(P066) Dosimetric Analysis of Proton Therapy for Prostate Cancer: A Single Institutional Experience

OncologyOncology Vol 29 No 4_Suppl_1
Volume 29
Issue 4_Suppl_1

Proton therapy for prostate cancer typically generates treatment plans that are below dose constraints defined in the photon literature, with the exception of a small subset of patients. In order to promote the best possible proton treatment plans, lower dose constraints for OARs should be considered.

Jing Zeng, Kent McCune, Matthias Cook, Grayden MacLennan, Malin Mao, George E. Laramore, Kenneth Russell, Jay Liao; University of Washington

BACKGROUND: With the increasing number of proton therapy centers in the United States, more patients with prostate cancer have access to proton radiation as a treatment option. While dose constraints for organs at risk (OARs) are well defined for photon treatment, less is known for proton radiation, and photon constraints are often used after correcting for relative biological effectiveness (RBE = 1.1). However, it is often possible to achieve lower doses to OARs with proton therapy. Therefore, we investigated dose to OARs in a series of patients treated at our institution to consider lowering dose constraints for the proton population.

METHODS: Consecutive patients with prostate cancer treated at our center from April–September 2014 were analyzed. All patients were treated with fiducial markers, daily kV image-guided radiation therapy (IGRT), full bladder, and rectal balloon. Clinical characteristics and OAR doses were extracted. Low-risk patients were treated to prostate plus 3–5-mm planning target volume (PTV) margin. Intermediate- and high-risk patients were treated to prostate plus proximal seminal vesicles, with optional pelvic nodal irradiation for high-risk patients. Treatment groups were compared with t-tests.

RESULTS: A total of 40 patients with prostate cancer were treated, with a median age of 68 years (range: 51–79 yr); 10 patients had low-risk disease, 21 had intermediate-risk disease, and 9 had high-risk disease (5 received whole-pelvis radiation). A total of 31 patients were treated with pencil beam scanning, and 9 patients were treated with uniform scanning. Median prescription was 79.2 Cobalt Gray Equivalent (CGE).

For the bladder: median V80 CGE = 4.9 cc (range: 0–13.8 cc) with constraint < 8 cc; median V70 CGE = 6.6% (range: 3.6%–22.1%) with constraint < 10%; and median V50 CGE = 11.5% (range: 6.1%–32.8%) with constraint < 35%. For the bladder wall (3-mm internal rind): median V80 CGE = 3.5% (range: 0%–14.5%) with constraint < 15%; median V70 CGE = 13% (range: 8%–31%) with constraint < 35%, and median V55 CGE = 16.5% (range: 10.8%–36.5%) with constraint < 50%.

For the rectum: median V81 CGE = 0 cc (range: 0–6.61cc) with constraint < 1 cc; median V70 CGE = 10.8% (range: 3.0%–19.3%) with constraint < 25%; and median V50 CGE = 19.6% (range: 10.9%–33.8%) with constraint < 35%. For the rectal wall (3–mm internal rind): median V81 CGE = 0 cc (range: 0–5.36 cc) with constraint < 1 cc; median V70 CGE = 22.6% (range: 5.7%–34.3%) with constraint < 25%; and median V50 CGE = 32.5% (range: 15.8%–43%) with constraint < 50%.

Comparing the low-, intermediate-, and high-risk disease groups, the only significant dose difference was in rectal wall V50 CGE (low = 28.4%, intermediate = 32.1%, high = 35.0%).

CONCLUSIONS: Proton therapy for prostate cancer typically generates treatment plans that are below dose constraints defined in the photon literature, with the exception of a small subset of patients. In order to promote the best possible proton treatment plans, lower dose constraints for OARs should be considered. 

Proceedings of the 97th Annual Meeting of the American Radium Society- americanradiumsociety.org

Articles in this issue

(P005) Ultrasensitive PSA Identifies Patients With Organ-Confined Prostate Cancer Requiring Postop Radiotherapy
(P001) Disparities in the Local Management of Breast Cancer in the United States According to Health Insurance Status
(P002) Predictors of CNS Disease in Metastatic Melanoma: Desmoplastic Subtype Associated With Higher Risk
(P003) Identification of Somatic Mutations Using Fine Needle Aspiration: Correlation With Clinical Outcomes in Patients With Locally Advanced Pancreatic Cancer
(P004) A Retrospective Study to Assess Disparities in the Utilization of Intensity-Modulated Radiotherapy (IMRT) and Proton Therapy (PT) in the Treatment of Prostate Cancer (PCa)
(S001) Tumor Control and Toxicity Outcomes for Head and Neck Cancer Patients Re-Treated With Intensity-Modulated Radiation Therapy (IMRT)-A Fifteen-Year Experience
(S003) Weekly IGRT Volumetric Response Analysis as a Predictive Tool for Locoregional Control in Head and Neck Cancer Radiotherapy 
(S004) Combination of Radiotherapy and Cetuximab for Aggressive, High-Risk Cutaneous Squamous Cell Cancer of the Head and Neck: A Propensity Score Analysis
(S005) Radiotherapy for Carcinoma of the Hypopharynx Over Five Decades: Experience at a Single Institution
(S002) Prognostic Value of Intraradiation Treatment FDG-PET Parameters in Locally Advanced Oropharyngeal Cancer
(P006) The Role of Sequential Imaging in Cervical Cancer Management
(P008) Pretreatment FDG Uptake of Nontarget Lung Tissue Correlates With Symptomatic Pneumonitis Following Stereotactic Ablative Radiotherapy (SABR)
(P009) Monte Carlo Dosimetry Evaluation of Lung Stereotactic Body Radiosurgery
(P010) Stereotactic Body Radiotherapy for Treatment of Adrenal Gland Metastasis: Toxicity, Outcomes, and Patterns of Failure
(P011) Stereotactic Radiosurgery and BRAF Inhibitor Therapy for Melanoma Brain Metastases Is Associated With Increased Risk for Radiation Necrosis
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