{'fraction_non_alphanumeric': 0.0631879331430901, 'fraction_numerical': 0.03383611903791276, 'mean_word_length': 4.8428571428571425, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
WE-AB-207B-09: Margin Reduction for Planning Target Volume (PTV) in Patients with Localized Prostate Cancer: Impact On Delivered Dose and Quality of Life.

PURPOSE
To estimate the delivered (cumulative) dose to targets and organs at risk for localized prostate cancer patients treated with reduced PTV margins and to evaluate preliminary patient reported quality-of-life (QOL).


METHODS
Under an IRB-approved protocol, 20 prostate cancer patients (including 11 control patients) were treated with reduced planning margins (5 mm uniform with 4 mm at prostate/rectum interface). Control patients had standard margin (10/6 mm)-based treatments. A parameter-optimized Elastix algorithm along with energy-mass mapping was used to deform and resample dose of the day onto the planning CT for each fraction to estimate the delivered dose over all fractions. QOL data were collected via Expanded Prostate cancer Index Composite (EPIC-26) questionnaires at time points pre-treatment, post-treatment, and at 2, 6, 12, 18 month follow-ups. Standardized QOL scores [range: 0-100] were determined and baseline-corrected by subtracting pre-treatment QOL data. Mean QOL differences between the margin reduced group and control group (QOLmr-QOLcontrol) were calculated for first 18 months.


RESULTS
The difference between the cumulative mean dose (Dmean) and the planned mean dose (±SD) for PTV, prostate, bladder, and rectum were -2.2±1.0, 0.3±0.5, -0.7±2.6, and -2.1±1.3 Gy respectively for the margin-reduced group, and -0.8±2.0, 0.9±1.4, - 0.7±3.1 and -1.0±2.4 Gy for the control group. Difference between the two groups was statistically insignificant (p=0.1). Standardized and baseline corrected QOLmr-QOLcontrol for EPIC domains categorized as "Urinary Incontinence", "Urinary Irritative/Obstructive", "Bowel", "Sexual", and "Hormonal" were 0.6, 12.1, 9.1, 13.3, and -0.9 for the 18 months following radiation therapy (higher values better). Delivered dose to rectum showed a weak correlation to "Bowel" domain (Pearson's coefficient -0.24, p<0.001), while bladder dose did not correlate to Urinary Incontinence/Irritative/Obstructive QOL domains.


CONCLUSION
The margin-reduced group exhibited clinically meaningful improvement of QOL without compromising the PTV dose. A larger number of patients and greater follow-up is needed to draw unequivocal conclusions. This work was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA.