulated radiotherapy (IMRT) for head and neck cancer. Materials/Methods: 317 patients underwent IMRT with daily image-guidance for newly-diagnosed squamous cell carcinoma of the head and neck to a median dose of 66 Gy (range, 60 to 74 Gy). Of these 317 patients, fifty-one (16%) underwent adaptive radiotherapy with modification of the original IMRT midway during treatment. Results: The 2-year local-regional control was 88% for patients treated with adaptive re-planning compared to 79% for patients treated without (p=0.01). The median time to local-regional recurrence for the 4 patients treated by adaptive radiotherapy was 7 months (range, 3 to 15 months) with all failures occurring within the high-dose planning target volume. Conclusion: While the use of routine re-planning is probably not necessary, our findings do suggest a significant benefit in appropriately selected patients. Head Neck, 2013.
    Head & Neck 08/2013; · 2.83 Impact Factor
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    ABSTRACT: Optimal treatment with radiation for metastatic lymphadenopathy in locally advanced cervical cancer remains controversial. We investigated the clinical dose response threshold for pelvic and para-aortic lymph node boost using radiographic imaging and clinical outcomes. Between 2007 and 2011, 68 patients were treated for locally advanced cervical cancer; 40 patients had clinically involved pelvic and/or para-aortic lymph nodes. Computed tomography (CT) or 18F-labeled fluorodeoxyglucose-positron emission tomography scans obtained pre- and postchemoradiation for 18 patients were reviewed to assess therapeutic radiographic response of individual lymph nodes. External beam boost doses to involved nodes were compared to treatment response, assessed by change in size of lymph nodes by short axis and change in standard uptake value (SUV). Patterns of failure, time to recurrence, overall survival (OS), and disease-free survival (DFS) were determined. Sixty-four lymph nodes suspicious for metastatic involvement were identified. Radiation boost doses ranged from 0 to 15 Gy, with a mean total dose of 52.3 Gy. Pelvic lymph nodes were treated with a slightly higher dose than para-aortic lymph nodes: mean 55.3 Gy versus 51.7 Gy, respectively. There was no correlation between dose delivered and change in size of lymph nodes along the short axis. All lymph nodes underwent a decrease in SUV with a complete resolution of abnormal uptake observed in 68%. Decrease in SUV was significantly greater for lymph nodes treated with ≥54 Gy compared to those treated with <54 Gy (P=.006). Median follow-up was 18.7 months. At 2 years, OS and DFS for the entire cohort were 78% and 50%, respectively. Locoregional control at 2 years was 84%. A biologic response, as measured by the change in SUV for metastatic lymph nodes, was observed at a dose threshold of 54 Gy. We recommend that involved lymph nodes be treated to this minimum dose.
    International journal of radiation oncology, biology, physics 07/2013; · 4.59 Impact Factor
  • Gynecologic oncology. 10/2012; 127(1 Suppl):S25-6.
  • Gynecologic Oncology. 10/2012; 127(1):S3.
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    ABSTRACT: To improve the quality and safety of our practice of stereotactic body radiation therapy (SBRT), we analyzed the process following the failure mode and effects analysis (FMEA) method. The FMEA was performed by a multidisciplinary team. For each step in the SBRT delivery process, a potential failure occurrence was derived and three factors were assessed: the probability of each occurrence, the severity if the event occurs, and the probability of detection by the treatment team. A rank of 1 to 10 was assigned to each factor, and then the multiplied ranks yielded the relative risks (risk priority numbers). The failure modes with the highest risk priority numbers were then considered to implement process improvement measures. A total of 28 occurrences were derived, of which nine events scored with significantly high risk priority numbers. The risk priority numbers of the highest ranked events ranged from 20 to 80. These included transcription errors of the stereotactic coordinates and machine failures. Several areas of our SBRT delivery were reconsidered in terms of process improvement, and safety measures, including treatment checklists and a surgical time-out, were added for our practice of gantry-based image-guided SBRT. This study serves as a guide for other users of SBRT to perform FMEA of their own practice.
    International journal of radiation oncology, biology, physics 12/2011; 83(4):1324-9. · 4.59 Impact Factor
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    ABSTRACT: Our goal was to evaluate brachial plexus (BP) dose with and without the use of supraclavicular (SCL) irradiation in patients undergoing breast-conserving therapy with whole-breast radiation therapy (RT) after lumpectomy. Using the standardized Radiation Therapy Oncology Group (RTOG)-endorsed guidelines delineation, we contoured the BP for 10 postlumpectomy breast cancer patients. The radiation dose to the whole breast was 50.4 Gy using tangential fields in 1.8-Gy fractions, followed by a conedown to the operative bed using electrons (10 Gy). The prescription dose to the SCL field was 50.4 Gy, delivered to 3-cm depth. The mean BP volume was 14.5 ± 1.5 cm(3). With tangential fields alone, the median mean dose to the BP was 0.57 Gy, the median maximum dose was 1.93 Gy, and the irradiated volume of the BP receiving 40, 45, and 50 Gy was 0%. When the third (SCL field) was added, the dose to the BP was significantly increased (P = .01): the median mean dose to the BP was 40.60 Gy, and the median maximum dose was 52.22 Gy. With 3-field RT, the median irradiated volume of the BP receiving 40, 45, and 50 Gy was 83.5%, 68.5%, and 24.6%, respectively. The addition of the SCL field significantly increases dose to the BP. The possibility of increasing the risk of BP morbidity should be considered in the context of clinical decision making.
