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Title: SU-G-JeP4-09: Impact of Interfractional Motion On Hypofractionated Pencil Beam Scanning Proton Therapy for Prostate Cancer

Abstract

Purpose: To investigate the impact of anatomy/setup variations on standard vs. hypofractionated anterolateral pencil beam scanning (PBS) proton therapy for prostate cancer. Methods: Six prostate cancer patients treated with double-scattering proton therapy, who underwent weekly verification CT scans were selected. Implanted fiducials were used for localization, and endorectal balloons for immobilization. New PBS plans using combination of lateral and anterior-oblique (AO) (±35 deg) beams were created. AO beams were added to spare the femoral heads during hypofractionation. Lateral beams delivered 50.4 Gy(RBE) to prostate plus 5-15mm of seminal vesicles and AO beams 28.8 Gy(RBE) to prostate, in 44 fractions. PTV was laterally expanded by 2.5% to account for range uncertainty. No range margins were applied for AO beams, assuming delivery with in-vivo range verification. Field-specific apertures with 1.2cm margin were used. Spot size was ∼9.5mm sigma for 172MeV @isocenter in air. Plans were optimized as single-field-uniform-dose with ∼5% maximum non-uniformity. The planned dose was recomputed on each weekly CT after aligning the fiducials with the simulation CT, scaled and accumulated via deformable image registration. Hypofractionated treatments with 12 and 5 fractions were considered. Equivalent doses were calculated for prostate (α/β= 1.5Gy), bladder and rectum (α/β= 3Gy). Results: The biological equivalentmore » prostate dose was 86.2 and 92.9 Gyeq for the hypofractionation scenarios at 4.32 and 7.35 Gy/fx, respectively. The equivalent prostate D98 was degraded by on average 2.7 Gyeq for standard, and 3.1 and 4.0 Gyeq for the hypofractionated plans after accumulation. Differences between accumulated and planned Dmean/D2/EUD were generally reduced when reducing the number of fractions for bladder and rectum. The average Dmean/D2/EUD differences over all patients and organs-at-risk were 0.74/4.0/9.23, 0.49/3.64/5.51, 0.37/3.21/3.49 Gyeq for 44, 12 and 5 fractions. Conclusion: Hypofractionation makes proton therapy of prostate more susceptible to interfractional motion-induced target dose degradation compared to the standard fractionation.« less

Authors:
; ; ; ; ; ;  [1]
  1. Massachusetts General Hospital and Harvard Medical School, Boston, MA (United States)
Publication Date:
OSTI Identifier:
22649459
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; COMPUTERIZED TOMOGRAPHY; DOSE EQUIVALENTS; FRACTIONATED IRRADIATION; FRACTIONATION; IN VIVO; LEAD SULFIDES; NEOPLASMS; PROSTATE; PROTON BEAMS; RADIOTHERAPY

Citation Formats

Moteabbed, M, Trofimov, A, Sharp, G, Wang, Y, Zietman, A, Efstathiou, J, and Lu, H. SU-G-JeP4-09: Impact of Interfractional Motion On Hypofractionated Pencil Beam Scanning Proton Therapy for Prostate Cancer. United States: N. p., 2016. Web. doi:10.1118/1.4957119.
Moteabbed, M, Trofimov, A, Sharp, G, Wang, Y, Zietman, A, Efstathiou, J, & Lu, H. SU-G-JeP4-09: Impact of Interfractional Motion On Hypofractionated Pencil Beam Scanning Proton Therapy for Prostate Cancer. United States. doi:10.1118/1.4957119.
Moteabbed, M, Trofimov, A, Sharp, G, Wang, Y, Zietman, A, Efstathiou, J, and Lu, H. 2016. "SU-G-JeP4-09: Impact of Interfractional Motion On Hypofractionated Pencil Beam Scanning Proton Therapy for Prostate Cancer". United States. doi:10.1118/1.4957119.
@article{osti_22649459,
title = {SU-G-JeP4-09: Impact of Interfractional Motion On Hypofractionated Pencil Beam Scanning Proton Therapy for Prostate Cancer},
author = {Moteabbed, M and Trofimov, A and Sharp, G and Wang, Y and Zietman, A and Efstathiou, J and Lu, H},
abstractNote = {Purpose: To investigate the impact of anatomy/setup variations on standard vs. hypofractionated anterolateral pencil beam scanning (PBS) proton therapy for prostate cancer. Methods: Six prostate cancer patients treated with double-scattering proton therapy, who underwent weekly verification CT scans were selected. Implanted fiducials were used for localization, and endorectal balloons for immobilization. New PBS plans using combination of lateral and anterior-oblique (AO) (±35 deg) beams were created. AO beams were added to spare the femoral heads during hypofractionation. Lateral beams delivered 50.4 Gy(RBE) to prostate plus 5-15mm of seminal vesicles and AO beams 28.8 Gy(RBE) to prostate, in 44 fractions. PTV was laterally expanded by 2.5% to account for range uncertainty. No range margins were applied for AO beams, assuming delivery with in-vivo range verification. Field-specific apertures with 1.2cm margin were used. Spot size was ∼9.5mm sigma for 172MeV @isocenter in air. Plans were optimized as single-field-uniform-dose with ∼5% maximum non-uniformity. The planned dose was recomputed on each weekly CT after aligning the fiducials with the simulation CT, scaled and accumulated via deformable image registration. Hypofractionated treatments with 12 and 5 fractions were considered. Equivalent doses were calculated for prostate (α/β= 1.5Gy), bladder and rectum (α/β= 3Gy). Results: The biological equivalent prostate dose was 86.2 and 92.9 Gyeq for the hypofractionation scenarios at 4.32 and 7.35 Gy/fx, respectively. The equivalent prostate D98 was degraded by on average 2.7 Gyeq for standard, and 3.1 and 4.0 Gyeq for the hypofractionated plans after accumulation. Differences between accumulated and planned Dmean/D2/EUD were generally reduced when reducing the number of fractions for bladder and rectum. The average Dmean/D2/EUD differences over all patients and organs-at-risk were 0.74/4.0/9.23, 0.49/3.64/5.51, 0.37/3.21/3.49 Gyeq for 44, 12 and 5 fractions. Conclusion: Hypofractionation makes proton therapy of prostate more susceptible to interfractional motion-induced target dose degradation compared to the standard fractionation.},
doi = {10.1118/1.4957119},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: The main purpose of this study is to investigate the optimum oblique-beam arrangement for bilateral metallic prosthesis prostate cancer treatment in pencil beam scanning (PBS) proton therapy. Methods: A computed tomography dataset of bilateral metallic prosthesis prostate cancer case was selected for this retrospective study. A total of four beams (rightanterior- oblique [RAO], left-anterior-oblique [LAO], left-posterior-oblique [LPO], and right-posterior-oblique [RPO]) were selected for treatment planning. PBS plans were generated using multi-field-optimization technique for a total dose of 79.2 Gy[RBE] to be delivered in 44 fractions. Specifically, five different PBS plans were generated based on 2.5% ± 2 mm rangemore » uncertainty using five different beam arrangements (i)LAO+RAO+LPO+RPO, (ii)LAO+RAO, (iii)LPO+RPO, (iv)RAO+LPO, and (v)LAO+RPO. Each PBS plan was optimized by applying identical dose-volume constraints to the PTV, rectum, and bladder. Treatment plans were then compared based on the dose-volume histograms results. Results: The PTV coverage was found to be greater than 99% in all five plans. The homogeneity index (HI) was found to be almost identical (range, 0.03–0.04). The PTV mean dose was found to be comparable (range, 81.0–81.1 Gy[RBE]). For the rectum, the lowest mean dose (8.0 Gy[RBE]) and highest mean dose (31.1 Gy[RBE]) were found in RAO+LAO plan and LPO+RPO plan, respectively. LAO+RAO plan produced the most favorable dosimetric results of the rectum in the medium-dose region (V50) and high-dose region (V70). For the bladder, the lowest (5.0 Gy[RBE]) and highest mean dose (10.3 Gy[RBE]) were found in LPO+RPO plan and RAO+LAO plan, respectively. Other dosimetric results (V50 and V70) of the bladder were slightly better in LPO+RPO plan than in other plans. Conclusion: Dosimetric findings from this study suggest that two anterior-oblique proton beams arrangement (LAO+RAO) is a more favorable option with the possibility of reducing rectal dose significantly while maintaining comparable target coverage and acceptable bladder dose.« less
  • Purpose: The safe clinical implementation of pencil beam scanning (PBS) proton therapy for lung tumors is complicated by the delivery uncertainties caused by breathing motion. The purpose of this feasibility study was to investigate whether a voluntary breath-hold technique could limit the delivery uncertainties resulting from interfractional motion. Methods and Materials: Data from 15 patients with peripheral lung tumors previously treated with stereotactic radiation therapy were included in this study. The patients had 1 computed tomographic (CT) scan in voluntary breath-hold acquired before treatment and 3 scans during the treatment course. PBS proton treatment plans with 2 fields (2F) andmore » 3 fields (3F), respectively, were calculated based on the planning CT scan and subsequently recalculated on the 3 repeated CT scans. Recalculated plans were considered robust if the V{sub 95%} (volume receiving ≥95% of the prescribed dose) of the gross target volume (GTV) was within 5% of what was expected from the planning CT data throughout the simulated treatment. Results: A total of 14/15 simulated treatments for both 2F and 3F met the robustness criteria. Reduced V{sub 95%} was associated with baseline shifts (2F, P=.056; 3F, P=.008) and tumor size (2F, P=.025; 3F, P=.025). Smaller tumors with large baseline shifts were also at risk for reduced V{sub 95%} (interaction term baseline/size: 2F, P=.005; 3F, P=.002). Conclusions: The breath-hold approach is a realistic clinical option for treating lung tumors with PBS proton therapy. Potential risk factors for reduced V{sub 95%} are small targets in combination with large baseline shifts. On the basis of these results, the baseline shift of the tumor should be monitored (eg, through image guided therapy), and appropriate measures should be taken accordingly. The intrafractional motion needs to be investigated to confirm that the breath-hold approach is robust.« less
  • Purpose: To investigate the effects of interfractional anatomy and setup variations on plans with anterior-oblique vs. lateral beams for prostate cancer pencil beam scanning (PBS) and passive scattered (PS) proton therapy. Methods: Six patients with low/intermediate risk prostate cancer treated with PS proton therapy at our institution were selected. All patients underwent weekly verification CT scans. Implanted fiducials were used for localization, and endorectal balloons for prostate immobilization. New PBS plans with lateral beams, as well as PBS and PS plans with anterior-oblique beams (±35 deg) were created. PBS plans used two different spot sizes: ∼10mm (large) and ∼5mm (medium)more » sigma at 25cm range and optimized as single-field-uniform-dose with ∼8% non-uniformity. No range uncertainty margins were applied in PBS plans to maximize rectal sparing. Field-specific apertures were used when planning with large spots to sharpen the penumbrae. The planned dose was recomputed on each weekly CT with fiducials aligned to the simulation CT, scaled and accumulated via deformable image registration. Results: The dose volume analysis showed that although difference between planned and accumulated dose remains negligible for plans with conventional lateral beams using both PS and PBS, this is not the case for plans with anterior beams. The target coverage in anterior plans was largely degraded due to the variations in the beam path length and the absence of range margins. The average prostate D95 was reduced by 7.5/15.9% (using PS/PBS) after accumulation for anterior plans, compared with 0/0.4% for lateral plans. The average mean dose in organs-at-risk decreased by 1% for lateral and 2% for anterior plans, similarly for PS and PBS. Spot size did not affect the dose changes. Conclusion: Prostate plans using anterior beams may undergo clinically relevant interfractional dose degradation. Corrective strategies guided by in-vivo range measurements should be studied before clinical application of this technique.« less