    Medical dosimetry: official journal of the American Association of Medical Dosimetrists 09/2011; 37(2):127-30. · 1.26 Impact Factor
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    ABSTRACT: To evaluate interobserver variability for contouring the brachial plexus as an organ-at-risk (OAR) and to analyze its potential dosimetric consequences in patients treated with intensity-modulated radiotherapy (IMRT) for head-and-neck cancer. Using the Radiation Therapy Oncology Group (RTOG)-endorsed brachial plexus contouring atlas, three radiation oncologists independently delineated the OAR on treatment planning computed-tomography (CT) axial scans from 5 representative patients undergoing IMRT to a prescribed dose of 70 Gy for head-and-neck cancer. Dose-volume histograms for the brachial plexus were calculated, and interobserver differences were quantified by comparing various dosimetric statistics. Qualitative analysis was performed by visually assessing the overlapping contours on a single beam's eye view. Brachial plexus volumes for the 5 patients across observers were 26 cc (18-35 cc), 25 cc (21-30 cc), 29 cc (28-32 cc), 29 cc (23-38 cc), and 29 cc (23-34 cc). On qualitative analysis, minimal variability existed except at the inferolateral portion of the OAR, where slight discrepancies were noted among the physicians. Maximum doses to the brachial plexus ranged from 71.6 to 72.6 Gy, 75.2 to 75.8 Gy, 69.1 to 71.0 Gy, 76.4 to 76.9 Gy, and 70.6 to 71.4 Gy. Respective volumes receiving doses greater than 60 Gy (V60) were 8.6 to 10.9 cc, 6.2 to 8.1 cc, 8.2 to 11.6 cc, 8.3 to 10.5 cc, and 5.6 to 9.8 cc. The RTOG-endorsed brachial plexus atlas provides a consistent set of guidelines for contouring this OAR with essentially no learning curve. Adoption of these contouring guidelines in the clinical setting is encouraged.
    International journal of radiation oncology, biology, physics 04/2011; 82(3):1060-4. · 4.59 Impact Factor
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    ABSTRACT: To investigate dose-volume consequences of inclusion of the seminal vesicle (SV) bed in the clinical target volume (CTV) for the rectum and bladder using biological response indices in postprostatectomy patients receiving intensity-modulated radiotherapy (IMRT). We studied 10 consecutive patients who underwent prostatectomy for prostate cancer and subsequently received adjuvant or salvage RT to the prostate fossa. The CTV to planning target volume (PTV) expansion was 7 mm, except posterior expansion, which was 5 mm. Two IMRT plans were generated for each patient, including either the prostate fossa alone or the prostate fossa with the SV bed, but identical in all other aspects. Prescription dose was 68.4 Gy in 1.8-Gy fractions prescribed to ≥95% PTV. With inclusion of the SV bed in the treatment volume, PTV increased and correlated with PTV-bladder and PTV-rectum volume overlap (Spearman ρ 0.91 and 0.86, respectively; p < 0.05). As a result, the dose delivered to the bladder and rectum was higher (p < 0.05): mean bladder dose increased from 11.3 ± 3.5 Gy to 21.2 ± 6.6 Gy, whereas mean rectal dose increased from 25.8 ± 5.5 Gy to 32.3 ± 5.5 Gy. Bladder and rectal equivalent uniform dose correlated with mean bladder and rectal dose. Inclusion of the SV bed in the treatment volume increased rectal normal tissue complication probability from 2.4% to 4.8% (p < 0.01). Inclusion of the SV bed in the CTV in postprostatectomy patients receiving IMRT increases bladder and rectal dose, as well as rectal normal tissue complication probability. The magnitude of PTV-bladder and PTV-rectal volume overlap and subsequent bladder and rectum dose increase will be higher if larger PTV expansion margins are used.
    International journal of radiation oncology, biology, physics 04/2011; 82(5):1897-902. · 4.59 Impact Factor
  • Fuel and Energy Abstracts 01/2011; 81(2).
  • Fuel and Energy Abstracts 01/2011; 81(2).
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    ABSTRACT: The preferential use of intensity-modulated radiotherapy (IMRT) over conventional radiotherapy (CRT) in the treatment of head and neck cancer has raised concerns regarding dose to non-target tissue. The purpose of this study was to compare dose-volume characteristics with the brachial plexus between treatment plans generated by IMRT and CRT using several common treatment scenarios. The brachial plexus was delineated on radiation treatment planning CT scans from 10 patients undergoing IMRT for locally advanced head and neck cancer using a Radiation Therapy Oncology Group-endorsed atlas. No brachial plexus constraint was used. For each patient, a conventional three-field shrinking-field plan was generated and the dose-volume histogram (DVH) for the brachial plexus was compared with that of the IMRT plan. The mean irradiated volumes of the brachial plexus using the IMRT vs the CRT plan, respectively, were as follows: V50 (18±5 ml) vs (11±6 ml), p = 0.01; V60 (6±4 ml) vs (3±3 ml), p = 0.02; V66 (3±1 ml) vs (1±1 ml), p = 0.04, V70 (0±1 ml) vs (0±1 ml), p = 0.68. The maximum point dose to the brachial plexus was 68.9 Gy (range 62.3-78.7 Gy) and 66.1 Gy (range 60.2-75.6 Gy) for the IMRT and CRT plans, respectively (p = 0.01). Dose to the brachial plexus is significantly increased among patients undergoing IMRT compared with CRT for head and neck cancer. Preliminary studies on brachial plexus-sparing IMRT are in progress.
    The British journal of radiology 01/2011; 84(997):58-63. · 2.11 Impact Factor
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    ABSTRACT: To compare intensity-modulated radiotherapy (IMRT) treatment plans generated by segmental multileaf collimator (SMLC) and helical tomotherapy (HT) techniques for patients with unresectable sinonasal cancer. SMLC-IMRT and HT-IMRT plans for 5 patients with cancer of the paranasal sinuses and nasal cavity were independently optimized using the Eclipse treatment planning system (Varian Medial Systems, Palo Alto, CA) and Tomotherapy HI-ART treatment planning system (Tomotherapy, Inc, Madison, WI). The goal was to deliver a prescribed dose of 70 Gy to at least 95% of the planning target volume (PTV) encompassing gross tumor over 35 treatments whereas respecting constraints to organs at risk, notably the ocular structures. HT-IMRT reduced the maximum doses to the optic chiasm, as well as to the ipsilateral optic nerve and retina (P < 0.05, for all). Maximum doses to these structures were reduced by 10%, 16%, and 14%, respectively, using HT-IMRT compared with SMLC-IMRT. Additionally, the mean dose to the ipsilateral lacrimal gland was reduced by 32% using HT-IMRT. With respect to conformality, HT-IMRT improved dose homogeneity by decreasing "hot-spots." The mean percentage of PTV70 receiving greater than 77 Gy (110% of the prescribed dose) was 4.0% for the HT-IMRT plans compared with 17.8% for the SMLC-IMRT plans (P = 0.001). HT-IMRT has the potential to improve dose homogeneity to PTVs whereas reducing dose to the optic structures. Clinical implications are discussed.
    American journal of clinical oncology 02/2010; 33(6):595-8. · 2.21 Impact Factor
  • Fuel and Energy Abstracts 01/2010; 78(3).
  • Fuel and Energy Abstracts 01/2010; 78(3).
  • J Perks, J Cui, M Mathai, J Purdy
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    ABSTRACT: Purpose: While the authors strongly support the concept of credentialing and formal QA to evaluate the ability of institutions to perform advanced technology protocols, we question the methodology currently used by the Radiological Physics Center (RPC) for SBRT as an extremely high failure rate is being seen. We have performed a series of tests to replicate the components of the RPC lung phantom thus giving insight into why institutions fail. Materials and Methods: The Quasar phantom was used to simulate a lung cross section. Firstly an end‐to‐end test was performed with the phantom scanned and simulated for treatment with 13 small, conformal fields, with a ionization chamber placed both centrally and then in the lung. Then a simulation of the RPC phantom planning procedure was performed where a homogeneous plan was created, the phantom was treated, then the heterogeneous calculation was performed and compared with measured dose. A film test was performed to show that the spatial distribution within the phantom was accurately predicted by the planning system. Finally an assessment was made of the changes that occur to the SBRT plan on the RPC phantom when the homogeneous dose distribution is recalculated under heterogeneous conditions Results: Every comparison of the dose measured with an ionization chamber against the planned dose was within 3% and the film test passed the department's IMRT test criteria of 3% / 3mm. Dramatic differences in dose gradient and target coverage were seen between the homogeneous and heterogeneous RPC plans. Conclusions: Tests can readily be performed with commercial materials to validate SBRT delivery. Large differences are seen in plans when heterogeneity corrections are used to correct homogeneous plans of small field lung targets. This may reveal a flaw in the methodology of the RPC testing procedure, leading to a high failure rate amongst national institutions.
    Medical Physics 05/2009; 36(6):2652-2652. · 2.91 Impact Factor
  • Fuel and Energy Abstracts 01/2009; 75(3).
  • Fuel and Energy Abstracts 01/2009; 75(3).
  • Fuel and Energy Abstracts 01/2009; 75(3).