  • Purpose: To assess the dosimetric impact caused by the interplay between intrafraction prostate motion and the intermittent delivery of proton pencil beam scanning (PBS). Methods and Materials: A cohort of 10 prostate patients was treated with PBS using a bilateral single-field uniform dose (SFUD) modality. Bilateral intensity-modulated proton therapy (IMPT) plans were generated for comparison. Because beam-on time in PBS was intermittent, the actual beam-on time was determined from treatment logs. Prostate motion was generalized according to real-time Calypso tracking data from our previously reported prospective photon trial. We investigated potential dose deviations by considering the interplay effect resulting frommore » the worst-case scenario motion and the PBS delivery sequence. Results: For both bilateral-field SFUD and IMPT plans, clinical target volume (CTV) D{sub 99}% coverage was degraded <2% owing to prostate intrafraction motion when averaged over the course of treatment, but was >10% for the worst fraction. The standard deviation of CTV D{sub 99}% distribution was approximately 1.2%. The CTV coverage of individual fields in SFUD plans degraded as time elapsed after the initial alignment, owing to prostate drift. Intensity-modulated proton therapy and SFUD demonstrated comparable results when bilateral opposed fields were used. Single-field SFUD plans that were repainted twice, which could reduce half of the treatment time, resulted in similar CTV coverage as bilateral-field plans. Conclusions: Intrafraction prostate motion affects the actual delivered dose to CTV; however, when averaged over the course of treatment, CTV D{sub 99}% coverage degraded only approximately 2% even for the worst-case scenario. The IMPT plan results are comparable to those of the SFUD plan, and similar coverage can be achieved if treated by SFUD 1 lateral field per day when rescanning the field twice to shorten the treatment time and mitigate intrafraction motion.« less
  • Purpose: To quantitatively evaluate the impact of interplay effect and plan robustness associated with intrafraction and residual interfraction prostate motion for pencil beam scanning proton therapy. Methods and Materials: Ten prostate cancer patients with weekly verification CTs underwent pencil beam scanning with the bilateral single-field uniform dose (SFUD) modality. A typical field had 10-15 energy layers and 500-1000 spots. According to their treatment logs, each layer delivery time was <1 s, with average time to change layers of approximately 8 s. Real-time intrafraction prostate motion was determined from our previously reported prospective study using Calypso beacon transponders. Prostate motion and beam deliveringmore » sequence of the worst-case scenario patient were synchronized to calculate the “true” dose received by the prostate. The intrafraction effect was examined by applying the worst-case scenario prostate motion on the planning CT, and the residual interfraction effect was examined on the basis of weekly CT scans. The resultant dose variation of target and critical structures was examined to evaluate the interplay effect. Results: The clinical target volume (CTV) coverage was degraded because of both effects. The CTV D{sub 99} (percentage dose to 99% of the CTV) varied up to 10% relative to the initial plan in individual fractions. However, over the entire course of treatment the total dose degradation of D{sub 99} was 2%-3%, with a standard deviation of <2%. Absolute differences between SFUD, intensity modulate proton therapy, and one-field-per-day SFUD plans were small. The intrafraction effect dominated over the residual interfraction effect for CTV coverage. Mean dose to the anterior rectal wall increased approximately 10% because of combined residual interfraction and intrafraction effects, the interfraction effect being dominant. Conclusions: Both intrafraction and residual interfraction prostate motion degrade CTV coverage within a clinically acceptable level. One-field-per-day SFUD delivered twice is as robust as the bilateral SFUD plan treated daily over the course of treatment.« less